linguistic and perceptual-motor contributions to the kinematic properties of the braille reading...

Human Movement Science 30 (2011) 711–730

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Human Movement Science

journal homepage: www.elsevier .com/locate/humov

Linguistic and perceptual-motor contributions to thekinematic properties of the braille reading finger

Barry Hughes a,*, Arend W.A. Van Gemmert b, George E. Stelmach c

a Department of Psychology, Research Centre for Cognitive Neuroscience, University of Auckland, Private Bag 92019,Auckland, New Zealandb Department of Kinesiology, Louisiana State University, Baton Rouge, LA 70803, USAc Motor Control Laboratory, Department of Kinesiology, Arizona State University, Tempe, AZ 85287, USA

a r t i c l e i n f o a b s t r a c t

Article history:Available online 5 August 2010

PsycINFO classification:2340

Keywords:BrailleReadingKinematicsMovement analysisHaptic perception

0167-9457/$ - see front matter � 2010 Elsevier B.doi:10.1016/j.humov.2010.05.005

* Corresponding author. Tel.: +64 9 373 7599; faE-mail addresses: [email protected] (B.

Stelmach).

Recordings of the dominant finger during the reading of braillesentences by experienced readers reveal that the velocity of thefinger changes frequently during the traverse of a line of text.These changes, not previously reported, involve a multitude ofaccelerations and decelerations, as well as reversals of direction.We investigated the origin of these velocity intermittencies (aswell as movement reversals) by asking readers to twice read out-loud or silently sentences comprising high- or low-frequencywords which combined to make grammatical sentences that wereeither meaningful or nonmeaningful. In a control condition weasked braille readers to smoothly scan lines of braille comprisedof meaningless cell combinations. Word frequency and re-readingeach contribute to the kinematics of finger movements, but neithersentence meaning nor the mode of reading do so. The velocityintermittencies were so pervasive that they are not easily attribut-able either to linguistic processing, text familiarity, mode of read-ing, or to sensory–motor interactions with the textured patternsof braille, but seem integral to all braille finger movements exceptreversals. While language-related processing can affect the fingermovements, the effects are superimposed on a highly intermittentvelocity profile whose origin appears to lie in the motor control ofslow movements.

� 2010 Elsevier B.V. All rights reserved.

V. All rights reserved.

x: +64 9 373 7450.Hughes), [email protected] (A.W.A. Van Gemmert), [email protected] (G.E.

http://dx.doi.org/10.1016/j.humov.2010.05.005

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712 B. Hughes et al. / Human Movement Science 30 (2011) 711–730

1. Introduction

Relative to visual print reading, the linkages between the perceptual, cognitive, and motor pro-cesses of braille reading have not been deeply investigated. It is clear that visual reading and braillereading must share common types of operations: both can be held to involve perceptual informationutilization, in letter, morpheme, and word recognition (with attendant demands on attention andmemory), as well as the range of syntactic and semantic operations that give text a specific interpre-tation (Daneman, 1988; Foulke, 1991). In addition, both are highly dependent on concurrent activemotor control: via fixations and saccadic eye movements or via finger movements. However, dissim-ilarities are also clear. As Bertelson (1995) and Millar (1997) have pointed out, braille reading is held tobegin with exhaustive and serial contact with the surface on which the text is embossed and to involvemovements that are smoother than saccades and fixations.1 As a consequence, empirically groundedmodels of braille reading need to show how the fingers move, how the interaction of skin and texturedsurface gives rise to pattern recognition, and if and how the linguistic processing of the braille code influ-ences these perceptual and motor operations.

Since the finger movements of the braille reader need to be controlled with a degree of precisioncommensurate with the spatial details of the braille code, as well as the temporal rate at which words,syntax, and semantic content can be processed, analysis of the reading movements would benefit frommeasurements of higher order variables, such as velocity and acceleration. Consider Panel A of Fig. 1.When reading a line of text with a single dominant finger, the position of a braille reader’s dominantreading finger is highly linear when plotted as a function of time. That is, the dominant finger tends tomove continuously from left to right, with contact maintained between skin and text surface. Similarposition-by-time data have been reported previously (see, e.g., Bertelson, Mousty, & D’Alimonte, 1985;Millar, 1997; Mousty & Bertelson, 1985). Finger position-by-time plots suggest that braille reading is‘‘smooth, with few variations in speed” (Bertelson, 1995, p. 94).

However, when the position data can be differentiated with respect to time, a measure of theinstantaneous velocity of the finger as it crosses text becomes available (Fig. 1B). Such computationsreveal that the finger rapidly alternates between phases of acceleration and deceleration and thatthere is considerable variability of velocity about the mean. Finger velocity tends to be neither con-stant nor smooth. Such an intermittent2 profile is by no means peculiar to this trial; it is representativeof all readings of all sentences by all individuals that we have recorded.

To what processes should such intermittencies be attributed? A priori, those exemplified in Fig. 1Bcan be attributed to more than one source. The fluctuations might originate by virtue of skin contactwith textured surfaces – that is, in haptic texture perception. Raised dots of the braille code are, at thislevel, differentially rough surfaces that may well generate position-based fluctuations in the frictionquotient. These fluctuations in resistance to movement across the surface might also impact thedischarge of cutaneous receptors and proprioceptive afferents, and therefore motor efference, all ofwhich characterize haptic explorations of texture (e.g., Hughes & Jansson, 1994; Katz, 1925/1989;Loomis & Lederman, 1986).

A second possibility is that, at the speeds characteristic of braille, the limb motor control systemsimply cannot generate either constant or smooth velocity profiles at the distal fingertips, even if thatis the intent of readers. Intermittent velocity traces may be an emergent feature of finger movementsthat are slow enough to permit letter and word recognition but not fast enough to constitute singulartrajectories.

