Cerebral lateralization of haptic perception: interaction of responses to Braille and music reveals a functional basis

Sensorimotor lateralization scaffolds cognitive specialization

In this chapter, we review hemispheric differences for sensorimotor function and cognitive abilities. Specifically, we examine the left-hemisphere specialization for visuomotor control and its interplay with language, executive function, and musical training. Similarly, we discuss right-hemisphere lateralization for haptic processing and its relationship to spatial and numerical processing. We propose that cerebral lateralization for sensorimotor functions served as a foundation for the development of higher cognitive abilities and their hemispheric functional specialization. We further suggest that sensorimotor and cognitive functions are inextricably linked. Based on the studies discussed in this chapter our view is that sensorimotor control serves as a loom upon which the fibers of language, executive function, spatial, and numerical processing are woven together to create the fabric of cognition.

Spatial reference and scanning with the left and right hand

Discrepant findings on performance by the two hands in spatial tasks make it difficult to infer spatial coding unambiguously. We tested the hypotheses (a) that the left hand is consistently better in haptic spatial tasks and (b) that adding spatial reference information produces more accurate coding in spatial tasks, independently task and hand effects. Instructions to use external cues from a surrounding frame as well as body-centred cues for reference produced highly significant increases in accuracy in haptic distance and location experiments. The distance experiments showed no hand differences. A small right-hand advantage with longer positioning movements in the recall of locations was significant when combined with left-hand scanning of the frame, but did not relate to reference conditions. Hand use interacted significantly with the location-versus-distance experiments, but showed no interaction with the spatial reference factor, which was highly significant in both experiments. The finding suggests that modes of coding need to be distinguished from cross-lateral effects of sensory input conditions. The study shows that varying reference information offers a potentially useful behavioural tool for distinguishing spatial coding from input and task conditions independently of hand performance. Methodological, practical, and theoretical implications are discussed.

Dichaptic scanning of Braille letters by skilled blind readers: lateralization effects

Dichaptic scanning of Braille letters was studied in 14 skilled blind readers, using Posner's paradigm. A right-hand (left-hemisphere) advantage was found when letters could be matched on the basis of their names (Name Identity Condition), a genuinely linguistic task, while no effects of lateralization appeared when matching could be performed on the basis of perceptual identity (Perceptual Identity Condition) or on "Different" responses. This result provides information about the cerebral lateralization of Braille reading and casts doubts about the current claim that linguistic material, when presented in the tactile modality, is initially analysed in a spatial code by the right hemisphere.

Influences of age at onset of blindness on Braille reading performances with left and right hands

Several previous studies suggest that early sensory deprivation produces a changed organisation of the cerebral cortex. This study compared the effects of early and late total blindness on a Braille reading task. This task is intended to induce a superiority of the left hand rather than the right because of the particular role played by the right hemisphere in Braille decoding. 38 strongly right-handed adults, accustomed to daily bimanual Braille reading, were tested. 21 subjects were born blind and 17 became blind during childhood before learning to read. Analysis indicated that previous visual experience can, under certain conditions, play a modulating role in manual superiority in Braille reading.

Lateralization of Categorical and Coordinate Spatial Functions: A Study of Unilateral Stroke Patients

Sixty patients with unilateral stroke (half with left hemisphere damage and half with right hemisphere damage) and a control group (N = 15) matched for age and educational level were tested in two experiments. In one experiment they were first shown, on each trial, a sample drawing depicting one or more objects. Following a short delay, they were asked to identify the drawing when it was paired with a drawing in which the same object(s) was transformed in categorical or coordinate spatial relations. In the other experiment, the same subjects first were shown, on each trial, a sample drawing. They then judged which of two variants (each in one type of spatial relation) looked more similar to the sample drawing. Typically, patients with left-sided stroke mistakenly identified the categorical transformation for the sample drawing in the first task; in the second task, they judged the categorical transformation as more similar to the sample drawing. Patients with right-sided stroke mistakenly identified the coordinate transformations for the sample drawing in the first task, and, in the second task, typically judged the drawings transformed along coordinate spatial relations as more similar to the sample drawing. These findings provide evidence for complementary lateralization of the two types of spatial perception. It can therefore be inferred that separate functional subsystems process the two types of spatial relations.

Perceptual fluency and affect without recognition

A dichotic listening task was used to investigate the affect-without-recognition phenomenon. Subjects performed a distractor task by responding to the information presented in one ear while ignoring the target information presented in the other ear. The subjects' recognition of and affect toward the target information as well as toward foils was measured. The results offer evidence for the affect-without-recognition phenomenon. Furthermore, the data suggest that the subjects' affect toward the stimuli depended primarily on the extent to which the stimuli were perceived as familiar (i.e., subjective familiarity), and this perception was influenced by the ear in which the distractor or the target information was presented. These data are interpreted in terms of current models of recognition memory and hemispheric lateralization.

