Behav. Res. Ther. Vol. 31, No. 5, pp. 487-493, 1993 0005-7967/93 $6.00 + 0.00 Printed in Great Britain. All rights reserved Copyright © 1993 Pergamon Press Ltd

A T T E N T I O N A L B I A S I N A N X I E T Y : S E L E C T I V E O R N O T ?

ELAINE FOX Department of Psychology, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand

(Received 20 August 1992)

Smnmary--Under certain circumstances, anxiety has been shown to be associated with a processing bias favouring threatening information. Much of the evidence has come from experiments utilising the modified Stroop colour-naming paradigm. However, the traditional Stroop stimuli does not allow for a good test of selective attention. The present study presented colour, neutral and threatening words in conditions where the distracting (word) and target (colour) information were presented: (i) together; or (ii) separately. High trait-anxious Ss took longer to colour-name threatening words than neutral words, even when the threatening material was presented outside the focus of attention. There were no differential responses to threat and neutral words for low trait-anxious Ss. High trait-anxious Ss were also distracted by separate colour words, which produced no interference for the low-anxious Ss. These results suggest that high-trait anxiety may be associated with a general inability to maintain attentional focus, rather than by an automatic attentional bias towards threatening information.

I N T R O D U C T I O N

Numerous studies have presented a modified version of the Stroop colour-word task (Stroop, 1935) to anxiety disordered patients, and to normal Ss with high and low trait-anxiety (see Mathews, 1990; Williams, Watts, MacLeod & Mathews, 1988 for reviews). The modified Stroop task involves presenting threatening and neutral words in varying colours. The Ss task is to name the colour the words are printed in while ignoring the meanings of the words (Mathews & MacLeod, 1985).

In comparison with matched controls, patients with a generalized anxiety disorder (GAD) take longer to name the colours of threatening words than to name the colours of neutral words (e.g. Mathews & MacLeod, 1985; Mogg, Mathews & Weinman, 1989). These findings have been extended to other anxiety disorders such as panic disorder (Ehlers, Margraf, Davies & Roth, 1988; McNally, Riemann & Kim, 1990; McNally, Riemann, Louro, Lukach & Kim, 1992) as well as to individuals with high levels of trait-anxiety (Richards & French, 1990; Richards & Millwood, 1989). This selective processing effect has usually been interpreted as exhibiting an underlying attentional bias towards threatening information in these groups. However, there are different forms which this bias may take. The question this paper addresses is whether these attentional biases are selective. In other words, does Stroop-like interference from threat-related stimuli indicate that threatening information is selectively attracting attention.

At first sight the answer to this question is no, since it is generally accepted in the attention literature that the Stroop task does not provide a good test of selective attention (Treisman, 1969). The empirical data suggest (e.g. Eriksen & Eriksen, 1974) that visual attention may be focused on an area of the visual field with a radius of about 1 ° of visual angle. Everything within this radius is attended. To appropriately test for selective attention the most usual method is to present the to-be-attended and the distracting information in spatially separate locations. For example, Gatti and Egeth (1978) modified the traditional Stroop colour-word task. The target on each trial was a centrally-fixed colour patch, and the distracting information was a colour name printed above and below the colour patch. It was found that even when colour patches and distracting words were separated by 5 ° of visual angle, reaction times (RTs) to name the colour patches were slower when the displaced words were incompatible colour words. Subsequent studies have confirmed these findings of the ability of spatially separate stimuli to interfere with target processing even at wide separations (e.g. Miller, 1991). These results have been interpreted as indicating that unattended stimuli are processed to a semantic level. While this interpretation has been questioned (Yantis & Johnson, 1990), the main point here is that, in order to demonstrate selective attention, it is necessary to present target and distracting information under conditions where selective attention is possible.

