Dichotic Test

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KUNNAMPALLIL GEJO JOHN

BASLP, MASLP

AUDIOLOGIST

KUNNAMPALLIL GEJO MASLP


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DICHOTIC LISTENING

Dichotic listening is a listening condition inwhich two different messages are presentedto two ears simultaneously ,but different

information to each ear



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Monotic ,a listening situation in which the

stimulus is applied to only one ear. Diotic, the same stimulus applied to two ears

Dichotic ,different stimuli applied to each of thetwo ears simultaneously.



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FACTORS AFFECTING DICHOTICLISTENING



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FACTORS AFFECTING DICHOTIC LISTENING

There are various factors known to affectdichotic listening. They can be mainlyclassified into:

Stimulus related task

Subject related task



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Stimulus related factors could be:

Intensity, frequency, temporal aspect (lageffect), phonetic effect, signal to noise ratio,synthetic versus non synthetic ratio, materialused, band width.

Subject related tasks could be:

Ear effect, age, gender, attention, practiceeffect, response mode.



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Stimulus Related Factors1) Temporal Aspect (lag effect)

When two different auditory signals are

presented simultaneously one to each ear, one ofthem is visually perceived as having a greaterperceptual salience than the other. This is known as

ear advantage.

A part from this, when one signal lags anothersignal in a ear then lagging signal will be perceived

better. This is called lag effect.



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The amount of time separation betweenmessage onset to overcome the right earadvantage (REA) was investigated by Berlin et

al. (1972). They found that when one of the CVtrailed the other by 30-60 msec the trailing CVbecome more intelligible then when it wasgiven simultaneously.

This time advantage occurred to the

lagging syllable and no to the leading syllable(Strddert-Kennedy, Shankdeder & Schumann,1940).


h d b l l h


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). This was supported by Berlin et al. (1973). In theirstudy they used 6 CV/pa, ta, ka, ba, da, ga/ nonsense syllable. These stimulus were paired, whoseonset were 0, 15, 30, 60, 90 msec apart. 12 adult

female served as subject. Results revealed REA when the syllable were

given simultaneously. The leading syllableintelligibility dropped when leading by 15 and 30msec and the intelligibility of lag ear improved.

Intelligibility of both lag and lead ear improvedbeyond 30 msec.

Binger & Raffin (1986) investigated identification ofthe dichotic CV at onset time asynchronies of 120,30, 60, 90 msec for 6 CV paired randomly. Resultsshowed significant REA at 0 msec, however thestudy did not support the presence of lag effect.



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Porter (1975) In a dichotic task, where signals were

presented with onset asynchronies varying from 0to 150 msec.Subjects identified the lagging signalmore accurately and reported them as clearer thanthe leading signal at 30 and 70 msec delay betweentwo ears. Beyond 70 msec lag no difference was

found. Rajgopal (1996); Puronile (2000) found an

improvement in score from 0 to 90 msec lag. Lageffect was also seen in children between age rangeof 8-17 years (Ganguly, 1996). Gelfand, Hollman,Walkmen & Pipes (1980) found aberration of lageffect for CV in elder subject.



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Darmin (1971), Porter (1978) studies have

demonstrated that REA and lag effect areindependent of one another and there isevidence that lag effect might be a case of

temporal masking not limited to speech stimuli.



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2) Phonetic Effects

Phonetic effect or stimulus dominance is aphenomenon where in higher scores are got one ofthe 2 competing syllable, the dominant oneregardless of the ear to which it is presented. Thiseffect is seen in natural CV syllables (Roeser, Johns,& Price, 1992).

In some respects, stimulus dominance is a moreinteresting phenomenon in dichotic listening, thanthe ear advantage. It occurs with greater frequencyand magnitude than the ear advantage.



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(a) Voiced versus Voiceless consonants

Berlin et al. (1973) reported that scores were higherfor voiceless stops [pa], [ta], [ka] than for voicedstops /ba/, /da/, /ga/ in pairs of natural syllables

contrasting in voicing.

The voiceless stops are said to be dominant than the

voiced stops. The findings were supported by Roser,

John & Price (1972) Wiceum, Risburn & Speaks(1981).


f h h d d d ff


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A few authors here studied different parameterwhich determines the voicing character of a sound,Repp (1976) studied the effect of variation in voiceonset time (VOT) on the perception of dichotic CVsyllables contrasting in voicing features.

