Dichotic and dichhaptic techniques

Brain Lateralization: A Comparative Perspective

Comparative studies on brain asymmetry date back to the 19th century but then largely disappeared due to the assumption that lateralization is uniquely human. Since the reemergence of this field in the 1970s, we learned that left-right differences of brain and behavior exist throughout the animal kingdom and pay off in terms of sensory, cognitive, and motor efficiency. Ontogenetically, lateralization starts in many species with asymmetrical expression patterns of genes within the Nodal cascade that set up the scene for later complex interactions of genetic, environmental, and epigenetic factors. These take effect during different time points of ontogeny and create asymmetries of neural networks in diverse species. As a result, depending on task demands, left- or right-hemispheric loops of feedforward or feedback projections are then activated and can temporarily dominate a neural process. In addition, asymmetries of commissural transfer can shape lateralized processes in each hemisphere. It is still unclear if interhemispheric interactions depend on an inhibition/excitation dichotomy or instead adjust the contralateral temporal neural structure to delay the other hemisphere or synchronize with it during joint action. As outlined in our review, novel animal models and approaches could be established in the last decades, and they already produced a substantial increase of knowledge. Since there is practically no realm of human perception, cognition, emotion, or action that is not affected by our lateralized neural organization, insights from these comparative studies are crucial to understand the functions and pathologies of our asymmetric brain.

Lateralization of Auditory Processing of Silbo Gomero

Left-hemispheric language dominance is a well-known characteristic of the human language system. However, it has been shown that leftward language lateralization decreases dramatically when people communicate using whistles. Whistled languages present a transformation of a spoken language into whistles, facilitating communication over great distances. In order to investigate the laterality of Silbo Gomero, a form of whistled Spanish, we used a vocal and a whistled dichotic listening task in a sample of 75 healthy Spanish speakers. Both individuals that were able to whistle and to understand Silbo Gomero and a non-whistling control group showed a clear right-ear advantage for vocal dichotic listening. For whistled dichotic listening, the control group did not show any hemispheric asymmetries. In contrast, the whistlers’ group showed a right-ear advantage for whistled stimuli. This right-ear advantage was, however, smaller compared to the right-ear advantage found for vocal dichotic listening. In line with a previous study on language lateralization of whistled Turkish, these findings suggest that whistled language processing is associated with a decrease in left and a relative increase in right hemispheric processing. This shows that bihemispheric processing of whistled language stimuli occurs independent of language.

Stimulus-Independence of Dichotic Testing for Perceptual Asymmetry: Sentences versus Unrelated Words

32 subjects heard two dichotic tapes, one of sentences and one of unrelated words. Difference scores between the ears on the two tapes inter-correlated .52 significantly, suggesting contrary to a previous report, some stimulus-independence of the right-ear advantage.

Die digotiese stimuleringstegniek en funksionele hemisferiese asimmetrie: evaluering van perseptuele, aandags- en geheuemodelle

Die laterale responsasimmetrie wat ná digotiese stimulering blyk, is op verskeie maniere verklaar. Dieselfde verklaringskonsepte as wat na aanleiding van bevindinge in die ouditiewe modaliteit geformuleer is, is sonder sistematiese en omvattende evaluering oorgeneem ter verklaring van soortgelyke asimmetrieë in die visuele, taktiele en motoriese modaliteite. In hierdie studie is die vyf mees algemene verklaringsmodelle geïdentifiseer, toetsbare afleidings daaruit gemaak en kernkonstrukte in 'n multifaktoriaalontwerp geoperasionaliseer met die oog op die evaluering van die relatiewe toereikendheid van hierdie modelle. 'n Digotiese syfertoets en vier digotiese woordtoetse is saamgestel. In laasgenoemde is fonologiese en semantiese veranderlikes gemanipuleer. Hierdie toetse is aan 64 persone met hoogs waarskynlike linkerhemisfeerspraaklokalisering onder verskillende aandags- en geheuekondisies gegee. Die oororde en lateraliteit, asook die kanaal van rapportering en moeilikheidsgraad van die taak is sistematies gekontroleer. Die response is op drie wyses nagesien. Toetsing vir betekenisvolle verskille is gedoen. By sowel die syfertoets as die woordtoetse is 'n betekenisvolle regteroorsuperioriteit verkry. Die mate van asimmetrie is nie konsekwent beter by bepaalde vlakke van spesifieke faktore soos deur die differensiële verklaringsmodelle voorspel nie, maar enkele betekenisvolle interaksies tussen veranderlikes kom voor. Die resultate steun die algemene funksionele hemisferiese asimmetriemodel en falsifieer die orde-effekgeheuemodel. Die differensiële geheue-, aandags- en persepsie(moeilikheidsgraad-)modelle blyk ontoereikend te wees ter verklaring van die responsasimmetrieë, maar aandags-, geheue-, en taakmoeilikheidsfaktore asook die interaksie tussen hierdie prosesse speel wel onder bepaalde kondisies 'n rol in die bepaling van die relatiewe grootte van die asimmetrie.