It may be that the intermittency of the velocity profile is owing to fluctuations in the ongoing de-mands of linguistic comprehension. Do the kinematics of the movements of braille readers similarly

1 The serial nature of braille reading also suggests certain similarities with listening (Mousty & Bertelson, 1992), which areworthy of pursuit, although reading is a more active perceptual process than is listening and is not complicated by speech-specificproperties such as coarticulation (see, e.g., Bertelson, Mousty, & Radeau, 1992).

2 The term intermittency is used in the motor control literature but does not, apparently, have a single consensual definition(Doeringer & Hogan, 1998). We propose to use it here to refer to the variability of the velocity trace, measured as the number ofinflections in the trace (more commonly known as acceleration zero-crossings) and we use the term to describe rather than toexplain.

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Fig. 1. Representative sample of movement (in the left–right direction) of the dominant reading finger during reading of asentence rendered in Grade 2 (contracted) braille. The upper Panel (A) plots finger position in the left–right dimension as afunction of time and the lower Panel (B) contains the left–right velocity of the finger as a function of time on the same trial.

B. Hughes et al. / Human Movement Science 30 (2011) 711–730 713

reflect the instantaneous demands of text perception and processing in a manner that is comparablewith print reading? Perhaps unfamiliar letter combinations, or rare words, or sentences of complexsyntax, or unpredictable content have the effect of briefly reducing the velocity of the moving fingerto accommodate longer lexical search, or parsing operations, or semantic processing. Psycholinguisticfactors are known to have consistent effects on the patterns of eye fixations and saccades in visualreading (for recent reviews, see Kliegl, Nuthmann, and Engbert (2006) and Rayner (1998)) and henceit would not surprise if there were analogous language processing modulations of reading movementsin braille.

Our major objective was to investigate how each of these factors contributes to the kinematic pro-files of the reading finger. First, we sought to establish the extent to which the kinematic character-istics of movements of the fingerpad over braille text are influenced by the texture composition ofthe braille cells, independently of needing to be read. We did this by asking readers to scan ‘‘assmoothly as possible” a single line of meaningless braille text comprised of repeated braille cells withzero, one, three, or five raised elements. We hypothesized that the velocity of scanning movementswould be higher and the intermittency lower than during reading because there were no requirementsto process text at any level. If the texture composition of braille cells influences the kinematics of fin-ger movements, we expected to find text with more raised cells to create more resistance to smoothleft–right movements and lines containing no raised cells at all to be scanned with the smoothestvelocity profiles.


To measure text processing effects on finger kinematics, we created sentences that varied in twoways: by comprising either high- or low-frequency key words, which were embedded in sentenceswith or without meaning. If language processing demands are directly reflected in finger kinematics,then we should observe reduced mean velocities, more intermittent velocities, and more frequentreversals when reading sentences with low-frequency words. We examined these hypotheses in con-junction with two others. We asked whether second readings of sentences were faster and smootherthan first readings, and whether the benefit of a second reading was greater for sentences with low-frequency words and/or sentences without semantic content. If first readings are slowed and mademore intermittent by vagaries of lexical access or a lack of semantic context, is this true for secondreadings where memory for – and hence anticipation of – text is possible? In addition, we requiredreaders to read either silently, so as to be able to repeat verbatim the contents of the sentences at com-pletion of reading, or to read out-loud. These tasks differ primarily in their working memory demands(greater for silent reading) and their phonological encoding (greater for reading aloud but not absentin silent reading). Silent and oral reading have been found to differ in their visual reading character-istics: fixation durations tend to be longer and saccade lengths shorter in oral reading (see Rayner,1984). Millar (1990) found that braille readers of all levels of experience were no faster on averagereading aloud than silently. We sought a replication of this finding, while leaving open the possibilitythat the reading modes would have the different effects on finger movement kinematics, includingvelocity intermittency.

2. Method

2.1. Participants

Twelve fluent braille readers (10 females; 2 males) provided informed consent under protocols ap-proved by the University of Auckland Human Participants Research Committee and the InstitutionalReview Board of Arizona State University. Ten participants were congenitally blind; two lost theirsight completely at age 10 y. Their ages ranged from 27 y to 75 y (mean: 44.9 ± 14.0 y). On average,participants began reading braille at 7.8 y (±4.2 y) although three did not begin reading braille untillater (at 10 y, 12 y, and 19 y). They had, on average, 34.5 y experience (±15.1 y) as readers. Under nor-mal circumstances, two participants would have used a single-finger to read; ten participants wouldhave read with more than one finger and, of these, nine would have read with the index finger of eachhand and one read with the index and middle fingers of each hand. For nine readers, the right indexfinger was the dominant finger; for three, the left index was dominant. Participants were paid $25 fora session and were reimbursed for all travel expenses.

2.2. Stimuli

We created one set of stimuli for scanning and two sets of sentences for reading. The scanning setcomprised lines of braille text that were to be ‘‘smoothly scanned”. We created eight such lines. Twoblank lines comprised no raised dots at all. Paired with each of these was a line comprising repeatedcells containing either one, three, or five raised dots per cell. In one of these formats, the cells wererepeated, without gaps, for the length of the line (we refer to these as ‘continuous cells’); in the otherformat, cells were clustered in lengths of four, five, and six cells, each cluster broken by a single blankcell (‘noncontinuous cells’) so as to have a superficial resemblance to words on a line.

