Dichotic listening

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In cognitive psychology, dichotic listening is a procedure commonly used to investigate selective attention in the auditory system. In dichotic listening, two different auditory stimuli (usually speech) are presented to the participant simultaneously, one to each ear, normally using a set of headphones. Participants are asked to attend to one or (in a divided-attention experiment) both of the messages. They may later be asked about the content of either message.

In a selective attention experiment, the participant may be asked to repeat aloud the content of the attended message, a task known as shadowing. As Cherry (1953)<ref name=Cherry>Cherry, E. C. (1953). Some experiments on the recognition of speech, with one and two ears. Journal of the Acoustical Society of America 25, pp. 975–979.</ref> found, people recall even the shadowed message poorly, suggesting that most of the processing necessary to shadow the attended message occurs in working memory and is not preserved in the long-term store. Performance on the unattended message is, of course, much worse. Participants are generally able to report almost nothing about the content of the unattended message. In fact, a change from English to German in the unattended channel usually goes unnoticed. However, participants are able to report that the unattended message is speech rather than non-verbal content.

Another example of a dichotic listening experiment is Cutting's (1976) demonstration<ref name=Cutting>Cutting, J. E. (1976). Auditory and linguistic processes in speech perception: inferences from six fusions in dichotic listening. Psychological Review 83, pp. 114–140.</ref> that listeners could correctly identify syllables when different components of the syllable were presented to different ears. The formants of vowel sounds and their relation are crucial in differentiating vowel sounds. Yet even though listeners heard two separate signals (no ear received a 'complete' vowel sound), they could identify the syllable sounds.

Dichotic listening can also be used to test the hemispheric asymmetry of a cognitive function such as language processing. A dichotic listening performance advantage for one ear is interpreted as indicating a processing advantage in the contralateral hemisphere. For example, Sidtis (1981)<ref name=Sidtis>Sidtis, J. J. (1981). The complex tone test: Implications for the assessment of auditory laterality effects. Neuropsychologia 19, pp. 103–112.</ref> found that healthy adults have a left-ear advantage on a dichotic pitch recognition experiment. He interpreted this result as indicating right-hemisphere dominance for pitch discrimination.