Hemispheric predominance assessment of phonology and semantics: a divided visual field experiment

The aim of the present behavioural experiment was to evaluate the most lateralized among two phonological (phoneme vs. rhyme detection) and the most lateralized among two semantic ("living" vs. "edible" categorization) tasks, within the dominant hemisphere for language. The reason of addressing this question was a practical one: to evaluate the degree of the hemispheric lateralization for several language tasks, by using the divided visual presentation of stimuli, and then choose the most lateralized semantic and phonological for mapping language in patients by using fMRI in future studies. During the divided visual field experiment by using words (semantic tasks) and pseudo-words (phonological tasks) as stimuli, thirty-nine right-handed participants were examined. Our results have shown that all tasks were significantly left hemisphere lateralized. Furthermore, the rhyme was significantly more lateralized than phoneme detection and "living" was significantly more lateralized than "edible" categorization. The rhyme decision and "living" categorization will be used in future fMRI studies for assessing hemispheric predominance and cerebral substrate for semantics and phonology in patients. Our results also suggest that the characteristics of stimuli could influence the degree of the hemispheric lateralization (i.e., the emotional charge of stimuli for words and the position of the phoneme to be detected, for pseudo-words).

The bilingual Loch Ness Monster raises its non-asymmetric head again-or, why bother with such cumbersome notions as validity and reliability? Comments on Evans et al. (2000)

All of the experimental studies of the past 25 years combined and the meta-analyses of their findings have not advanced our knowledge of the lateralization of language in bilingual speakers one bit. We are left with a clutter of inherently uninterpretable contradictory results. Successive studies do not contribute a single brick to the edifice or a single piece to the puzzle-only more confusion. study is no exception. So far, there has been no demonstration of the validity of any experimental paradigm claiming to measure degree of language laterality in bilingual speakers. Experimentation is pointless unless the nature of what is alleged to be lateralized is clearly defined and the validity of the measures employed has been established. Because of the lack of validity of the paradigms used in bilingual laterality studies, experiments and meta-analyses of their findings cannot have any scientific significance. Like their predecessors, Evans et al. pay lip service to a number of methodological problems, but ignore their implications and simply carry on anyway. The authors ought to demonstrate, rather than assume, that degree of visual half-field advantage for single words corresponds to degree of lateralization of any component of language (even if only of words).

Processing of spatial locations: hemispace effects during encoding but not recall

Traditionally, functional differences in the visual modality between the two hemispheres are investigated by tachistoscopic procedures. In these experiments, the stimuli reach the contralateral hemisphere first, and results are commonly interpreted on the basis of neuroanatomical access models. However, numerous studies demonstrated that the hemispace where the stimulus is perceived also plays a critical role in producing laterality effects ("hemispace effects"). In the present experiment, subjects were instructed to memorize the relative spatial positions of six figures horizontally aligned on a presentation board. The presentation board was located either to the left, to the right or in front of the subjects (left, right and central learning positions). During a recall phase, each figure was presented in the center of a computer screen and subjects were required to indicate by keypress whether a figure had been located in the left or right half of the presentation board. As in the learning phase, the computer screen was located to the left, the right or in front of the subjects (left, right and central recall positions). We found that the positions of the figures initially memorized in the left hemispace were recalled faster than figures initially memorized in the right hemispace. Hemispatial position during recall had no effect on performance. These results are discussed with respect to hemispheric specialization and theories of hemispace effects.