Each reading set comprised 16 novel sentences, rendered in contracted or Grade 2 braille3 onstandard braille paper using software from Duxbury Systems and a Juliet Pro60 embosser (EnablingTechnologies). For each set, four sentence types were created by including (1) high-frequency wordsor (2) low-frequency words, factorially combined with sentences which either (3) did or (4) did not havecoherent meaning. Four tokens of each sentence type were created (see Appendix). Each sentence was

3 Although readers typically advance to Grade 2 after having learned Grade 1 Braille, experienced and fluent readers find Grade 1braille frustratingly difficult to read. For details of the full Grade 2 code, see http://www.brailleauthority.org/.

http://www.brailleauthority.org/


based on a template containing four key words: two nouns, one adjective and one verb. The one adjectiveper sentence was located either prior to the first noun or prior to the second noun, in a counterbalancedmanner. Most sentences contained both a definite article (the) and an indefinite article (a, an) in a coun-terbalanced manner. All sentences were novel and grammatically correct, but half were intentionallymeaningless (i.e., unlikely to ever be read under any circumstance) while half were intended to besemantically coherent (i.e., to be sentences that one could imagine reading, given some context). Weoperationally defined high-frequency words as those that appear more than 30 times per million wordsfor nouns and verbs or more than 20 times per million words for adjectives, and low-frequency words asthose that appear no more than 10 times per million for nouns, verbs, and adjectives (Johansson & Hof-land, 1989). High-frequency sentences contained words with the following mean frequencies (standarddeviations in parentheses) frequencies: nouns: 115.1 (±64.5); verbs: 169.2 (±198.9); adjectives: 82.4(±66.1). Low-frequency sentences contained words with the following mean frequencies: nouns: 3.1(±2.1); verbs: 2.4 (±1.3); adjectives: 1.6 (±0.8). Each sentence was contained on a single line of textand varied in length when measured by the number of braille cells. In order to minimize anticipatoryeffects associated with reading, we did not seek to control for word or sentence length.

2.3. Movement recording

We used a 30.5 cm by 30.5 cm digitizing tablet (Intuos by Wacom) with a spatial resolution of0.01 cm in each direction. The digitizer’s grip pen was fitted to a light-weight finger attachmentand attached to the reader’s dominant reading finger. Once securely attached, the pen was in a nearvertical position in relation to the finger and did not rotate with finger movements.4 The pen tipwas located 3–10 mm from the center of the reading finger (depending mostly on individuals’ preferredfitting of the pen attachment). The digitizer was capable of recording the location of the pen without di-rect contact with the surface. Temporal accuracy was limited by the digitizer’s 200 Hz clock speed whichwas well in excess of the 100 Hz sampling rate of the location of the pen tip using MovAlyzer (v. 4.2, fromNeuroscript, LLC) to sample and store these coordinates for subsequent analyses.

2.4. Procedure

Participants were tested individually in a single session, lasting approximately 1.5 h. The scanningtask required participants to move ‘‘as smoothly as possible” along the line of braille cells from begin-ning to end. They were not advised how best to do this, nor were they encouraged to strive for anyparticular speed or movement property. The two sets of sentences were read by all participants,but each set was read in a different reading mode; i.e., one was silently read, remembered and re-peated verbatim, the other was read out-loud. The assignment of participant to sentence set was coun-terbalanced, as was the order in which the reading conditions were applied. The scanning and readingphases were also counterbalanced for order. Participants read each sentence twice and, within a set,all trials were presented in a randomized order. Participants were asked to read as fast as possible, gi-ven that they were as accurate as possible, using only the self-designated dominant reading finger.Participants were guided to the beginning of the sentence and the reading finger was placed in contactwith the surface to left of, but not on, the first cell of the sentence. Participants were free to beginreading after any latency period of their choosing and were permitted to move at any speed, in anydirection, at any time, so long as they performed the reading task as required. All sentences weremonitored by the experimenter for accuracy.

4 It occurred to us that the pen mounting on the finger, when combined with lateral scanning movements, may produce minutechanges in the location of the pen tip (induced rotations of the pen about its mounting), especially since the pen tip was not incontact with the reading surface. It is not straightforward to rule this out, although we have performed several control tests. Whenmounted securely, the pen does not move, even minutely, when the finger is moved at a variety of velocities in the 5–10 cm/srange and then suddenly stopped. To come at the question another way, we found that movements at this relatively low velocitywhen the pen is held as if writing produce almost identical patterns of intermittency. Finally, we have developed a differentrecording method, reducing the vertical height of the pen by mounting the pen tip at the finger but relocating the pen’s electronicsto a fitting on the forearm. This produces no major change in the nature or frequency of the intermittencies during either readingor scanning.


2.5. Data processing

During all movements of the finger the pen tip’s coordinates were sampled at 100 Hz. These datawere then differentiated with respect to time to compute velocity and again to compute accelerationin the x (left–right) and y (up–down) dimensions. The raw data were low-pass filtered (set at 12 Hz)with a dual-pass fourth order Butterworth filter. Unless otherwise stated, all analyses were directed tomovements in the left–right dimension. Post-processing involved cropping the data to remove twotypes of artefacts: (1) the latency between initial contact and movement initiation, which involvedeither no movement at all or minor relocations in any direction and (2) movements made after thetrailing edge of the reading fingerpad was beyond the last cell of the sentence and did not then under-go any reversal to an earlier portion of the sentence. These cropped data were used in all analyses andfigures presented below. In the analyses reported below, we focus on three kinematic indices of read-ing performance: (1) mean velocity (in cm/s), (2) the number of acceleration zero-crossings per sen-tence, and (3) the number of reversals made per sentence.

