the effects of distraction on the vigilance …
TRANSCRIPT
THE EFFECTS OF DISTRACTION ON THE VIGILANCE
PERFORMANCE OF PARANOID AND NONPARANOID
SCHIZOPHRENICS
by
STEVEN C. PARKISON, B.A., M.A.
A DISSERTATION
IN
PSYCHOLOGY
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for
the Degree of
DOCTOR OF PHILOSOPHY
ADDroved
Accepted
December, 19 79
S f : f
>J ^ ,»^ l-A. ^.•^
ACKNOVJLEDGEMENTS
I would like to express my sineerest appreciation to
Professor Robert P. Anderson for his direction of this
dissertation and to the other members of my committee.
Professor Charles Haleomb, Associate Professors Vernon
Perez, and Richard Carlson, Assistant Professor Michael
Bieber, and Dr. Harold Davis for their helpful advice and
criticism. I am especially indebted to Professor Robert
Anderson for not only his help with this dissertation, but
also for his continued support and guidance in my profes
sional development.
IJL
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
LIST OF TABLES v
LIST OF ILLUSTRATIONS vi
Chapter
I. INTRODUCTION 1
Theoretical Background 2
Silverman Theory 4
Broadbent Theory 12
Experimental Problem 17
Vigilance Task 19
Hypotheses 24
II. METHODS 27
Experimental Design 27
Subjects 2 8
Vigilance Task 32
Procedures 3 5
Statistical Analysis 36
III. RESULTS 39
Statistical Design 39
A Priori Analysis 40
Post Hoe Analysis 47
2.2.2.
IV. DISCUSSION 56
A Priori Results 56
Post Hoe Results 59
Limitations 64
Implications for Future Research 66
Treatment Implications 6 7
V. SUMMARY AND CONCLUSION 6 9
REFERENCES 7 5
APPENDICES 81
A. VENABLES AND O'CONNOR SCALE FOR
RATING PARANOID SCHIZOPHRENIA 82
B. AUDIOTAPE INSTRUCTIONS 8 5
C. INFORMED CONSENT 86
IV
LIST OF TABLES
Table
1. Mean IQ, Ages, and Educational
Levels for the Subjects by Groups 31
2. Primary Medications 32
3. Power for Correct Detections, False Alarms, and Misses 41
4. Correct Detections for Paranoid and Nonparanoid Subjects 41
5. Analysis of Variance Source Table for Correct Detections 4 2
6. False Alarms for Paranoid and Nonparanoid Subjects 45
7. Analysis of Variance Source Table for False Alarms 45
8. Omission Errors for Paranoid and Nonparanoid Subjects 4 6
9. Analysis of Variance Source Table for Omission Errors 4 7
10. Correct Detections: Simple Main Effects for BC Treatment Groups 50
11. Omission Errors: Simple Main Effects for BC Treatment Groups 54
V
LIST OF ILLUSTRATIONS
1. Graphic Representation of Silverman Theory 13
2. Graphic Representation of
Broadbent Theory 15
3. Vigilance Task Booth 34
4. Experimental Design, SPF 22.6, N=60 37
5. Interaction of Distraction Condition by Diagnostic Class by Monitoring Period . . . . 43
6. Correct Detections for Paranoid and Nonparanoid Schizophrenic Subjects Combined Across Time 49
7. Correct Detections for Diagnosis and Across Time 51
8. Omission Errors for Paranoid and Nonparanoid Schizophrenic Subjects Combined Across Time 53
9. Omission Errors for Diagnosis and Across Time 55
VI
CHAPTER I
INTRODUCTION
The purpose of this research was to examine and evaluate
two theories related to attentional deficits in persons with
schizophrenia. While attentional deficits in schizophrenics
have been investigated for some twenty years, the present
study was an attempt to investigate and elucidate the contra
dictions between the theory of Silverman (1964a) and that of
Broadbent (1958) concerning attention. Both theories appear
to have considerable research support, but they differ dia
metrically on the concept of distraetibility in subtypes of
schizophrenia. The investigation attempted to assess the
concept of distraetibility as one manifestation of atten
tional defificts among paranoid and nonparanoid schizo
phrenics while considering the conceptualization of the two
theories on this point. The purpose of such an examination
was to resolve the apparent conflict between the two the
ories and secondarily, to add to the understanding of
individuals currently considered to be schizophrenic.
In the first chapter the areas of major conflict between
the theories are developed and research hypotheses delineated.
The initial section of this chapter describes both theories
and the research support of each. Following sections sum
marize the position of each theory on the concept of
1
distraetibility and provide a statement of the general
research question. The visual vigilance task and its rele
vance to the study of attentional deficits among schizo
phrenics is presented in the next section. Finally, the
hypotheses are presented which merge the theoretical and
empirical directions that were investigated.
Theoretical Background
It is difficult to find a theoretical discussion of
schizophrenia in a text or paper without encountering either
implicit or explicit statements that schizophrenics are in
poor contact with reality. Generally in these discussions
a precise definition of contact with reality is not given;
however, it can be implied that this break with reality
includes changes in basic perceptual processes, i.e. percep
tion of size, shape, color, etc. Much of the work with
projective techniques is suggestive of those perceptual
deficits (Beck, 1938, 1944; Rapaport et al., 1968). Due to
the complex psychological processes involved in projective
testing, it is difficult to ascertain exactly what basic
perceptual processes are involved.
The investigation of schizophrenia has been a continuing
focus of mental health research. Much of the research in
the early part of this century was of a descriptive, clin
ical nature (Kraepelin, 1919). In the last few decades a
more systematic attempt has been made to investigate the
perceptual disorganization that is a primary symptom of the
schizophrenic disorder. Unfortunately, much of the research
has examined schizophrenia as if it were a homogeneous scheme
of classification. In the last 20 years this fallacy has
been explicated and recent research efforts have demonstrated
the need for a more precise taxonomy of schizophrenia CBuss
& Lang, 19 65; Silverman, 19 64a; Weiner, 1958; Ziegler &
Phillips, 19 61). Several recent reviews have indicated that
subtypes of schizophrenia differ across various perceptual
testing procedures (Buss & Lang, 1965; Lang & Buss, 1965).
Even with the abundance of theoretical, clinical, and empir
ical data a good deal of speculation still remains concerning
the nature of the schizophrenic syndrome.
On the clinical level, it has long been recognized that
impaired attention is a dominant feature of schizophrenia.
Weekowicz and Blewett (1959) concluded that: "The abnormal
ities of thinking and perception in schizophrenic patients
can be described as an inability to attend selectively or to
select relevant information" (p. 927). In a review of
studies on set impairment in schizophrenic patients, Shakow
(1962) hypothesized that: "It is as if, in the scanning pro
cess which takes place before the response to a stimulus is
made, the schizophrenic is unable to select out the material
relevant for optimal response" (p. 9).
There are numerous studies which have demonstrated that
schizophrenics do poorly on almost any experimental task
when compared to normal persons. Numerous theories, such as
response interference CCameron, 193 8; Chapman, 19 61; Lester,
1960), response hierarchy collapse (Broen & Storms, 1961,
1966, 1967), and irrelevant focus (Shakow, 1950, 1962, 1963)
have been proposed as explanations for perceptual disorders
in the schizophrenic individual. Two recent theories,
Silverman (1964a, 1972) dealing with scanning behavior and
Broadbent (1958) dealing with filtering, have been perhaps
the most wisely substantiated and investigated. Both of
these theories deal with attentional processes in-depth, but
differ in the hypothesized effects of distraction, partic
ularly with paranoid and nonparanoid schizophrenics.
Silverman Theory
The Silverman theory deals with the cognitive controls
of attention. Before beginning a description of the theory
the concept of attention must be articulated. The contem
porary literature has suggested that attention consists of
two components, the number of distinct objects that can be
perceived in a single momentary presentation, and the length
of time a person can attend to one thing (English & English,
1958), Dykman (1971) considered attention to consist of four
components: alertness, stimulus selection, focusing, and
vigilance. Regardless of the terminology utilized in
descriptions of attention, two concepts appear to be shared
by most definitions of attention. The first of these con
cepts is called an extensive factor and refers primarily to
what Silverman (1964a) describes as "the degree to which
stimuli are sampled from the environment." Simply stated,
this factor refers to the number of stimuli an organism
samples from both the external and internal environments at
any point in time. The second component of attention is a
selective factor; i.e., of the total number of stimuli avail
able to the organism in the environment, which stimuli are
sampled as relevant and which are considered irrelevant and
not sampled. Selection is the articulation of a stimulus
field into components that are relevant and salient and those
that are irrelevant.
In delineating the cognitive controls of attention as
defined above, Silverman (1964a) hypothesized two major
principles. The first of these, the scanning principle,
deals with the first component of attention, i.e., degree of
stimulus sampling. The second major principle, the field-
articulation principle, deals with what elements in a
stimulus field exert a dominant influence over the organism.
Scanning control specifically refers to individual
differences in the extensiveness to which stimuli are sam
pled from the environment. Thus scanning may be considered
simply as the breadth of attention. Piaget (19 50), in
discussing developmental factors, suggested that perception
is subject to a great deal of distortion early in life. Per
ceptions are anchored on dominant objects in the environment.
This anchoring causes objects in the center of the visual
field to be overestimated. Piaget terms this phenomena the
"centration effect" and hypothesized that as individuals
mature they learn to shift attention to and from the center
of the visual field, thus correcting for overestimation. The
longer the duration of a centration, i.e.,the longer the
stimulus is viewed, the greater is the tendency to over
estimate the magnitude of that stimulus. Errors of over-
estimation are thus considered to be due to a narrowing of
the perceptual field by reduced scanning. This scanning
mechanism takes on special significance when applied to
studies of schizophrenia. Normal groups typically show mod
erate scanning as inferred from tasks requiring size estima
tion, while schizophrenics either show extreme or minimal
scanning on these tasks. The major support for the Silverman
theory of scanning has come from studies utilizing variations
of this size estimation hypothesis of scanning.
