Learning disabilities, distinctive encoding, and hemispheric resources

The purpose of this study was to isolate possible sources of learning ability differences in distinctive encoding of item-specific and relational information. Two mechanisms postulated as underlying ability group differences were attentional capacity (as inferred from the magnitude and direction of correlations between primary and secondary recall) and resource monitoring strategies (as reflected in measures of selective attention and laterality). In Experiment 1, learning disabled and nondisabled childrens' word recall was compared on dichotic listening recall tasks that included nonorienting instructions, and orienting instructions that directed children's attention toward semantic, phonemic, or structural word features. Disabled children showed lower recall and more diffuse selective attention to word features than nondisabled children. Reciprocity (negative correlations) between targeted and background words within and between ability groups was comparable, except when targeted word features were phonemically organized. Experiment 2 indicated that disabled childrens' cued recall was inferior to that of nondisabled children, even though both ability groups produced comparable symmetrical recall patterns related to ear presentations. Taken together, the results suggest that the locus of disabled childrens' distinctive encoding deficiencies is related to resource monitoring strategies during interhemispheric processing.     

Hemispheric specialization in learning disabled readers' recall as a function of age and level of processing

This study was designed to test the inadequacy of two theoretical accounts of learning disabled readers' memory deficiencies. Two age groups of learning disabled and nondisabled readers were compared on diotic and dichotic listening recall tasks for semantically organized, phonemically organized, and categorically unrelated word lists presented in either the left, right, or both ears. Dependent measures were free recall, serial recall, recall organization, and hierarchical organization. As expected, recall increases were a function of age, group, and level of word processing. However, the results clearly demonstrated that age and group recall differences were an interaction of both mode of presentation and level of processing. The recall differences between reading groups were attributed to word knowledge (superordinate categorization) rather than recall organization within cerebral hemispheres or differences in hemispheric capacity, per se.     

Decision making in dual-task environments: analysis of hemispheric competition effects

Performance degradations in multitasking situations have been reported frequently as a predictable effect of competition that arises from different processing demands whose hemispheric locations are too proximal. This model might be useful in explaining performance deficits in complex workplaces. To test this assertion, a laboratory study was designed to create an analogue of the processing demands required by a tactical decision-making task performed by 24 right-handed men. Vocalization, dichotic listening and decision-making performance were assessed under single- and dual-task conditions. The results were consistent with the predictions from hemispheric competition in the case of dichotic listening but not with vocalization. The results are discussed in terms of their implications for both research and systems design.     

Do semantic memory deficiencies underlie learning disabled readers' encoding processes?

This study investigates the extent to which learning disabled readers' atypical encoding relates to their deficiencies in semantic memory. Inferences related to ability group performance were based on the assumption that encoding involves the matching of incoming information against a featural representation of that information in semantic memory. To this end, learning disabled and nondisabled readers in two age groups were compared on dichotic listening recall tasks that included orienting and nonorienting instructions. Orienting instructions directed children's attention toward semantic, phonemic, or structural word features. Dependent measures were lateralization, free recall, retrieval organization, and selective attention. The efficiency of allocating attentional resources was inferred from correlations between central and incidental recall. Primary results included the following: Disabled and nondisabled readers' ear asymmetry differences were dependent upon age, orienting instructions, and type of word list; disabled readers' recall and organization scores were lower than skilled readers'; however, both ability groups benefitted from orienting instructions compared to nonorienting instructions; during orienting instructions, disabled readers were less able than skilled readers to divide their attention between target and nontarget word features, especially during interhemispheric processing conditions; and the relative efficiency of allocating attentional resources differed qualitatively between the two ability groups. The results suggest that ability group variations reflect the structure of the memory trace in interaction with ear presentation and encoding processes. It is inferred that disabled readers' inferior memory traces reflect the quantity and internal coherence of information stored in semantic memory as well as the means by which such information is accessed.     

