Dichotic listening in children: the reflection of verbal and attentional changes with age

A sample of 290 kindergarten children (147 girls), all native Hebrew speakers, were tested by two dichotic listening tests: (a) a digits test (low verbal workload) and (b) a words test (high verbal workload). The same subjects were tested one year later (at the end of their first year at school) by the same tests. In both tests and both testing sessions the free recall procedure was used. It was found that the performance difference between ears significantly decreased and overall performance significantly increased in the digits test in the second testing session. Differences between sessions in ear difference in the words test were not significant, although overall performance in the second session increased. These data lend support to the hypothesis that the change with age in the between-ears difference is mainly related to an improvement in verbal processing efficiency, which in turn allows the allocation of more verbal resources to the inferior input channel, without a decrease in resources allocated to the preferred one. As expected, increase in available verbal resources was clearly manifested under low verbal workload conditions but not under high workload conditions, where task demands did not allow significant increase in verbal resources to be allocated to the inferior channel. This hypothesis also predicted highly consistent ear preference owing to its being solely determined by the verbal processors of the dominant-to-speech hemisphere. The inconsistent ear preference between tests found in more than a third of the subjects of this sample could not therefore be accounted for by the stated hypothesis. The analysis of performance in subjects who showed left-ear preference in only one test and right-ear advantage on the other occasions indicated that whenever the left ear was preferred it was accompanied by significantly smaller ear difference and lower overall performance compared with those manifested by the same subjects in the same test in the other testing session. These data are better accounted for by the hypothesis that two different pools of resources are involved in splitting attention between ears in the free recall of dichotically presented verbal stimuli: one which is controlled by verbal processors of the dominant-to-speech hemisphere and the other by a spatial attentional mechanism. However, it seems that changes in dichotic test performance within the first year at school can mainly be attributed to increase in verbal resources rather than to improvement in allocation of spatially controlled resources.