Dichotic listening

Dichotic Listening Test
Medical diagnostics
MeSH	D004007
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Dichotic Listening is a psychological test commonly used to investigate selective attention within the auditory system and is a subtopic of cognitive psychology and neuroscience. Specifically, it is "used as a behavioral test for hemispheric lateralization of speech sound perception." During a standard dichotic listening test, a participant is presented with two different auditory stimuli simultaneously (usually speech). The different stimuli are directed into different ears over headphones. Participants are asked to pay attention to one or both of the stimuli. Later, they are asked about the content of either the message they were asked to attend to or the message that they were not told to listen to.

In the late 1960s and early 1970s Donald Shankweiler and Michael Studdert-Kennedy of Haskins Laboratories used a dichotic listening technique (presenting different nonsense syllables) to demonstrate the dissociation of phonetic (speech) and auditory (nonspeech) perception by finding that phonetic structure devoid of meaning is an integral part of language and is typically processed in the left cerebral hemisphere. A dichotic listening performance advantage for one ear is interpreted as indicating a processing advantage in the contralateral hemisphere. In another example, Sidtis (1981) 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.

During the early 1970s, Tim Rand demonstrated dichotic perception at Haskins Laboratories. In his study, the first stimuli: formant (F1), was presented to one ear while the second and third stimuli:(F2) and (F3) formants, were presented to the opposite ear. F2 and F3 varied in low and high intensity. Ultimately, in comparison to the binaural condition, "peripheral masking is avoided when speech is heard dichotically." This demonstration was originally known as "the Rand effect" but was later renamed "dichotic release from masking". The name for this demonstration continued to evolve and was finally named "dichotic perception" or "dichotic listening." Around the same time, Jim Cutting (1976), an investigator at Haskins Laboratories, researched how 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. Even though the listeners heard two separate signals with neither ear receiving a 'complete' vowel sound, they could still identify the syllable sounds.

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