Interhemispheric transfer in schizophrenics, depressives, and normals with schizoid tendencies

Although several studies suggest that schizophrenics suffer from an impairment in the interhemispheric transfer (IHT) of information, methodological weaknesses in these studies preclude clear interpretation of their results. This study addresses these criticisms in order to provide a clearer test of the IHT theory. Schizophrenics, depressives, normal controls, and normals with schizoid tendencies were assessed on five measures of IHT (verbal and nonverbal dichotic listening, intermanual transfer, bimanual block design, finger sequence repetition) and two measures of unilateral hemispheric processing (lateral eye movements, auditory thresholds). Results consistently failed to support an IHT deficit interpretation of schizophrenia. Schizoid normals had a significantly greater right-ear advantage on verbal dichotic listening than both psychiatric groups, a result suggesting enhanced left-hemisphere activation in schizoid normals. It is concluded that the IHT theory requires stronger empirical substantiation than has been obtained to date to warrant further consideration as a central theory of schizophrenia.     

Preferred recall order and recall accuracy for two messages presented simultaneously over a single auditory channel

Ss in the dichotic listening task prefer, and are more accurate with, the channel-by-channel order of recall-recalling all information presented to one ear followed by the information presented to the other ear. Current explanations for these effects rely upon the fact that the two messages are presented over separate input channels. The present study tested this hypothesis directly by presenting two messages simultaneously to a single auditory channel. Groups of Ss were instructed to recall two pairs of digits presented simultaneously over a single channel (1) in any order (free recall), (2) in the order received (simultaneous order), or (3) in sequential groups (successive order). Ss in the free recall task preferred recalling items in successive order. However, Ss instructed to recall in simultaneous order were as accurate as those instructed to recall in successive order. These data imply that accuracy with, but not preference for, the successive order of recall depends upon whether input is to one or two channels.     

Cerebral specialization and verbal-motor integration in adults with and without Down syndrome

Persons with Down syndrome (DS) tend to exhibit an atypical left ear-right hemisphere advantage (LEA) for the perception of speech sounds. In the present study, a recent adaptation of the dichotic listening procedure was employed to examine interhemispheric integration during the performance of a lateralized verbal-motor task. Although adults with DS (n = 13) demonstrated a right ear-left hemisphere advantage in the dichotic-motor task similar to their peers with (n = 14) and without undifferentiated developmental disabilities (n = 14), they showed an LEA in a free recall dichotic listening task. Based on a comparison of the laterality indices obtained from both dichotic listening procedures, it appears that the manifestation of lateral ear advantages in persons DS may dependent on the response requirements of the task.     

Information processing and speech lateralization in learning-disabled children

The relationship between information processing and speech lateralization was investigated in learning-disabled children. The Kaufman Assessment Battery for Children (K-ABC) assessed simultaneous and successive processing while a dichotic listening paradigm with free recall and directed attention conditions assessed speech lateralization. A three-factor ANOVA design conducted on the dichotic data revealed that normal children demonstrated stronger right ear advantage (REA); whereas learning-disabled showed weaker right ear advantage. Further, lambda analyses conducted on individual subjects revealed that the learning-disabled did not demonstrate the REA, were not biased attenders, and did not get more right ear than left ear items when attention was directed to one ear. Multiple-regression analysis was used to predict sequential processing from the dichotic data for both groups. Learning-disabled children demonstrated a substantial deficit in sequential processing as compared to normal children. These results indicate that learning-disabled children may not have adequate cerebral lateralization of receptive speech processes, shift their attention more readily, and are more inadequate in sequential processing that presumably subserves language functioning. Perhaps learning-disabled children have deficiencies of processor capacity of salient areas of the left (language) hemisphere.     

