Braille Reading and Left and Right Hemispace

#AUTHOR: Bradshaw, John L.; Nettleton, Norman C. and Spehr, Karen

#TITLE: Braille Reading and Left and Right Hemispace

#ORGANIZATION: Monash University, Clayton, Victoria 3168, Australia

#CATEGORY: Braille Reading

#PUBLICATION: Neuropsychologia, Vol. 20, No. 4, 493-502, 1982

#ABSTRACT: Twelve blind adults were timed in locating phonologically and semantically defined targets in Braille lists. The "reading" hand was placed either out from or across the body, i.e. in ipsilateral or contralateral hemispace. Despite strong and consistent, if idiosyncratic, hand superiorities for all types of list, contrary to two previous reports there was no evidence of either a general left hand preference or an overall left hand superiority. Moreover neither the magnitude nor the direction of hand superiorities changed when hands were tested in contralateral hemispace. At least in this complex continuous task hemisphere hand connections appear more important than hemisphere-hemispace relationships. Left-hand (or left hemispace) superiorities in tactual tasks of a verbal nature may only occur with novel unfamiliar or perceptually degraded materials

BRAILLE READING AND LEFT AND RIGHT HEMISPACE

JOHN L. BRADSHAW*, NORMAN C. NETTLETON and KAREN SPEHR

Monash University, Clayton, Victoria 3168, Australia

(Accepted 15 February 1982)

Abstract- Twelve blind adults were timed in locating phonologically and semantically defined targets in Braille lists. The "reading" hand was placed either out from or across the body, i.e. in ipsilateral or contralateral hemispace. Despite strong and consistent, if idiosyncratic, hand superiorities for all types of list, contrary to two previous reports there was no evidence of either a general left hand preference or an overall left hand superiority. Moreover neither the magnitude nor the direction of hand superiorities changed when hands were tested in contralateral hemispace. At least in this complex continuous task hemisphere hand connections appear more important than hemisphere-hemispace relationships. Left-hand (or left hemispace) superiorities in tactual tasks of a verbal nature may only occur with novel unfamiliar or perceptually degraded materials.

INTRODUCTION

WHILE a few studies [1-3] have reported a right-hand superiority in tactual tasks requiring temporal analysis, there is now abundant evidence of a left-hand/right hemisphere superiority for a variety of tactually guided spatial tasks, both monohaptic [4-9] and dichaptic [10-16]. Indeed a general left-side superiority in tactual sensitivity has been reported for many body parts [17]. With blind subjects, the left hand may prove superior in reading Braille characters [18-20], though as HARRIS [20] observes this effect may be strongest in those dextrals (sometimes a majority) who prefer to use the left hand. With sighted subjects and Braille or Braille-like materials, these left-hand superiorities are often very prominent [20-24], possibly as a consequence of the comparative novelty and unfamiliarity of such stimuli which are perceived more in visuospatial than in verbal. terms.

Laterality effects, e.g. a right visual field, ear or hand superiority in a verbal task, or a left- sided superiority in a task emphasizing spatial or holistic processing aspects, are usually ascribed to the prepotency of the contralateral sensory pathways and hemispheric specialization for certain modes of information processing. Alternatively, one might appeal to some hemispheric mechanism involved in the perception and/or mediation of activities in the contralateral hemispatial field, i.e. the external space to the left or right of the body midline. In most experiments, the hemispace in which a stimulus is presented and the ear, visual field or hand of its presentation are systematically confounded. In the visual modality, CORBALLIS, et al [25] presented single letters to subjects whose heads were either upright or tilted. They found that accuracy of report depended partly upon the locations of letters in gravitational coordinates, and partly on retinal coordinates, suggesting that lateral asymmetries may depend on a perceptual as well as a retinal interpretation of the two visual fields. In the auditory modality, MORAIS [26, 27] found that a right-sided advantage processing speech sounds depended upon the perception of whether a sound was to the left or right, rather than the ear of entry, and that the apparent spatial position of auditory signals (as a consequence of using a dummy loudspeaker) was sufficient to eliminate (but not to create) an asymmetry. We can ask whether sounds from a particular direction in perceived auditory space have a stronger representation in the auditory cortex of the left hemisphere than sounds apparently coming from other directions. Generally, do behavioural asymmetries reflect the cortical mapping of sensory space in addition to the neural representation of the proximal locus of stimulation in the lateralized sense organ?

One way to unconfound these two factors, the laterally located sense organ with its associated neuro-anatomical pathways, and hemispace, is to employ the tactual modality with the subject crossing his arms across the body mid]ine, such that e.g. the left hand (normally superior in tactual-spatial recognition tasks) is now in right hemispace. Is its superiority maintained, reduced or reversed? BOWERS and HEILMAN [28] required blindfolded subjects to perform a line bisection task, using rods. Not only was the best performance when the left hand was in left hemispace, and the worst when the right hand wa.s in right hemispace, but, overall, line bisection was more accurate when either hand performed in left rather than right hemispace. They concluded that both hemisphere-hemispace and hemisphere-hand connections contributed to the laterality effects.

