The type of psychological test which is commonly used to investigate the lateralization of brain and selective attenuation within the auditory system of the brain is known as Dichotic listening.
This test is mostly used in the field of neuroscience and cognitive psychology.
The general setup of a standard dichotic listening test is such that the participant taking part in the tst is presented with two different stimuli simultaneously into different ears of the participant using headphones.
Here the participant is asked to focus on both of the sounds and later on are asked either about one of the stimuli or both of them in case they were not asked to ignore one of the stimuli.
In this article we will discuss Dichotic Listening.
The first scientist to systematically use the dichotic listening test in his work was Donald Broadbent.
During the 1950s, Broadbent asked participants in his test to either focus on one or both of the sequence of digits by employing the dichotic listening test during his studies of attention.
He also further suggested on the basis of his work that due to the limited capacity, the information processing system for human selects which stimuli channel to attend to which later on led to the derivation of the filter model of attention.
Doreen Kimura, in the 1960s, drew conclusions about lateral asymmetry in the brain of auditory processing using dichotic listening tests.
On the basis of her tests she demonstrated that the participants of good health have a tendency of superior reception of verbal stimuli in the right ear and perception of melodies in left ear.
Using the results from this study and other studies she carried out using neurological patients with brain lesions, she deduced that there was a predominance for melodic perception of the right hemisphere and predominance of speech perception of the left hemisphere.
During the period of early 1970s and later 1960s, Michael Studdert-Kennedy and Donald Shankweiler of Haskins Laboratories used the dichotic listening tests to explains the dissociation of auditory and phonetic perception is an integral part of language by finding the phonetic structure devoid of meaning and is usually processed through the left cerebral hemisphere.
If there is a dichotic listening performance advantage in one of the ears, it can also be interpreted as an enhanced processing advantage in the area of contralateral hemisphere.
Another example of it can be the study done by Sidtis which proved that adults used to have an advantage of left-ear for a dichotic listening pitch.
He also concluded that the results indicate the dominace of pitch discrimination for right hemisphere.
Tim Rand, during the early 1970s, also demonstrated the dichotic perception at Haskins Laboratories.
In his study, the second and third stimuli:(F2) and (F3) were presented in one ear of the participants whereas the first stimuli: (F1) was presented in the opposite ear.
In this study the F2 and F3 stimuli were varied in high and low intensity.
This demonstration of varying intensities in one ear with the main stimuli in the other ear was firstly known as the “Rand effect” which was later on called as “dichotic release from masking”.
During the same time another researcher at Haskins Laboratories, Jim Cutting, also researched in the area of syllables using dichotic listening tests.
He carried out studies using where participants were able to join different components of the syllable to form the one syllable even when presented to different ears.
The different formants of vowel sounds are crucial still the participants were able to identify the vowel even after hearing incomplete components of the sound in different ears.
There is not just one type of listening but many. For example, Passive listening.
Dichotic fused words test (DFWT)
This is a modified version of the basic dichotic listening test and was put forward by Jonson in 1977.
This test was further modified in the early 1980s by Hawles and Wexler to get more accurate data pertaining to language function of hemispheric specialization.
In this dichotic fused words test (DFWT), each participant is exposed to the pairs of monosyllabic rhyming consonant vowel consonant (CVC) words with each word varying from the initial consonant.
The main difference in this test is as such the stimuli used in this test are aligned and constructed in such a manner that partial interaural fusion occurs and subjects who take these tests generally report and experience only one stimulus per trial.
Some of the major advantages of these methods, according to Zatorre, are the influence on stimulus on ear asymmetries can be assessed and eliminated, minimizing the attentional factors as the effect is localized to midline and percept is unitary and stimulus dominance effect may be calculated explicitly.
The high test reliability obtained by Hawles and Wexler study was 0.85, higher this value means that the data collected from this study is consistent.
Testing with emotional factors
Researchers also developed an emotional version of the dichotic listening test.
In this test the participants listen to the same word in both ears but with different emotions that can be either a surprised voice or a sad or a happy one.
Afterwards, the participants are asked to identify the tone of the word spoken in both ears.
According to the previous research, the right ear shows an advantage in recognizing speech sounds because of the evidence from Wenicke’s area and Broca’s area which are both situated in the right ear or left hemisphere.
Whereas the left ear is much better in processing non-linguistic material.
The results coming from the emotional dichotic tests are consistent with the previous studies with the participants having the tendency to recognize the emotion more correctly towards their left ear than the right one.