The bilingual-dichotic method for learning a foreign-language vocabulary

The bilingual-dichotic method organizes native and foreign words in paired-associate learning for optimum compatibility with study behaviour and asymmetric cerebral hemispheric specialization. Slow-paced auditory presentations alternate dichotic (simultaneous, native word at left ear and foreign word at right ear) and diotic (foreign word at both ears) input while the student views the word list in parallel to the dichotic format (native word-foreign word). More college students attained the criterion of perfect cuedrecall and in significantly less study time using the bilingual-dichotic method to learn English-Russian word pairs compared with those using the conventional (diotic Russian) or a reversed-ear dichotic control method. The new method yielded superior overall performance with significantly more accurate recall of the Russian words, and with shorter latencies of response than that obtained with the conventional method. Analysis suggests the bilingual-dichotic method combines attentional strategies with the right-ear advantage for dichotic verbal material to enhance rehearsal processes of learning. Practical applications of this new method for learning foreign vocabulary may be found in the early stages of foreign-language learning in coordination with other exercises.     

Musicians processing music: Measurement of brain potentials with EEG

Abstract

In the present study, the EEG was recorded from the scalp of musicians while mentally active in their field. Analytic, creative and memory processes of the brain were observable using a special electrophysiological method called DC-potential recording. Music students listened to a sequence of four notes and subsequently were either to reverse the sequence (task 1 = analytic) or to compose a new continuation (task 2 = creative). In task 3, the initial segment of a well-known melody was presented and had to be continued (memory task). All tasks had to be solved mentally (imagery). In tasks 1 and 2, either tonal or atonal sequences were presented.

While processing, the results show that the analytic task elicited the highest brain activity. The analytic task involved mainly parieto-temporal areas of both hemispheres, the left hemisphere showing a tendency for domination. The memory task produced predominant activity over the right hemisphere. The creative task caused the lowest brain activation and elicited an unexpected lateralisation to the left, though we expected creativity to be a right hemispheric holistic-synthetic phenomenon.

Comparing listening with processing of the perceived music, we found a significant shift from an insignificant right hemispheric to an insignificant left hemispheric predominance (except with the memory task). This indicates that musicians do not lateralise to the left hemisphere per se when listening to music. Whether one finds a left hemispheric lateralisation in listening tasks or a right hemispheric one probably depends on the amount of simultaneous analytic-sequential processing the musician undertakes.     

Lateral asymmetry in subgroups of dyslexic children

It has been proposed that in examining hemispheric dominance in dyslexics, investigators must make a distinction between subtypes of the disorder. Using the Denver Reading and Spelling Test, 72 dyslexics were divided into three groups: dysphonetics, dyseidetics, and nonspecifics. Three measures of hemispheric dominance were administered: a dichotic listening test, a hemiretinal test with linguistic stimuli, and a hemiretinal test with spatial stimuli. Results indicated that the three subgroups of dyslexics did not differ from one another on measures of hemispheric dominance. Dyslexics, taken as a group, tended to show an exaggerated right ear advantage on the dichotic listening test, in comparison with that of controls. It was proposed that the dichotic listening test may be confounded by attentional deficits in the dyslexics.     

Neuropsychological assessment of learning disabilities: a discriminant analysis

The neuropsychological test scores of 23 learning disabled children were compared with those of a matched population of normal children in the 9-1 to 13-1 age range. All children were administered the Wechsler Intelligence Scale for Children-Revised (WISC-R), a dichotic listening task involving both free and directed recall conditions, a handedness inventory, the Tactile Performance Test and the Category Test from the Halstead-Reitan Neuropsychological Test Battery. A multivariate analysis of variance resulted in a significant separation between groups (p less than .001) using these procedures. A stepwise discriminant function analysis revealed that both of the directed dichotic tasks contributed the most of all 13 measures to the significant group separation. In addition, other cognitive tasks found to discriminate normal from learning disabled children include general verbal processes, concept formation, and tactile memory. These findings suggest that the directed dichotic listening procedure and the WISC-R Verbal IQ measure are reasonably valuable clinical tools in the classification of learning disabilities.     