Haptic perception of linear extent

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.

The tactual horizontal-vertical illusion depends on radial motion of the entire arm

We sought to clarify the causes of the tactual horizontal-vertical illusion, where vertical lines are overestimated as compared with horizontals in L and inverted-T figures. Experiment 1 did not use L or inverted-T figures, but examined continuous or bisected horizontal and vertical lines. It was expected that bisected lines would be perceived as shorter than continuous lines, as in the inverted-T figure in the horizontal-vertical illusion. Experiment 1 showed that the illusion could not be explained solely by bisection, since illusory effects were similar for continuous and bisected vertical and horizontal lines. Experiments 2 and 3 showed that the illusory effects were dependent upon stimulus size and scanning strategy. Overestimation of the vertical was minimal or absent for the smallest patterns, where it was proposed that stimuli were explored by finger movement, with flexion at the wrist. Larger stimuli induce whole-arm motions, and illusory effects were found in conditions requiring radial arm motion. The illusion was weakened or eliminated in Experiment 4 when subjects were forced to examine stimuli with finger-and-hand motion alone, that is, their elbows were kept down on the table surface, and they were prevented from making radial arm motions. Whole-arm motion damaged performance and induced perceptual error. The experiments support the hypothesis that overestimation of the vertical in the tactual horizontal-vertical illusion derives from radial scanning by the entire arm.

Modality Specificity as a Criterion for Diagnosing Central Auditory Processing Disorders

A central "auditory" processing disorder (CAPD) is an auditory perceptual dysfunction that cannot be explained on the basis of peripheral hearing loss. As a concept, CAPD has not been completely validated, and many issues continue to be controversial. A primary issue of concern is whether currently used tests to evaluate CAPD are sensitive to factors that are not of an auditory perceptual nature. In this paper, we consider the case for modality specificity as a criterion for improving the specificity of diagnosing CAPD. Demonstrating the modality-specific nature of sensory processing deficits is one way to rule out nonperceptual factors as explanations for observed dysfunction.

Spatial field advantages for tactile line bisection as a function of hemispheric specialisation inferred from dichotic listening

Thirty left-ear advantaged (LEA) and 30 right-ear advantaged (REA) right-handed subjects performed tactile line bisection (TLB) in left and right spatial fields, and at midline. REA subjects were found to perform significantly better in the right spatial field than in the left and LEA subjects significantly better in the left than in the right. Significant directional deviations were found only at midline with the left hand deviating to the right and the right hand to the left. These findings suggest that TLB is primarily a spatial task subserved by feedforward motor processes and that directional deviations are due to the differential scaling of egocentric space.

The influence of attention on the dichotic REA with normal and learning disabled children

Recently, Mondor and Bryden (Neuropsychologia, 29, 1179-1190, 1991; Percept. Psychophys. 52, 393-402, 1992) developed a lateralized cueing technique which appears to be a more powerful method than is the forced-attention technique (Bryden, 1978) of controlling the contribution of attentional biases to auditory perceptual asymmetries. This lateralized cueing technique was used to determine the influence of attentional biases on perceptual asymmetries obtained for normal and specific learning disabled (LD) children. Subjects were instructed to attend to, and report from, only the ear in which the cue sounded. The interval between the onset of the cue and the onset of the dichotic trial is varied so as to control the amount of time available to subjects to allocate attention to the cued ear. Results indicated that, for normal children capable of performing the task at a better than chance level, a large REA apparent at 150 msec Stimulus Onset Asynchromy (SOA) was attenuated at longer cueing intervals (450 and 750 msec SOA). For LD children, the magnitude of the initial REA appeared to be attenuated at 450 msec SOA. Thus, these data demonstrate that for normal children as well as for children with specific learning disabilities, attentional factors may contribute to the magnitude of the REA.

