Shifts in children's ear asymmetry during verbal and nonverbal auditory-visual association tasks: a 'virtual stimulus' effect

Dichotic consonant-vowel-consonant (CVC) syllables were presented to 96 right-handed children between the ages of 8 and 12 years. Children were assigned either to a "code" condition that entailed translating the CVCs into English words or to a "bird" condition in which the CVCs had to be matched to cartoons of birds. A differential ear asymmetry for the code and bird tasks developed linearly across four blocks of trials. By Block 4, the code task yielded a significant right-ear advantage and the bird task yielded no ear advantage. The results are inconsistent with any model that attributes ear asymmetries entirely to fixed structural characteristics of the nervous system. Instead, ear asymmetries are influenced by the subject's categorization of the stimuli, i.e., by "virtual stimuli". These appear to be constructed over time (blocks of trials).