Hemispheric laterality and dissociative tendencies: differences in emotional processing in a dichotic listening task

The present work investigates whether the hemispheric processing of both verbal and emotional stimuli, studied by means of a dichotic listening task, differs between normal high and low dissociators as assessed by the Dissociative Experiences Scale (DES; Bernstein & Putnam (1986). Development, reliability and validity of a dissociation scale. Journal of Nervous and Mental Disease, 174(2), 727-735). Two groups of subjects (50 high and 50 low dissociators), participated in the experiment. The task consisted in identifying both verbal and emotional stimulus-targets, respectively, on successive sessions. Reaction time and response accuracy were registered and analysed using ANOVA (Analysis of Variance). The interaction between stimuli (verbal, emotional), channel (right ear, left ear), and dissociation level (high, low) reached statistical significance in terms of accuracy measures (d': F(1,98)=4.75; p<.05). Both high and low dissociators exhibited the expected right ear advantage (REA effect) on verbal targets. On the other hand, whereas low dissociators exhibited the expected left ear advantage (LEA effect) on emotional targets, high dissociators failed to follow this typical pattern of hemispheric asymmetry: both hemispheres exhibited similar performances. These results confirm the hypothesis that dissociation is related to changes in hemispheric processing, specifically of emotional information.     

Fifty years of dichotic listening research - still going and going and…

This year celebrates 50 years of research in auditory laterality and hemispheric asymmetry, using a dichotic listening approach. The discovery of the "right ear advantage" in 1961 by Doreen Kimura to dichotic presentations of phonetic stimuli paved the way for new studies of how speech perception and related language processes are lateralized in the human brain. The articles in this special issue, celebrating the first 50 years of dichotic listening research, reveal both the breadth and depth of current research, with contributions spanning from basic research to clinical applications, from behavioral studies to studies using advanced neuroimaging techniques, and with contributions from all over the world. It is my hope as Guest Editor that the next 50 years will be as productive as the first 50 years.     

Memory and encoding of spoken discourse following right hemisphere damage: evidence from the Auditory Moving Window (AMW) technique

We investigated the hypotheses that impaired discourse processing following right hemisphere damage is mediated by task difficulty and is associated with deficits in discourse encoding. Spoken discourse passages differing in contextual predictability were presented to right hemisphere-damaged (RHD) patients and to non-brain-damaged (NBD) controls for subsequent recall using the Auditory Moving Window paradigm. To manipulate processing difficulty, speech segments were of normal or accelerated speech rates. The recall results showed that RHD adults recalled less than NBD controls overall and failed to recall major idea units better than minor idea units for high predictability passages presented at accelerated speech rates. Both RHD patients and NBD controls failed to recall major idea units better than minor idea units for low predictability passages, regardless of speech rate. The encoding results showed that RHD adults were both slower overall and differentially slower than NBD controls when listening to accelerated passage segments. Taken together, the encoding and recall results are consistent with the view that extracting passage gist under difficult listening conditions is especially vulnerable for patients with right hemisphere strokes.     

What learning-disabled readers fail to retrieve on verbal dichotic tests: A problem of encoding,retrieval, or storage?

Three theoretical models were assessed as a framework for capturing learning-disabled readers' faulty word retrieval. To this end, learning-disabled and skilled readers were compared on verbal dichotic listening tasks for free recall and cued recall of word lists organized by semantic, phonemic, and structural features. The results indicated that disabled readers were comparable on free recall but were inferior to skilled readers on cued recall. No ability group differences were found for categorical and noncategorical recall intrusions during the cued recall phase. Cued recall performance was further analyzed for individual differences in memory trace structure (via the Tulving & Watkins, 1975, reduction method), ear asymmetry, and the allocation of attention to word features prior to cuing. Results indicated that during the cued recall phase, disabled readers' memory traces were inferior in structure to those of skilled readers, even though the two ability groups produced comparable symmetrical recall patterns for the ear presentations. Further, disabled readers had lower selective attention scores for the interhemispheric processing of information prior to cuing than did skilled readers. Taken together, the results suggest that, prior to cued recall, disabled readers suffer from attentional difficulties during interhemispheric processing, which in turn influences the structural formation of their memory trace.This research was supported by a grant from the U.S. Office of Special Education and Rehabilitative Services. Special appreciation is given to Greelley District IV schools for providing subjects, to Missy Reda and Stephanie Contros for the data collection, and to two anonymous reviewers for their critical comments on a draft of this article.     