Variation in VOT had a systematic effect on theprobability of hearing the fused stimuli as voiced orvoiceless sounds, changing the VOT of the voicelessstimuli had a larger effect than changing the VOT ofa voiced stimulus.

Porter & Berlin (1976); Rajagopal Ganguly &Yathiraj (1996) reported that regardless of ear ofpresentation, the voiceless syllables are reportedcorrectly when compared to the voiced syllables.



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Mannah (1971) found slightly different results.

In her study it was found that unvoicedconsonants were more intelligible than thevoiced, but it was not always true.

She reported more intelligible identification ofvoiced items over unvoiced when either VOT orbounding alignment more simultaneous andonset trailed.



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(b) Place of articulation cues

Another way to describe the pattern of stimulus

is to focus on the place features. Porter, Troendle &Berlin (1976) used 6 CV/pa, ta, ka, ba, da, ga/ pairedrandomly. Results revealed that velars were moreoften reported correctly than alveolars, which inturn are reported more correctly than labials (i.e.

velar >alveolar>labials). Similarly results by Berlinet al. (1973) found that velars were reported morecorrectly followed by the bilabial and the apical withless correctness (i.e. Velars > Bilabials > alveolars).

Speaks et al. (1988) used 8 pairs in which velarcompeted with non velar (bilabials and alveolar).



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(C) Vowels and Consonant

Most of the studies show little or no REA forvowel (Shenkwniler & Studdert Kennedy, 1967;Darwin 1969, Studdert Kennedy & Shank Weiler,1970) revealed REA for vowels in a consonantcontext which was interpreted to mean that vowels

surrounded by transition or acoustic correction ofvocal tract adjustments towards a given target willhave a REA,

Berlin et al. (1973) suggested that the REA inspeech like task may be related to the use of anyacoustic event which is perceptually linkable to arapid gliding motion of the vocal tract, as in atransition.



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Even in vowel some are better perceived than the

others, Weise & Home (1973) they dichotically

presented 10 vowels (American) in CVC syllable

where the consonant was kept constant and vowelswere varied.

The vowels were classified into long vowel andshort vowel. Results showed that REA better forlong vowels compared to short vowels. In long

vowels /a, ae/ were perceived better than /e. 0/

which in turn were perceived better than /i, u/. Inshort vowels /E/ were perceived better than /I, U/.


Studies have been done on different positions of the


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Studies have been done on different positions of theconsonants. Shewen, Natheneon Sent (1968)reported equal REA for initial and final consonant innatural CVC syllables. In contrast to this study,

Darwin (1969) reported stronger REA for finalconsonants position when presented dichotically.Studdert-Kennedy & Shankweiler (1970) alsoreported strong REA to final consonant in naturalspeech stops.

Possible explanation for the stimulus dominanceSpeaks et al. (1981)

Inherent intelligibility (II)

Lag effect (LE)

Prototype matching hypothesis (PMH) Burst amplitude

Speaks et al. (1981) tried to test each of thesenotion



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Inherent intelligibility:

It might be assumed that certain syllables aremore intelligible than others and that the

differential intelligibility would be evidentregardless of whether the syllables are presenteddichotically or in some other mode. Speak et al.(1981) tested this notion.

They presented 6 CV syllables, dichotically indifferent SNR in 4 listeners. They found that the 2most intelligible (dominant) syllables dichoticallywere /ba/ & /da/.

However, they were least dominant in dichoticpresentation. So binaural intelligibility scores innoise did not explain dichotic stimulus dominance(inherent intelligibility is not a satisfactoryexplanation).


Lag effect


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Lag effect:

Another possibility in the lag effect which hasbeen explained by Berlin (1973).

They studied the dominance of voiceless overvoiced stops in voicing contrast pair of naturalsyllables. Voiceless stops were found to have longerVOT than voiced stops.

Therefore, when competing stops are aligned byreference to the onset of noise burst, the largeramplitude vocalic position of the voiceless stops isdelayed relative to the vocalic position of the voiced

stops. Hence, it was reasonable that the later arriving

voiceless stops (vocalic position) might interruptprocessing of the earlier arriving voiced stops.



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Speak et al. (1981) however, had reported findingscontrary to the above study.

He pointed out that lag effect can accounted for

Overall voiceless dominating over voiced/ka/>/ta/, /ga/>/ba/, /ga/>/da/. This all can be explained

with respect to lag effect because all the dominantshad a longer VOT.