Raush (1952) compared 30 paranoid schizophrenics, 30
nonparanoid schizophrenics, and 30 normal control subjects
on a task of size estimation. The results revealed that non-
paranoids and controls were not different; however, the
paranoid subjects consistently underestimated the size of
7
the standard light source. Raush concluded that because of
a greater sampling of the perceptual field, i.e., extensive
scanning, the paranoid group consistently had less centra-
tions, therefore underestimated the stimulus. An earlier
study (Voth, 1947) had found similar differences utilizing a
different but similar perceptual task.
Hartman (19 62), in a rather complex investigation of
size estimation, found differences between groups of delu
sional schizophrenics, non-delusional schizophrenics were
found to overestimate the size of stimuli. Normals fell
between these two groups on size estimation. Since delusions
are more typical of paranoid schizophrenics and hallucinations
most typical of nonparanoid schizophrenics, this study sub
stantiates the previous findings.
In an investigation utilizing somewhat different meth
odology, Lovinger (19 5 6), compared the performance of normals
with that of schizophrenics in estimating the size of two
discs presented at different distances. The schizophrenic
group evidenced overestimation of the stimulus which would
indicate, according to the centration hypothesis (Piaget,
1950), that they were minimal scanners.
Gardner and Long (1959, 1962a, 1962b) demonstrated in
normals that size estimates were correlated with photographs
taken of eye movements. They developed a size estimation
task that was highly related to the photographs taken of
8
subjects' eye movements while they were taking the task.
Results revealed that subjects who showed greater eye move
ments also demonstrated greater size underestimation, a
result predicted from Piaget's theory of centration. Sub
jects who consistently overestimated size were found to show
little or no eye movement.
Utilizing the Gardner and Long (1962a, 1962b) procedure
for estimating object size, Silverman (1964b) tested his
scanning theory on a group of 17 paranoid schizophrenic
patients and 26 nonparanoid schizophrenic patients. All of
the subjects were taking antipsychotic medication as part of
their treatment at the time of test administration. The
results were as predicted; the nonparanoid schizophrenics
showed significantly more size overestimation than the
paranoids.
In a more recent study, Schooler and Silverman (19 69)
combined a number of perceptual estimation tasks in one
study and found that paranoid schizophrenics consistently
underestimated the stimulus while nonparanoid schizophrenics
consistently overestimated it.
Based on the 1969 study, Silverman (1972) expanded his
original theory of scanning behavior in schizophrenics. He
postulated that these scanning styles were defensive maneuvers
designed to avoid anxiety in the environment. As Silverman
stated concerning the paranoid schizophrenic patient:
defensive maneuvers of the paranoid thus dispose him to constantly scan environmental input for possible threats to self-esteem and to deal with such threats by selectively examining and translating their meaning, (p. 370)
Thus, the paranoid schizophrenic has learned to be hyper-
alert or hypervigilant to the presence of cues in the envi
ronment which often precede or co-occur with anxiety producing
events. In describing the defensive aspects of minimal scan
ning for the nonparanoid Silverman stated; "minimal scanning
schizophrenics appear to avoid anxiety by directing their
attention away from the environment and into internal pro
cesses such as hallucinations" (p. 370). Thus, it appears
that the nonparanoid schizophrenic is able to gate out anxiety
producing stimuli in the environment by narrowing scanning
behavior.
The following section will deal with the selective
aspects of attention. More precisely, it will be concerned
with those aspects that determine which elements in a stimu
lus field exert a dominant influence.
Early investigations by Piaget (1950) have shown that
the perceptual differentiation of complex stimulus fields
is a developmental phenomenon beginning from a rather global
and diffuse perception to a more refined and articulated
stance. Work in the past 20 years by Witkin and his eol-
leages (Wapner & Werner, 1957; Witkin et al., 1954; Witkin
et al., 19 62) has shown that wide variations are found in
10
the degree of articulation of self and objects even among
adults. Primary evidence for this conclusion comes from
four areas: 1) results from the rod and frame experiments
on perceptual separation, 2) restructuring of stimulus fields
in the embedded figures test, 3) perceptual inhibition in the
color-word test, and 4) differentiation of field on the
tilting-room-tilting-chair task.
The field-articulation concept was further elaborated
by Gardner (19 61) in explaining selective attention on tasks
requiring differentiation of perceptual incongruity. Like
the Witkin studies, successful performance on Gardner's
tasks required the subject to attend to only one set of cues
while disregarding the other sets. Thus, the field-
articulation concepts of Silverman combine the Witkin con
cept of field dependence-independence, Piaget's attention
formation strategies, and Gardner's selective attention
concepts.
Application of this concept to the schizophrenic syn
drome was attempted by Weiss and Sherman (1961) utilizing
the Stroop Color-Word test. This task required the subject
to disregard the distraction effects of the printed names of
colors, while attending only to naming the color in which
the words were written. The results revealed that paranoid
schizophrenics showed less response interference than
11
nonparanoids who showed greater interference as measured by
slower response time.
Witkin et al. (1954) investigated field dependence-
independence among paranoid schizophrenics utilizing the
tilting-room-tilting-chair technique. Of 12 paranoid schizo
phrenic patients tested, seven were found to be markedly
field-independent (high field-articulated) while only 3 were
found to be field dependent (low field-articulated).
Utilizing an embedded figures test, Taylor (195 6) studied
schizophrenic patients rated as delusional or hallucinatory.
Hallucinatory patients were found to require significantly
longer response times to identify the figures when compared
to patients rated as delusional. The distraction effects of
the task appeared to affect the nonparanoid patients to a
greater extent than paranoid schizophrenic patients. Again
the delusional classification is a classification of the
paranoid syndrome.
In reviewing the research in this area, Silverman (i964a)
concluded that paranoid schizophrenics are consistently found
to be high field-articulators who break environmental stimuli
down into discrete categories while the nonparanoid adapts a
global, unartieulated view of the world.
The Silverman theory can be integrated and stated quite
succinctly. Extreme scanning and field-articulation charac
terize the attentional response styles of paranoid subtypes
12
of schizophrenics, while minimal scanning and undifferen
tiated field-articulation are associated with the catatonic
simple, and hebephrenic subtypes, i.e./nonparanoid
schizophrenics.
Concerning distraction effects, Silverman (1972) hypoth
esized that due to the extreme scanning and high field-
articulation of the paranoid schizophrenic, distraction has
little or no effect. The paranoid schizophrenic, according
to this theory, breaks the environmental field down into
discrete units from which relevant stimuli can be separated.
The nonparanoid schizophrenic because of the minimal scan
ning and low field-articulation is unable to separate rele
vant stimuli from distraction and thus is more suseeptable
to distraction. A graphic representation of the above
hypothesis is presented in Figure 1.
Broadbent Theory
Broadbent's theory (19 58, 19 71) of attention is commonly
referred to as a filter theory. This theory was originally
developed from investigations of attention in normals and
of late, has been utilized increasingly as an explanation of
attentional defects in schizophrenics. Filter theory is
based on the conceptualization by Broadbent that, "A nervous
system acts to some extent as a single communication channel,
so that it is meaningful to regard it as having a limited
capacity"(1958, p. 297). The capacity of this communication
13
Paranoid Schizophrenic
Nonparanoid Schizophrenic
Scanning Control
Extensive Information-search Minimal
Field-articulation Control
Segmentalizing-analytie Differentiation Global
Relational
Hypo Distraetibility Hyper
Figure 1. Graphic representation of Silverman theory
14
channel is defined by the amount of information contained in
the sensory event being processed. Sensory events do not
enter this channel directly, but rather after being processed
at the receptors they are held in a short-term store. Decay
is rapid in this store if events are not selected by a selec
tive filter to enter the limited capacity processing channel.
Broadbent has theorized that, "the selection is not com
pletely random, and the probability of a particular class of
events being selected is increased by certain properties of
the events and state of the organism" (1958, p. 297). The
filter aspects of the theory are the important properties
concerning schizophrenia. A graphic representation of the
theory appears in Figure 2.
Payne was the first to apply Broadbent's concepts,
especially those of filtering, to investigations of perceptual
disorders in schizophrenia. Payne et al. (1959) speculated
that the overinclusive thinking found with most paranoid
schizophrenics was due to a defect in the central filter
mechanism. This defect allowed irrelevant data, both inter
nal (irrelevant thoughts and associations) and external, to
enter the processing channel. Thus, the paranoid schizo
phrenic is flooded with both relevant and irrelevant material,
while the nonparanoid schizophrenic with a selective filter
is not affected by the irrelevant stimuli (Payne, 1961).
15
Limited Capacity
Channel
Selective
Filter
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u B u QUO
jc: 0) -p w 4J en
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16
Payne and Caird (1967) tested the above hypothesis util
izing a reaction time task. Fifteen paranoid and 15 non-
paranoids schizophrenics were chosen as subjects for the
investigation. Subjects were required to press a telegraph
key as quickly as possible when a tone was sounded. The
dependent variable was reaction time. Four different levels
of audio distraction were presented during the task. The
results revealed significantly slower reaction times for the
paranoid schizophrenic group under all levels of distraction.
An interesting secondary finding was that baseline reaction
times for nonparanoid schizophrenics were significantly
below those of the paranoids. The authors concluded this
difference was due to a generalized motor retardation in the
nonparanoid group.
In a later study utilizing a dichotic listening task,
Payne et al. (1970) found overinclusive schizophrenics (para
noid subjects) were significantly more distractable than
underinclusive or nonparanoid schizophrenics. The task
consisted of having the subjects listen and repeat words
spoken over headphones. Subjects were instructed to listen
to stimuli presented over just one earphone, while distract
ing words were presented over the other earphone. According
to the filter theory paranoid schizophrenics should be more
affected by the distraetor condition. At least for distrac
tion presented auditorily, the results of the study confirmed
the hypothesis.