3. Results

3.1. Smooth scanning

The participants were asked to scan lines of meaningless text ‘‘as smoothly as possible”, the pur-pose of which was to determine exactly how smooth ‘‘smooth movements” can be generated by braille

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Fig. 3. Mean scanning data, plotted as function of the line format (continuous or noncontinuous) and the number of raised dotsin each repeated braille cell. Panel A: mean (with standard error bars) finger velocity as a function of position. Panel B: meansquared deviation from the average velocity. Panel C: the number of acceleration zero-crossings. In each panel the dashed linecorresponds to the grand mean for that measure.


readers. Velocity plots upon which the following analyses are based are shown in Fig. 2. These plotsindicate that braille readers cannot easily generate movements that are kinematically smooth evenif they are consciously smooth.

Analysis of variance (ANOVA) of mean velocity revealed a significant effect of the number of raiseddots in the cells, F(3, 33) = 3.68, p = .02, g2 = .25. Post hoc analysis showed that mean velocity wasslower when the lines contained repeated cells with zero or one raised dot than when the lines werecomprised of repeated 3- or 5-dot cells. ANOVA revealed no effect on mean velocity of the continuityof the cells, F(1, 11) = 0.62, p = .45, and continuity and raised dot number did not interact,F(3, 33) = 1.11, p = .36. Panel A of Fig. 3 presents these data which suggest that preferred scanningvelocities are slightly impacted by the number of textured elements, but not by their arrangement.

Two different measures of velocity intermittency are presented in Panels B and C of Fig. 3. Thegrand mean of squared deviations from the mean was 3.48 and ANOVA revealed a main effect ofthe number of raised dots in each of the cells, F(3, 33) = 5.89, p < .01, g2 = .35. Pairwise comparisonsshowed that deviations from the mean were greater for the empty lines; whenever the lines containedsome raised dots, variability was reduced, but not otherwise according to the number of raised dots.Inserting blank cells had no effect on the mean squared deviation from the mean, F(1, 11) = 0.55,p = .47, and the two factors did not interact, F(1, 11) = 0.91, p = .44.

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Fig. 4. Sample traces of all participants reading sentences containing high-frequency words (Panel A) or low-frequency words(Panel B). The grey areas indicate the locations of braille words, which are also included. Velocity values less than zero signifyreversals.


Although sentence scanning took approximately 5 s, participants generated movement profileswith an average of 50.30 acceleration zero-crossings. ANOVA revealed a significant effect of line for-mat, F(1, 11) = 5.53, p = .04, g2 = .34, with scans of continuously repeating cells (mean 53.71) produc-ing more zero-crossings than noncontinuous cells (46.90). The content of the lines did not affect thezero-crossing count, F(3, 33) = 1.46, p = .24, and line format and line content did not interact,F(3, 33) = 2.45, p = .08.

Table 1Characteristics of individual participants and their mean reading kinematic measures. Braille years signifies a participant’s estimateof the number of his or her years as a fluent braille reader.

Age Sex Braille years Mean velocity No. zero crossings No. reversals

27 F 12 2.39 117.9 12.853 F 44 4.69 56.9 2.126 F 16 3.31 75.7 1.854 F 45 2.26 116.4 7.753 F 44 3.20 80.6 11.236 F 28 2.84 104.4 14.555 M 48 2.38 105.7 9.875 M 62 2.33 105.3 4.441 F 20 4.22 71.8 5.143 F 37 4.93 57.3 0.844 F 36 2.19 108.6 15.932 F 22 1.28 185.9 26.1


These analyses suggest that while velocity and the variability of velocity are influenced by thenumber of raised dots being traversed (fewer cells encourage greater velocities, which are also morevariable), the transitions from acceleration to deceleration are more influenced by the continuity ofthe raised dots: punctuating the raised dot sequences with blank cells had the effect of reducing thismeasure of velocity intermittency, even though it did not reduce the mean velocity with which suchlines were traversed.

3.2. Reading analyses

Sample velocity plots upon which the reading analyses are based are shown in Fig. 4. Table 1 showsindividual readers’ details and mean performance. From the raw data, we computed mean readingvelocity5 as a function of reading mode, reading repetition, constituent word frequency, and sentencemeaning. Collectively, the four sentence tokens of each combination of word frequency and sentencemeaning were considered a control factor and were not included in the statistical analyses reported be-low. Our readers had no difficulties reading the experimental material accurately: in the silent readingcondition 3% of the trials were in error and in the oral reading condition a total of six errors were madeover 384 trials.

The first indicator that reading is different from smooth scanning is that mean reading velocitieswere less than half those generated when smoothly scanning (3.00 vs. 7.25 cm/s, respectively). Inaddition, scanning and reading velocity traces both reflect considerable intermittencies (cf. Figs. 2and 4). To the extent the scanning movements are faster (with sustained values in excess of 20 cm/s) they tend to be smoother in profile. Few instances of reading velocities in this range are observed.To the extent the movements are slower, peaking at 10 cm/s or less, the number of inflection pointsincreases.

3.3. Reading velocity

Fig. 5 (Panel A) shows the summary data of the variables on reading velocity. Mean velocity acrossall conditions averaged 3.00 cm/s. The fastest reader averaged 4.93 cm/s; the slowest 1.28 cm/s.