Left or right carotid endarterectomy in patients with atherosclerotic disease: ipsilateral effects on cognition?

We evaluated hemispheric functions ipsilateral to the side of carotid endarterectomy (CEA) in patients with a severe stenosis in the left or right carotid artery. Assessments took place 1 day before and 3 months after CEA. Only right-handed males were included. Nineteen patients underwent surgery of the left carotid artery and 17 of the right. Valid instruments for hemispheric function were included, such as verbal dichotic listening, finger tapping, and a lateralised test for motor planning. Results showed that, preoperatively, patients had lower scores compared to norms on the laterality tests, and on a visuoconstructive test. There was no evidence of ipsilateral improvement related to side of surgery. Left ear dichotic listening improved, which was seen in both left and right surgery groups. Also in both groups, left- and right-hand movement speed in the motor planning test decreased. Conclusion is that beneficial ipsilateral cognitive change after CEA in patients with severe stenosis in one of the carotid arteries may not be demonstrated, even if valid instruments for hemispheric function are included.     

Effect of directed attention on cerebral asymmetries in stuttering adults

9 stutterers and 9 nonstutterers were administered a dichotic digits test under conditions of free recall and directed attention. Analysis indicated right-ear preference for both groups and no differences between the free recall and directed listening conditions. Results are discussed in relation to previous studies in which dichotic digit-stimuli were presented to stutterers.     

The Role of Dichotic Listening Performance and Tasks of Executive Functions in Reading Impairment: A Discriminant Function Analysis

This study focused on the role of dichotic listening performance for the identification of reading impaired subtypes. Dichotic listening (DL), using verbal stimuli, has shown to be a valid measure of language lateralization. Usually, lateralization is estimated from the proportion of right ear over left ear accuracy during a free recall test procedure. However, it has been suggested that a more accurate estimate of laterality can be obtained by using a directed attention procedure. A sample of 43 reading disabled children of whom 18 showed signs of impaired language comprehension skills and 25 without language comprehension impairments, were compared to 20 age, and gender, matched controls on dichotic listening performance in both an unbiased free recall task and in a directed attention task using consonant-vowel syllables as dichotic stimuli. A laterality index was calculated for left and right ear stimuli reported during both the free recall condition and the attended ear-scores for the two directed attention conditions. Although both DL procedures yielded significant group differences, with a lower laterality score for the reading disabled compared to the controls, there was no main effect of DL-procedure or group × procedure interaction. Taken alone, DL performance could correctly classify 42% of the reading impaired samples, but together with other measures of executive functions, discriminant function analyses yielded 90.74% accuracy in classifying reading impaired children. The result indicates that DL together with tests of executive functions are valuable tools for assessment of reading impaired subjects.     

Writing induces a right hemisphere linguistic advantage in dysphonetic dyslexic children: implications for attention and capacity models of laterality

An experiment demonstrated a complete hemispheric processing reversal in 10 male, dysphonetic dyslexic children that occurred during a dichotic listening test of their verbal working memory. Requiring a written response to dichotic digits produced a right hemisphere/left ear superiority in the dysphonetic dyslexics whereas normal subjects and other dyslexics maintained a left hemisphere/right ear advantage. This reversal was unaffected by changes in task difficulty. A second experiment assessed the influence on producing the reversal of concurrent manual interference with left hemisphere verbal processing (responding orally vs. manually) and selective right hemisphere priming (Forward Writing vs. Backward Writing). The dysphonetic children reverted to a strong left hemisphere superiority when recalling the dichotic digits orally. Backward writing produced no ear advantage in either direction. The findings suggest that dysphonetic dyslexia may be related to (1) left hemisphere processing demands that exceed capacity, (2) easily activated right hemisphere processing strategies and (3) failure to coordinate linguistic processing interhemispherically. The results supported a novel hybrid conceptualization of dyslexia consisting of a synthesis of selective activation, and dual processor-limited capacity, theories.