17
Wishner and Wahl (1974) compared schizophrenic and non-
schizophrenic psychiatric patients on a dichotic listening
task with distraction. Schizophrenics were found to do less
well, as measured by correct detections and interpenetration
errors from the distraetor, than the non-schizophrenic
patients. While this study tends to confirm the filter
hypothesis, it is confounded by the grouping together of the
schizophrenic patients as if they were a heterogeneous group.
Thus, it was not appropriate to draw a conclusion concerning
the paranoid-nonparanoid schizophrenic subtypes.
In a recent study Lenner et al. (19 77) compared paranoid
schizophrenics, nonparanoid schizophrenics, and normals on
dichotic listening'strategies. The most effective strategy
was one in which all words to one ear were repeated first
while words to the other were held and repeated after the
first list. The result revealed that while normals and
paranoids used the same strategy, the paranoids made more
errors and were significantly slower in their response to
the task. The authors concluded that differences between
the paranoid and nonparanoid schizophrenics were due to dif
ferences in filtering; thus it may be inferred that the two
groups adopted different styles of attending to the stimulus.
Experimental Problem
While both the Silverman and Broadbent theories hypoth
esize attentional deficits in schizophrenics and both
18
theories are partially supported by previous research evi
dence, the theories are diametrically opposed in terms of
the predictions that can be made concerning the effects of
distraction. Silveinnan (1964a, 1972) hypothesized that sus-
ceptability to distraction should be significantly less
among paranoid schizophrenics than that of the narrow scan
ning, low field-articulation nonparanoid schizophrenic
because of the increased scanning and high field-articulation
of the paranoid schizophrenic. The prediction from this
theory would be that under conditions of distraction the
nonparanoid schizophrenics would perform less well due to
their suseeptability to the distraction. Evidence for this
prediction is derived from the embedded figures task (Silver
man, 1964a; Taylor, 1956) and color-word test (Weiss &
Sherman, 19 61).
The Broadbent theory, utilizing a filter concept,
hypothesizes that due to deficits in the filter mechanism
that fails to exclude impending stimuli, the paranoid indi
vidual is more suseeptable to the effects of distraction.
While this hypothesis has some research support (Lerner et
al., 1977; Payne & Caird, 1967; Payne et al., 1970) it must
be remembered that this evidence is confined to distraction
in the auditory modality.
Silverman's theory is supported exclusively by evidence
derived from studies of the visual modality while support
19
for the Broadbent theory is from studies of the auditory
modality, i.e./dichotic listening. As yet no studies of the
effects of distraction on the visual modality such as pro
vided by a vigilance or signal detection tasks have been
attempted with populations of paranoid and nonparanoid schizo
phrenics. The present study attempted to reconcile the dif
ferences between the two theories concerning distraction in
the visual modality with paranoid and nonparanoid
schizophrenics.
Vigilance Task
A vigilance task is synonymous with a signal detector
task or continuous performance task. For consistency the
investigator has elected to use the term vigilance task
throughout the paper.
A vigilance task provides one of the best approaches to
the study of attention. A number of investigators (Bakan,
196 6; Jerison, 19 67; Maekworth, 19 70) have contended that
due to the flexibility of the task along with the parameters
that can be accurately measured the vigilance task provides
the best paradigm for attentional investigations.
Norman Maekworth (1950) was one of the earliest inves
tigators to systematically study the vigilance task in
assessing attention. His earlier experiments investigated
the critical behavioral dimensions involved in detection of
radar signals by observers. The first formal vigilance task.
20
that of observing the hand of a clock simulating the observ
ing of a rado screen, was developed for this project. This
paradigm has become one of the most often used vigilance
tasks in the study of human attention (Davies & Tune, 19 69).
While vigilance has been defined in a number of ways,
the definition by Maekworth of "a state of readiness to
detect and respond to certain specified small changes occur
ring at random time intervals in the environment (19 57, p.
389)" appears to have gained the widest acceptance. Basi
cally the typical vigilance task is a simple discrimination
or detection task with parameters such as stimulus frequency,
duration, and intensity. A subject in the vigilance experi
ment is presented with a number of stimuli of two classes:
(1) signals which are to be reported and non-signals, or
(2) events which are usually to be ignored. The vigilance
task differs from a typical discrimination experiment in
four basic ways. First, signals are presented in infrequent
intervals with no warning of presentation. Second, periods
of uninterrupted vigil are maintained. While these periods
may vary from five minutes to several hours, the usual period
is a half-hour to one hour. Third, the stimuli are psycho-
physically intense. This means that in a normal population
stimuli are nearly always reported with few, if any, false
alarms (responses to non-signals). Fourth, the signals are
considered weak by many observers. This parameter does not
21
contradict the third parameter above, but rather refers to
the attention demanding characteristics of the stimuli. A
subject must attend to the stimuli in order to detect an
occurrence.
As Davies and Tune (1969) have noted, the primary effect
encountered during a vigilance experiment is one of a drop in
both average correct detections and false alarms as a func
tion of time. Jerison (19 63) found that within the first
half-hour of a vigilance experiment a continuous decrement
was noted that stabilized after fifteen minutes of the task.
Maekworth (19 50) in his early experiments also noted this
performance decrement.
While the modern vigilance task was originally developed
from work on alertness of military radar operators it has
recently been widely applied to the study of attention in
"special" populations. A bibliography of studies of vigi
lance (Haleomb & Blaekwell, 1969) reported a number of inves
tigations in which special populations were used as subjects.
Such special populations consisted of brain damaged individ
uals , elderly individuals, introverts, and extroverts.
Recently, children with learning disabilities and hemodial
ysis patients have been studied utilizing the vigilance task.
Jerison (1963) has indicated that the vigilance task
provides an accurate simulation of attention-demanding sit
uations in real life. He hypothesized that the subject in
22
a vigilance task does the same sort of thing in the task that
is required in responding to the ordinary environment, albeit
more structured and more controlled. Jerison found that the
relative isolation and long uninterrupted periods during the
task aided in the adoption of a nonlaboratory oriented set
contrary to the usual set of a laboratory guinea pig. He
also found that the stimuli used were relatively close to
those encountered by the subject in everyday life thus im
proving the generalizability of the vigilance task. Jerison
also noted that the simplicity of the vigilance task was a
feature that improved accuracy of attentional studies. By
separating the attentional aspects of a stimuli from higher
level processing, the simplicity of the task was highly
advantageous. Jerison concluded that the vigilance experi
ment offered an excellent paradigm with which to study and
analyze the parameters of attention.
DeRenzi and Faglioni (1965) utilized the vigilance task
in comparing brain damaged and normal individuals. The results
of this study indicated that the vigilance task was more
efficient in discriminating the 166 brain damaged patients
from the 139 normal controls than the Raven Progressive
Matrices (a nonverbal test of intelligence).
Tune (1966) studied the Eysenek (1955) dimensions of
introversion-extroversion with a vigilance task. The results
revealed no difference when correct detection scores were
23
compared, but significantly fewer false alarms for the intro
verted subjects. Other differences in personality and tem
perament have been found by Hogan (196 6) using the Maudsley
Personality Inventory. Haleomb and Kirk (1965) in motiva
tional investigations, and Colquhon (1960) showing differences
between introverts and extroverts in performance on a vigi
lance task.
Anderson, Haleomb and Doyle (19 73) found the vigilance
task a useful tool in identifying and discriminating hyper
active children from normal children.
The vigilance parameter of distraction has been rela
tively well researched in normal populations and has special
relevance to the present investigation. Typically, distrac
tion in a vigilance experiment is referred to as division of
attention and requires the subject to attend to the relevant
vigilance stimuli as well as disregard a second distraetor
stimulus. Broadbent (1958) first suggested the investigation
of this parameter as a test of his filter theory of attention.
Baker (19 61) studied the effects of distracting stimuli
that was not part of the main vigilance task. In this exper
iment it was emphasized to the subjects that the vigilance
task was of primary importance and the distraetor stimuli
had no relation to it. Normals were chosen as the subject
population. Results revealed that distraction had no effect
on vigilance performance. Alluisi (19 67) and Well (1971)
24
used reaction time as the dependent variable in experiments
similar to Baker's and likewise found no effect of distrac
tion on reaction time in normals.
Doyle, Anderson, and Haleomb (19 7 6) showed that hyper
active children were affected by a distraetor in a visual
vigilance task. The hyperactive children revealed a higher
niimber of false alarms and tried physically to block out
the distraetor. The hypoactive and normoactive children
did not differ on these parameters.
Taken together the results of the above vigilance
studies strongly suggest four general conclusions concerning
the application of the vigilance task. First, a vigilance
task is both a viable and appropriate paradigm with which
to study human attention, i.e., attention in schizophrenics.
Second, the inclusion of a distraetor secondary to the main
vigilance task adds to the dimensions of attention that can
be explored. Third, normal individuals are capable of
tuning out irrelevant stimuli while responding accurately to
the experimental task. Last, that distraction tends to
enhance the vigilance decrement along a number of parameters.
Hypotheses
In light of the general experimental question that was
raised in this chapter, the following hypotheses were pro
posed for study in this investigation. Three dependent
variables from the vigilance task were chosen: 1) correct
25
detection of the stimuli, 2) errors of omission or misses of
the occurrence of a stimulus, 3) false alarms, i.e., detect
ing a stimulus when the stimulus is not present.
1« Under non-distractor conditions of a vigilance task,
paranoid schizophrenic subjects will detect stimuli at levels
equal to that of nonparanoid schizophrenic subjects. This
hypothesis appeared viable in light of the results of the
dichotic listening task research and it is consistent with
the Broadbent theory of attention.
2. Under distraetor conditions of a vigilance task non
paranoid schizophrenic subjects will correctly detect a
significantly greater number of signals than the paranoid
schizophrenic subjects. This hypothesis was considered
appropriate because of the Broadbent theory and results of
dichotic listening experiments.
3. During non-distractor conditions of a vigilance
task, paranoid schizophrenic subjects will show vigilance
decrements over a 30-minute task equal to decrements shown
by nonparanoid schizophrenics. The absence of distraction
was expected to equalize the two groups on vigilance decre
ment according to Broadbent's theory.