ANOVA revealed main effects of word frequency, F(1, 11) = 15.85, p < .01, g2 = .59, and of repetition,F(1, 11) = 176.00, p < .01, g2 = .94. Sentences comprising high-frequency words were read at a mean

5 We use the distance by time metric (cm/s) rather than cells or words per second. Our focus on kinematics is one reason for this,but it also seems problematic to use cells read per unit time when it is not clear whether one should include the dimensions of thecell alone (columns of raised dots are separated by a center-to-center distance of 2.5 mm) or partition the sizable gap(approximately 3.7 mm) as belonging to one cell or its neighbor. In addition, the braille code is not perfectly standardized in termsof cell spacings (examples can be found online: http://www.tiresias.org/research/reports/braille_cell.htm), so a cells/s metric doesnot always constitute the same distance in various instantiations of the braille code.

http://www.tiresias.org/research/reports/braille_cell.htm

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Fig. 5. Panel A: mean reading velocity in cm/s (with standard error bars), as a function of reading mode (silent or oral), wordfrequency, sentence meaning, and re-reading. Panel B: mean number of intermittencies in the velocity trace. Panel C: meannumber of reversals. Conditions are coded such that word frequency – (h)igh or (l)ow – is crossed with sentence meaning (M) ornonsense (N). R1 is the first reading (grey bars) and R2 the second reading (black bars). The grey-shaded bars indicate firstreadings, the black bars indicate second readings, and the dashed line indicates the mean value in that reading mode.


velocity of 3.19 cm/s; those comprising low-frequency words were read 0.38 cm/s slower. Secondreadings were made at 0.71 cm/s greater velocities (3.36 cm/s vs. 2.65 cm/s). We also found an inter-action of word frequency and repetition, F(1, 11) = 7.63, p = .02, g2 = .410: the benefit of a second read-ing was greater for sentences with low-frequency words. Neither reading mode (F(1, 11) = .134,p = .73) nor sentence meaning (F(1, 11) = 1.26, p = .29) had significant effects on mean reading veloc-ity. No other effects were significant.


3.4. Velocity intermittency6

On average, and even when we did not include reversals in the analysis, readers’ velocity profilescontain almost 100 distinct acceleration zero-crossings. Zero-crossing frequency was not significantlyaltered if participants read silently (mean: 101.1) or aloud (96.7), F(1, 11) = 0.44, p = .52, or read sen-tences with (98.2) or without (99.5) meaning, F(1, 11) = 0.32, p = .58 (see Fig. 5B). Zero-crossing fre-quency was, however, significantly lower when the sentences contained high- (88.3) rather thanlow-frequency (109.5) words, F(1, 11) = 17.47, p < .01, g2 = .61, and when the sentences were readfor the second time (83.32 vs. 114.45), F(1, 11) = 28.98, p < .01, g2 = .72. Word frequency and repetitionalso interacted, F(1, 11) = 9.94, p = .01, g2 = .48. The effect of a second reading was greater for sen-tences with low-frequency words: they contained 40 fewer zero crossings on the second reading whilethose for high-frequency sentences contained 22 fewer zero crossings. In addition, we found amoderate word frequency by sentence meaning interaction, F(1, 11) = 5.15, p = .04, g2 = .32: nonsensesentences induced more zero-crossings than meaningful sentences but only when the content wordswere high frequency (with low-frequency words, the trend was reversed).

3.5. Reversals

Reversals, we presume, represent attempts by the reader to recover from a state of misperceptionor misunderstanding by moving the finger back to an earlier portion of the text. Word frequency andreading repetition each had large effects on both the number of times a reader reversed direction.7 AsFig. 5C shows, even in the condition in which readers made the fewest number of reversals in readingdirection, the mean was more than three per sentence. In other conditions, readers could average almost20 reversals. Fewer reversals were observed with high- than low-frequency words F(1, 11) = 13.12,p < .01, g2 = .54. Fewer reversals occurred during second readings than first readings, F(1, 11) = 21.80,p < .01, g2 = .66. We also found a word frequency by repetition interaction, F(1, 11) = 9.77, p = .01,g2 = .47: the effect of re-reading a sentence on reversals was larger with low-frequency words thanhigh-frequency ones.

Although reading out-loud was not more likely to induce reversals than silent reading,F(1, 11) = 0.57, p = .47, and sentence meaning had no effect on reversal frequency, F(1, 11) = 0.21,p = .66, these factors interacted, F(1, 11) = 7.62, p = .02, g2 = .66. Reversals were more likely to occurduring the silent reading of meaningful sentences and during the oral reading of nonsense sentences,suggesting that these large-scale interruptions in reading are driven by different processing demandsin the two modes.

4. Discussion

Eye movements have long been considered an important and unobstrusive window onto the cog-nitive processes associated with reading (e.g., Just & Carpenter, 1980; Rayner, 1998; Rayner & Sereno,1994; Underwood, 1985) as well as reading disorders such as dyslexia (e.g., Pollatsek, 1983). Themeasurement of saccade timing and fixation durations is central to understanding the functionalcharacteristics of saccades and fixations in reading which, in turn, constitute major points of differ-ence in competing models of reading (Reichle (2006) and Reichle, Rayner, and Pollatsek (2003), focuson these differences). Braille reading, involving as it does continuous, serial, and exhaustive contact

6 The frequency of acceleration zero-crossings is not the only measure of the changes in velocity while reading that we haveconsidered. Fourier analyses reveal very few differences in the velocity spectrum, by any of our independent variables. Root meansquared deviation from the average velocity, which we used in describing the scanning movements, similarly failed to revealsystematic effects with the variables we use here.

7 In the visual reading literature, it is common to distinguish reversals or regressions from refixations (see Rayner (1998), for abrief review). The former are saccades in the reverse direction to a word that had already been fixated. The latter are saccadesmade to a different fixation point on the word currently fixated, saccades which may be in either direction. While such adistinction is possible in braille, and can be observed in practice (see Fig. 4), we consider a reversal to be any movement in theright–left direction.


with the text, lends itself to a different but equally important kinematic analysis. Computation ofvelocity profiles, which has not previously been conducted with braille, permits a fine-grained anal-ysis of how single-finger braille reading occurs in detail and in real time (Hughes & van Gemmert,2008; Hughes, van Gemmert, & Stelmach, 2009).8 We have shown here that this method permits mea-surement of kinematic variables that are not easily recoverable via other techniques (Bertelson, Mousty,& D’Alimonte, 1985; Breidegard et al., 2008; Davidson, Wiles-Kettenmann, Haber, & Appelle, 1980; Mil-lar, 1997). Among the observable features of reading that this method reveals are the highly intermit-tent velocity profiles that the finger traces as it moves rightward across lines of text, the range ofvelocities with which finger tends to move, as well as the number and kinematic properties of reversals.