Hemispheric specialization in visual, tactile and crossmodal assembling tasks

There is ample evidence that the right or non-language related hemisphere of the brain is superior in processing of spatial information. This issue appears less clear when a task involves elaborate mental operations that require the integration of spatial information at a stage beyond mere perceptual discrimination. Examples are block design tasks, which are frequently used as estimates of general intelligence. Results of these tests have been contradictory as to whether there is a right hemispheric advantage for their execution. This study was aimed to look at a possible hemispheric preponderance in block design tasks comparing visual, tactile and crossmodal spatial performance. A two-dimensional template had to be reproduced by arranging cubes with surfaces different in both colour and texture. In the visual condition the template was given in the visual modality and the cube arrangement was under visual control. In the tactile condition the template was presented tactually and the cube assembly had to be done under entirely tactual control. In the crossmodal condition the template was presented visually and the assembly was restricted to tactual control. Task completion time (TCT) and number of correct responses (NCR) were compared between right hand and left hand responses. Only in the crossmodal condition a constant left hand superiority of performance was found. Non-crossmodal tasks did not show a constant hemispheric preponderance. In the tactile condition allowing for easy differentiation of input to one or the other hemisphere TCTs varied only according to the compatibility of side of afferent input and side of assembling action irrespective of the hemisphere engaged. It is concluded that mental operations requiring spatial assembling not necessarily engage the non-dominant hemisphere to a larger extent than the language dominant hemisphere. For crossmodal information processing, however, the non-dominant hemisphere appears to be superior.

Cerebral lateralization of familiar and unfamiliar music perception in nonmusicians: a dual task approach

In a dual task procedure that controls for attentional trade-off effects, asymmetrical interference effects were observed in dual task conditions of finger tapping and concurrent processing of familiar and unfamiliar music. Laterality effects suggested that perception of orchestral presentations is largely lateralized to the left hemisphere in both males and females. In a second dual task condition of vocalization and music processing, both males and females displayed interference in speech production during concurrent music processing. Males showed greater left hemispheric interference effects during simultaneous vocalization and music processing.

Music during learning of a tactual-spatial task affects later response generalization

Equal numbers of men and women learned a finger maze, with half of the subjects initially using their right hands and the other half using their left hands. To reach criterion, subjects receiving music in the ear ipsilateral to the hand used required more trials than did those receiving no music. Furthermore, when the right hand ran the maze, music played to the ipsilateral ear also delayed learning, compared with music played contralaterally. Binaural music delayed learning when the left hand was used but not when the right hand was used. Possible causes of these effects are suggested. When subjects switched hands and relearned the maze, the number of trials to criterion depended on the group subjects were in during initial learning and not on the group they were in during the hand reversal (response generalization) trials. Although the music condition used determined the effect of music on initial learning and on response generalization, some evidence is presented that indicates that the two effects are not entirely interdependent and that they may even involve different mechanisms.

Perceptual asymmetries in the somatosensory system: a dichhaptic experiment and critical review of the literature from 1929 to 1986

Dichhaptic matching of 3-D nonsense shapes was used to assess sex-specific differences in haptics. In an initial object exploration/description phase, strategy was manipulated with instructions to encode each object using either a visual image (which was drawn) or verbal description (tape recorded). These drawings or tape recordings were subsequently used on their own to identify each object. Attempts were made to maintain similarity between the verbal and spatial procedures, to avoid methodological biasing of hand superiorities (e.g., the same number of alternatives and the same presentation times were used). Differences in hand superiority did not, however, result. To obtain a broader perspective, a critical review table was compiled of the entire somatosensory asymmetry literature. Clear patterns emerged for all types of task when results potentially stemming from methodological biases and those based on only certain levels of samples were excluded. Somatosensory perceptual asymmetries are not robust, although hand superiorities are in the predicted direction when they do occur; nevertheless, we find little support for sex-specific asymmetries in these studies. Dichhaptic presentations lack the efficacy of other somatosensory (as well as tachistoscopic) tasks overall, possibly because of the time scale necessary for free haptic exploration.

Music Affects Learning of a Braille-Like Task by Sighted Subjects

24 consistently right-handed male college students felt sets of four Braille symbols with either the right or the left index finger and identified by touch alone which two of the four symbols in each set were identical. During the task music was played to either the right ear, the left ear, both ears, or neither ear. Significantly fewer errors were made when the music was in the ear contralateral to whichever hand performed the task. The ipsilateral, binaural, and no-music groups did not differ significantly from each other. It is suggested that monaural music to the ear contralateral to the engaged hand led to reduced interhemispheric competition acting on the hemisphere controlling the hand. Such a facilitating effect may be of practical importance in tasks during which one hemisphere receives the bulk of the task-related sensory input and/or processes the final order from the brain to the task-related muscles.