However, lag effect cannot be accounted for/ga/ > /pa/ (voiced dominating voiceless though it has

lesser VOT compared to voiced)

Failure of dominance of /ba-da/

Dominance of synthetic syllable getting reversed(> indicates the dominance)

So lag effect was also not a satisfactoryexplanatory for stimulus dominance



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Proto type Matching Hypothesis

Repp (1976) proposed proto type matchinghypothesis & Category goodness hypothesis toexplain stimulus dominance.

Proto type matching hypothesis: The perceptual

system is assumed to determine how well astimulus match any of the several category prototypes (templates).

When 2 competing dichotic stimuli enter the

system, the stimulus that is close to the proto typewill tend to dominate over a stimulus that is farfrom the proto type.



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Category goodness model says that stimuli that are

distant from the category boundary are likely todominate than those lying close to the boundary.This distance from a proto type or a boundary isassumed to be a function of acoustic characteristics

of the stimulus. Repp (1976) claimed support from his experiment by

systematically manipulating the F2 and VOT of thestimulus. He reported that stimulus dominance can

be changed systematically with variation in the VOTof the coupling stimulus.



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However, analysis of results of Speaks et al.

(1981) showed that only 5 of the 15 syllablespairs showing agreement between predictionand observation. Murphy (1970) had alsoobtained almost identical results of Speaks et al.(1981).

Thus, Repps model was not a very satisfactory inexplaining this phenomenon of stimulus

dominance.



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Burst Amplitude

Another explanation given was concerned withthe relative amplitude of the brief moment ofarticulatory release.

Since the spectral properties of burst of fricationconstitutes one cue for perceiving the differentclasses of stops (Halley et al. 1957), burst may alsobe partly responsible for producing stimulusdominance.

The peak intensity of burst as well as its duration isgenerally greater in voiceless stops than the voiced(Klatt, 1975) because of the greater drop in pressureacross the oral occlusion at the movement ofrelease for a voiceless stops.



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Speaks et al. (1981) measured peak intensity of

initial burst frication of 6 steps /p, t, k, b, d, g/. It

was seen that the velar /k, g/ has greatest peak

intensity followed by alveolar and labials.

Although difference in burst intensity accounted

for the presence of or absence of significantstimulus dominance fairly well, magnitudes ofstimulus dominance could not be predicted well.

This could explain the reverse pattern observed in

one of the pairs where voiced stops were dominantover voiceless.



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(3) Effect of Intensity

Effect of intensity on dichotic listening has

not been studied extensively. It was found in astudy by Roeser, John & Prince (1972) tested 32normals using Dichotic digit at intensity level of10, 30, 50, 70 dB SL with respect to SRT.

Results revealed fewer correct responses atlower intensity i.e. at 10 dB SL. Also right-leftdifference did not vary as a function of intensity.



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Speaks & Bissonette (1975): They used 6 CVsyllables and they presented them in pairsdichotically using 4 intensities levels 80, 70, 60, 50dB SPL. The experiment was done in 2 phases. Inthe first phase speech level in the right ear wasattenuated in 8 dB steps from each of four reference

intensities. In the second phase speech level in the left ear was

amplified in 8 dB steps. Results showed that theREA was cancelled by attenuation of signal level inthe right ear, but the amount of attenuation tocancel the REA varied with reference intensity (i.e.22 dB for 80 dB SPL to 5 dB for 50 dB SPL referenceintensity).



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Reyon (1969) in contrast showed that the right ear

advantage was held constant when the left ear

signal was 6 dB more intense than the right ear.

Some investigators report that the intensity of thesignal does influence the response received.

Dobie & Simmons (1971) found that when twospeech sounds are presented simultaneously to the2 ears, the subjects were able to report accurately

the input to either ear until the signal amplitude to

the unattended ear exceeded that of the attendedear by 15 dB.


Bloch & Hellige (1989) investigated the effect of


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Bloch & Hellige (1989) investigated the effect ofrelative difference in intensity level of the stimulipresented to the 2 ears. The results indicated thatidentification of stimuli presented to one ear

improved when those stimuli were relatively higherin intensity than the stimuli presented to the otherear.

(4) Effect of frequency

Sidihs (1980, 1981) presented dichotically puretone of low frequency and required his right handedsubjects to report whether subsequent test tone(3rd tone) was or was not one of the tones. Underthese conditions he found no ear advantage.

