Perceptual asymmetry differences between major depression with or without a comorbid anxiety disorder: a dichotic listening study.

Predictions that anxious and nonanxious depression would differ in perceptual asymmetry (PA), as well as in sensitivity for perceiving emotional words, were evaluated using dichotic listening tasks. A total of 149 patients having a major depressive disorder (51 with and 98 without an anxiety disorder) and 57 healthy controls were tested on fused-word and complex tone tasks. The anxious and nonanxious depression groups showed a consistent difference in PA across tasks; that is, the anxious group had a larger left-ear advantage for tones and a smaller right-ear advantage for words when compared with the nonanxious group. There was no group difference in sensitivity for perceiving emotional words. Patients having an anxious depression appear to have a greater propensity to activate right than left-hemisphere regions during auditory tasks, whereas those having a nonanxious depression have the opposite hemispheric asymmetry.     

Are variations among subjects in lateral asymmetry real individual differences or random error in measurement? Putting variability in its place

The current research investigates sources of variability in subjects' asymmetry scores on commonly used laterality tasks. In particular, subjects' asymmetry scores on four bilateral tachistoscopic tasks and one free-vision task were entered into a principal component analysis (PCA) in order to investigate components that explain the maximum variance of the sample. The results indicate that about half of the variation (45.2%) in asymmetry scores on both tachistoscopic and free-vision tasks is attributable to individual differences in characteristic perceptual asymmetry. The amount of variance explained by this characteristic perceptual asymmetry component is similar in a sample of dextrals and a sample of sinistrals. No significant relation was revealed between individual differences in characteristic perceptual asymmetry and performance on various verbal and spatial cognitive tasks.     

Variations in characteristic perceptual asymmetry: modality specific and modality general components.

The current study investigates sources of between-subjects variation in asymmetry scores on visual half-field and dichotic listening tasks. For each of these presentation modalities, subjects were given multiple laterality tasks. Results indicate that about 50% of the between-subjects variations in asymmetry scores in each modality is attributable to individual differences in perceptual asymmetries that are not stimulus-specific, referred to as "characteristic perceptual asymmetries" in this paper. In addition, the question of whether individual differences in characteristic perceptual asymmetries are modality specific, modality general, or both was investigated by entering subjects' asymmetry scores from visual half-field and dichotic listening tasks into a principal component analysis. The results of this analysis indicate that there are both modality specific and modality general influences on subjects' characteristic perceptual asymmetries.     

Multitask investigation of individual differences in hemispheric asymmetry

Right-handed subjects (N = 120) participated in four different laterality tasks designed to measure aspects of cerebral hemisphere asymmetry: identification of dichotically presented consonant-vowel syllables (CVs), examination of the effects of concurrent repetition of CVs and concurrent anagram solution on finger-tapping by the right and left hands, lateralized identification of CVs presented tachistoscopically to the left and right visual fields, and left/right biases on a free-vision face task involving judgments of emotion. Ear differences in the dichotic listening task were related to the pattern of lateralized interference in the dual-task finger-tapping paradigm. There were no other significant relations between pairs of tasks, but when the present results are considered in the light of other recent experiments, there appears to be a relation between lateral bias on the free-vision face task and visual field differences in tachistoscopic identification. The pattern of results has implications for hypothesized individual differences among right-handers in cerebral dominance for verbal processes, input pathway dominance, and asymmetric arousal of the two cerebral hemispheres.     

Comparative neuropsychology of the dual brain: a stroll through animals' left and right perceptual worlds

Perceptual asymmetries in humans typically manifest themselves under quite unnatural settings (e.g., tachistoscopic viewing and dichotic listening) and this has put into question their real biological significance. In animals with laterally placed eyes, however, perceptual asymmetries are ubiquitous in the normal, everyday behavior, as revealed by the differential use of the lateral visual field of the left and right eye in a variety of tasks. Data are presented showing how preferential use of the left and right eyes influences visual discrimination learning and detour behavior in chicks; similarities with detour tests performed in fish and evidence for asymmetries in eye use in animals with larger binocular overlap (e.g., anuran amphibians) are discussed. Implications of these perceptual asymmetries on the formation and fate of memory traces are put forward, with examples from unihemispheric sleep and lateralization of spatial memory in chicks. Finally, speculations about the evolutionary origins and possible adaptive advantages of perceptual asymmetries in vertebrates are presented.     

