Ear preference in the dichotic presentation of patterned nonverbal stimuli
Date
1968
Authors
Spellacy, Frank Jared
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Abstract
Right ear superiority in the identification and recall of dichotically presented verbal sounds has been frequently demonstrated in right handed persons. This finding has been attributed to left cerebral hemisphere dominance for speech and the assumption that the crossed auditory neural paths are stronger than the ipsilateral ones. An analogous model has been proposed for nonverbal sounds. This model suggests that the left ear, and by implication the right cerebral hemisphere, shows a significant superiority in nonverbal auditory perception. The
literature suggests that this conceptualization is too broad since some nonverbal sounds fail to show the expected ear difference.
The left ear superiority has been shown most clearly when music was used as a stimulus. The intent of the present study was to replicate this finding using different experimental methods than have been used previously, to investigate the effect of varying length of the interstimulus interval, and to attempt to isolate those aspects of music which may be critical in demonstrating a right hemisphere functional superiority.
Four types of stimuli were examined: music, rhythm, timbre, and pitch patterns. The latter three stimuli were selected to represent component parts of music. The experimental stimuli were presented one pair at a time. Each dichotic pair was followed by a single identification foil which was either a new sound or one of the members of the experimental pair. The subjects (S) identified the foil by responding yes or no.
Ss were right handed young adults of both sexes who had shown a right ear superiority on a verbal dichotic listening test. Sixty-four Ss were assigned to one of two experimental groups. Group one had a five second interstimulus interval (I3I) separating the dichotic pair from the recognition sound; for group two this interval was twelve seconds. Two dependent variables were examined: number of correct responses and response time.
A left ear superiority in identifying musical stimuli was found for the experimental group with short ISI but not for the group with long ISI. No significant ear difference was demonstrated for the other three stimulus conditions (rhythm, timbre, and pitch) in either time group. There was a significant overall tendency for Ss to make correct responses more rapidly to stimuli presented to the left ear as compared to the right ear. However, this difference was not statistically significant within any one stimulus condition. Overall performance, i.e., the number of correct identifications, was affected by type of stimulus and length of ISI. Recognition time was significantly affected by the type of stimulus, length of ISI, and sex of S.
These results are interpreted in terms of left ear superiority for nonverbal stimuli under immediate memory conditions. Left ear superiority for nonverbal sounds apparently is subject to rapid decay since it can not be demonstrated under delayed recognition conditions. As predicted, an overall effect of left ear superiority was found for both the number of correct responses as well as response time. Supplementary analyses of the performance of Ss over time suggest that the phenomenon of left ear dominance is affected by decreasing attention.