However, when he added higher harmonics offundamental frequency to each of dichotic tones,left ear advantage was observed. He concludedthat the right hemisphere was specialized for theanalysis of steady state harmonics information



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Divenyl K. Efron (1979) used same paradigm asabove on strongly left ear dominant subjects forpure tones. The results showed that the progressive

addition of temporal and spatial information (Usingspeech token) caused right ward shift of eardominance.

(5) Synthetic versus Natural CV

Most of the studies reviewed so far used eithernatural or synthetic stimulus. House et al. (1970)investigated the difference in result due to syntheticversus natural CVs. They presented same CVs (both

natural and synthesized) to some listeners. Theirresults showed essentially no difference in REA forboth synthetic and natural CV.


(6) Effect of signal to noise ratio (SNR)


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(6) Effect of signal to noise ratio (SNR)

Signal to noise ratio affects perception ofdichotic listening.

Weiss & House (1973) performed a dichoticcompeting vowels task at two SNR (0 dB SNR & -10 dB SNR) in 13 subjects. The presentation level

was kept at 70 dB SPL. Results revealed that asthe SNR becomes poorer, the over all scoresreduced and the REA became more pronounced.At favorable SNR ear preference were notapparent.



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(7) Effect of Bandwidth

Berlin & McNeil (1976) reported that theintelligibility of one channel can be decreased whenthe information transmitted to the other isincreased by reducing frequency band width.

Thompson et al. (1974): The dominance of right

ear over left ear was observed when there was ahigh frequency cut off set at 4 kHz followed by anequal ear performance when high frequency cut offwas 3 kHz and revealed a poor performance of the

right ear when cut off frequency was 2 kHz. Thedifference was found to be marked betweenchannels when frequency was 1.5 kHz.


(8) Effect of stimulus material used


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(8) Effect of stimulus material used

Several test procedure have been developed tomeasure dichotic listening. All the dichotic speech

tests are aimed at reducing both external andinternal redundancy. So that it becomes difficult for

the subject to respond. Test material commonly

used are:

Dichotic digit test (Kimura, 1961)

Dichotic CV test (Berlin, 1972)

Synthetic sentence identification (Speak & Jerger,1965)

Dichotic rhyme test (Waxler & Lalwace, 1983)

Stagger spondaic word (Katz, 1961)KUNNAMPALLIL GEJO MASLP


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Koomer & Carmel (1981) conducted study usingdichotic CV and dichotic digit on normal andlearning disabled children between age 7-10years and results revealed that no significantdifference in ear advantage between the 2material. Also, the learning disabled

performed significantly lower than thenormal group on dichotic digit.



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Obrzut, Bolick & Obrzut (1996) supported thehypothesis that perceptual asymmetric can be

strongly influenced by the type of stimulus materialused and the effect of attentional strategy. In thisstudy 12 academically high performing childrenmean age of (10.8 years) were administered 4 typesof dichotic stimuli (word, dichotic CV and melodies

in 3 condition of free recall, directed right anddirected left).

While expected right ear advantage for words andCV syllables and the expected left ear advantage for

melodies were found under free recall, the directedcondition produced varied results depending on thenature of the stimuli.


(9) Effect of stimulus familiarity


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(9) Effect of stimulus familiarity

Nachshon & Carmon (1975) studied the effect ofspeech lateralization, stimulus familiarity and their

interaction on ear superiority. CV syllables

6 consonant (3 familiar)

4 vowels (2 familiar)

The test was done in 4 contexts that are FF, FN, NF,NN (F-Familiar, N-Not familiar) e.g. in FN condition

familiar stimulus (vowel or consonant) was given toleft ear and the non-familiar stimulus was given toright ear.



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Results revealed that in FF or NN conditionconsonant showed REA and the recall ofvowel are same for both the ears (as

expected). NF consonant showed stronger right ear

superiority and NF vowels showed right earsuperiority (due to interaction of familiarity

and language effect). This shows strongeffect of stimulus familiarity.



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SUBJECT RELATED FACTORS(10) Ear difference or Ear effect

Generally, when a speech is presenteddichotically to normal listener, higher scores areobtained from the material presented to right

ear than to left ear. This is right ear advantageand is believed to reflect dominance of lefthemisphere for speech and language perception(Studdert et al. 1970).