Defective stimulus set attention in generalized epilepsy

This study examined auditory selective attention in primary generalized and complex-partial (temporal lobe) epileptics using binaural and dichotic versions of the Continuous Performance Test. The patient groups did not differ from normal controls when only one channel was presented or when divided attention (simultaneously monitoring two channels) was required. However, generalized epileptics had significantly depressed hit rates when directed attention (responding to critical stimuli in only one channel) was required. These results suggest a contribution of brain stem “arousal” mechanisms to stimulus set attention. In addition, right ear perceptual advantages were found on these dichotic monitoring tasks, lending support to the contention that short-term auditory memory and verbal report are not required for the dichotic ear effect.     

Role of task factors in visual field asymmetries

Any tachistoscopic study of cerebral hemisphere asymmetry imposes a variety of task demands on the participants, ranging from demands imposed by specific viewing conditions to demands imposed by response output requirements. The present article discusses the role of several task factors that influence processing after the initial reception of the stimulus input, suggests a theoretical rationale for some of the effects of these task factors, and considers implications for future studies of visual laterality. The task factors discussed include both those that are relevant for minimizing artifacts that have nothing to do with hemispheric asymmetry and those that are relevant for interpreting hemispheric asymmetry in terms of specific perceptual and cognitive processes.     

Hemispheric lateralization of bilaterally presented homologous visual and auditory stimuli in normal adults, normal children, and children with central auditory dysfunction

Two experiments were conducted to examine the performance of normal adults, normal children, and children diagnosed with central auditory dysfunction presumed to involve the interhemispheric pathways on a dichotic digits test in common clinical use for the diagnosis of central auditory processing disorder (CAPD) and its corresponding visual analog. Results of the first experiment revealed a significant right ear advantage (REA) for the dichotic listening task and a left-visual-field advantage (LVFA) for the corresponding visual analog in normal adults and children. In the second experiment, results revealed a significantly larger REA in the children with CAPD as compared to the normal children. Results also revealed a reversed cerebral asymmetry (RVFA) for the children with CAPD on the visual task. Significant cross-modal correlations suggest that the two tasks may reflect, at least in part, similar interhemispheric processing mechanisms in children. Findings are discussed in relation to differential diagnosis and modality-specificity of CAPD.     

Preattentive bias for emotional information in panic disorder with agoraphobia.

A combined emotional Stroop and implicit memory (tachistoscopic identification) task with 3 types of words (panic-related, interpersonal threat, and neutral words) and 2 exposure conditions (subliminal, supraliminal) was administered to 35 patients with panic disorder and 35 age- and sex-matched controls. The patients showed Stroop interference for panic-related words both sub- and supraliminally and a similar but not equally robust effect on interpersonal threat words. On the tachistoscopic identification task, the patients identified more panic-related words than the controls did but showed no implicit memory bias effect. The patients' subliminal Stroop interference for panic-related words was found to correlate with trait anxiety and depression, although not with anxiety sensitivity.     

The effects of method of measurement upon children''s performance on visual perceptual tasks

Sixty-four first-grade children of average or above intelligence who did not evidence visual perceptual dysfunction were administered a series of visual perceptual tasks. The tasks evaluated the skills of visual figure-ground perception and form discrimination and involved four methods of measurement of these abilities: tachistoscopic, untimed, naming, and recognition. Results indicated considerable method of measurement influence upon task performance. Implications of the results for both researchers and practitioners are discussed.     