As this test was harder than the previous one so the responses submitted by participants were mostly incorrect.
Manipulation of voice onset time (VOT)
One of the basic manipulations during dichotic listening tests that have given more insights regarding brain function is the manipulation of voice onset time (VOT).
Till now, there are four VOTs which are used commonly in designing of dichotic listening tests: long-short(LS) pair where a consonant vowel (CV) syllable with a long VOT is presented to the left ear and a CV syllable with a short VOT is presented to the right ear, also short-long(SL), short-short(SS), long-long(LL) pairs.
Rimol, Hughdahl and Eichele, in 2006, reported in their study that the SL pair has the largest right ear advantage (REA) in healthy adults whereas the LS pair shows a unique left ear advantage (LEA).
A study among children ranging from 5-8 years have shown that the short VOTs are dominated by the long VOTs when LS pairs are presented under dichotic conditions.
Further studies also show that the children of around age 9, lack the ability to exert cognitive flexibility like adults to control the stimulus driven bottom up processes.
It was further demonstrated by Arciuli that this cognitive flexibility can result in dropping of proficiency with different complex tasks like reading.
Dichotic listening tests have also been used by neuropsychologists in the field of speech perception and language asymmetry to explore the role of singular neuroanatomical structure and can be used as a lateralized speech assessment task.
Hugdahl researched on the frontal lobe function and dichotic listening performance in right and left lesioned frontal lobe nonaphasiac patients and compared them with the healthy ones.
In the study that was carried out 36 participants were exposed to 36 dichotic trials with different pairs of CV syllables and later on each participant was asked to identify the syllable they heard best.
The results were as expected, the right lesioned patients showed an advantage in their right ear which was comparable to the healthy group whereas the left lesioned group displayed impairment when compared to the healthy group and right lesioned group.
This study also concluded that the dichotic listening involving frontal lobes into a neuronal circuitry can be a critical aspect to speech perception.
In the same way Hugdahl and Westerhausen also worked on the role of corpus callosum in speech perception and dichotic listening.
One of the other uses of dichotic listening is that it can be used to test the language processing or hemispheric asymmetry.
Doreen Kimura during the early 1960s reported that when a participant was presented with dichotic verbal stimuli it produced a right ear advantage (REA).
She related this REA to the language processing and localization of speech in the dominant left hemisphere of the cerebral cortex.
According to the studies reported by Dorren, this given phenomenon was related to the left sided dominance for language processing and structure of the auditory nerves.
One of the main points about REA is that it does not apply to the sounds that are not related to speech.
In a study shown by Studdert-Kennedy and Shakweiler they explore the CVC syllable pairs in the light of dichotic listening.
Six vowels are paired with the six stop consonants and the variation in final and initial consonants are analyzed.
According to their study, REA is the weakest when only the vowel is changed but strongest when the sound for final and initial consonants is different.
Selective attention experiments differ from the general dichotic listening tests as in this experiment the participants are asked to repeat aloud the message and its content what they are listening to.
This task in general is known as shadowing. According to Colin Cherry, people are usually not good with shadowing a message and are unable to recall most of it, he further suggested that this may be because most of the message was processed in the working memory of a person and was not being stored in the long term store memory.
Performance results for the same test on an unattended message comes out to be even worse than this.
Participants involved in the study are unable to recall any content of the unattended message and are even unable to recognize the change in language from English to German.
However, the only thing the participants were able to report was that the unattended message is a speech message rather than a non-verbal content.
Moreover, if a little tweak is done to the unattended message like embedding certain information to it such as that of the listener;s name then the message is more likely to be remembered and noticed.
Conway, Bunting and Cowen presented the demonstration to this example in which they asked some participants to shadow words in one of the ears while ignoring the words in the other ear.
At some point of the experiment, the participant’s name was spoken in the words spoken towards the ignored ear and the end the question was whether the participant would report their name being spoken in the ignored ear.
Participants with a higher working memory were able to block off that distracting information and were able to ignore it.
Also some certain words when spoken in the ignored ear were able to distract the participants e.g like sexual words which suggests that there is more work to be done and unattended information also needs more analysis as certain keywords can divert attention.
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FAQ about Dichotic Listening
What is Dichotic listening training?
Dichotic listening tasks require you to try listening to different speeches in both ears at the same time.
What is a Dichotic task?
Dichotic listening task involves sending different messages to both ears of a participant and then to ask whether they were able to understand both messages and can recall them or not.