This study had several aims. We wished first to determine how robust is the left-hand superiority with blind subjects engaged in Braille reading tasks involving list searching (the only two previous studies which have addressed this issue [18,20] both in fact failed to obtain an uriequivocal left-hand superiority), secondly to compare the effects of tasks designed differentially to engage phonological or semantic processing mechanisms (respectively perhaps relatively more and less likely to engage the left hemisphere language system), and lastly to compare hand superiorities when the operating hand was in ipsilateral or contralateral (i.e. across the body) hemispace.

METHOD

Materials

Forty lists were prepared, 24 experimental lists., four general practice lists and 12 specific practice lists. The general practice and the experimental lists each consisted of 52 items, each item being of four letters. Specific practice lists were 26 items long. There were six types of experimental list, presented in six blocks, each block consisting of two, specific practice lists followed by four experimental lists. The first two types of list required the subject to detect girls names in lists of boys' names, and vice versa. Names were selected from a group of 29 boys' names and 26 girls names, all of four letters. Within a list some of the list items were repeated, but no targets were repeated. The second two types of list required the detection of a vowel in lists of four-letter consonant strings, or vice versa. All vowels and all consonants were used. Where targets were consonants, no target was repeated. All letters used were equally distributed. The last two types of list required I he detection of a B or P or T or D among lists of four-letter strings consisting of F L, M, N, S and X, or the detection of in F or L or M or S among lists of B, D, G, P, T, and V. Again there was an equal distribution of all letters used, with no repetitions of a target within a list This last type of list was thought most likely to engage left hemisphere phonological mechanisms while the first type (boys' and girls' names) might possibly engage right hemisphere or bilateral semantic processors [29].

The general practice lists required the subject to search for words in lists of nonwords, or to search for nonwords in lists of words In both cases, half the words were drawn from the high frequency end of the KUCERA FRANCIS [30] word count ( above 100 per million) and half from the low frequency end (below two per million). Nonwords were pseudo-homophones, i.e. incorrectly spelled words, e.g. GOTE, FAID, etc. In all lists, targets were pseudo randomly distributed, with the occasional target occurring at the beginning or end of a list. In a long list of 52 four-letter items, there were either five or six targets. half the lists containingfive, half six. Specific practice lists (two of which were presented before each type of experimental list) were short (26 items) and eontaincd either two or three targets.

Lists were typed on to Haven Systems Board double-bond-strength paper with an I BM electric Braille typewriter Model 12. Short practice lists were 25.6 cm long and 2.3 cm wide, and long lists were 51.6cm long and 2.3 cm wide. Each Braille character was 6 mm long and 3.5 mm wide.

Subjects

Six male and six female subjects were recruited, their ages ranging from 28 to 57 yr Four of either sex had been blind since birth, two males from 6 months and one female from 3 yr and another female from 6 yr. All subjects had been reading Braille since they first learned to read as children, i.e. around 6 yr of age. All were completely without any pattern vision, and seven had no residual vision at all. Three of either sex were University or College graduates aud all of the rest had attained at least the equivalent of year 10 education and were or had been employed in positions demanding a high level of literacy. Two were professional musicians Five of eithcr sex were clearly dextral, in that they reported consistently using the right hand for the following 9 item questionnaire: lighting a match, using a toothbrush, using scissors, unscrewing a lid from a jar, winding a clock, combing hair, drinking from a mug, hammering a nail, using a knife with a fork. One male reported using his left hand for unscrewing a lid and winding a clock, and one female reported using her left hand for lighting a match, using a toothbrush and scissors, combing her hair and hammering a nail. Unlike previously reported findings [18-20], only two of our 12 subjects (both male) reported normally preferring to use their left hand in reading Braille, both of whom were completely dextral in all other respects in terms of the 9-item questionnaire. A further subject reported that she was equally happy with either hand; the remaining nine preferred to use the right. All subjects were free of upper or lower limb injury, disease or deformity.

Procedure

There were four experimental conditioris: left hand uncrossed, right hand uncrossed, left hand crossed (i.e. in right hemispace) and right hand crossed (i.e. in left hemispace). Lists were mounted on a wooden clipboard (62 cm by 41 cm) with four rubber feet. The board was positioned to the left or right of the subject's midline, as far out as could be comfortably achieved, as he or she sat at a table. The index finger alone was employed. While most subjects normally preferred to use one or other hand, none were unable to use their nonpreferred hand.