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Asbornsen (1994) reported that about 90% ofthe normal right handed population and 60% of

left handed population show a right ear

advantage. The right ear superiority is seen forboth meaningful and non-sense syllables

(Stienkwerler et al. 1967) and backward speech

(Kimura, 1968). In contrast, a left ear superiority

has been reported for some non-speech stimulussuch as music, sound effects (Curry, 1967).



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(11) Effect of age

The variation of age in dichotic listening can bereferred as developmental dichotic listening.

Ingram (1975) reported that a right earadvantage was indicated on dichotic listening taskat the age of early as 3 years.

This is suggestive of the left hemisphere dominanceto certain extent for speech function by that age.This study supports the findings of Kimura (1961,

67) where she found that the right ear advantageappeared no later than the age of 6 years for speechand language hemisphere dominance.



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Some researchers here shown that the magnitudeof right ear advantage increases with age becomingmore lateralized (Sate, Bekliear & Gelbel, 1975)while other have shown it to be constant throughout (Berlin et al. 1973, Kinsborne, 1978).

The magnitude of right ear advantage wasstudied using different stimuli, Bellis (1996) studyrevealed a greater right ear advantage in childrenwhen complex linguistically loaded dichotic stimuliwere used than with the use of less complex stimuli.

As the child matures, the right ear advantage willdecreases, reaching adult values by approximately11 to 12 years.



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. The left ear deficit or right ear advantage has beenexplained as a result of relatively greater decline in

right hemisphere function with increasing age(Goldstein & Shilling, 1981). Another possibility isloss in efficiency of inter hemisphere transfer due tocomprise of auditory pathways in the corpuscallosum (Hellige, 1993).

(12) Effect of Gender Berlin et al. (1978) showed REA in males and

females in the age range of 5 to 13 years. A total of150 right handed children participated in the study.

Subjects listened dichotically to 60 pairs of non-sense syllables. No difference between genders wasfound as a function of age.



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Remington et al. (1974) presented non-syllablesdichotically and observed a significant REA for males.

Jerger et al. (1994) investigated effect of age andgender on dichotic sentence identification (DSI). Theresults suggested that gender different exist in theeffect of age on the left ear deficit. In both ears, it wasalmost 30% for males and only 10% for female.

McCoy et al. (1977) studied the effect of age andsex on dichotic listening Stagger spondaic word (SSW)test results revealed that older individualperformance poorer than younger individuals. Males

tended to perform significantly poorer than female.There was no significant difference between youngmales and females.



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Hiscock & Beckie (1993) in their experiment with 58

children (7-10 years) instructed them to attend to

left ear and REA was over come for dichotic CVstimulus.

In contrast to above studied, several studies done

on children indicate that normal right handedchildren of various age show a right ear advantagefor dichotic verbal stimuli even when instructed to

attend to left ear. However, most of studies on

directed attention indicate that perceptualasymmetries can be influenced by the effect of

attention strategy employed.


(13) Practice Effect


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( 3)

The absolute advantage of right ear over leftear did not change significantly with practice.

Velar were most often reported correctly thanalveolar which in turn were reported morecorrectly than labials even after practice.

Minetts & McCantry (1979) studied the effect oftraining on Stagger spondaic word (SSW )test.He found an increase in the over all correctresponse as a result of practice.



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(14) Effect of Response mode

There are evidence which suggest that inhumans the 2 cerebral hemisphere alter in the

degree to which they are involved in processing

differ kind of information. The mode is an

important factor in establishing preferentialprocesses by one hemisphere over the other.

Subject can indicate the perception of the test

items by pointing, selecting, repeating or by

writing. There are 2 types of response mode, openset and closed set response.



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Olsen & Mehkin (1979) reported that the closed setld b d ith di d d l ti


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response could be used with disordered population.He also found that closed set responses providegood estimate of word recognition performance.

Thus, it suggests that the closed set provide higherscores. Ear advantage was studied by usingdifferent modes of responses. Janke (1973)administered dichotic test of monosyllabic CV in 38male right handed and 50 male left handed.

Different response modes CV verbal, written,pointing were utilized. Result suggests that earadvantage scores were not influenced by responsemode. Similar results were found by Krishnan &Yathiraj (2001) 10-11 years children were taken andthey performed a dichotic CV test using tworesponse mode (oral and written) and resultsrevealed that REA was not influenced by responsivemode.


Summary:


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Factors affecting dichotic listening are:

Stimulus related

Temporal aspect: When one signal lags another signal in a ear

then lagging signal will be perceived better lag effect. Lag ofaround 30-60 msec is required to over come right ear advantage.