Music affects learning of a braille-like task by sighted subjects

24 consistently right-handed male college students felt sets of four Braille symbols with either the right or the left index finger and identified by touch alone which two of the four symbols in each set were identical. During the task music was played to either the right ear, the left ear, both ears, or neither ear. Significantly fewer errors were made when the music was in the ear contralateral to whichever hand performed the task. The ipsilateral, binaural, and no-music groups did not differ significantly from each other. It is suggested that monaural music to the ear contralateral to the engaged hand led to reduced interhemispheric competition acting on the hemisphere controlling the hand. Such a facilitating effect may be of practical importance in tasks during which one hemisphere received the bulk of the task-related sensory input and/or processes the final order from the brain to the task-related muscles.

Left-arm dominance in active positioning

The relative accuracy of the left and the right arms in active positioning was studied in a group of 24 male right-handed undergraduates. The task required active positioning of the left and right arms at each of the four angular positions (30 degrees, 45 degrees, 60 degrees, and 75 degrees). The left arm was more accurate in active positioning than the right arm. There was a progressive increase in error for both arms as the arms flexed more in reducing the angle at the joint. Results are discussed in light of suggestions concerning the superiority of the right hemisphere in the processing of kinesthetic and proprioceptive information.

Hemispheric specialization for tactile perception opposed by contralateral noise

The aim of this study was to investigate the contribution of each cerebral hemisphere in the categorization of tactile information with and without contralateral tactile noise. Two groups of subjects rated the dissimilarity of paired stimuli varying in shape and texture presented to the left or right hand, with contralateral noise in the other hand for one group only. Analysis of variance on derived structured indices showed a general left hand advantage in the treatment of this haptic information. Moreover, a group by hand interaction revealed that noise-exposed subjects showed better differentiation of tactile information for stimuli presented to the left hand. The data suggest a unidirectional interference by the left hemisphere in the processing of tactile information in noise-free conditions and that quality of interhemispheric transfer of information may modulate cerebral functional lateralization.

Dichaptic-visual form matching in adults

Although previous visuo-dichaptic matching studies report hemispheric asymmetries in spatial-form perception, more recent studies have failed to support these findings. Three cross-modal matching experiments examined hemispheric asymmetries in adult spatial-form matching. In the first experiment, subjects simultaneously felt two eight-point or 12-point tactile shapes patterned after Vanderplas and Garvin (1959) for four seconds and were then required to identify both shapes from a visual response array. Results showed subjects were significantly better identifying eight point shapes. A marginally significant feeling hand by pointing hand interaction indicated that recognition accuracy was higher when shape ipsilateral to the pointing hand was identified. In the second experiment, only one of the two tactile shapes had to be identified from the visual array. Results showed a significant interaction between complexity and feeling hand, where the left and right feeling hands were respectively better at identifying 12-point and eight-point shapes. The third experiment was an attempt to more directly examine the Witelson (1976) experiment using her spatial-form stimuli. Results showed no significant laterality nor stimulus-response compatibility effects. These findings are discussed in terms of cerebral asymmetry and stimulus-response compatibility models.

Hemispheric asymmetry in the perception of emotional sounds

Three experiments were conducted to investigate hemispheric asymmetry for the perception of emotional sounds. Pairs of human nonspeech sounds were presented dichotically in a forced choice recognition task. Under divided attention conditions (Experiments 1 and 2) an left ear advantage (LEA) emerged during the second block of trials. Performance accuracy for the left and right ears was equal during the first block of trials. Under selective attention conditions (Experiment 3) an LEA emerged during the first block of trials. The results suggest that attention influences the rate of development of the laterality effect but not the direction of the effect.

Laterality of cross-modal spatial processing

This study examined the laterality of spatial-form perception in normal adults using a cross-modal matching paradigm involving visual and tactile processing. Randomly generated eight-point and 12-point Vanderplas and Garvin (1959) patterns were used as the stimuli. In a visual-to-tactile task, a lateralized visual pattern was followed immediately by a haptic task requiring subjects to discriminate which of two simultaneously felt shapes matched the visual pattern. In a tactile-to-visual task, subjects decided which of two simultaneously felt shapes matched a lateralized visual pattern presented after haptic manipulation. There were no main effects for laterality or for sex differences. Matching accuracy was better in the visual-to-tactile task and for less complex stimuli. A visual field by feeling hand interaction showed best recognition accuracy when visual-feeling hand combinations on the same side of the body were used in the two matching tasks. These data reflect a stimulus-response compatibility explanation of spatial-form perception that is consistent with a behavioral and not a cerebral asymmetry model.