Frequency-shift detectors bind binaural as well as monaural frequency representations

Previous psychophysical work provided evidence for the existence of automatic frequency-shift detectors (FSDs) that establish perceptual links between successive sounds. In this study, we investigated the characteristics of the FSDs with respect to the binaural system. Listeners were presented with sound sequences consisting of a chord of pure tones followed by a single test tone. Two tasks were performed. In the "present/absent" task, the test tone was either identical to one of the chord components or positioned halfway in frequency between two components, and listeners had to discriminate between these two possibilities. In the "up/down" task, the test tone was slightly different in frequency from one of the chord components and listeners had to identify the direction (up or down) of the corresponding shift. When the test tone was a pure tone presented monaurally, either to the same ear as the chord or to the opposite ear, listeners performed the up/down task better than the present/absent task. This paradoxical advantage for directional frequency shifts, providing evidence for FSDs, persisted when the test tone was replaced by a dichotic stimulus consisting of noise but evoking a pitch sensation as a consequence of binaural processing. Performance in the up/down task was similar for the dichotic stimulus and for a monaural narrow-band noise matched in pitch salience to it. Our results indicate that the FSDs are insensitive to sound localization mechanisms and operate on central frequency representations, at or above the level of convergence of the monaural auditory pathways.     

Dichotic word-perception of aphasic and normal subjects.

The present investigation examined the role of the right cerebral hemisphere in linguistic perception following a left cerebral insult which had resulted in aphasia. Auditory dichotic procedures were utilized to investigate the ear-preferences of 30 aphasic Ss, grouped relative to the amount of time since the onset of left cerebral insult, and a group of 10 normal control Ss. An oral-response task and a pointing-response task were given. Statistical analyses showed a significant left-ear preference for aphasic Ss who were more than 6 mo. post-cerebral insult; however, Ss less than 6 mo. post-cerebral insult did not demonstrate a significant ear-preference under auditory dichotic stimulation. In contrast, a significant right-ear preference was noted for the normal controls. Significant differences were not shown for the aphasic or control groups on the oral and pointing tasks.     

Ear asymmetry in perception of emotional non-verbal stimuli

Hemispheric asymmetry for perception of non-verbal emotional human voices was investigated in normal subjects by dichotic listening utilizing non-verbal responses. As in former experiments, a slight but significant left ear superiority was found. This finding suggests that mediation of these stimuli is done by the right hemisphere. The dominant role of the right hemisphere in this perceptual task is discussed in terms of an earlier development of this hemisphere.     

Apparent shift in visual field preference after unilateral stroke

Patients with either a left- or a right-hemisphere stroke lesion scored higher in tasks of word-picture matching and of nonverbal shape matching when information was presented tachistoscopically (120 msec) to the visual field (VF) projecting to their undamaged hemisphere. Left-hemisphere stroke patients (n = 13) were dissociated from right-hemisphere stroke patients (n = 15) by low word recognition from memory and by low right VF but nearly normal left VF accuracy in word-picture matching or shape matching; the former appeared to rely upon processing of word meaning by the right hemisphere. In contrast, right-stroke patients had higher right than left VF scores in both tasks, and their discrimination of nonverbal shapes via the right VF was not different from that of controls (n = 15). Preferred processing by the VF projecting to the undamaged hemisphere appeared as a shift in perceptual asymmetry but may indicate, in support of a "direct access" model, that each hemisphere responds more or less efficiently to word and to nonverbal shape discriminations.     

Directional scanning and cerebral asymmetries in processing visual stimuli.

A perceptual exploration task involving three horizontal linear arrays of stimuli was administered to 167 children ranging in age from 3 to 7 yr. It was found that the well organized, predominantly right-to-left responses of very young children were eventually replaced by left-to-right patterns. A tachistoscopic test showed that Ss who gave right-to-left responses to the linear arrays showed hemispheric asymmetry of perception. The results were interpreted as supporting the view that directional response tendencies are related to hemispheric asymmetry.     

Processing of visually presented vowels in the cerebral hemispheres

The respective efficiency of the cerebral hemispheres in processing visually presented vowels is discussed and examined in a tachistoscopic experiment with normal subjects. It is suggested that results from dichotic listening experiments cannot be used to predict performance on the same material in the visual modality. The physical characteristics of the stimulus, in both modalities, contribute to the pattern of hemispheric advantage and cannot be ignored in the interpretation of results from dichotic listening and tachistoscopic experiments.     

