Several auditory processing deficits have been reported in children with dyslexia. In order to assess for the presence of a binaural integration type of auditory processing deficit, dichotic listening tests with digits, words and consonant-vowel (CV) pairs were administered to two groups of right-handed 11-year-old children, one group diagnosed with developmental dyslexia and an age-matched control group. Dyslexic children performed more poorly than controls from their left ears when listening to digits and words and from their right ears when listening to CVs. Direction of ear advantage varied across individuals in both groups when tested with digits and CVs, but ear advantage was stable with words. Several factors that may have contributed to inconsistencies in direction of ear advantage are discussed. When the children were tested in a directed response mode, degree of ear advantage differed significantly between groups with both words and digits. More dyslexic than control children demonstrated clinically significant reductions in dichotic listening performance, but no uniform pattern of deficit emerged. Only the double correct score and the left ear score with CV pairs were predictive of word recognition performance in dyslexic children. Binaural integration deficits are present in some children with dyslexia. Auditory processing disorder assessment may help delineate factors that underlie or are associated with reading impairment in this population.

Children with and without behavioral dichotic left-ear deficits participated in an event-related potential study with quasidichotic presentations of familiar fairy tale segments. Electrical activity was recorded from the scalp while the children listened for semantically and/or syntactically anomalous words from either the right side or the left side while competing segments of the fairy tale were simultaneously presented from the opposite side. Latencies and amplitudes were averaged for each target condition within the group with dichotic left-ear deficits (LED) and the group with normal dichotic listening performance (WNL). Individual global field power waveforms and topographic brain maps were generated for the average response in each of the two listening conditions, target right and target left. Cross-correlations were performed on the grand averaged global field power waveforms to measure the degree of synchrony between target right and target left responses in both groups. Integration functions were performed to compare the accumulated sum of voltages during target (right and left) and control (right and left) conditions. WNL children produced typical ERP responses to the target words in both target right and target left conditions. Responses from LED children were at delayed latencies in the target left condition and were at reduced amplitudes in both target conditions. Topographic brain maps revealed more lateralized scalp distributions and greater activation of frontal regions in LED children in the target left condition. Cross-correlational and integration function results demonstrated interaural asymmetries in responses from the LED children. Overall results suggest that slowed neural conduction times, poor interhemispheric transfer of neural activity, and a failure to suppress competing information arriving at the right ear may be involved in poor left-sided processing in children with behavioral left-ear dichotic deficits.

Functional magnetic resonance images were acquired while children with and without dyslexia identified incongruous words embedded within fairy tale segments in a quasidichotic listening task. All children produced greater activation in the left hemisphere than in the right hemisphere during the binaural separation listening task. Children with dyslexia, who had a higher incidence of a dichotic left ear deficit from prescanning behavioral tests, produced fewer hits and more misses than control children while monitoring their left ears in the scanner. Control children produced stronger left hemispheric activation for ipsilateral left ear input than right hemispheric activation for ipsilateral right ear input, but ipsilateral activation patterns in children with dyslexia were symmetrical. Children with dyslexia who monitored their right ears first produced the lowest left hemispheric activation overall, suggesting that priming of the right ear may have inhibited the ability of children with a left ear deficit to adequately identify target words presented toward their left ears while in the scanner.

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