Dichotic listening: what does it measure?

Auditory lateralization was investigated in 26 right-handed and 26 left-handed, normal subjects using seven different dichotic listening tests in each proband (free recall of digit lists, free recall of consonant-vowel (CV) syllables, four different CV syllable monitoring paradigms, and free recall of Morse codes). Reliabilities calculated with the formula of Spearman-Brown were low for digit recall (0.29, corrected for test length: 0.50), but good for CV recall (0.83), CV monitoring (0.75-0.88), and Morse code recall (0.50, corrected for test length: 0.88). Nevertheless, interest correlations were low, both for right- and left-handers (negative correlations ranging from -0.44 to -0.05, positive correlations ranging from 0.01 to 0.51). Only 38-77% of the right-handed and left-handed subjects retained one direction of ear advantage across any combination of two tests. The data suggest that different dichotic tests reveal different results. This may be due to psychometric, procedural, or phonetic properties. We conclude that individual predictions of language dominance are not justified using the dichotic tests evaluated in the present study.

Processing asymmetries for complex sounds: comparisons between behavioral ear advantages and electrophysiological asymmetries based on quantitative electroencephalography

This experiment extends our earlier work on individual differences in ear advantages for complex sounds (Lauter 1982, 1983, 1984) to examine the results of combined behavioral and qEEG testing in the same subjects. Results include: (1) between-subject differences in absolute values together with between-subject agreements in terms of relative values, observed both for ear advantages (EAs) and hemisphere advantages (HAs); (2) within-subject agreement between behavioral (EAs) and physiological (HAs) measures of asymmetries; and (3) preliminary findings related to the interpretation of qEEG asymmetry data, such as the influence of hand movements on auditory-cortex qEEG recordings, and persistence of activation effects in which asymmetries evoked during a stimulation condition may be reflected in resting asymmetries observed during a subsequent control condition.

The influence of attention on the dichotic REA

Laterality researchers have frequently neglected to control for possible attentional components of perceptual asymmetries. Attention was manipulated in a dichotic listening paradigm by presenting a pre-exposural tone cue to the ear from which the subject was required to report. The time period between the onset of the cue and the onset of the trial (Stimulus Onset Asynchrony--SOA) was varied such that the time available to orient attention was manipulated. In two experiments, sizeable REAs were apparent at the shortest SOA (150 msec) but were substantially attenuated at longer intervals (450 and 750 msec SOA). In addition, a much larger effect of SOA on left-ear than on right-ear performance was observed. These effects were taken as evidence of an attentional bias to the right ear in the typical dichotic listening situation.

Functional Hemispheric Asymmetry and Psychological Differentiation

A differentiation model is proposed in which a relationship between neuropsychological (perceptual) differentiation on the one hand, and psychological (personality) differentiation on the other hand is hypothesized. An empirical investigation of the basic hypothesis is reported. The fit of the global model to empirical data is evaluated with the aid of the RAMONA program for path analysis with latent variables. In the advanced model differentiation is assumed to be a formal property of an organismic system. Neuropsychological differentiation is conceptualized in terms of the extent of functional hemispheric asymmetry (FHA), and operationalized in the auditory and visual modalities with the aid of the dichotic stimulation technique (DST) and the divided visual field technique (DVFT). Psychological differentiation is conceptualized in terms of the degree of healthy, optimal personality functioning (OPF), and is operationalized with indices of communicative competency, degree of self-actualization and of personal autonomy. A significant relationship between FHA and OPF was found. This indicates a correspondence between the degree of differentiation in diverse domains of functioning (perceptual and personality-wise), in healthy, normal subjects. In this study phenomena described in different specialization areas of psychology (neuropsychology and personology) are linked in a shall bridge theory for which empirical support has been found. This is a modest step towards interdisciplinary understanding.