Phonetic effect:

The voiceless stops are dominant over voiced stops.

Velar > alveolar > labials Vowels does not show REA in isolation

In consonant context long vowel dominate short vowels

Stronger REA for final consonants (however studies also try to

contradict this) Burst amplitude may account for stimulus dominance fairly well.

SNR: Poorer the SNR more will be the right left difference.



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.

Bandwidth: Intelligibility of one channel can bedecreased while the information transmitted inthe other is increased by reducing frequencybandwidth.

Stimulus material: Dichotic CV were moredifficult compared to other tests.

Stimulus familiarity: Strong effect of stimulus

familiarity compared to ear advantage


Subject related


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Subject related

Ear effect: 90% of the normal right handed population and 60% ofleft handed population show a right ear advantage.

Effect of age: REA was seen for very young children also. In elderlyindividual the REA is maintained but there is aberration of lageffect.

Effect of gender: Studies report of no gender difference. However,

so studies report of males performing poorer than female. Effect of Attention: Most of studies on directed attention indicate

that ear advantage can be influenced by the effect of attentionstrategy employed.

Practice effect: Performance improves as the practice increases.

Effect of response mode: Closed set task gives better scorescompared to open set. Also, most study indicates that there is nodifference in scores with different modes (oral, written, pointingetc.).



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Dichotic listening involves the presentation ofstimuli to both ears simultaneously, but different

information to each ear. Dichotic listening hasvarious applications in many areas. Also manyapplications have been delineated in the field ofspeech and hearing too.

Applications Determining the site of lesion based on dichotic

tests.

Applications of dichotic listening in speech andlanguage disorders.

Dichotic tests for evaluation of different centralauditory processes.



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Dichotic Tests:

Dichotic digit test (DDT)

Dichotic consonant vowel test (dichotic CV)

Staggered spondaic word (SSW)

Competing sentence test (CST)

Synthetic sentence identification with contralateral competing message (SSI-CCM)

Dichotic rhyme test (DRT)



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Normative data:

Here we will discuss how the scores varies withdifferent dichotic tests used, material used andwhat are the possible effects of maturation andlaterally effects on the scores. The comparisonbetween the western studies and Indian studies is

also made. Dichotic digit test cited in Bellis (1996)

In the norms provided there was a significantright ear advantage noticed in early ages as shownand the laterality effect decreased as a function ofage and children attained adult like scores with agearound 10-11 years.



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But, Regishia (2003) reported quite opposite

results in children with same age range on aDichotic digit test (DDT) task in Kannada.There was minimal REA noticed in early yearsand the laterality effect was not so evident in

children



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Dichotic CV test:

Moumita (2003) obtained normative data ofdichotic CV test on adults age ranged 18-25 years.

She also used different lag times in dichotic

presentation to both ears. The scores indicated that

there was a significant REA at all lag times andscores did improve as lag time was increased.However, there was no laterality difference seen

between males and females and both shows

essentially REA ruling the hypothesis that there islack of asymmetry in females.



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Norms

Onset lags R ear L ear

0 msec

30 msec Rt

30 msec Lt

90 msec Rt

90 msec LtMale

Female

92%

93%

91%

94%

93%92%

93%

87%

88%

88%

87%

89%87%

87%



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Dichotic CV in children: Ganguly, (1996) foundthe following results which indicated a REA inboth the age groups but, both the group yieldedpoorer scores. The poorer scores can beattributed to the fact that the test was recorded

on a tape rather than a CD which can havepossible additional noise that can deterioratethe quality of CV syllables hence scores.



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Group right left

8

12 years13 17 years

(58%)(59%)

14.50 (48%)15.48 (50%)



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Competing sentence test (CST) :

Normative values in children aged 5-10 years

indicated 100% in the strong ear, where as inweak ear ranges from 0-100%, the scoresreported to improve with age and attained adultscores by age 11.

These findings suggest a significant effect ofmaturation on the Competing sentence test (CST)with the ear advantage decreasing as the functionof increasing age of the child. There was decreasein laterally effect with increase in age as shown.



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Age range right left

8 8.11 years

9 9.11 years

10 10.11 Years

11 11.11 years

12 years

adult

82%

90%

90%

90%

90%

39%

74%

80%

90%

90%



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Competing sentence test in Kannada byHemalatha (1982) in adults aged 18-25 years

revealed that there was a significant REA inmales but there was a lack of ear advantage infemales, which indicates that there is lack of

asymmetry in females as supported by otherstudies.