4. In a distraction condition, paranoid schizophrenic
subjects will exhibit a greater vigilance decrement across
task time than nonparanoid schizophrenics. According to
the Broadbent theory a defect in the filter of paranoid
26
schizophrenics is expected to increase the vigilance discre-
ment of this group.
5. Under a non-distractor condition of a vigilance
task, paranoid schizophrenic subjects will have false alarms
at levels equal to nonparanoid schizophrenic subjects. It
was believed that due to the absence of distraction in this
condition neither group of subjects will find correct detec
tion of the occurrence of the stimuli particularly difficult.
6. Under distraetor conditions of a vigilance task^
paranoid schizophrenic siibjects will make a significantly
greater number of false alarms than the nonparanoid schizo
phrenic subjects. According to the Broadbent theory, this
hypothesis was considered viable because of the greater
interference of the distraetor upon the paranoid schizo
phrenic group.
7. In a non-distractor condition of a vigilance task,
paranoid schizophrenics will commit errors of omission
(misses) at levels equal to that of nonparanoid schizo
phrenics . This hypothesis was the inverse parameter of
hypothesis 1 and for the reasons stated above is considered
appropriate.
8. In the distraetor condition of a vigilance task,
nonparanoid schizophrenic subjects will commit significantly
less errors of omission (misses) than the paranoid schizo-
phrenic subjects. This hypothesis was the inverse of hypoth
esis 2 above and was considered appropriate for the above reasons.
CHAPTER II
METHODS
The subjects selected for the study were assigned to
one of four groups based on the categories of paranoid
schizophrenic versus nonparanoid schizophrenic, and distrac
tion versus no distraction. Each subject completed 30
minutes of a semi-structured interview after which the para
noid or nonparanoid classification was made. Following
this, the subjects completed a 30-minute visual vigilance
task. In this chapter the experimental design, subject pop
ulation, vigilance task, and the statistical analyses are
described.
Experimental Design
The investigation was designed to make use of the vigi
lance task to measure the effects of distraction on two
subtypes of schizophrenia; i.e., those patients who were
paranoid and those who were nonparanoid. Subjects were
selected from among the inpatient psychiatric population at
a state hospital. While treatment medications were not
manipulated in any manner, subjects were matched on this
variable as well as several others such as age, sex, and
intelligence.
Two conditions of the vigilance task were utilized.
The first was a basic visual vigilance task without
27
28
distraction. The second condition of the vigilance task was
the same as the first condition with the exception of the
addition of a visual distraetor. Differences across the two
conditions as well as between groups in each condition were
analyzed in terms of scores on the test. To aid in analysis,
the 30-minute task time was broken into five-minute segments
and analyzed across segments.
Subjects
Subjects were 60 psychiatric inpatients at Big Spring
State Hospital, Big Spring, Texas. There were two groups of
patients composed of 30 paranoid schizophrenics and 30 non
paranoid schizophrenics (hebrephrenie, catatonic, simple,
chronic undifferentiated, and schizo-affective subtypes).
Schizophrenic patients with a paranoid or nonparanoid
diagnosis were initially identified by psychiatric ward per
sonnel. After this initial identification, medical and
psychological files of perspective subjects were screened
for current diagnosis, diagnosis from any previous hospital
izations, and the results of any previous psychological
tests. Subsequently, each prospective subject was rated
on the Short Scale for Rating Paranoid Schizophrenia
(Venables & O'Connor, 19 59) by a hospital staff member who
had first-hand knowledge of the patient's behavior on the
ward. The Venables and O'Connor (1959) scale measured such
diagnostic components as persecution, grandeur, ideas of
29
references. It was utilized as a cheek on diagnostic class
ification. The scale has been widely used in research with
schizophrenics (Appendix A).
As an additional check on diagnostic subtype classifica
tion, subjects selected were interviewed by the experimenter
utilizing the Tsuang and Winokur (19 74) interview scale for
rating paranoid and nonparanoid schizophrenic classification.
This scale is a brief, well-validated, semi-structured inter
view instrument for rating paranoid and nonparanoid schizo
phrenic subjects for research purposes. A paranoid or
nonparanoid schizophrenic subject was included in the
investigation only if all of the above stated indices were
in clear agreement as to diagnostic subgroup classification.
Patients were excluded from the study for the following
reasons: (a) signs or reports of central nervous system
damage (organieity), (b) current addiction to a psychoactive
substance other than treatment medication, (c) severe visual
handicap present or noted in the patient's records such that
perception of the stimulus material was in doubt, or (d)
evidence of anxiety or of gross confusion so prevalent as to
hamper completion or understanding of the task.
Subjects were randomly assigned to vigilance task condi
tions (distraction/non-distraction). No attempt was made to
match the two groups on variables such as age, sex, intelli
gence, and educational level. Davies and Tune (19 69), in
30
reviewing a large number of studies dealing with these vari
ables, concluded that none of the above variables were sig
nificantly related to performance on the vigilance task.
The only specific performance related limitation was
that subjects be of adequate intelligence defined in the
present study as an IQ of 70 or above. The general level of
intellectual functioning was thus assessed from intelligence
measures routinely administered at the psychiatric facility.
The mean IQ's as well as ages, and educational levels
for the subjects by groups are shown in Table 1. As may be
seen from this data, the subject groups were closely matched
on these variables.
Recently Strauss (1973) has suggested that controlling
for length of hospitalization in schizophrenic samples intro
duced a wide variety of sampling biases into research with
this population. Strauss also suggested that this was par
ticularly important on the paranoid-nonparanoid dimensions
of schizophrenia. Since a primary focus of the investigation
was the differential nature of paranoid and nonparanoid per
formance and in light of the above suggestions, no effort
was made to control for length of hospitalization or ehronic-
ity. An attempt was made to sample groups of patients from
both the acute and chronic populations.
Since the entire sample population was receiving medica
tion, the effects of this variable were considered. The
TABLE 1
MEAN IQ, AGES, AND EDUCATIONAL LEVELS FOR THE SUBJECTS BY GROUPS
31
Group IQ Ages Education Level
No. No. Males Female
Nonparanoid Nondistraction
Paranoid Nondistraction
Nonparanoid Distraction
Paranoid Distraction
89
92
88
93
34
31
42
36
10.6
10.6
9.0
11.2
11
11
method of choice to control for the possible effects upon
vigilance performance of medication was to achieve a "drying
out" period, i.e., drug free period. Due to ethical prob
lems produced by utilization of such a program, the drug
free period was not possible within the hospital setting.
As a next best alternative, an attempt was made to match
subjects not only on type of medication, but also on daily
dosage level. Therefore, patients remained on current
medication regimes for this investigation.
The major antipsychotic medications by groups as well
as by daily dosage for the various groups are shown in Table
2. As may be noted, considerable matching was achieved for
the medication aspects of this study.
32
TABLE 2
PRIMARY MEDICATIONS
Primary Ant ipsychot ic Medications by groups and da i ly dosage. Number of P a t i e n t s
if it
Phenothiazme Dosage Butyrophenones Dosage Other
Nonparanoid Nondistraction 8 375 mg. 6 450 mg. 1
Paranoid Nondistraction 7 400 mg. 7 400 mg. 1
Nonparanoid Distraction 9 500 mg. 6 300 mg.
Paranoid Distraction 7 400 mg 5 450 mg. 2
All medication dosages in Chlorpromazme equivalence.
Vigilance Task
The primary evaluative tool in this investigation was
a basic visual vigilance task. The task required the subject
to sit in a 1.25 meter by 1.25 meter sound attenuated, car
peted, air-conditioned booth housed in the Texas Tech Univer
sity Mobile Psychology Laboratory. The mobile lab was
parked on the hospital grounds. The visual stimulus display
consisted of a 5 centimeters by 7.5 centimeters screen
directly in front of the subject. This display screen was
surrounded by a visual distraetor of flashing lights for the
distraction condition. The subject was required to respond
to detections of the stimulus by pressing a button contained
33
in a hand grip attached to the display unit by a 60 centi
meter insulated wire (see Figure 3).
The actual stimulus material consisted of a combination
of two numbers, 8 and 3, presented by a digital logic cir
cuit housed in the portable laboratory. Responses were
recorded electronically by a counter and printer. Three
combinations of these numbers were presented; 8-3, 3-3, 8-8,
with the 8-3 combination being the criterion signal. This
criterion signal occurred only ten times within any five-
minute interval. A maximum of 60-eriterion signals were
distributed over the 30-minute vigilance period. A stimulus
was presented every 2 seconds with duration of presentation
being 0.2 seconds.
Verbal instructions concerning performance on the task
were presented uniformly by an audio tape recording. The
actual instructions presented are included in Appendix B. A
five-minute practice period without distraction was given to
ascertain the subject's understanding of the task. Follow
ing this practice period, the subject was again instructed
in the task and for subjects in the distraction condition
advised of the presence of the distraetor. Subjects in this
condition were told to ignore the distraetor, being advised
that it had no relation to successful performance on the
task. The distraetor stimulus consisted of a three-sided
display containing six small General Electric neon lights,
34
I I
.•^^^t^kkV^*.^
-p o o
m
EH
0 O c:
•H >
0
•H fa
35
two on each of the three sides. This display was affixed
around the outside perimeter of the inner display booth
approximately 30 centimeters from the stimulus display. The
lights in the distraetor array were controlled by a relax
ation oscillator circuit and flashed in a random order
during the vigilance task. Rate of presentation, brightness,
and duration of distraetor lights were equal to that of the
actual vigilance display.
Procedures
Potential subjects for the study were initially iden
tified by nursing personnel and approached on the wards by
the investigator. The investigation was explained, in detail,
by the investigator to each potential subject. The potential
subjects were then asked to sign a consent to participate
form. Ten subjects refused to sign this form and were not
included in the study.
After potential subjects were interviewed, records
screened and questionnaires completed by ward personnel,they
were reeontaeted for completion of the actual vigilance task.