Asymmetries in face perception: component processes, face specificity and expertise effects

Three experiments were carried out to analyze the component processes contributing to observed asymmetries in face perception, to determine whether these asymmetries occur for complex visuospatial stimuli other than human faces, and to investigate the effects of expertise on the asymmetries. Two component processes contributed to the observed asymmetries: perceptual bias (PB) in the observer and face asymmetries (FA). There was no PB effect for complex visuospatial stimuli other than human faces (landscapes, abstract paintings and animal faces). Expertise effects were investigated by examining the judgments of Chinese and Caucasian subjects for own-race and other-race faces. A PB was found for both Caucasian and Chinese faces, but the size of the effect was not related unequivocally to expertise. Caucasian subjects showed a PB for own-race faces only, but Chinese subjects showed a PB for both Chinese and Caucasian faces. There was no FA effect for Chinese faces, even when the composites were perceived as more dissimilar than the Caucasian composites, for which there was an FA effect. The implications of these results for the theoretical interpretation of perceptual asymmetries are discussed.

Manual asymmetry in weight discrimination: hand preference or hemispheric specialization?

One-handed weight discrimination was investigated as a function of hand, hand preference and hemispheric specialization. Differential thresholds (DLs) were measured for the left and right hands and left- and right-handed male and female subjects. DLs were found to be lower for the hand contralateral to the ear that proved superior in a verbal dichotic listening task. These results establish the existence of a manual asymmetry for the discrimination of lifted weight with the advantage accruing for the hand contralateral to the non-language cerebral hemisphere.

Direction and location of movement in kinesthetic judgements of extent

In unimanual kinesthetic judgements, larger ipsilateral extents felt equal to smaller contralateral ones. This was more likely to be due to a limb's general "intentional" tendencies towards its own ipsilateral hemispace than to e.g. differential attentional tendencies or the effects of muscular tension when crossing the midline. However hand asymmetries in this respect cannot account for the "pseudoneglect" phenomenon of setting the subjective midpoint of a felt rod slightly too far to the left. This phenomenon may instead be due to an asymmetric deployment of attentional and processing resources.

Attentional functions in listening and schizophrenia. A selective review

Maintaining the focus on one sound object or shifting it to another are considered to be two important attentional functions in selective listening, which may serve to differentiate attentional deficits in schizophrenics with respect to their psychopathology. To avoid confounding attentional control with effects of cerebral organization (laterality) as in dichotic listening, it is suggested that spatial hearing is taken into account when testing these attentional operations.

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.

Reading comprehension performance and laterality: evidence for concurrent validity of dichotic, dichhaptic and EEG laterality measures

EEGs were recorded while 55 boys read and answered questions about passages. Concurrent validity between parietal alpha ratios obtained from these recordings and dichotic/dichhaptic scores supports their utility as measures of lateral processing. The evidence was particularly strong between right hand advantage for dichhaptically presented sequential patterns and left hemispheric activity while answering. Results also indicate that coefficients for dichotically presented digits and alpha ratios during silent reading are indices of receptive laterality and measure the deployment of lateral structures rather than degree of structural laterality. This supports a dynamic rather than static model of lateral processing during receptive language.

Afferent and efferent models of visual perceptual asymmetries: theoretical and empirical implications

Visual laterality studies are reviewed in the framework of an afferent hierarchical information-processing model. According to this model, the hemispheres are viewed as separate information-processing systems, each with its own components and resources, as well as a common pool of resources. Information is shared across interhemispheric pathways. The magnitude and direction of visual field differences are determined by two factors: the processing efficiency of the components in one hemisphere relative to the other and interhemispheric transmission to components that are functionally localized to only one hemisphere. Rules are derived for weighing the relative contribution of these to visual field differences. As designed, the model can accommodate dynamic features characteristic of competing efferent (attentional) models without sacrificing its basic structure. The model's adequacy and usefulness for interpreting and guiding research on normal and brain-damaged people is discussed.