We began by suggesting that the intermittency of the velocity profiles could be owing to one ormore factors: (1) haptic perceptual effects arising from the mechanical contact of an actively movingfingerpad and a highly textured surface, (2) a motor system that can generate low-velocity move-ments, but neither smooth nor constant low-velocity movements, and (3) the linguistic characteristicsof the material being read.

When asked to scan lines ‘‘as smoothly as possible”, readers do not in fact move smoothly. At thespeeds chosen, all velocity traces reveal high degrees of intermittencies. This suggests that movementsin the range chosen by participants (typically twice as fast as they would move when reading) do notresult in a smooth or even constant velocity traverse of the line (see Fig. 2). This is important since itsuggests that participants are either not aware of the extent to which intentionally smooth move-ments are not smooth, or that they are aware but are not able to do much about it.

Since reading increases the intermittency of the trace, language-related factors generally appear toinfluence the velocity profiles. However, since frequent intermittencies in the velocity trace can befound during scanning braille characters without being able to read them, we suspect the influenceis not direct. Relative to reading, scanning reduces by half the number of acceleration zero crossingsbut does not eliminate them. Nor can factors related to braille as texture be held to cause these inter-mittencies. Since we found only weak effects of texture density on scanning velocity and velocitysmoothness, it does not appear that the mechanical interaction of skin and texture surface systemat-ically contributes to the movement kinematics we have found.

With respect to reading, we have shown that some linguistic characteristics have a significant ef-fect on the kinematic details of the braille reading finger. We asked whether manipulations of wordfrequency and sentence meaning in sentences would affect reading velocity or its intermittency.The former has strong effects but the latter has only minor ones. Word frequency has long been knownto exhibit strong effects on visual reading of single words in isolation as well embedded in longer pas-sages (for a review, see Rayner (1998)). Finding word frequency effects on mean braille reading veloc-ity, on velocity intermittency and on reversal frequency suggests that the effects have a similarinformation processing origin, in the time course for lexical access and recognition, as in visual read-ing. Complicating matters, however, is that in print reading, evidence of the effect is often quite spe-cific to the nature of the visual perception and processing. For example, low-frequency words areknown to attract longer fixations than high-frequency words. However, visual word frequency effectsare also manifested in other ways (such as word skipping), such that high-frequency words, by virtueof having been recognized parafoveally, or confidently anticipated without having been perceived, arenot fixated at all. Neither fixations nor skipping are evident in braille reading.

Sentences containing multiple words of high frequency generated 14% greater mean readingvelocities, 24% fewer acceleration zero-crossings and were characterized by exactly half as manyreversals. On the other hand, we have produced no evidence that the meaningfulness of sentenceshad any effect on the kinematics of reading finger movements. Data from Bertelson (1995) and

8 In this experiment we asked experienced braille readers to adopt a single-finger reading mode, an unusual requirement for allbut two of our participants. Under normal reading conditions, nine of our readers would use multiple fingers and both hands toread. Despite the single-finger reading constraint, all participants were nonetheless able to read with a high degree of accuracy. Ofcourse, developing techniques for measuring reading with multiple fingers across both hands is also necessary. However, any suchdevelopment would need to be yoked to a reliable and accurate method for measuring attentional allocation across fingers andhands. Until this method has been developed, measurement of the single-finger reading movements ensures that informationprocessing (both perceptual and motor) is directed to this single channel and that the movement properties of this finger areindicative of properties of on-line processing.


Mousty and Bertelson (1985) have shown that reading coherent text promotes faster overall readingspeeds than does reading randomly ordered words, even when the task required that in all condi-tions, participants read ‘‘aloud, at a sustained pace” (Mousty & Bertelson, 1985, p. 222). Our sen-tences were not random strings of words; they maintained a grammatical coherence even whenthey were meaningless. As such, the sentences did not prevent readers from anticipating, for exam-ple, that the word they were beginning to read was likely to be an adjective not a verb, or verb not anoun. We anticipated that asking participants to read novel, syntactically correct but semanticallyempty sentences would have the effect of slowing their reading speed and making the intermitten-cies in velocity more evident (Morton, 1964). However, this was not the case. Reading nonsense didnot clearly alter any kinematic parameter that we measured. It remains to be experimentally estab-lished whether stricter demands on comprehension of the text than we required here produceclearer and more direct effects of sentence meaning on reading finger kinematics (see also Carreiras& Alvarez, 1999; Millar, 1988).

A second reading of a sentence not only had the effect of permitting 27% higher mean velocities, butthese velocities profiles contained 27% fewer acceleration zero-crossings. Re-readings also had thebenefit of entailing fewer and less time-consuming reversals (44% and 55%, respectively). The robustre-reading effect on multiple kinematic variables suggests that readers remembered important ele-ments of a sentence from first encountering it and were able to move the finger forward at higher,smoother velocities as a consequence. There are good reasons for exercising caution in assigningcauses to this effect, however. It may be that the re-reading benefit is located in anticipatory atten-tional processes that raise the expectation of the presence of specific words before actually contactingthem. The benefit may also be due to a residually active lexical access that makes processing faster orless prone to delay. Either way, increases in mean velocity would result. But whether the velocity in-crease has a direct or indirect effect on velocity smoothness remains to be determined. Second read-ings did not entirely remove either intermittencies or reversals: second readings still created over 80acceleration zero-crossings and five reversals per sentence, on average. We return to this issue below.