Subjects were escorted individually from their respective
wards to the Texas Tech University Mobile Psychology Lab
oratory. Upon arrival at the mobile lab each subject was
given a tour of the lab and then seated in the testing room.
At the conclusion of the vigilance task each subject was
escorted back to the ward. Three subjects, all paranoid
36
schizophrenic males, refused to participate after viewing the
mobile lab.
Statistical Analysis
The statistical design of this experiment corresponded
to a mixed design (Lindquist, 1953; Winer, 1962) where there
were repeated measures on some elements. Kirk's (19 6 8)
nomenclature for this experimental design was SPR-22.6. This
paradigm was a split-plot factorial, with two between-bloek
treatments and one within block treatment. A graphic repre
sentation of the complete design appears in Figure 4.
As shown in Figure 4, there were two levels of diagnostic
classification (A); two levels of vigilance condition (C); and
six levels of blocks of trials variable (B). These repre
sented the investigations independent variables; vigilance
condition (distraction and non-distraction); diagnostic
classifications (paranoid schizophrenics and nonparanoid
schizophrenics); and time block effects (for every five
minutes of the thirty-minute vigilance task). Because all
subjects received all block conditions (the entire 30-minute
vigilance task), this factor was the within-bloek or
repeated measure treatment.
Three dependent measures were utilized. These measures;
correct detections, misses and false alarms, constituted
eritical components of the vigilance task. These measures
were determined for every 5-minute block of time during the
37
AC^,
AC^2
^ 21
AC22
^ 1
n=15
n=15
n=15
n=5
^2
n=15
n=15
n=15
n=15
^3
n=15
n=15
n=15
n=15
^4
n=15
n=15
n=15
n=15
^5
n=15
n=15
n=15
n=15
^6
n=15
n=15
n=15
n=15
Where:
A = levels of diagnostic classification
A^ = Paranoid schizophrenics A2 = Nonparanoid schizophrenics
C = Levels of vigilance condition
C, = Non-distraction condition C2 = Distraction condition
B = Blocks of trials (repeated measures)
B, = First 5 minutes Bp = Second 5 minutes B-. = Third 5 minutes B. = Fourth 5 minutes Be = Fifth 5 minutes B^ = Sixth 5 minutes o
Figure 4. Experimental Design, SPF 22.6, N=60
38
30-minute vigilance task. While reaction time has been used
in many vigilance experiments (Davies & Tune, 19 69), it was
felt that due to the medication component involved in this
investigation that measurement of this variable was hope
lessly confounded. Therefore, reaction time was not used as
a dependent variable. Three separate ANOVA's were subse
quently performed with these data, one for each dependent
variable.
The total N was 60 with the smallest cell being composed
of 15 patients. The following n's were thus provided for
each variable; 30 for each diagnostic level; 30 for each
level of vigilance condition; and 60 for each block level.
CHAPTER III
RESULTS
The purpose of the study was to determine if nonparanoid
schizophrenics and paranoid schizophrenics perform differently
on a vigilance task in either a distraction or non-distraction
condition. The non-distraction condition was a visual vigi
lance task. The distraction condition was provided by a
display of flashing lights presented simultaneously with the
vigilance task.
Three types of data or dependent variables were collected:
(a) number of stimuli correctly detected, (b) number of
misses, and (c) number of false alarms. In order to analyze
the vigilance performance decrements across time each of the
types of data were collected in successive five-minute inter
vals across the 30-minute experimental task.
Statistical Design
The statistical design corresponded to a mixed design
(Linguist, 1953; Winer, 1962) where there were repeated
measures on some elements. The statistical technique util
ized to analyze the data was a split-plot factorial analysis
of variance (SPF-pr.q: .Kirk, 1968). Diagnostic category
(paranoid versus nonparanoid schizophrenia) and the presence
or absence of distraction constituted the between block
treatments. The six successive five-minute intervals of
39
40
the thirty-minute vigilance task constituted the within block
treatment.
The total N was 60 with the smallest cell composed of
15 patients. Thus the following n's were provided for each
variable; 30 for each diagnostic category; 30 for each level
of vigilance condition; and 60 for each time block level.
Statistical power of a particular investigation indi
cates the probability that a test will reveal that a
phenomenon exists. Statistical power at the .05 alpha
level was computed for each treatment effect using Cohen's
(19 69) procedure. The statistical power for each treatment
effect is presented in Table 3.
A Priori Analysis
Eight separate a priori hypothesis were considered in
the investigation.
Hypothesis 1\ Under non-distractor conditions of a vigi
lance task, paranoid schizophrenic subjects will detect
stimuli at levels equal to that of nonparanoid schizophrenics
subjects. As may be seen from these analyses (Table 4 and
Table 5), no difference between paranoid and nonparanoid
schizophrenic subjects was found in the non-distraction
condition (F=2.94; df=l,56). These results support hypoth
esis 1 and therefore is accepted.
Hypothesis 2 Under distraetor conditions of a vigilance
task nonparanoid schizophrenic subjects will correctly detect
41
a significantly greater number of signals than the paranoid
schizophrenic subjects. No difference between paranoid and
nonparanoid schizophrenic subjects was found in the distrac
tion condition (F=2.94; df=l,56) (Table 4 and Table 5).
These results do not support hypothesis 2 and therefore it
is rejected.
TABLE 3
POWER FOR CORRECT DETECTIONS, FALSE ALARMS, AND MISSES
Condition
A-Distraetion
C-Diagnosis
AxC
B-Time Interval
AxB
BxC
AxBxC
CORRECT
Group
Paranoids Mean S.D.
Nonparanoids Mean S.D.
Correct Detection
.15
.99
.76
.57
.12
.29
.09
TABLE 4
False Alarms
.65
.90
.18
.22
.10
.07
.08
DETECTIONS FOR PARANOID NONPARANOID SUBJECTS
With Distraction
9.4 .92
8.7 2.28
Misses
.15
.99
.76
.57
.12
.29
.09
AND
Without Distraction
7.6 2.53
8.5 2.05
TABLE 5
ANALYSIS OF VARIANCE SOURCE TABLE FOR CORRECT DETECTIONS
42
Source df MS
Between Subjects
A-Distraction Level
C-Diagnosis
A x C
S.W. Groups
1
1
1
56
1.00
93.02
55.22
18.81
.05
4,94*
2.94
Within Subjects
B-Time Intervals
A x B
B x C
A X B X C
C X Subj W. Group
5
5
5
5
280
5.37
1.87
5.77
.83
1.30
4.14**
1.44
4.45**
.64
P<.05. * * P<.01.
Hypothesis 3 During non-distractor conditions of a
vigilance task, paranoid schizophrenic subjects will show
vigilance decrements over the 30-minute task equal to
decrements shown by nonparanoid schizophrenics. No differ
ence was found between paranoid and nonparanoid schizophrenic
subjects across the 30-minute task time in the non-distractor
condition (F=.64; df=5,280) (Table 5). Further clarification
of this relationship is found in Figure 5. These results
support hypothesis 3 and therefore it is accepted.
43
CO s o H
U w E-" ixl Q EH U
« O O
10.0
9. 5
9.0
8.5
8.0
7. 5
7 .0
6.5
6.0
5 . 5
5.0
V ^
•s, ^ - •
\
^ v
Paranoid
- - - - Nonparanoid
N
N
Distraction'^
Nondistractio
\ Nondistrction
\
\ Distraction
10 15 20 Minutes
25 30
Figure 5. Interaction of distraction condition by diagnostic class by monitoring period.
44
Hypothesis 4 In a distraction condition, paranoid
schizophrenic subjects will exhibit a greater vigilance
decrement across task time than nonparanoid schizophrenics.
No difference was found between paranoid and nonparanoid
schizophrenic subjects across the 30-minute task time is
the distraetor condition (F=.64; df=5,280) (Table 5).
Figure 5 presents a graphic representation of this relation
ship. These results do not support hypothesis 4 and there
fore is rejected.
Hypothesis 5 Under a non-distractor condition of a
vigilance task, paranoid schizophrenic subjects will have
false alarms at levels equal to nonparanoid schizophrenic
subjects. The results by diagnostic category and across
the distraction conditions are presented in Table 6. As may
be seen from the analysis, no differences between paranoid
and nonparanoid schizophrenic subjects was found in the non-
distractor condition (F=.53; df=1,156) (Table 7). These
results support hypothesis 5 and therefore is accepted.
Hypothesis 6 Under distraetor conditions of a vigi
lance task, paranoid schizophrenic subjects will make a
significantly greater number of false alarms than the non
paranoid schizophrenic subjects. No difference between
paranoid and nonparanoid schizophrenic subjects was found
in the distraction condition (F=.53; df=l,56) (Table 6 and
Table 7). The results do not support hypothesis 6 and
therefore it is rejected.
45
TABLE 6
FALSE ALARMS FOR PARANOID AND NONPARANOID SUBJECTS
Group
Paranoids Mean S.D.
Nonparanoids Mean S.D.
With Distraction
0.9 2.0
1.7 2.3
Without Distraction
1.3 4.4
3.5 6.5
TABLE 7
ANALYSIS OF VARIANCE SOURCE TABLE FOR FALSE ALARMS
Source df MS
Between Subjects
A-Distraetion Level
C-Diagnosis
A x C
S.W. Groups
Within Subjects
B-Time Intervals
A x B
B x C
A X B X C
C X Subj w. Group
1
1
1
56
5
5
5
5
280
110.00
195.07
40.67
76.78
8.46
5.76
3.90
4.67
6.99
1.43
2.51
.53
1.21
.83
.55
.67
46
Hypothesis 7 In a non-distractor condition of a vigi
lance task, paranoid schizophrenics will commit errors of
omission (misses) at levels equal to that of nonparanoid
schizophrenics. No difference between paranoid and non
paranoid schizophrenic subjects was found in the distraction
condition (F=2.94; df=l,56) (Table 8 and Table 9). These
results support hypothesis 7 and therefore it is accepted.
