Dichotic Listening: Definition And Characteristics

Dichotic listening is one of the behavioral techniques based on perceptual lateralization most used in neuropsychology. This technique is used in the context of research on functional hemispherical specialization, namely the relative predominance of one hemisphere or another in the context of certain cognitive functions.

As we already know, the left hemisphere specializes in language. In addition to speech, this hemisphere handles grammar processing. The right hemisphere is responsible for visio-spatial processing, the perception of objects and faces.

What is it about ?

Dichotic listening is a technique based on the simultaneous presentation of two distinct auditory stimuli, one in each ear. The stimuli presented can be words or syllables, letters, or even musical sounds. Other parameters may also vary, such as the inter and intra stimuli interval, the number of presentations, the intensity, etc. (1)

In this technique, projections from the auditory pathway to the cerebral cortex are ipsilateral and contralateral. Thus, the information that each ear receives is projected into the two cerebral hemispheres.

During dichotic listening, the ipsilateral pathways are inhibited. Thus, the information received in one ear passes exclusively to the opposite cerebral hemisphere. What happens therefore is that if there is a lesion in one of the cerebral hemispheres, there will be a deficit in the contralateral ear due to the lesion in the context of dichotic listening.

A standard dichotic listening test counts a relatively high number of these dichotic syllables, and often the subject identifies a greater number of syllables by the right ear (OD) than by the left ear (OG). To refer to this phenomenon, we speak of the Right Ear Benefit (AOD). (3)

Characteristics of dichotic listening

This advantage of the right ear, Kimura (4,5) explains it according to two hypotheses. The first is that, as we mentioned earlier, the ipsilateral pathways inhibit themselves. Thus, only the contralateral pathways remain functional. On the other hand, testing, both clinical and neurophysiological, indicates that in the majority of people, language is represented in the left hemisphere.

From these conclusions, AOD can therefore be explained by the fact that the information received by the right ear follows a shorter and direct path to the left hemisphere (contralateral pathways).

The information received by the left ear must then travel the contralateral pathways to the right hemisphere, and from there, pass through the transcallous pathway to the left hemisphere in order to be decoded. This affects the quality of its plot and results in responses with greater latency and more errors. (2)

Influence of attention

According to various authors, the AOD obtained in the framework of dichotic listening could reflect other cognitive processes different from those related to the lateralization of language. For example, the asymmetry in the arousal or the interhemispheric activation, or the memorial effects and the caring effects, which are the most studied. (6)

Dichotic listening applied to schizophrenia

In the context of schizophrenia, certain cognitive functions are impaired. For example, attention, working memory and, above all, executive functions.

Thus, various studies have shown that people affected by schizophrenia have various characteristics in common. First of all, there is a greater proportion of deaf people. In addition, the asymmetry of the planum temporale and the Silvio fissure is less and the advantage of the right ear decreases.

Dichotic listening applied to major affective disorders

Some facts about the study of visual and auditory lateralization applied to major affective disorders :

• Patients with melancholic depression show exaggerated DOA compared to healthy patients
  • Most exaggerated AOD occurs when anxiety is absent

• Patients with social phobia show less DOA than healthy patients

So it seems that melancholic depression is associated with exaggerated DOA. The spectrum of anxiety disorders would then be associated with insufficient AOD.

Thus, this technique can also be applied in the context of other pathologies. With people suffering from dyslexia or multiple sclerosis, for example, this technique is also used. Its field of application in neuropsychological practice is very wide. In addition, it results from a measurement of temporal lobe and corpus callosum function, as well as selective attention and executive functions.

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