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Auditory P300 Responses Evoked by Perceptually Different Between-Category CV Stimuli

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Auditory P300 Responses Evoked by Perceptually Different Between-Category CV Stimuli § Ji Young Lee Department of Audiology and Speech Pathology, University of Tennessee Health Science Center, Tennessee, USA Background & Objectives: Event-related potentials (ERPs) research has shown that the P300 reflects the categorical perception of speech sound. Using within-category or across-category stimuli, research has reported the controversial findings whether the P300 represents phonetic processing rather than acoustic processing, or acoustic processing as well. The present study explored whether the P300 response is sensitive to the perceptually different between-category consonant-vowel (CV) stimuli, and if so, whether the P300 response varies as a function of deviancy of between-category CV stimuli. Methods: The P300 was measured in an oddball paradigm from 10 normal hearing adults. Based on the results of identification test of a speech continuum, 1 within- category CV was selected as a standard stimulus and 2 between-category CVs were selected as deviant stimuli. The 2 deviant stimuli consisted of the weak deviant (WD) and strong § Correspondence to deviant stimuli (SD). A total of 600 stimuli were composed of 480 standard stimuli (80%), 60 Ji Young Lee, WD (10%), and 60 SD (10%). Results: (1) the P300 was elicited by both WD and SD, (2) the Department of Audiology and P300 amplitude was larger in SD than WD, (3) the P300 amplitude was larger over central and Speech Pathology, parietal regions than the frontal region, and (4) the P300 latency was not different for deviancy University of Tennessee Health condition and scalp distribution. Discussion & Conclusion: The results indicate that the P300 Science Center, 578 South Stadium Hall, can reflect the sub-phonetic or acoustic processing of speech sound. The scalp distribution of University of Tennessee, the P300 is more dominant in the centro-parietal regions. (Korean Journal of Communication Knoxville, Tennessee Disorders 2012;17:499-507) 37996-0740, USA email: [email protected] Key Words: event related potentials, P300, oddball paradigm, category perception, between- tel: +1 865 974 4494 category stimuli, VOT Ⅰ. Introduction Event related potentials (ERPs) refer to the electrical brain activities which are temporally synchronized Speech perception is a human’s high-level cognitive to some specific tasks. As ERPs have proven to reflect processing. Much research has examined how human the high level processing such as cognition, attention, hear acoustic cues, recognize speech sound, and under- or memory, a lot of research has studied the speech stand the meaning of language. Of them, categorical and language processing using ERPs. For the past perception has been widely studied behaviorally and decades, ERPs have been widely used to investigate electrophysiologically. According to categorical per- the time course of the neural system related to acoustic- ception, we perceive gradually changing physical phonetic, phonological, semantic, and syntactic pro- information in terms of the psychological category cessing (Bonte et al., 2006). Particularly, it has been represented in our brain. Thus, the speech sounds in of interest to researchers in the area of neurology, the different phoneme category can be discriminated cognitive psychology, and neuroscience in that it better than the speech sounds within the same phoneme is a noninvasive procedure and can provide brain category when they have the same physical dif- response with high temporal resolution. ferences (Liberman et al., 1957; Studdert-Kennedy The P300 is one of the most studied ERP components et al., 1970). due to the robust and reliable peak (Patel & Azzam, ■ ■ ■ Received July 20, 2012 Final revision receiv ed August 26, 2012 Accepted August 30, 2012. ⓒ 2012 The Korean Academy of Speech-Language Pathology and Audiology http://www.kasa1986.or.kr 499 Korean Journal of Communication Disorders 2012;17:499-507 2005). The P300 is most commonly elicited by the category (WC), and across-category (AC) conditions low probability stimulus in an oddball paradigm at the native and non-native (Hindi) phonetic bound- where a low probability stimulus (or deviant stimulus) ary. Hindi listeners perceive 1st-6th sound as /ba/, is presented randomly in a series of high probability 7th-10th as /da/, and 11-16th as retroflex /Da/ while stimulus (or standard stimulus). The less demanding English listeners perceive 1st-6th as /ba/ and 7th-16th st th th the task is, the greater the P300 amplitude is (Polich, as /da/. 