VERBAL AND NONVERBAL PROCESSING AMONG LEFT- AND RIGHT-HANDED GOOD READERS AND READING-DISABLED CHILDREN.

Abstract

Differences in cerebral lateralization of verbal and nonverbal stimuli between left- and right-handed good readers and left- and right-handed reading-disabled children were examined. The study utilized the dichotic listening paradigm and examined the effects of directed attention on the processing of consonant-vowel (CV) and tonal stimuli by the four groups. The sixty subjects included fifteen right-handed good readers (eleven females and four males, mean age 10-3), fifteen left-handed good readers (eight females and seven males, mean age 10-5), fifteen right-handed reading-disabled children (six females and nine males, mean age 10-5), and fifteen left-handed reading-disabled children (four females and eleven males, mean age 10-8). All left-handed subjects had sinistral relatives. A three-factorial analysis of variance resulted in a significant left ear advantage (LEA) for tonal stimuli across all directed attention conditions for all groups. When presented with CV stimuli, the right-handed good readers produced a significant right ear advantage (REA) across all attentional conditions. The left-handed good readers and left-handed reading-disabled children were left ear (LE) dominant in the free recall and directed left conditions but produced a shift toward the right ear (RE) during the directed right condition. Right-handed reading-disabled children demonstrated a REA during free recall and directed right but were able to direct attention to the LE in the directed left condition. The study provided initial findings on the auditory processing of simple tonal stimuli among anomalous groups of children and documented the strong LEA found in previous studies of adult subjects. Verbal processing results for right-handed good readers and reading-disabled children confirmed previous findings with these populations. Reversed verbal processing (right hemisphere) was documented in both left-handed groups in two of the experimental conditions. The results provide additional support for the structural theory of lateralization and suggest reversed or bilaterialized processing abilities for language in strongly left-handed good reader children. Components of the attentional bias model are necessary to explain the effects of directed attention on the auditory perceptual asymmetry found in the reading-disabled groups.