Subjects were given the general practice lists first, one for each of the four hand positions (conditions). This was followed by the six experimental blocks. Within each block the two specific practice lists preceded one for either hand in the uncrossed mode followed by the four experimental lists (one for each hand condition). Block presentation was systematically varied between subjects, as were the hand-position conditions, and individual list order was randomized. Subjects were instructed at the beginning of each trial as to the nature of the list and targets. T hey were told that they would not be aible to predict the position or number of targets. They were timed with a stopwatch from start to finish of a list, and called out aloud target items as and when they encountered them. Faint pencil marks placed beside each target identified theseto the experimenter who recorded targets detected and errors of omission and commission Subjects were required to read the lists to themselves as fast as possible, compatible with a minimum of mistakes. Their reading finger was first placed directly to the left of the first item before each trial began. The duration of testing varied from l½ to 2½ hr.

RESULTS

Average list search times, by subjcct, were subjected to Analysis of Variance by Task (three levels--names search, vowel/consonant task, and letter-sound task), Hand (left or right), Position (crossed or uncrossed) and Sex. Only one factor, Task, proved significant, F(2, 20)= 35.2, P<0.00l, the names task proving the easiest (71.5 sec per list) and the letter sound task the most difficult or slowest (104.9 sec). No other main effects or interactions even approached significance. Thus the values for the left hand (91.6 sec) and the right (91.9 sec) were practically identical as were those for thc uncrossed (92.0 scc) and crossed (91.5 sec) poisitions. Seven of the 12 subjects proved in the uncrossed condition to be faster with their left hand, and six in thc crossed. The absence of an interaction between Hand and Position, F(1,10)=0.009, in both cases the mean difference between hands being less than half a second, indicates little initial support either for the proposttion of a left-hand superiority in reading Braille, or for the hemispace hypothesis. However there were considerable individual differences in magnitude of hand superiority (disregarding direction), ranging the uncrossed condition from 101 sec to 1.6 sec (mean 26.1 sec), and in the crossed condition from 77.2 sec to 0.3 sec (mean 23.4 sec).Thus most subjects were fairly strongly left- or right-hand superior (though the direction varied between subjects), one hand being on average about 30% faster than the other. It can therefore still be asked whether the faster hand in the uncrossed condition continues to be the faster in the crossed condition, or whether the difference is reduced or reversed. Such a reduction in or reversal of superiority would be consistent with the hemispace hypothesis. While by inspection nine out of 12 subjects did in fact demonstrate such an effect, the overall magnitude of the reduction (from 26 to 21 sec) was not great, and when subjected to Analysis of Variance by Slower/Faster Hand (in terms of the uncrossed position) and Position (Crossed/Uncrossed), only the former main effect proved significant, F (1, 11)=7.92, P<0.025, the interaction being quite nonsignificant, F (1, 11) =1.2, P> 0.05. Thus the faster hand in the uncrossed posture appears to maintain its superiority even in the crossed posture, and we must conclude that the hemispace model is therefore unsupported.

To determine whether the three tasks differed with respect to obtained hand superiorities, the "phonological" task (searching e.g. for B, P, T or D among lists of F, L, M, N, S and X or vice versa) perhaps being more likely to contact left hemisphere mechanisms than the "semantic" (searching for boys' names among girls' or vice versa), we subjected the data to Analysis of Variance by Hand and Task. While Task of course proved significant as before, F (2, 22)=38.6, P<0.001, no other effects even approached significance, indicating that all three tasks were processed similarly. Indeed nine out of 12 subjects were completely consistent in the direction of their hand preferences across all three tasks, the inconsistencies in the other three subjects being very small.

Subjects made two types of error, omissions and commissions (false alarms), though overall the total error rate was extremely low, too small for meaningful statistical analysis. There were more errors of omission (an average of 11.1) than of commission (1.7). With respect to omissions, approximately the same number were made by the left (5.3) and the right (5.8) hands, and by the unerossed (6.6) and the crossed (4.6) positions; across subjects. no consistent trend of any sort was discernible. With respect to errors of commission (i.e. false alarms), while on average more were made by the right hand (1.4) than the left (0.3), this stemmed almost entirely from the behaviour of a single subject (5 and 0 errors respectively). seven of the subjects making no errors at all. There was no difference between uncrossed (0.9) and crossed (0.8).