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This has not been the case for many studies investigating attentional biases in anxiety. What has been established empirically is that threatening material presented in the focus of attention delays RTs to other information presented in the focus of attention. Whether the locus of this interference is at the level of perceptual analysis, at the level of response selection, or at some intermediate semantic stage cannot be determined with this paradigm (see Seymour, 1977). Demonstrations of interference effects with threatening material for anxious Ss could indicate that threatening material captures attention, but may not necessarily indicate that the meaning of the word automatically attracts attention away from an attended area. As Mathews (1990) points out, " . . . interference in this paradigm could be produced by the subsequent emotional reactions to words, or by a defensive shift in attention away from them" (p. 458). For example, it may be the case that anxious people cannot avoid processing threatening information presented at the centre of attentional focus, but they may be adept at screening out threatening information presented outside the focus of attention.

However, selective processing of threat words have been demonstrated in a very different paradigm to the Stroop task. MacLeod, Mathews and Tata (1986) presented word pairs on a computer screen. The Ss task was to read aloud the upper word in each pair and to press a response key any time a small dot appeared on the screen. Dot probes could appear in the same spatial location as either the top or bottom words. GAD patients were faster in detecting the dot probe if it replaced a threatening word, while non-anxious control Ss were faster when the dot probe replaced a non-threatening word. These results indicated that threat stimuli were more likely to hold the attention of anxious patients. Subsequently, attentional biases in this paradigm have been found in normal Ss with high trait-anxiety relative to low trait-anxiety (Fox, 1992), particularly when state-anxiety is elevated (MacLeod & Mathews, 1988). In all of these studies the word-pairs were separated on the vertical axis by about 1.5-2 ° of visual angle, which provides a good measure of the distribution of visual attention. However, as this is quite a different paradigm from the Stroop task the findings could reflect quite different conscious strategies on the part of the Ss (cf. Mathews, 1990). Furthermore since both locations were relevant (as the dot could appear in either spatial location), the best strategy for Ss would be to constantly shift attention between the two locations. This is therefore not a good test of the capacity to ignore distraction which appears outside the focus of attention.

The present study had a within-S design where Ss were presented with a 'traditional' Stroop task (words printed in different colours) as well as a 'separated' Stroop task (colour patches and words separated on the vertical axis). The presentation of target (colour patch) and distracting (word) information at a spatial separation of more than 1 ° of visual angle, should provide optimum conditions for spatial selectivity. If threatening information automatically attracts attention in Ss with high trait-anxiety, then the amount of interference produced by distracting (threatening) information should be fairly similar for these two tasks. If threatening information captures processing resources when presented in the focus of attention, but does not produce an attentional shift, then relatively greater interference should be apparent in the traditional Stroop task.

METHOD Subjects

The Spielberger STAI trait-anxiety scale (STAI: Spielberger, Gorsuch & Lusthene, 1970) was administered to 81 students in a third-year undergraduate psychology class. The class median on the trait-anxiety scale was 46. 18 Ss with trait-anxiety scores above 46 (High-anxious: HA), and 18 with trait-anxiety scores below 46 (Low-anxious: LA) were randomly selected and asked to participate in the experiment. All Ss agreed to take part and were paid NZ $5.00. There was no difference in ages between the two groups, whose mean ages were: HA, 24.5 y; LA, 23.2 y.

Materials

Two experimental tasks were used: a traditional Stroop task where words were printed in various colours; and a separated Stroop task, where colour patches were presented with words printed above and below the colour patch. Stimuli were presented on white cards 40 × 40 cm. All words were printed in block capitals and were 0.5 cm high. For the separated Stroop task, colour bars

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were 0.5 cm high and 1.5 cm wide. Words were printed at an edge-to-edge separation of 1 cm above and 1 cm below the colour bar. At a viewing distance of approx. 40 cm this gave a spatial separation between the colour bar and the distracting word of about 1.4 ° of visual angle. The centre-to-centre separation was 1.5cm, approx. 2.1 ° of visual angle. This should allow for adequate spatial separation between the target and the distracting information.