By contrast, we found no evidence that reading out-loud was kinematically distinct from readingsilently. These modes of reading did not differ in their mean velocity nor in the intermittency of theirvelocities. The only effects of reading mode on performance were interactive ones, such that readersmoved the finger slightly differently in one mode than in another. This supports earlier conclusionsthat modes of reading do not impact reading speeds. For example, Millar (1990) found that readingspeed was no different when reading aloud or reading silently (or, indeed, doing each of these whilesimultaneously performing a secondary task), although Knowlton and Wetzel (1996) found the formerto be faster if silent reading demanded comprehension but reading aloud did not. We have no evi-dence that having to retain each word in working memory for the duration of reading had a deleteri-ous effect on either mean velocities or kinematics, relative to reading out-loud, a task which has beenconsidered automatic for fluent print readers (see, e.g., Brown, Gore, & Carr, 2002; McCann, Reming-ton, & van Selst, 2000; but see also Reynolds and Besner (2006)). However, there are other readingmodes yet to be explored kinematically, such as proof reading and target word search which may re-veal quite different patterns of exploration.

Reversals are known to be a feature of braille reading as well as visual reading. Millar (1997) isexhaustive in her account of reversals (which she terms regressions) and why they occur (pp. 161–172). In addition to being corrections for processing errors, Millar suggests that reversals may notactually be examples of re-reading material not fully processed. Instead, she suggests that theymay sometimes be the second phase of reading ahead movements which braille readers use as pre-view or, perhaps, as information to prevent (initially directed ahead in the text). That is, what lookslike a reversal may actually be the return to the point in the text from which the anticipatory move-ment was launched. Consistent with this interpretation, we found reversals to increase when sen-tences contain low-frequency words and halve on second readings. More significantly perhaps, wehave shown that almost all sentences attract reversals, that reversals were observed to originateat all locations in the sentence and most often from the key words. Almost all reversals involvedmovements to (a) a more leftward position on the same word, but not necessarily to its beginningor (b) to the word immediately preceding that currently being crossed. There are only a fewinstances in which the reversal was directed to a word more remote than that immediately to


the left (and when this occurred it was to cross a function word). Millar may be correct about rever-sals, but examination of traces containing reversals indicates that the movement velocity precedinga reversal is not unusually fast (as may be expected if readers are moving rapidly ahead in order togain a degree of preview); indeed the second traverse of a section of text already reversed throughtends to be faster. However, teasing apart these two possibilities will be important and nothingprevents both being true.

Bertelson (1995) and Mousty and Bertelson (1992) consider reversals to serve as the major‘‘repair device” for comprehension or disambiguation in braille reading. This we take to mean thatreversals enable the re-reading of text whose processing was not complete, or perhaps whose pro-cessing was beginning to lag in time behind the current location of the finger by an amount notcomfortable to the reader. Such a delay between finger location and comprehension is conceivableby virtue of the briefer but still measurable eye-mind lag in print reading (see, e.g., Rayner & Sereno,1994). We are not in a position to determine conclusively if reversals are repair movements. Itseems likely that they may often be, and our data suggest that since most reversals are to wordscurrently being read or immediately prior, the locus of difficulties requiring ‘‘repair” are at the lex-ical or sublexical levels.

Our data show other potentially important characteristics of reversals. Like forward-directedmovements, reversals occur with the finger maintaining contact with the reading surface. This is con-sistent with Bertelson’s (1995) claim that all braille movements (including reversals and line returns)are made while in contact with the surface. Otherwise their kinematic characteristics are quite differ-ent. Reversals are notable for the velocity with which they are executed. The fastest sections of anyvelocity profile were likely to be reversals, where velocities in excess of 20 cm/s are observable and,unlike forward movements, which are characterized by intermittencies and brief stoppages, reversalsoften possess smooth, bell-shaped, symmetrical profiles (see the examples in Fig. 4). Such profiles aretypically associated with rapid aiming movements to visible targets. To observe them in braille read-ing is to raise the prospect that braille readers retain in memory (as they read) not only individualwords’ meanings and grammatical roles, but those words’ spatial locations, and that representationsof those locations serve as targets to which reversals can be aimed. Since we do not know the targetwords to which these reversals were aimed, it is not possible to measure their accuracy, however. It isapparent that reversals play a very common and distinctive role in braille reading and warrant furtherexamination as part of that skill.

The data suggest that the intermittency of the velocity trace has more to do with the speed of themovements and their underlying motor control than with either the meaning of the text or the text ashaptically perceived texture. Panels A and B of Fig. 5 suggest that mean velocity and the number ofacceleration zero-crossings are negatively correlated. In order to more precisely measure this relation-ship, we plotted, for every trial, the mean velocity against the number of acceleration zero-crossings,and doing so in such as way as to preserve the identity of the sentences being read. If the intermitten-cies are a function of low-level motor control properties then we should expect to find the data fallingalong a single function with little difference between reading conditions. On the other hand, if the con-tents of the text directly contribute to the intermittency then we should find clear alignments by con-dition, especially word frequency and re-reading. For example, we might expect to find that whilemean velocity in two or more conditions is similar, each produces quite different numbers of zero-crossings. Fig. 6 was created by finding the best fitting exponential function to one condition, the(arbitrarily selected) low frequency, first reading data (Panel A). If the fit to these data is not appropri-ate for high-frequency words, or second readings (the two most impactful factors in our analyses),then the data and the exponential function (Panels B–D) should not be good matches. However,Fig. 6 shows that they continue to match when the sentences contain high-frequency words, and/orare read for a second time. Second readings are faster and smoother than first readings but this factordoes not shift the function laterally. The effect of a second reading is to shift the data along the samefunction, with proportionately higher mean velocities and fewer acceleration zero-crossings. The sameholds for the change from low- to high-frequency words: the shift is along the underlying functionrather than laterally displaced from it. Indeed, the same plots for line scanning rather than reading(Fig. 6E), indicate that when scans occur at velocities comparable to braille reading (e.g., less than8 cm/s), there is a close resemblance to the reading function. These plots suggest that the relationship