TABLE 8
OMISSION ERRORS FOR PARANOID AND NONPARANOID SUBJECTS
Group
Paranoids Mean S.D.
Nonparanoi Mean S.D.
ds
Without Distraction
2.4 2.53
1.5 2.05
With Distraction
0.6. .92
1.3 2.28
Hypothesis 8 In the distraetor condition of a vigilance
task, nonparanoid schizophrenic subjects will commit signif
icantly less errors of omission (misses) than the paranoid
schizophrenic subjects. As may be seen from this analysis
(Table 8) no difference between paranoid and nonparanoid
schizophrenic subjects was found in the non-distraction
condition (F=2.94; df=l,56) (Table 9). These results do not
support hypothesis 8 and therefore it is rejected.
47
TABLE 9
ANALYSIS OF VARIANCE SOURCE TABLE FOR OMISSION ERRORS
Source
Between Subjects
A-Distraction Level
C-Diagnosis
A x C
S.W. Groups
Within Subjects
B-Time Intervals
A x B
B x C
A X B X C
C X Subj w. Group
P<.05.
P<.01.
df
1
1
1
56
5
5
5
5
280
MS
1.00
93.02
55.22
18.81
5.37
1.87
5.77
.83
1.30
F
.05
4.94*
2.94
4.14**
1.44
4.45**
.64
Post Hoc Analysis
One problem came to the foreground following a priori
analysis. Since the distraction condition appeared to have
no effect upon both the paranoid and nonparanoid schizo
phrenic subjects, this variable tended to mask any of the
other variables involved in an interaction. This meant that
information concerning differences between paranoid and non
paranoid subjects regardless of level of distraction was
being lost. Therefore a post hoc analysis was attempted to
elucidate possible differences between diagnostic groups.
48
Correct Detections. While no difference was found for
the level of distraction condition alone (Table 5), a signif
icant difference was obtained by a diagnostic category.
Paranoid schizophrenic subjects obtained significantly more
correct detections than did nonparanoid schizophrenic sub
jects (F=4.96; df=l,56; p<.03). A significant effect was
also found across the time intervals (F=4.14; df=5,2 80;
p<.002). The mean correct detections for all subjects irre-
gardless of diagnostic or distraction group membership is
demonstrated in Figure 6.
There was a significant interaction (BxC) between the
six-time intervals and the two diagnostic groups. Analysis
of the simple main effects was performed to clarify the
nature of this interaction (Kirk, 1968) (Table 10, Figure 7).
Analysis of the simple main effects indicated that the
paranoid schizophrenic subjects obtained significantly more
correct detections than the nonparanoid schizophrenic sub
jects during the last two 5-minute monitoring periods (F=li.53;
F=10.28; df=l,336; p<.01). For the first four monitoring
intervals no significant differences were found between
paranoid and nonparanoid schizophrenic subjects. Within
groups, the analysis of simple main effects revealed that
only the nonparanoid schizophrenics had significantly differ
ent numbers of correct detections across time intervals
(F=8.23; df=5,280; p<.001).
49
1 0 . 0
9 . 8
CO 9 . 6 s o H 9 . 4
E-" 9 . 2 w Q
g 9 .0
g 8 .8 u
§ 8 , 6
8 . 4
8 . 2
8 . 0
1 0 15 20
Minutes
25 30
Figure 6. Correct detections for Paranoid and Nonparanoid schizophrenic subjects combined across time.
50
TABLE 10
CORRECT DETECTIONS: SIMPLE MAIN EFFECTS FOR BC TREATMENT GROUPS
Source
Between Groups
C-Diagnosis
Between C
Between C
Between C
Between C
Between C
Between C
Within Groups
at
at
at
at
at
at
bl
b2
b3
b4
b5
b6
B-Time Intervals
Between B
Between B
B x C
at
at
cl
c2
df
1
1
1
1
1
1
5
5
5
MS
1.35
3.74
8.81
16.01
48.59
43.34
53.36
2.35
5.77
F
.32
.89
2.09
3.80
11.53*
10.28*
8.23*
.36
4.45*
P<.01.
In testing the difference among means, Tukey's HSD
statistic (Kirk, 1968) was utilized. This analysis revealed
that the nonparanoid schizophrenics showed significantly more
correct detections in the first ten minutes of the monitoring
interval than in the last ten minutes of monitoring (q=7.35;
q=4.8; df=l,336; p<.05).
False Alarms. The analysis of variance source table for
the analysis of false alarms is presented in Table 7. No sig
nificant differences were found for any comparison of groups
51
9.4
9.2
9.0
g 8.8 o H
S 8.6 w E H
g 8.4 E-» U 8.2
8 8.0 s
7.8
7.6
7.4
7.2
\
Paranoid
- - - Nonparanoid
10 15 20
Minutes
25 30
Figure 7. Correct detections for diagnosis and across time.
52
on false alarms. Likewise, none of the interactions were
found to be significant. Both diagnostic classes obtained
low numbers of false alarms.
Omission Errors. No difference was found for the level
of distraction condition, while a significant difference was
obtained by diagnostic category (Table 9). The paranoid
schizophrenic subjects obtained significantly less errors of
omission than did nonparanoid schizophrenic subjects (F=4.96;
df=l,56; p<. 03). A significant effect was also found across
the time intervals (F=4.14; df=5,280; p<.002) (Table 9, Figure
8) .
There was a significant interaction (BxC) between the
six-time intervals and the two diagnostic groups. Analysis
of the simple main effects was performed to clarify the
nature of this interaction (Kirk, 19 68) (Table 11, Figure 9).
Analysis of the simple main effects indicated that the
paranoid schizophrenic subjects obtained significantly less
omission errors than the nonparanoid schizophrenic subjects
during the last two 5-minute monitoring intervals (F=11.53;
F=10.28; df=l,336; p<.01). For the first four monitoring
intervals no significant differences were found between para
noid and nonparanoid schizophrenic subjects. Within groups,
the analysis of simple main effects revealed that only the
nonparanoid schizophrenic subjects had significantly differ
ent numbers of omission errors across time intervals (F=8.23;
df=5,280; p<.001).
53
2.4
2.2
2.0 w u o 1.8 u
w 1.6
o 1.4
w
•H 1.2 e o (d 0)
S .8
/
/
/
/
.6
.4
.2
10 15 20 Minutes
25 30
Figure 8. Omission errors for paranoid and nonparanoid schizophrenic subjects combined across time.
54
TABLE 11
OMISSION ERRORS: SIMPLE MAIN EFFECTS FOR BC TREATMENT GROUPS
Source
Between Groups
C-Diagnosis
Between C at bl
Between C at b2
Between C at b3
Between C at b4
Between C at b5
Between C at b6
Within Groups
B-Time Intervals
Between B at cl
Between B at c2
B x C
df
5
5
5
MS
1
1
1
1
1
1
1 .35
3 . 7 4
8 . 8 1
1 6 . 0 1
4 8 . 5 9
4 3 . 3 4
. 3 2
.89
2 . 0 9
3 . 8 0
1 1 . 5 2 *
1 0 . 2 8 *
53.36
2.35
5.77
8.23*
.36
4.45*
P<.01.
In testing the differences among means Tukey's HSD
statistic (Kirk, 1968) was utilized. This analysis revealed
that the nonparanoid schizophrenics showed significantly
less errors of omission in the first ten minutes of the
monitoring interval than in the last ten minutes of monitor
ing (q=7.36; q=4.8; df=l,336; p<,05).
55
03
O 05
W
g H CO CO H s o
4 . 0
3 .5
3 . 0
2 .5
2 . 0
1.5
1.0
Nonparanoid
•Paranoid
/
**—••- ~
10 15 20 Minutes
25 30
Figure 9. Omission errors for diagnosis and across time.
CHAPTER IV
DISCUSSION
The purpose of this chapter is to discuss the present
study results in light of previous research on attentional
deficits in schizophrenics. The a priori results will be
considered, followed by a discussion of the post hoc anal
ysis results. The limitations of the investigation, both
statistical and methodological are discussed along with
suggestions for future research on attentional deficits in
this population.
A Priori Results
In reviewing the results obtained on the correct detec
tion variable, it appeared that no significant difference
existed between paranoid and nonparanoid schizophrenics on
any of the hypothesized dimensions. In considering the
mean correct detections for the diagnosis by distraction
condition analysis (AxC), (Table 4), the greatest difference
appeared to be between distraction and non-distraction con
ditions in the paranoid schizophrenic group. This suggests
the paranoid sample increased correct detections when dis
traction was added to the vigilance task. The nonparanoid
sample remained virtually unchanged from one condition to
the other. While this difference is not statitically sig
nificant, it is in a direction opposite to that expected
56
57
from a filtering theory perspective (Broadbent, 1958, 1971).
The scanning theory of Silverman (1964a) easily accounts for
this difference by considering paranoid schizophrenics to be
scanners and therefore, hypervigilant and not suseeptable to
the effects of distraction. The addition of a distraetor in
close proximity to the actual relevant stimuli appeared to
focus the scanning of the paranoid group to the relevant
stimulus thus increasing accuracy of performance.
While observing subjects during the task through a one
way window, the paranoid schizophrenics in the non-distractor
condition frequently looked around the booth during the task.
On the other hand, during the distraction condition, their
paranoid counterparts were observed to look no further than
the frame of the distraetor task. In both distraction con
ditions nonparanoid schizophrenic subjects were noted to
stare at the stimulus presentation window and did not glance
around, even at the distraetor. Paranoid and nonparanoid
schizophrenic subjects also showed no difference in vigilance
decrement during the distraction conditions (AxBxC).
In reviewing the results obtained from the false alarms
data it appeared that no difference existed between non
paranoid and paranoid schizophrenics on any of the conditions,
The actual data revealed very low numbers of false alainns
across both groups. These results are contradictory to
numerous clinical reports in which hyperactivity is reported
58
as a symptom in schizophrenia, especially paranoids. How
ever, the results take on new perspective when the effects
of medication are considered. Since one property of anti
psychotic medication is to tranquilize the patient, then
results such as these are not totally unexpected. Under
these conditions errors of omission (misses) would be more
expected than errors of commission (false alarms).