For the traditional Stroop task, 3 test cards were constructed, one for each word-type: Colour words, Neutral words, Threatening words. These words were printed in five colours: red, blue, green, brown and yellow. Each card contained 80 words printed in 8 rows of 10 words each. For the Colour words, 20 colour words were selected and were printed in the 5 colours, each colour appeared 4 times, and no colour word was printed in its own colour. For the Neutral words, 20 neutral words matched with the threatening words on the dimensions of word frequency and word length were selected. These words were presented in the 5 colours, each colour appearing 4 times. For the Threatening words, 20 threatening words (10 relating to physical threat, 10 relating to social threat) were selected from those used by Mathews, Mogg, May and Eysenck (1989). For each of these three conditions, each set of 20 words were presented 4 times, so that 80 words were printed on each card, and each colour appeared 16 times. These words were randomly presented on each card with the constraint that the same colour should not appear consecutively.

For the separated Stroop task, three cards were also constructed. The same 20 colour-word stimuli were used for the Colour words condition. For the Neutral words condition, a new set of 20 neutral words matched with the (new) threatening words on word length and word frequency were selected. Finally, for the Threatening words condition, a further 20 (10 physically, 10 socially) threatening words were selected from Mathews et al. (1989). 80 colour-patches were presented on each test card, each flanked by the same word above and below. The colour-patch/word stimuli were printed in 8 rows of 10 stimuli each.

Procedure

On arriving at the laboratory each S completed the state-anxiety scale of the STAI, and the Beck Depression Inventory (BDI: Beck, Ward, Mendelson, Mock & Erbaugh, 1961). Each S was tested individually. Subjects were told that they would be presented with two tasks. One would involve naming the colour that words were printed in. Instructions were to name aloud the colour of the ink (moving from left to right) as fast as possible, while ignoring the words. For the second task they were instructed to name the colour of the colour patches from left to right as quickly as possible, ignoring anything else on the card.

9 Ss in each group completed the traditional Stroop task first, then after a 2 min break they completed the separated Stroop task. The remaining Ss completed the two tasks in the reverse order. Cards were held up approx. 40 era in front of the Ss. Timing began when the first colour was named and ended when the last colour was named. Performance was timed with a stopwatch and was also recorded using a RQ 305S Panasonic tape-recorder to check the accuracy of responses.

For both the traditional and the separated Stroop tasks, the experimental conditions were presented in the same order for all Ss: Colour words, Neutral words and Threatening words. The threatening words were presented last as it has been shown that presenting threatening stimuli prior to neutral stimuli produces a carry-over effect which impairs performance on the neutral stimuli (McKenna, 1986). Any practice effects due to this ordering would tend to go against the experimental hypothesis.

RESULTS Mood measures

Table 1 shows the mean STAI and BDI scores for both groups. Independent t-tests revealed that the groups differed significantly on trait-anxiety, t = 8.8, P < 0.001, and on the BDI, t = 6.3, P < 0.001, but not on state-anxiety, t = 1.6.

Colour-naming times

Table 2 shows the mean colour-naming times for Colour words, Neutral words and Threatening words for the traditional and separated Stroop tasks for HA and LA groups. These data were

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Table 1. Mean Spielberger Trait and State Anxiety Inventory and Beck Depression Inventory scores

Mood measure

Group Trait Anxiety State Anxiety BDI

High anxious Mean 51.9 40.5 6.7 SD 4.1 10.6 2.4

Low anxious Mean 34.9 35.0 2.5 SD 6.9 9.2 1.2

analysed by means of a Group (HA, LA) x Task Type (Traditional Stroop, Separated Stroop) x Word Type (Colour words, Neutral words, Threatening words) ANOVA with repeated measures on the last two factors. Subject interaction was the error term.

There were significant main effects for Group, F(1,34) = 27.1, P < 0.001, Task Type, F(1,34) = 34.6, P < 0.001 and Word Type, F(2,68)= 124.6, P < 0.001. However, these effects must be considered in the context of a significant three-way interaction between these factors, F(2,68) = 5.9, P < 0.01. This interaction was explored by conducting simple-effects ANOVAs for each Group and each Task Type separately.