When we turn to the two male subjects who reported that they normally preferred using their left hand in Braille reading, and the one female who reported ambilaterality in this respect, all three proved superior with their left hands in this experiment, as did one of the two subjects who failed to evince full dextrality on the 9-item questionnaire. Three of the other seven fully dextral subjects who reported that they preferred using their right hand in Braille gave a left-hand superiority, while the other four gave a right-hand superiority. Thus we are also unable to confirm the claim [18-20] that most blind dextrals prefer to use their left hand, though perhaps not surprisingly it does indeed seem to be the case that the minority who prefer to use the left hand are in fact better with that hand

DISCUSSION

To our knowledge, this is only the third study [18, 20] which has tested the lateralized reading of Braille in the long-term blind. Despite how secondary sources have in the past tended perhaps incorrectly to report such studies, we find in a long and carefully controlled study little evidence of a major contribution from the left hand in Braille reading by the blind or of a differential hemispheric effect in processing at the phonological or semantic levels. Hand superiorities were found to be idiosyncratic, largely consistent between tasks, but inconsistent across subjects. Among the three males and four females who proved superior with their left hands were to be found the only three subjects who either normally preferred to use their left hand (two) or who could use either hand equally well (one), and one of the two subjects who, by questionnaire, was not fully dextral. However at least from this Australian sample of 12 long-term blind subjects we must conclude that neither an overall left-hand superiority nor a general left-hand preference in Braille reading is a robust phenomenon.

With respect to the reported [20-24] left-hand superiority in nonblind readers of Braille or Braille-like characters, this not unexpected phenomenon very probably stems from a right hemisphere preprocessing component for novel, unfamiliar stimuli which at this level of experience are viewed and processed by subjects in largely spatial terms. Thus with visually- presented single letters, instead of a normal right field superiority, a left-field superiority is found with laterally masked stimuli [31], perceptually degraded letters [32, 33], mirror reversed stimuli requiring spatial transformations [34, 35], elaborate, florid or "Gothic" typefaces [36], or when the subject must attend to structural features [37-39]. With judged physical identity of letter pairs again a left-field superiority is reported [4042], when short interstimulus intervals favour visuospatial matching [43], or even with name identity matching during the early trials of a long sequence [32]. A novel or unfamiliar script may generate a left-field superiority which later reverts to the "normal" right-field superiority when familiarity is gained [44,45]. With words, a left-field superiority is reported during the initial preprocessing stages of difficult or unfamiliar materials [46], or with exposures too short to permit categorical identification, though long enough for lexical decisions in terms of lower level orthographic features [47, 48].

Developmental age, therefore, and/or the length of the period in which familiarity has been gained in processing such tactual configurations, may be important determinants of a laterality effect. RUDEL and her associates [21, 22] found that a left-hand superiority in learning and discriminating Braille-like configurations only appeared with (sighted) children older than 10 yr. However, the patterns and task were difficult and unfamiliar, and the authors admit that these factors may have been a major cause of the laterality effect, with, perhaps, right hemisphere "configurational" processing becoming more manifest at the later developmental age. Indeed they dismiss the possibility of there being any special connection between tactual processing and the right hemisphere, though we note that HARRIS and CARR [49] reinvoke this old idea of hemispheric modality specificity, appealing to the skin's inferior spatial resolving power and the greater spatio-temporal nature of tactual processing, both of which may require the compensatory effect of right hemisphere processing in reading Braille. HERMELIN and O'CONNOR [19], with blind subjects, found stronger and more consistent left hand superiorities in true Braille reading with children (under age 10) than with adults. They admit that the experimental tasks differed between the two age groups; the adults read single letters while the children read sentences, which makes a direct comparison between the ages somewhat difficult. Moreover, in line with our own reasoning, they point out that with adults Braille reading is no longer so difficult or novel. We can therefore conclude that with the long term blind who have had many years of experience in reading Braille, there is perhaps no strong reason to expect a left-hand superiority, though strong idiosyncratic hand and hemisphere differences may appear. Indeed in the present study it is notable that all three tasks produced essentially similar perform ance patterns, with hand superiorities at the individual subject level being largely consistent between tasks.

With respect to the hemispace hypothesis, though most subjects were fairly strongly and consistently left- or right-hand superior, the faster hand in the uncrossed condition remained the faster in the crossed; a predicted reduction in the overall magnitude of this superiority in the crossed condition, though apparent in nine of the 12 subjects, failed even to approach statistical significance. We must therefore conclude that at least in this relatively complex, continuous information processing task, laterality effects are much more strongly determined by the prepotency of contralateral sensory pathways and hemispheric specialization, than by hemispheric mechanisms involved in the perception of stimuli in the contralateral hemispatial field. The three studies, visual [25], auditory [26] and tactual [28] which found evidence of such an effect all employed discrete stimulus presentations rather than continuous processing tasks, and all quite independently concluded that both mechanisms, neuro-anatomical and hemi-attentional, were likely to be involved. It seems desirable therefore to confirm the contribution of the second component in the tactual modality by employing a version of WITELSON'S [15,16] discrete dichaptic tasks, verbal and spatial, with hands both in the uncrossed and the crossed positions.

AcknowIedgements-This work was supported by the Australian Research Grants Committee. We wish most sincerely to thank Mr BEN HEWITT from the Royal Victorian Institute for the Blind for all his unstinting assistance, and the blind subjects who so willingly participated in this study.

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