The results obtained from the errors of omission (misses)
data, suggest that no significant difference existed between
paranoid and nonparanoid schizophrenics in any of the hypoth
esized directions. Since this variable is the inverse of
correct detections much of what was stated earlier applies
here. The mean errors of omission for the diagnosis by dis
traction analysis (AxC) revealed the greatest difference was
between distraction conditions for the paranoid schizophrenic
group. Although this difference was not statistically signif
icant it does present an interesting trend. Paranoid schizo
phrenic subjects improved their omission errors fourfold when
the distraetor stimulus was added unlike the nonparanoid
group which showed virtually no change. This trend, albeit
not statistically significant, is in the direction predicted
by Silverman. Whereas Broadbent has hypothesized that para
noids would be impaired by distraction, it would appear that
distraction had the effect of improving performance in this
group. Thus, the results are supportive of Silverman. In
59
the correct detection analysis, the diagnosis by distraction
by time block (AxBxC) interaction was not significant.
Post Hoc Results
The post hoe analysis consisted of examining the main
effects and simple main effects remaining in the spli-plot
statistical analysis after the interactions hypothesized
a priori were scrutinized.
Several interesting features appeared in the post hoc
analysis of the correct detection data. When the main effect
of distraction was considered it was found that the distrac
tion condition had no effect. No difference was found
between the group without the distraction task and the group
with the distraetor included. These results suggested that
either the methodology involved with the distraetor was weak
or that this population does not respond to distraction as
other previous researched populations have responded. This
result will be more fully discussed later in this chapter.
When the effects of distraction were ignored and the
subjects were simply grouped on the basis of paranoid versus
nonparanoid schizophrenia a significant different was found.
Paranoid schizophrenic subjects detected significantly more
stimuli correctly than did nonparanoid schizophrenics. This
result is difficult to account for theoretically from Broad-
bent's perspective. On the other hand, Silverman has
repeatedly stated that paranoid schizophrenics continually
60
scan for any changes in the environment as a defense against
anxiety producing stimuli. This hypervigilance to change
could account for the better performance by the paranoid
group.
The most revealing post hoe analysis for correct detec
tions was the interaction of time intervals by diagnostic
membership. Here the difference between paranoid and non
paranoid schizophrenic subjects was most clear (Table 10).
The analysis of simple main effects revealed that paranoid
subjects correctly detected stimuli at levels above their
nonparanoid counterparts in the last two time intervals.
Also, the paranoid schizophrenic subjects showed no vigilance
decrement across the 30-minute task time while the nonparanoid
schizophrenic group did show a significant decrement. It
appeared that the paranoid group not only were more vigilant
but were able to remain so throughout the entire 30 minutes
of the task. This result is startling considering the pre
vious work on the vigilance task which has consistently
demonstrated the existence of vigilance decrements. The
paranoid schizophrenic group in this study was not only able
to maintain a steady perf03nnance, but appeared to improve at
the end of the 30-minute task time, a result which strongly
favors the Silverman theory of attention. Just as Silverman
(1964a) has predicted, the paranoid schizophrenics
61
continually scanned the environment for changes and did so
without a reduction in performance.
The Silverman (1964a) concept of defense is particularly
useful in understanding these results as applied to precep-
tual response patterns for mastering anxiety. Silverman
(196 4a) suggested that during early developmental phases of
schizophrenia isolation, repression, denial, and other
psychological defenses lose effectiveness. The individual
regresses to more primitive and basic forms of defense such
as provided by perceptual distortions, e.g., hypo- or
hypervigilance. The paranoid schizophrenic subjects in this
investigation appeared to have scanned the environment more
frequently than the nonparanoid schizophrenic subjects.
This leads to the tentative hypothesis that paranoid schizo
phrenics learn the most effective means of reducing or
escaping anxiety is to be hypervigilant to changes in their
environment that signal the onset of noxious events. How
ever, this perceptual response style is paradoxical; while
it maximizes the probability of receipt of information about
impending threatening situations, it also increases the like
lihood of encountering aversive stimulation. In an attempt
to resolve this paradox, paranoid schizophrenics constantly
reinterpret relationships between motives of others and
events in an attempt to screen out anxiety. This resolution
is seen clinically in paranoids defense of projection and
62
the development of a delusional system for interpreting
events in the environment.
In commenting on the early social history of the exces
sive scanning paranoid schizophrenic (Arieti, 1955) stated:
The parents of the paranoid type do not criticize the patients for their actions; they generally accuse the patients for their intentions or for lying. The child learns to defend himself by anticipating these accusations, and therefore becoming anxious and suspicious, or by developing a faculty of rationalizations. He has to find almost a legal or technical way to protect himself from insinuations and accusations. (p. 159) . . . Other cases instead of focusing their attention on their pseudo-rational defenses, seem to sense or magnify any kind of hostility in the environment. (p. 140)
Thus, preparanoid individuals use a perceptual defense
of constantly scanning environmental input for possible
anxiety provocating stimuli. Such stimuli are dealt with by
selectively examining and translating their meaning.
On the other hand, minimal scanning nonparanoid schizo
phrenics avoid anxiety by directing their attention away
from the environment. If these individuals were to com
pletely direct their attention from the environment and into
internal processes they would presumably experience anxiety
greater than that which they are trying to avoid. Prolonged,
self-induced sensory deprivation would operate to prevent
nonparanoid schizophrenics from complete withdrawal since
they must register stimulation in order to live. The isola
tion experiments of Bexton, Heron and Scott (1954), the
63
hypnosis studies by Breman and Gill (1947), and the spaeial
orientation research by Held and Hein (1958) make it clear
that what may appear in the nonparanoid schizophrenic as
directing attention away from environmental stimuli cannot
be considered a total shift of attention to internal pro
cesses. Rather, it appears that the nonparanoid schizo
phrenic anchors perception on dominant objects (minimal
scanning).
As this process occurs, stimuli that are initially
perceived as global, articulated wholes become unartieulated
and fragmented. Such fixedly motivated attention functions
to gate out stimuli that may possibly be anxiety producing
for the individual. The nonparanoid subjects in this inves
tigation did not completely direct their attention away from
the environment, but rather anchored perception on the
vigilance stimuli. Arieti (1961) observed that with in
creases in stimulation nonparanoid schizophrenics, divide
objects into progressively smaller fragments. He has labeled
this phenomenon "Awholism." With the lessening of scanning
of nonparanoid schizophrenics fragmented wholes become more
and more unlike the original stimulus. Thus, another kind
of perceptual distortion takes place. The extreme minimal
scanning behavior of nonparanoid schizophrenics becomes
analogous to the pathological staring behavior observed
among individuals who are in semistuporous conditions.
64
The results of this investigation suggested that para
noid and nonparanoid schizophrenics differ in perceptual
orientation to the environment. Paranoids were significantly
more vigilant when compared to their nonparanoid counter
parts. This result favors a position supporting Silverman's
theory of much more than Broadbent's theory.
Limitations
This study had both methodological and statistical lim
itations. The distraetor stimulus consisted of six small
bulbs mounted on a panel surrounding the actual vigilance
stimulus. Previous investigations with the vigilance task
found that distraction was a significant variable in effect
ing performance on the task. Also previous work with schizo
phrenics produced results suggesting again that distraction
was a potent variable in research with schizophrenic samples.
Yet in this study the effects of distraction were minimal
at best.
In reconsidering the particular distraetor used in this
study several features are apparent. The light produced by
each bulb on the distraetor panel was small. In the original
formulation of the distraetor this was planned because of
concern about the possible effects a more powerful bulb might
have on patients taking antipsychotic medications. It has
been recognized for some time that antipsychotic medications
lower the seizure threshold of patients. This phenomenon
65
has been documented in a number of reports (Appleton & Davis,
1973; Klein & Gittelman-Klein, 1976; Weiner & Levitt, 1978).
Since the distraetor task chosen for this research appeared
to function much like a strobe light, which have been used
to induce seizures, a smaller, dimmer bulb was chosen to
avoid the production of seizures especially among patients
who had been taking antipsychotic medications for prolonged
periods. The effects of this choice may have been to reduce
the distraetor to a point where little if any distraction
actually took place.
A statistical limitation may have been the criteria for
selection of patients into either paranoid or nonparanoid
groups. In reviewing previous research with paranoid and
nonparanoid schizophrenics it was found that few studies
gave adequate attention to selection procedures in separating
patients into one of the two groups. The selection utilized
in this research was particularly stringent in order to
avoid the criticism of poor sampling and thus invalid results
and conclusions when applied to the two groups. Methodolog
ically, these procedures were anything but a limitation for
the selection produced groups that were at extremes on the
paranoid-nonparanoid continuum. Statistically these proce
dures had the effect of reducing the sample size and thus the
statistical power of the design.
66
Implications for Future Research
The area of perceptual differences between paranoid and
schizophrenics is a fruitful one for future research. Results
of the present study create some new questions in this area.
The effects of different types of distraction of varying
intensities is a question that remains unanswered. Some
suggestions in this area would be the use of a distraetor
that involved more psychological intense content than flash
ing lights. These stimuli could consist of pictures of indi-
duals, pictures of groups of people or even different colored
lights. Because of the limitations of utilizing flashing
lights as a distraction with this population, another choice
would be the use of auditory distraction. This cross-
modality interference could increase the effectiveness of
distraction. Another possibility is to change the character
istics of the distraetor for each 5-minute period, thus
decreasing the possibility of adaption by the subject.