For the HA Ss on the traditional Stroop task, there was a significant effect for Word Type, F(2,34) = 59.6, P < 0.001. Tukey tests revealed that naming times on the Colour words were 24.2 sec slower than naming times on the Neutral words (P < 0.01). Naming times for the Threatening words were 6.4sec slower than the Neutral words (P < 0.01). There was also a significant effect for Word Type in the separated Stroop task, F(2,34) = 29.4, P < 0.001. Naming times were slower for the Colour words than for the Neutral words (+9.5 sec: P < 0.01) and slower for the Threatening words than for the Neutral words (+4.0 sec: P < 0.05).

The same analyses were computed for the LASs. Once again a significant effect for Word Type was found for the traditional Stroop task, F(2,34)= 127.4, P < 0.001, such that Ss took longer to name the ink colour of Colour words than of Neutral words (+22.7 sec: P < 0.01). However, in contrast to the HA Ss, naming times were equivalent for the Neutral and Threatening words. For the separated Stroop task there were no significant differences in naming times between the three word types for LA Ss, F < 1.

DISCUSSION

In a within-subjects design significant Stroop effects were found when Ss were required to name the ink-colour of an incongruent colour word, for both high and low trait-anxious Ss. Significant interference also occurred when the colour and the incongruent word were separated by 2.1 ° of visual angle for the HA but not for the LASs. This suggests that the L A S s were better able to ignore distracting information presented outside the focus of attention. The HA Ss took longer to name the colour of threatening words relative to neutral words, whether the colour and word were integrated (+6.4sec) or separated (+4.0see). Threatening words did not produce any interference for the low-anxious Ss.

These results replicate previous findings that high trait-anxious Ss are impaired in naming the ink-colour of threat-related words relative to neutral words (e.g. Richards & French, 1990). This finding was extended to include conditions where the distracting information was presented

Table 2. Mean performance time (sec) and standard deviations for the three tasks by the high trait-anxious and low trait-anxious groups for the traditional and separated Stroop stimuli

Traditional Stroop stimuli Colour words Neutral words Threatening words

Groups ~ SD .~ SD .~ SD

High anxious 71. l 9.2 46.9 12.3 53.3 11.7 Low anxious 61.6 6.8 38.9 7.2 38.6 7.5

Separated Stroop stimuli High anxious 78.2 I 1.8 68.7 11.4 72.7 12.0 Low anxious 55. I 14.3 54.6 12.3 54.3 12.2

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separately from the target, and provides a clearer test of the selectivity of attention. The finding that high trait-anxious Ss were distracted by threat-related stimuli 2.1 ° of visual angle away from the focus of attention suggests that this unattended information was semantically processed. This supports previous findings that high trait-anxiety is characterized by the deployment of visual attention towards the source of threat (Fox, 1992; MacLeod & Mathews, 1988). However, it was also found that HA Ss were distracted by separate colour words as well as by threatening words, which indicates that HA Ss may have a general difficulty in ignoring distracting information. In other words the attentional bias may not be specific to threat-related material. It is particularly interesting that the L A S s did not experience any interference from either colour or threat words in the separated Stroop task. On the basis of these results, it may be speculated that HA Ss are unable to avoid processing distracting information in general. The observed interference effects may therefore be a function of a general inability to maintain attentional focus, rather than by an automatic attentional bias towards threat-related information.

Mathews, May, Mogg and Eysenck (1990) addressed this question directly. They required currently anxious (GAD), recovered GAD and matched control Ss to search for a neutral target while ignoring distractor words, which could be either threat-related or neutral. It was found that all distractors (whether threat or neutral) disrupted the performance of the currently anxious group, whereas only the threat distractors disrupted the recovered group. These effects were only found under conditions of visual search (i.e. when target location was unknown). No significant group differences emerged when Ss were required to maintain attention on a specific spatial location (i.e. when target location was known). Mathews et al. (1990) suggest on the basis of these results, that it may be only when a perceptual task involves attentional search that differences emerge between anxious and non-anxious groups.