Cerebral and sex differences in the categorization of haptic information

This study investigated the extent to which each cerebral hemisphere categorizes stimuli varying in texture and shape. Eighteen right-handed subjects, nine males and nine females, rated the perceived dissimilarity between pairs of stimuli presented to both hands and to the right or left hand, with haptic noise in the contralateral hand. Results suggest a right hemisphere competence in the categorization of both texture and shape information. Furthermore, males showed better separation of categories for stimuli presented to both hands only.

Dichotic and dichhaptic techniques

Auditory and tactual asymmetries frequently demonstrate right side advantages for verbal stimuli and the opposite effects for nonverbal stimuli. Such asymmetries may, however, reflect the perceived position of events in space, rather than the role of anatomical afferent pathways with suppression of ipsilateral by contralateral routes. Consequently, despite popular tradition, simultaneous competitive stimulation (dichotic or dichhaptic) may be unnecessary. We review the reliability and the relatively low validity of such techniques for predicting hemispheric specialization in various clinical and normal populations. We discuss the role of stimulus factors, the various indices and measures, the effect of order and mode of report, division of attention, task difficulty and memory factors.

Tactual-kinesthetic matching of horizontal extents by the long-term blind: absence or reversal of normal left-side underestimation

Ten adults, who were blind from infancy or childhood, laterally slid a horizontal rod within a short length of pipe located at the body midline, until the rod extremities were tactually-kinesthetically judged to be equidistant from the ends of the pipe. Whereas sighted subjects normally set the left extremity of the rod closer to the midline than the right irrespective of arm posture, crossed or uncrossed, blind subjects, especially those blind from birth showed trends in the opposite direction. The role of vision is discussed with respect to the development and expression of asymmetries relating to the coding of extracorporeal space.

Interhemispheric integration of information in a surface estimation task

Normal subjects were asked to estimate the total surface of two black spots presented tachistoscopically, either both to the right or both to the left visual field, or bilaterally to either visual field. Performance was highest with unilateral left visual field presentation and lowest with bilateral presentation of the spots. Interhemispheric integration varied with the quantitative relation between the stimuli in the left and right visual fields. Errors may be due in part to an insufficient cooperation of the left hemisphere and/or to an ignorance of the right hemisphere and/or to an unreliable transfer by the cerebral commissures.

Aphasic dyslexia of Braille in a congenitally blind man

Due to an ischemic attack a congenitally blind man became aphasic. He had a severe Wernicke's aphasia and aphasic dyslexia of Braille. The patient had been a very expert Braille reader before his illness. Two texts of 250 words each were read and the results analysed. One text was in basic Braille and the other in contracted Braille. Results of the analysis are discussed with regard to processes in reading Braille and problems of dyslexia.

Braille reading and left and right hemispace

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 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.

Cerebral lateralization: relation to subject's sex

Patterns of reflective LEM's have been correlated to a number of cognitive and personality variables, bu the relationship to sex, education, and mental illness is unclear. In this study females produced significantly more R-LEM overall indicating a preferential use of left hemisphere mechanisms when they initiate reflective thought. Females also produced more R-LEM for verbal nonemotional material, suggesting stronger lateralization of language abilities to their left hemisphere. Emotional and spatial stimuli were less well lateralized to the right hemisphere in females, and education was an unimportant variable for both sexes. Schizophrenia was independently associated with increases in total R-LEM indicating increased left hemisphere activity in this group.

Muscular or directional preferences in finger movement as a function of handedness

Right handed, left handed, and "ambiguous" male and female subjects performed circular index finger movements. Analysis of preferred direction of movements showed that strong right handers tend to move both left and right index fingers in the same direction, and familial left handers tend to move them in opposite directions. Since right handers tend to possess a strongly dominant left hemisphere, while familial left handers exhibit a high degree of cerebral lateral equipotentiality, the result indicates that interhemispheric interference in a motor skill consists of activation of inappropriate muscles of the non-preferred hand by the dominant ipsilateral hemisphere as its attempts to force that hand to conform to the direction of movement preferred by the dominant hand.

Handedness and Hemispheric Asymmetry in the Control Of Movements

This study investigated the influence of hemispheric specialization of function on the motor performance of the hands. Right-handed (n=7), ambidextral (n=21), and ambisinistral (n=12) subjects performed Fitts' (1954) reciprocal tapping task under two conditions with each hand. Conditions had the same index of difficulty but differed in movement precision. The left hand of right-handers was superior in the condition requiring the greatest amount of preprogramming. Conversely, the right hand was not superior in the condition having the greatest demand for feedback control. For ambidextrals, left-hand superiority in the relatively preprogrammed condition was also revealed. Ambisinistrals showed no significant difference between conditions with either hand. The results partially support the hypothesis that the motor performance of the hands mirrors the dominant processing mode of their contralateral hemisphere. Failure to find supportive evidence in ambisinistrals is consistent with the contention that they lack hemispheric specialization of function.