The paradigm and methodology utilized for this study
could easily be used in assessing treatment effects from
such interventions as antipsychotic medications. The recent
direction of medication research has been toward finding
which antipsychotic medications are most effective for which
types of schizophrenic patients. The methodology used here
having already proved its effectiveness in differentiating
67
paranoid from nonparanoid schizophrenics may help answer the
question of matching patient to medication. These results
also increase specualtion about character styles and their
influence on the development of psychopathology. For in
stance clinical experience has indicated that obsessive
compulsive individuals tend to break environmental input
down into separate, distinct parts much as the paranoids
in this study appeared to do. Conversely, hysterical indi
viduals are more global and focused in their approach to
environmental input and tent to be like the nonparanoids in
this study. While speculative, these ideas suggest a further
direction for future research.
Treatment Implications
While the results of a single study without replication
should never be the sole basis for treatment this study does
suggest several areas for further research on treatment with
this population. Since at this time medication is the treat
ment of choice with schizophrenic populations the paradigm
used in this study would make an excellent way to assess the
effects of this treatment.
The diagnostic implications of these results are also
encouraging. Since as May (196 8) points out effective psycho
therapeutic techniques vary depending upon the type of
schizophrenia involved, a test such as the vigilance task
68
could help in diagnosis and therefore treatment. Using the
vigilance task to assess psychotherapeutic techniques could
also help to refine and improve these techniques.
CHAPTER V
SUMMARY AND CONCLUSIONS
It is difficult to find a textbook or discussion of
schizophrenia without a review of the deficits found in
schizophrenic individuals. These deficits have been the
subject of investigations for some 80 years. In the early
part of the century the research was of a descriptive,
clinical nature. In the last few decades a more systematic
attempt has been made to investigate perceptual disorganiza
tion which is a primary part of the schizophrenic disorder.
Unfortunately, much of the research has examined schizo
phrenia as if it were a homogeneous category. In the last
20 years this fallacy has been revealed and recent research
efforts have expressed the need for a more precise taxonomy
of schizophrenia. Even with the abundance of theoretical,
clinical and empirical evidence a good deal of speculation
still remains concerning the nature of the schizophrenic
syndrome. The focus of this investigation was the
paranoid-nonparanoid dimension of the schizophrenic syndrome.
The present line of investigation arose from the con
tradictions between the theory of Silverman (196 4a) and that
of Broadbent (1958) concerning attentional differences
between paranoid and nonparanoid schizophrenics. While both
69
70
theories appeared to have considerable research support, they
differed diametrically on the concept of distractability.
The Silverman theory deals with the cognitive controls
of attention and hypothesized two major principles. The
first being a scanning control and deals with the degree of
stimulus sampling. The second principle, the field-
articulation principle, deals with what elements in a stimulus
field exert a dominant influence over the individual. The
prediction from this theory concerning distraction is that
paranoid schizophrenics show little or no effect from dis
traction due to extreme scanning and high field-articulation.
On the other hand nonparanoid schizophrenics are predicted
to be highly suseeptable to the effects of distraction.
The Broadbent theory of attention is referred to as a
filter theory. This theory is based on the conceptualiza
tion of a single channel, limited capacity nervous system
with the capacity to filter distraction. From this concep
tualization paranoid schizophrenics are thought to have a
filter defect that allows all environmental input into the
channel without filtering while nonparanoids are thought to
filter out irrelevant input. The prediction from this theory
concerning distraction is that due to defective filtering,
paranoid schizophrenics would be suseeptable to the effects
of distraction while nonparanoids who filter out stimuli
would not be affected by distraction.
71
A vigilance task was chosen as the paradigm for this
investigation because it provided one of the best approaches
to the study of attention. Recent research with the vigi
lance task has indicated its usefulness as a tool to study
both attention and distraction phenomena. The study was
carried out at the Big Spring State Hospital, Big Spring,
Texas. The global research question revolved around the
differential effects of distraction on both paranoid and
nonparanoid schizophrenics.
The subjects were selected through a procedure which
involved a 30-minute screening interview. Secondly, records
were screened. Third, a screening instrument was completely
by ward personnel about each subject. When subjects were
classified and agreed to participate, they were assigned to
one of the four groups: 1) paranoid-distraction, 2)
nonparanoid-distraction, 3) paranoid-non-distraction, 4)
nonparanoid-non-distraetion. While treatment medications
were not manipulated, subjects were matched on this variable
as well as age, sex, and intelligence. Sixty subjects were
utilized. Each of the four groups contained 15 subjects.
The dependent variables taken from the vigilance task
were: 1) correct detections measured by the number of
stimuli correctly detected, 2) false alarms as measured by
the number of non-correct stimuli perceived as correct
stimuli, and 3) errors of omission as measured by the number
72
of presentations of correct stimuli that went undetected by
the subject (misses). The 30-minute vigilance task time was
broken up into six, five-minute blocks. These blocks were
then compared to determine the presence of a vigilance
decrement.
The a priori analysis indicated that the paranoid schizo
phrenics and nonparanoid schizophrenics did not differ on
ability to perform during distraction. In fact the distrac
tion appeared to have little, if any, effect upon performance
as measured by correct detections. False alarms were virtu
ally nonexistent for both conditions and diagnosis. Errors
of omission also showed no difference when compared across
diagnosis and distraction.
The post hoc analysis, which consisted of comparisons
in the design remaining after those hypothesized, indicated
paranoid and nonparanoid schizophrenics did differ. Paranoid
schizophrenics were able to correctly detect the relevant
stimuli at levels significantly above those of nonparanoid
schizophrenics. While the errors of commission were no
different, paranoids showed significantly fewer errors of
omission than their nonparanoid schizophrenic counterparts.
Also paranoid schizophrenics showed no vigilance decrement
over the 30-minute task time while nonparanoid schizophrenics
revealed a significant drop in perfoirmance in the last ten
minutes of the task.
73
These results implied that paranoid and nonparanoid
schizophrenics did differ in attentional ability. The para
noids as hypothesized by Silverman (1964a), were more
vigilant to changes in the environment than nonparanoids.
These results appeared to support the Silverman theory to
a greater degree than the Broadbent theory in that the filter
deficit implied by Broadbent to decrease performance by the
paranoid schizophrenics was not evident. Just the opposite
occurred in that paranoids did better than the nonparanoids.
The lack of an effect by the distraetor is still unclear and
may be due to either a true lack of distraction effect or to
design faults in the distraetor presentation. Future research
may help answer this question.
The conclusion of this study are as follows:
1. Paranoid and nonparanoid schizophrenics differ in
their response to a vigilance task designed to
measure attentional deficits.
2. Paranoid schizophrenics are more vigilant to changes
in the environment than nonparanoid schizophrenics.
3. Paranoid schizophrenics do not demonstrate a vigi
lance decrement during a 30-minute vigilance task
while their nonparanoid counterparts do show a
vigilance decrement.
4. Silverman's theory of attention appears to account
for paranoid-nonparanoid differences in attention
74
to a greater degree than the Broadbent theory of
filtering.
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APPENDICES
A. VENABLES AND O'CONNOR SCALE FOR RATING
PARANOID SCHIZOPHRENIA 82
B. AUDIOTAPE INSTRUCTIONS 85
C. INFORMED CONSENT 86
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85
APPENDIX B: AUDIOTAPE INSTRUCTIONS
Practice Session
Please listen carefully and I will tell you what we
wish you to do. First, make yourself comfortable. If at
any time you don't feel well, or you need to leave, just
knock on the door. Grip the blue handle so you can press
the little button on top. Here is what we are going to do.
As long as you see two 3's or two 8's, just let them go,
but if you see an 8 and 3 blink at the same time, press
the button. Don't press the button until 8 and 3 blink
together side by side. Let's practice it first for five
minutes. You will be finished when the two lights come
on and stay on. Do you have any questions? Okay, let's
start the practice.
Experimental Session
Now we are going to do the same thing for thirty
minutes. Remember, watch the numbers and press the button
when the 8 and 3 blink at the same time. Don't press the
button when two 8's or two 3's blink. (For distraction
condition: this time some lights around the numbers will
be blinking on and off, but don't pay any attention to them.
They are not important. Just look at the numbers in the
center.) Also just like the practice session, you will be
finished when the two lights come on and stay on. Are there
any questions? Okay, here we go.
86
APPENDIX C: INFORMED CONSENT
Name of Project: Effects of Distraction on Vigilance Performance.
The purpose of this investigation is to see how different people perform on a vigilance task. This will be done by having you press a button when the numbers 8 and 3 appear on a screen in front of you. A short interview will precede this task. This whole procedure will be done in one meeting which will last approximately one hour at a mutually convenient time.
Your participation and performance on both the interview and task will be kept completely confidential and will not be placed in your folder. Your participation is completely voluntary and your choice to participate or not to participate will in no way affect your treatment at this hospital.
This will not harm you in any way. Participation in the study should not be upsetting in any manner, but remember that you are free to stop at any time without affecting your treatment or length of stay in the hospital.
Although you may not personally receive any specific benefits as a result of your participation, this study may lead to improvements in mental health care. The investigator, Steven Parkison CTexas Tech University), will be available to answer additional questions concerning this study at any time. You are also welcome to consult with any member of the Human Assurance Committee, or Consent Committee, of this hospital concerning the research.
A. Certification of person explaining proposal
I have explained the above items to Name of person giving consent
and believe that understands each of the items. (he/she/they)
Date Investigator's Signature
We were present at the explanation of the above items to_ name of person
and we believe that ^understands each of the giving consent (he/she/they)
items.
Date
Witness
Date
Witness
87
B. Certificate of person giving consent
I understand each of the above items relating to the participa-
^^^^ °^ in the research of
Name of patient Name of project
under the care of__ , and I hereby consent to Investigator
_ participation in the research project, Cmy/his/her)
—_ Date Signature of person giving consent
Relation to Patient (Patient/parent/Guardian)
C. Certificate of assent by proposed subject (If the above consent is given by a person other than the patient and the assent of the patient is also required, the following certification should also be completed for signature by the patient.)
I understand each of the above items relating to the participa
tion of in the research of Name of patient Name of project
under the care of , and I hereby agree to my Investigator
participation in the research project.
Date Signature of Patient