However, some recent results with high and low trait-anxious students at a time of high stress (close to exams) suggests that high trait-anxiety may be characterized by the automatic and selective cognitive processing of threat stimuli. Rutherford and MacLeod (1990) (cited by MacLeod & Hagan, 1992) required their Ss to name the ink colour of threat and neutral words. Half of these words were presented for only 20 msec, and were pattern masked to prevent conscious awareness of their semantic content. Even under these conditions, the high trait-anxious students showed reliable interference from threat words, relative to low trait-anxious students. Since interference effects on the masked exposure trials could not have been mediated by a conscious strategy, these patterns of selectivity must reflect an automatic cognitive process in these non-clinical Ss. These results have been subsequently replicated by MacLeod and Hagan (1992). In a correlational study, they found that the degree of interference from threat stimuli in masked exposure trials was related to the level of trait and state-anxiety. However, no interference from threat words was observed in the unmasked conditions, leading the authors to suggest that "when stimuli are presented in a manner that permits their conscious identification, high trait-anxious normal Ss may be capable of strategically negating this automatic processing bias" (MacLeod & Hagan, 1992: p. 157).

It is clearly important for theories of cognition and emotion to establish at what point in the cognitive system selective biases are occurring. In cognitive psychology there has been much debate about whether attentional selection is 'early' or 'late' (see Lambert, 1985 for discussion). Briefly, late selectionists argue that all stimuli are identified to a semantic level, and then selected for further processing. In contrast, an early selection view argues that only low-level perceptual features are processed rather than full semantic analysis. On the basis of the evidence for attentional bias in anxiety, it is appealing to suggest that anxious individuals semantically process information at a non-conscious level (e.g. MacLeod & Hagan, 1992), and that threatening information thus processed then captures attentional resources (e.g. Mathews et al., 1990). The finding in the current experiment that information presented outside the focus of attention disrupts performance for high trait-anxious Ss supports this interpretation.

However, there is a methodological problem with much of the research in anxiety which precludes a strong conclusion that HA people automatically process stimuli to a level of meaning. Cognitive psychologists make a distinction between repetition priming and semantic priming. Repetition priming is the finding that when words are repeated over the course of an experiment, low-level perceptual features (e.g. letters) may lead to lexical access. For example, if the word HUNGER is repeated, on the third or fourth repetition, a H and a G may be all that are required

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to identify the word. In contrast , semantic priming is the demonstra t ion that the meaning o f the word has been activated, and that related semantic information will therefore be 'primed' . For example, the word N U R S E may be identified significantly faster if it is presented immediately after the word D O C T O R than if it is presented after the word H O U S E . The demonstra t ion o f a semantic priming effect indicates that stimuli have been identified to a level o f meaning as long as repetition priming effects can be ruled out.

I f the a rgument is that anxiety is associated with the semant ic analysis o f stimuli, which may then capture attention, it is clearly impor tant to ensure that repetition priming effects are not confounding the data. Unfortunately, many experiments on attentional bias in anxiety (including the present one) have used a small set o f distracting stimuli which were then repeated over the course o f an experiment (e.g. Dawkins & Furnham, 1989; Ehlers et al., 1988; MacLeod & Hagan, 1992; McNal ly et al., 1992). However, reliable attentional biases have also been shown for anxious individuals under condit ions where word stimuli were presented only once (e.g. Fox, 1992; MacLeod et al., 1986; MacLeod & Mathews, 1988; Richards & Millwood, 1989). However in all o f these studies, the distracting information was probably attended.

In conclusion, an impor tant goal for research on the cognitive characteristics o f anxiety is to establish where in the cognitive system bias is occurring. A focused attention paradigm, where distracting information is presented outside the focus o f attention, and where target location on each individual trial is cued (see Yantis & Johnston, 1990) would be a powerful test o f the ability o f anxious patients to selectively at tend to a target and to ignore distracting information. Recent findings that high trait-anxiety is characterized by an automat ic processing bias o f threatening material, even when this material cannot be consciously identified, have impor tant implications for the understanding of anxiety (Rutherford & MacLeod, 1990; MacLeod & Hagan, 1992). I f this effect was replicated using non-repeat ing distracting words, this would indicate that the locus o f the attentional bias in anxiety is at a semantic rather than at a perceptual level.

Acknowledgement--This research was supported by a grant from the Victoria University of Wellington Internal Grants Committee.

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