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Norms:

gender right left

Males

Females

96%

95%

89%

94%



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Dichotic Rhyme Test(DRT)

Bellist (1996) reported no significant effect of

age on DRT and scores were 32 60% per ear.Musiek (1989) reported a score of 30-73% in rightand a score of 27-60% in left ear.

So based on all the normal scores discussed

above it can be concluded that Dichotic RhymeTest (DRT) and Dichotic consonant vowel test(dichotic CV)

DCV are the difficult tests which produces lowscores and Dichotic digit test ( DDT )and sentence

tests reveals high scores and easy to performyielding high scores. There was REA seen in all thetests.



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Mueller et al. (1987) evaluated head injured patients withDDT and found both ear scores poorer in subjects with leftTemporal lobe lesion and only left ear scores were reduced in

right Temporal lobe lesion. So DDT is quiet a sensitive testin detecting cortical lesion.

Berlin et al. (1972) used dichotic CV with and withouttime staggering using nonsense syllables in patients with

temporal lobe lesions. Preoperatively ipsilateral ear scoreswere better than contra lateral. But post operatively therewas further reduction in contra lateral scores and ipsi scoreswere enhanced. This was seen both in right temporal lobeand left temporal lobe lesions.

Speaks et al. (1975) found low scores for the ear contra toside of brain lesion in all patients with temporal lobe lesionusing dichotic CV test.


B) I t h i h l i ( ll


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B) Inter hemisphere lesions (corpus callosumlesion)

Musiek & Pinheiro (1985) reported that lesionsof the auditory portion of the corpus callosumresults in severe left ear deficits on dichotic speechtasks that require verbal report of the stimuli.

Musiek (1985) administered Dichotic rhyme test

(DRT) to complete split brain patients. The splitbrain patients yielded expected poor left ear scoresand demonstrated right ear enhancement. Theright ear enhancement on DRT may suggest arelease from central auditory competition in left

hemisphere.



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Springer et al. (1975) reported high right ear scores and poorleft ear scores on dichotic CV in split brain patients as callosal

pathway is severed and information from the left ear is nottransmitted.

Baron et al. (1986) performed DDT on patientsunderwent anterior sectioning of corpus callosum. Betterscores for right ear than left pre-op and post op there was

little change in scores were noticed. C) Brainstem lesions

Jerger & Jerger (1975) revealed poorer scores of the earcontra lateral to lesioned hemisphere on Synthetic sentenceidentification with contra lateral competing message (SSI-

CCM) but found normal results on SSI-CCM in intra axial andextra axial brainstem lesions. So SSI-CCM is sensitive forcortical lesions.



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Jerger & Jerger (1975) compared Staggeredspondaic word( SSW )in 10 patients with intra axiallesions. They got 44% poorer scores for contralateral ear and 16% poorer scores for ipsi ear to sideof lesion. Since intraxial lesions effects only contralateral pathways so contra ear more effected than

ipsi. Jacobson et al. (1983) performed dichotic tests (SSI-

CCM, DCV & SSW) on 20 patients with multiplesclerosis. They concluded that DCV was thesensitive test among all in detecting site of lesion in

subjects with multiple sclerosis. Berlin (1975)reported similar findings in patients with MGBlesion.



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C)Intracranial lesion:

Subjects(4 adult males with mean age of 40yrs)with intracranial lesion showed poorperformance on Dichotic digit test .A

significantly poorer performance in the earcontra lateral to the lesioned hemisphere wasevident in two subjects

(Shivshankar,JISHA,19918,67-71)


Auditory processing in speech language disorders


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Auditory processing in speech language disorders

A) Stuttering

The persons with stuttering are believed to have

symmetrical hemispheres which lead to the lack of cerebraldominance creating a mistiming of motor impulses to bilateralspeech muscles producing dysfluent speech (Travis, 1936).Dichotic listening techniques have been used with normal andpersons with stuttering for the purpose of finding a dominant or

leading hemisphere and to prove or disprove theory of cerebraldominance.

Curry & Gregory (1969) conducted a study to studyperformance of patients with stuttering on dichotic listeningtasks, which were supposed to reflect cerebral dominance.

20 subjects with stuttering and 20 normals evaluated onthree tasks. Normals showed significant REA as oppose to othergroup which showed no significant laterality in favour of lefthemisphere.



