Dichotic Ear-Order Effects with Nonverbal Stimuli

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Normal right-handed subjects were required to identify four nonlinguistic sounds (pitch contours presented dicbotically in pairs) under each of the following conditions: (1) identification of the 2 stimuli in any order ; (2) identification of the two stimuli, first from one ear (e.g., always the left), and then from the other ear. Here, the report orders were known by the subject in advance of the onset of dichotic pairs; (3) identification in ear orders indicated only at the offset of each dichotic presentation; (4) identification (in any order) after verbal associates were taught to each stimulus. All four conditions tested the efficiency of the right and left cerebral hemispheres in processing nonverbal information (as reflected in accuracy of identification from contralateral ears). Conditions (2) and (3) tested the efficiency of each ear as a report ear .(first report) and as a storage ear (second report), and whether or not prior attentlonal set influences accuracy. The last condition assessed the effect of verbal labeling on left-hemispheric (right ear) accuracy in the perception of nonverbal material. Perceptual lateralization was not obtained under conditions of free report, nor with first-ear reports. The use of verbal labels did not increase right-ear accuracy. When considering only those items reported second, i.e., the stored items, the left ear (right hemisphere) was more efficient than the right ear; this effect was enhanced in the preinstruction (attentional) condition. Results support the idea that the storage mechanism may be more sensitive to laterality differences than the perceiving and reporting mechanism.