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Fig. 6. Scatter plot of individual participants’ mean velocity on each trial plotted against the number of acceleration zero-crossings on that trial. The panels show the data from each of the levels of word frequency (low, high) and readings (first,second). For purposes of comparison, the best fitting exponential function in Panel A is replotted in Panels B–D (see text forfurther details). Within a panel, the circles indicate nonsense sentences, the squares meaningful sentences; white filled symbolsindicate reading aloud, grey ones indicate reading silently. Panel E plots the data for scanning, not reading, with the best fittingfunction from Panel A superimposed and the abscissa extended relative to Panels A–D (x: continuous cells and +:noncontinuous cells).


between reading velocity and reading intermittency can be well described by functions with similarparameters and that while some linguistic and task-related factors can have effects on movementvelocities and smoothness, these changes are superimposed on (rather than directly cause) a highlyintermittent velocity trace.

The intermittency of velocity trace has been a topic of interest since Woodworth (1899). It has beenshown that many target-directed movements have profiles with more than one acceleration zero-crossing, particularly when the targets to which movements are directed are small (e.g., Meyer,


Abrams, Kornblum, Wright, Smith (1988)). However, increases in the frequency of accelerationzero-crossings have also been observed when such movements are performed in the absence of visualguidance (Doeringer & Hogan, 1998) so visual adjustments are not the cause of all intermittency. It ispossible that movements that are intended to be performed at constant velocities, or over longerdurations, are comprised of many submovements, each with its own acceleration-deceleration cycle.For example, DiPietro, Hogan, Krebs, and Volpe (2005) have argued that zero-crossings are not indic-ative of motor ‘‘noise” but reflect the necessary construction of slow movements from more elemen-tary submovements. Is it possible to interpret the intermittencies observable in our velocity traces assubmovements, as individual movements whose concatenation gives rise to the translation of thefinger across a line of text? Or, to put the question another way, can the traverse of the braille readingfinger across a line of text, not a single planned movement, but a series of movements each of rela-tively brief duration and extent? Fradet, Lee, and Dounskaia (2008) suggested that several submove-ment types characterize movements under different task constraints: some are owing to visualcorrections of movements, others are due to targeting constraints, while others are caused by low-level muscular control and noise. Braille reading and slow motor control are mutually informativeresearch domains.

Irrespective of their origin, acceleration-deceleration fluctuations could compromise the accuracyof perception which is ongoing during these fluctuations. That is, the rate at which cells of a wordcross the (receptive fields of the) fingerpad is a function of the velocity of the finger. But if velocitiesare constantly changing, might such changes give rise to perceptual confusion or inaccuracy? Mightsuch perceptual errors be an additional potential cause of reversals and re-readings? Research in hap-tic perception is not unanimous as to whether space–time ambiguities even arise with raised textures(e.g., Connor & Johnson, 1992; Hsiao, Johnson, & Twombly, 1993; Lederman, 1983), or whether percep-tual accuracy depends on afferent access to finger velocities (Cascio & Sathian, 2001; Chapman,Tremblay, Jiang, Belingard, & Meftah, 2002; Hughes & Jansson, 1994).

Given the theme of this special issue, and in conclusion, we note that graphonomics, as a specificresearch enterprise, was borne of the need to enhance the spatial and temporal precision of measure-ments if accurate models of control processes of writing and drawing movements were to emerge (see,e.g., Thomassen, 1986). The need is as pressing in the case of braille reading and the reasons are thesame. Neither the naked eye nor video-recordings easily permit the accurate recovery of the finger’sinstantaneous velocity, nor its patterns of accelerations and decelerations, as the finger encounterstextures loaded with meaning. The technique that we have used to compute the velocity and acceler-ation profiles of the finger during braille reading is an advance over older methods and has the poten-tial to provide us with a more highly resolved view of the movements of the braille reading finger as itencounters varieties of text and texture and to power empirical and theoretical advances in the read-ing of braille.

Acknowledgments

This research was supported from grants from the University of Auckland Research Committee andthe Royal Society of New Zealand (Bilateral Research Assistance Programme) to the first author andthe research was conducted while he was Visiting Research Scholar at Arizona State University. Por-tions of the research were presented at the 20th Annual Convention of the Association for Psycholog-ical Science, Chicago (May 2008) and the European Conference on Visual Perception, UtrechtUniversity, Netherlands (August 2008). We thank several anonymous reviewers of earlier versionsof this work for their valuable comments, as well as, Somesh Chakrabarti, Natalia Dounskaia, TerriHedgpeth Miya Rand, Hans-Leo Teulings, and the skilled braille readers without whom the researchcould not have taken place.

Appendix

Sentences presented as two sets (A and B) of four conditions. Sentence types are coded high (H) orlow frequency (L), meaningful (M), or nonsense (N). Participants read all sentences, but were assigned


(in a counterbalanced manner) one set to silently read and one to read out-loud. All words werespelled in the American form (e.g., -ize, color). Each sentence began with the same symbol ( ) to indi-cate that the following letter would be capitalized and concluded with the symbol for a period ( ). Thenumbers in square brackets indicate the key words’ frequencies per million words (Johansson &Hofland, 1989). Note that some words, such as model, can be used as nouns, adjectives and verbs;we restricted our count to the relevant part of speech.

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Appendix (continued)


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linguistic and perceptual-motor contributions to the kinematic properties of the braille reading...

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