Semantic and visual memory codes in learning disabled readers

Two experiments investigated whether learning disabled readers' impaired recall is due to multiple coding deficiencies. In Experiment 1, learning disabled and skilled readers viewed nonsense pictures without names or with either relevant or irrelevant names with respect to the distinctive characteristics of the picture. Both types of names improved recall of nondisabled readers, while learning disabled readers exhibited better recall for unnamed pictures. No significant difference in recall was found between name training (relevant, irrelevant) conditions within reading groups. In Experiment 2, both reading groups participated in recall training for complex visual forms labeled with unrelated words, hierarchically related words, or without labels. A subsequent reproduction transfer task showed a facilitation in performance in skilled readers due to labeling, with learning disabled readers exhibiting better reproduction for unnamed pictures. Measures of output organization (clustering) indicated that recall is related to the development of superordinate categories. The results suggest that learning disabled children's reading difficulties are due to an inability to activate a semantic representation that interconnects visual and verbal codes.     

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.     

Attentional deficit in learning-disabled children: evidence from visual half-field asymmetries

The structural theory of cerebral lateralization has been typically used to explain hemispheric asymmetries. However, the attentional model of brain functioning may help resolve some of the inconsistent findings with groups of learning-disabled children. To test this hypothesis, a visual half-field paradigm for word recognition was employed in a group of 26 learning-disabled and 26 normal children matched for sex, chronological age, and handedness. Three experimental conditions (unilateral, cued unilateral, and bilateral) and two word error types (visually and acoustically confusable words) were analyzed. The results indicated that normals produced the expected RVHF superiority under all experimental conditions, but the learning-disabled produced the expected RVHF superiority only under the cued unilateral condition. Learning-disabled children also made significantly more visually and acoustically confusable errors than normals and unlike normal children increased the number of acoustic errors in the RVF under bilateral stimulation. These results provide evidence that learning-disabled children may process information inefficiently and have brain activation patterns that are more susceptible to attentional effects.     

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.     

Time sharing and dichotic listening asymmetry in normal and learning-disabled children

Time-sharing and dichotic listening techniques were used to examine cerebral lateralization for language function in 48 normal and 48 learning-disabled children. All subjects were matched according to age, sex, and handedness. An analysis of results indicated that both nornal and learning-disabled children demonstrated left hemisphere lateralization of language function on the time-sharing and dichotic listening tasks. However, no developmental trends were evident for either group. Differences observed in the performance of the normal and learning-disabled children may relate to how each group utilizes “verbal strategies” and processes simultaneous information in the left hemisphere. The results strongly question the notion that attributes learning disabilities to incomplete or delayed language lateralization and lend support to the notion that cerebral lateralization is not a developmental phenomena.