![]() ![]() The dichotic listening technique has been used to explore laterality effects in subjects with agenesis of the corpus callosum, partial and complete commissurotomy 12, congenital hemiplegia 13, acquired and congenital brain injury 14 and cortical hemispherectomy 15. However, in a large scale study of subjects ranging from age 10 to older adults, it was concluded that handedness did not affect any of the findings, and no sex differences were seen in children and older adults 11. The analyses of dichotic listening can be complex, as some studies indicate that handedness, age, and gender may interact with the dichotic listening scores 10. ![]() Changes in the bottom‐up and top‐down capacities may also interact with the functions of the reading network in the brain 9. The bottom‐up processes are innate, favouring the right ear, while response to the top‐down forced‐left condition is seen first at around the age of 10 8. In the forced‐left condition, on the other hand, the instruction is opposite to the stimuli‐driven bottom‐up perception, and demands strategies for executive cognitive control 7. In the forced‐right condition, the instruction to report from the right ear follows the “bottom‐up” bias towards the right ear stimulus, resulting in an increase of the right ear advantage. These two instructions reflect different cognitive processes. ![]() The forced‐right and forced‐left conditions are seen as tests of attention. The laterality index is a measure of the relative difference between the ear scores independent of correct responses. The scores of correct responses, to both left and right ear stimuli, indicate the degree of lateralisation. Younger children are known to have a less pronounced right ear advantage, but parallel to language development, there is a gradual shift towards the left hemisphere 6. Whereas a right ear advantage is seen in the majority of older children and adults, a left ear advantage is seen in about 10% of the population 5. On the other hand, a left ear advantage reflects the superior processing capacity for the left ear stimulus in the right hemisphere, and a no ear advantage reflects no superior processing of any ear in either hemisphere. This has also been validated through studies using brain imaging 4. Since the typical pathway for language processing is contralateral, a right ear advantage in the nonforced condition reflects the superior processing capacity for the right ear stimulus in the left hemisphere. The right ear advantage (right ear advantage) is a benchmark finding, showing a preference to report stimuli presented to the right ear 3. In the forced‐right condition, the subject is instructed to report the stimuli played to the right ear, and in the forced‐left condition, the subject is instructed to report the stimuli played to the left ear. In the nonforced condition, the subject is asked to report freely what he or she heard the best 2. The common dichotic listening paradigm consists of three different instructions. For example, it has been used with a concurrent visual task to investigate the extent to which visual and auditory attention compete with one another-an important issue for understanding when and how humans are able to multitask.ĭuring a typical dichotic listening assessment, the subject is presented with pairs of consonant–vowel syllables (such as /ba/ and /da/) via headphones one syllable is played to the right ear, and the other is played simultaneously to the left ear 2. Individuals with dichotic listening deficits often have difficulty hearing in the presence of background noise 1.ĭichotic listening has been used for many purposes to understand the nature and capacities of selective attention. In order to perceive the acoustic messages in both ears, the outer, middle, and inner ears must be working properly, but more importantly, the auditory brainstem nuclei, auditory cortical neurons, as well as neurons in the corpus callosum must be functioning properly. ![]() Binaural separation is the ability to perceive an acoustic message in one ear while ignoring a different acoustic message in the other ear 1. Binaural integration is the ability to perceive different acoustic messages presented to the left and right ears at the same time 1. Dichotic listening can be broken into two different processes: binaural integration and binaural separation 1. Dichotic listening training Dichotic listeningĭichotic listening is the auditory process that involves listening with both ears. ![]()
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