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But Dorman & Porter (1975) reported oppositeresults and found no significant differences incerebral speech lateralization between subjectswith stuttering and normals.

Bhat (1999) found significant differences betweenthe right ear and left ear scores on dichotic CV testin 20 adult male subjects with stuttering. She alsofound REA though not significant at 0 msec, 30msec right lag and 30 msec left lag but a significantLEA at 90 msec lag to right and 90 msec lag to left.

She attributed this to the problem in reticularactivating system which controls attention.



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B) Learning disability(LD)

There had been mixed results of various dichotic

tests on children with learning disability. Brydan (1970) showed that children with LD

wont show typical REA and scores are poorer on adichotic CV task. Higher LEA was reported in

children with LD in a study by Morton & Siegal(1981).

Ganguly, Rajagopal & Yathiraj (1996) reportedthat on dichotic CV task children with LD performedpoorer as compared to normal Sobta (1973) alsoshowed essentially normal REA for 24 children withdyslexia on DDT.



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Olsen (1983) administered DCV SSW on 50 normal


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Olsen (1983) administered DCV, SSW on 50 normalsubjects and 67 patients with right TL lesion or left

TL lesions. Results indicated a large range of

performance in normal subjects for different DCV

test material. In comparing DCV and SSW testresults of the 14 patients with below normal

dichotic CV scores only three had abnormal SSWresults before surgery and five after surgery. Clearlythe SSW test is not as difficult and is less sensitive

to cortical lesions than the DCV. The test must be

difficult if it is to be sensitive to lesions of temporallobe, particularly in the anterior portion of the

temporal lobe.


Musiek & Morgan (1981): Results of DDT, CST and SSW on af l l f


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case of vasculitis. DDT, SSW & CST scores were normal forright ear and impaired for left ear before treatment andscores improved to all tests after improvement.

Jerger & Jerger (1978) compared SSW & SSI-CCM in varietyof disorders.

Non-auditory CNS lesion 100% on SSI-CCM, but 10% of themshowed deficits on SSW.

VIIIth nerve lesion: Normal on SSI-CCM but slight deficits on SSW.

Brainstem lesion: Normal on SSI-CCM but abnormal on SSW.

Temporal lobe disorders: Impaired scores on both tests in left ear andnormal on right ear.

Aphasics: Impaired right ear scores in both tests.

Collard et al. (1982) reported abnormal results on CST for72% of their temporal lobectomy candidates. Theyconcluded CST more sensitive than SSW, DDT and DCV.



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Other applications:

A) Hemispheric laterality Dichotic tasks are used to assess the laterality

aspect of verbal stimuli, non-verbal stimuli ex

musical, melodic stimuli etc., A REA is expected in

right handed individuals on a verbal dichotic tasks.However, opposite ear advantage or no laterality

can be expected in left handed individuals. This has

been attributed to the functionally superior contra

lateral pathways than ipsilateral pathway (Sidtis,1981).



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B) Maturation and Dichotic listening

Dichotic listening on children suggests thatthe more linguistically loaded the stimulipresented are the more pronounced thematurational effects are likely to be so the

sentence tests are the preferred choice whenstudying maturational aspects. These dichotictests can be used to study the maturational

process of the brain and auditory pathway.


Berlin, Hughes & Bell (1973) studied performance ofchildren aged 5 to 13 on test of dichotic CV


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children aged 5 to 13 on test of dichotic, CVnonsense words. The performance improved withage in identification of words which reflects an

increase in the brains ability to process two channelstimuli as a function of age.

Processing of dichotic speech stimuli requiresadequate interhemispheric communication viacorpus callosum (CC) as well as integrity of bothtemporal lobes. Poor left ear performance ondichotic sentence tasks in children may reflect adecreased ability of the CC to transfer complexstimuli from the right hem to left. As with age

myelination of CC is complete and left scoresapproaches as of adults (Musiek, Gallegly & Brain,1984).



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C) Conductive pathology effects:

An attempt has been made to see the effects ofhistory of otitis media with effusion (OME) onauditory processing through various dichotic tests.Klausen et al. (2000) found that children in OMEgroup showed a more pronounced REA than

controls. But Keith, Lawleen & Cotton (1985) found no

difference between normals and OME group onSSW task. James (2003) found that there wereauditory processing problems in children with

history of otitis media with effusion later inchildhood on a dichotic CV task.



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Dichotic Test

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