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The right ear advantage for verbal stimulus

Dichotic listening experiments have shown that different sorts of input show different ear preferences. Subjects with left-hemispheric language lateralization, which possibly constitute more than 95 percent of the population [Lind, Uri, Moen, and BjerkanLind et al.2000], are more accurate in reporting items arriving at the right ear than items arriving at the left ear when the input is verbal. This tendency is commonly referred to as the right-ear advantage (REA) for verbal stimulus. Conversely, the majority of people have a left-ear advantage (LEA) for tasks involving the recognition of music or environmental sounds [BrydenBryden1988].

There are two explanations of these ear advantages in dichotic listening:

i)
The structural theory
ascribes the advantages to anatomic properties of the auditory system. Kimura (1967) explains the REA for verbal stimulus by the fact that the right ear is connected to the language dominant left hemisphere of the brain and the left ear to the right hemisphere through the contralateral pathways. She claims that the contralateral pathways are more preponderant than the ipsilateral pathways which constitute the link between the ear and the hemisphere on the same side.
ii)
The attentional theory
also maintains that the basis of the laterality effect is lateralized cortical functions, but emphasizes the influence of attention in priming a particular hemisphere. An expectation of verbal stimuli, for instance, serves to prime the language dominant hemisphere and make it extra sensitive to stimuli [KinsbourneKinsbourne1970,KinsbourneKinsbourne1973,KinsbourneKinsbourne1975].

Current evidence indicates that neither of these two views, in their most extreme forms, is entirely correct. If attentional mechanisms were all that was relevant, then one would predict that it would not be possible to activate both the left and the right hemisphere simultaneously. According to Bryden (1988), however, one can obtain REAs for verbal material and LEAs for non-verbal material at the same time. On the other hand, it is proven that attentional factors do make some difference: the same dichotic stimuli that produce an LEA when one expects non-verbal stimuli, can produce a REA when one expects verbal stimuli [Spellacy and BlumsteinSpellacy and Blumstein1970]. It therefore seems that both structural and attentional components are relevant to the production of dichotic laterality effects.


next up previous contents
Next: Dichotic methods Up: Dichotic listening Previous: Dichotic listening
Janne Cecilie von Koss Torkildsen
5/10/2002