1 , 5 and 9 sound was used for native th th th 2007). The P300 is an endogenous and nonsensory phonetic contrast, and 8 , 12 , and 16 sound was specific response (McPherson & Ballachanda, 2000). used for non-native phonetic contrast as stimuli. It has been known that the amplitude of P300 reflects The four sequential CV syllables (e.g. /ba/ 5- /ba/ 5 stimulus probability and task relevance, and its la- - /ba/ 5 - /ba/ 5 for CO; /ba/ 1- /ba/- 1 /ba/- 1 /ba/ 5 tency reflects stimulus evaluation time (Johnson & for WC; /ba/ 9 - /ba/ 9 - /ba/ 9 - /ba/ 5 for AC) were Donchin, 1980; Picton & Hillyard, 1988; Sutton & presented. The results showed both MMN and P300 Ruchkin, 1984). The longer latency has been elicited were more sensitive to phonetic contrasts rather than for the psychological disordered or brain damaged acoustic ones, using across-category and within- people compared to normal people (Onofrj et al., category stimuli. 1991; Sangal, Sangal & Belisle, 1999). The P300 has Dalebout & Stack (1999) explored the MMN and the most negativity over centro-parietal midline P300, using a /da/ to /ga/ continuum. There were three scalp sites (Duncan et al., 2009). stimulus conditions of the most difficult (7th-9th pair), The P300 is currently in greater interest for clinical difficult (subject’s individual 2-step pair with the application such as diagnosing the pathological status highest discrimination performance), and easy contrast st th and predicting/monitoring the progress. Numerous (1 -9 pair). The results showed that for most dif- clinical research has been done, including people ficult, difficult, and easy contrasts, the MMN was with Attention Deficit Hyperactivity Disorders (ADHD), elicited in 50%, 25%, and 50% of the subjects whereas Alzheimer’s disease, cochlear implant, and hearing the P300 was elicited in 0%, 33%, and 100% of the impairment (Kileny, 1991; Barrett, 1993; Jordon et subjects. They concluded that P300 is elicited by al., 1997; Hutchinson & McGill, 1997; Salamat & phonetic/phonemic differences while MMN is elicited McPherson, 1999; Jeon & Polich, 2003). by acoustic differences. To examine how perceptually deviant contrasts the Tampas, Harkrider & Hedrick (2005) investigated P300 is sensitive to, the effect of stimulus frequency, the MMN and P300, using speech contrasts (two intensity, and duration has been studied (O’Brien & within- category CV stimuli) and nonspeech contrasts Stuart, 2001; Vesco et al., 1993). Though the P300 to (two glides of which frequency ramp matched the speech sound has not been deeply studied compared formant transitions of CV). The results showed that to tone sound, research has shown that the P300 the MMN was elicited by the nonspeech only while reflects the categorical perception of speech sound the P300 was elicited by both the speech and non- (Horev, Most & Pratt, 2007; Maiste et al., 1995). Using speech with larger amplitude and shorter latency in within- category or across-category stimuli, research nonspeech. They concluded the acoustic and phonetic has reported the controversial findings as to whether information are processed in parallel at the level of the P300 represents phonetic changes rather than MMN up to P300. acoustic changes (Dalebout & Stack, 1999; Dehaene- The objective of the present study was to explore Lambertz, 1997), or acoustic changes as well (Tampas, whether the P300 response is sensitive to between- Harkrider & Hedrick, 2005). category stimuli, and if so, whether the P300 response To investigate the acoustic versus phonetic sen- varies as a function of the deviancy of between-category sitivity of Mismatch Negativity (MMN) and P300, CV stimuli. To minimize the factors related with Dehaene- Lambertz (1997) constructed a /ba/-retroflex speech perception other than acoustic feature, non- /Da/ continuum and designed control (CO), within- sense CVs were used as stimuli. From a /bi/-/pi/ 500 Lee / Auditory P300 Responses Evoked by Perceptually Different Between-Category CV Stimuli continuum, one within-category CV was selected as using a high quality microphone (Spher-O-Dyne), a standard stimulus and two between-category CVs which was saved as a file sampled at 44.1 kHz (CSRE, were selected as deviant stimuli based on the results Version 4.5). This /bi/ sound was used as an endpoint of behavioral identification test. Two between-category stimulus (i.e. Stimulus 1) after getting rid of the minor deviant stimuli consisted of weak deviant (WD-the noise at the beginning burst to make VOT 0 msec. deviant stimulus is acoustically closer to the standard The total duration of Stimulus 1 was 347 msec. The stimuli) and strong deviant (SD-the deviant stimulus noise burst portion of synthetic /pi/ was used to ma- is acoustically farther from the standard stimuli). nipulate voice onset time systematically. By digitally There are three specific research questions in this increasing the noise burst by 6 ms from the Stimulus study. The first question was whether the P300 is 1 (i.e. prototypical /bi/), a nine-step series of a /bi/-/pi/ elicited by between-category stimuli. It was hypothe- continuum was constructed so that the Stimulus 9 sized that the P300 would be elicited to both WD (i.e. prototypical /pi/) had VOT of 64 msec (Adobe and SD. The second question was whether the P300 Audition, Version 1.5). is different for deviancy condition (WD, SD). In other From the results of identification test on a /bi/-/pi/ words, it was whether the P300 varies as a function continuum, one within-category CV was selected as of deviancy of between-category stimuli.
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