The effect of stimulus type and directed attention on dichotic listening with children

This research investigated the effect of stimulus type and directed attention on dichotic listening performance with children. A sample of 12 (5 male, 7 female; mean age 10.5 years) high academically performing children were administered four types of dichotic stimuli (words, digits, CV syllables, and melodies) in three experimental conditions (free recall, directed left, and directed right) to examine perceptual asymmetry as reflected by the right-ear advantage (REA). While the expected REA for words and CV syllables and the expected LEA for melodies were found under free recall, the directed conditions produced varied results depending on the nature of the stimuli. Directed condition had no effect on recall of CV syllables but had a dramatic effect on recall of digits. Word stimuli and directed condition interacted to produce inconsistent perceptual asymmetry while directed condition reduced overall recall for melodies. The findings lend support to the hypothesis that perceptual asymmetries can be strongly influenced by the type of stimulus material used and the effect of attentional strategy employed.     

Cross-modal correlation of dichotic and tachistoscopic language laterality tasks: the importance of familial sinistrality

Previous studies have found little if any correlation between dichotic and tachistoscopic language laterality task performance asymmetries. Problems with these studies have been that quite dissimilar auditory and visual tasks have often been used, and the reliability of the asymmetry measures has generally been unknown or, when known, relatively poor. We assessed the cross-modal correlation for two tasks, the Bilateral Object Naming Latency Task (BONLT) and the Dichotic Object Naming Latency Task (DONLT). These tasks are highly similar and have demonstrated high reliabilities. A significant, though rather small, cross-modal correlation was found (r = +.28). When cross-modal correlations were computed for FS- and FS+ subjects separately, no correlation was found for FS+ subjects (r = +.02), but the correlation for FS- subjects was highly significant (r = +.54, p less than .004). This led us to reexamine some previously collected data (P.L. Van Eys and W. F. McKeever, 1988, Brain and Cognition, 4, 413-429) which had administered two highly reliable language laterality tasks (the BONLT and the Dichotic Consonant Vowel Task), but had not assessed cross-modal correlation. A significant cross-modal correlation was found for FS- but not for FS+ subjects. The results are consistent with the hypothesis of H. Hecaen, M. De Agnostini, and A. Monzon-Montes (1981, Brain and Language, 12, 261-284) which suggests that one effect of FS+ is to induce a greater heterogeneity of localizations of different language processes.     

Assessment of the relationship of cerebral hemisphere arousal asymmetry to perceptual asymmetry.

This study examined the hypothesis that characteristic individual differences in cerebral hemisphere arousal asymmetry are related to individual differences in perceptual asymmetry observed in verbally based visual half-field tasks. The study used electrophysiological measures of arousal asymmetry rather than behaviorally derived measures (Levy, Heller, Banich, & Burton, 1983). Measures of alpha asymmetry were obtained from 20 right-handed males during a baseline relaxation condition and during a visual half-field version of the lexical decision task. Reaction time measures of perceptual asymmetry were obtained during this task. The results indicated that a basal arousal asymmetry measured at the temporal recording location during the baseline condition was significantly related to individual perceptual asymmetry during the subsequent lexical decision task. This basal arousal asymmetry was relatively stable across different task conditions. A task-related arousal asymmetry measured at the parietal location during the lexical decision task also made a significant contribution in predicting individual perceptual asymmetry. These two measures of individual arousal asymmetry were able to predict 50% of the variance in perceptual asymmetry. The implications of the results for explaining more wide-ranging individual differences in behavioral style and personality are discussed.     

Spatial and Selective Attention in the Cerebral Hemispheres in Depression, Mania, and Schizophrenia

Two tachistoscopic tests examining distinct aspects of attention were administered to normal subjects and patients with depression, mania, and schizophrenia. The first examined spatial attentional bias using happy-sad chimeric faces, known to elicit a perceptual bias to the left side of space in normal right-handers provided the right cerebral hemisphere is intact. The second used a lateralized version of the Stroop task, a traditional test of selective attention. Normals showed the expected leftward perceptual bias but showed equivalent susceptibility to the Stroop effect in both visual fields. As previously demonstrated with chimeric faces viewed in free vision, depression and mania were associated with weak and strong biases respectively with schizophrenics showing no bias to either side of space. The relationship between perceptual bias, as assessed by reaction time and absolute performance and the Stroop effect, showed differences according to diagnosis. This may be interpreted as evidence for the dissociability of attentional processes as well as lateralized differences in the pattern of cerebral activation in affective disorders and schizophrenia. The independence of performance variables on these tests in the schizophrenic group points to severe neuropsychological dysfunction.