1. S. Kramer1, K. Tucker1, A.L. Moro1, E. Service1, J.F. Connolly1
Electrophysiological Correlates of Subphonemic Processing in Spoken Word Recognition
S. Kramer1, K. Tucker1, A.L. Moro1, E. Service1, J.F. Connolly1
1Department of Linguistics and Languages, McMaster University, Hamilton, Ontario, Canada
Coarticulation
Stimuli
Results (cont’d)
76 monosyllabic English words with CVC structure.
Onsets were oral (/p, t, b, d/) or nasal (/m, n/) anterior stops.
Vowels were the corner vowels (/i, u, æ/ ɑ/.
Codas were oral stops (/p, t, k, b, d, g/).
Onset of each token was spliced to a nucleus+coda of another token. Congruent tokens had onset spliced to nucleus+coda of another production by the same speaker of the same word; incongruent tokens had onset spliced to nucleus+coda of another word said by the same speaker.
(a)
(b)
(c)
(d)
(e)
(f)
Fig. 2
In natural speech, a single phoneme may have a number of acoustic-phonetic realizations as a result of overlapping articulatory gestures. The phoneme /k/, for example, is produced differently in the words “keep” and “coop” as anticipation of the following vowel (a high front vowel in “keep” and a high back vowel in “coop”) triggers slight changes in tongue position on the syllable onset (Arbour 2012). Variations in the subphonemic content of the speech signal have been shown to provide cues which may be used in spoken word recognition. Mismatches between subphonemic and phonemic information have been shown to have both behavioural and electrophysiological effects on speech processing (McQueen et al. 1999, Archibald & Joanisse 2011).
By comparing the effects of different types of coarticulatory violations on three EEG/ERP components, this experiment sought to examine at which point in the speech perception process listeners make use of subphonemic cues.
Recording
EEG was recorded on 64 channels (BioSemi ActiveTwo, Ag/AgCl electrodes). EEG was recorded using a bandpass of 0.01Hz to 100Hz, and sampled at 512Hz. Online, data were referenced to the nose tip; offline, data were referenced to the mastoids and filtered to a bandpass of 0.1Hz to 30Hz.
Results
Fig. 3: Grand Averages of Incongruent Trials at P1
Incongruent in: Height
Backness
Both uV
Fig. 4: Grand Averages of Incongruent Trials at CP1
Incongruent in: Height
Backness
Both uV
Event-Related Potentials
(ERPs)
(a)
(b)
(c)
Fig. 1
N100 – A negative-going multimodal waveform peaking approximately 100ms after stimulus onset. Reflects early sensory processing; modulated by stimulus features such as dB (Steinhauer & Connolly 2008). Not shown to be sensitive to subphonemic incongruity (Archibald & Joanisse 2011).
P200 – A positive-going multimodal waveform peaking approximately 200ms after stimulus onset. Thought to reflect stimulus detection in the auditory cortex; sensitive to stimulus intensity (Steinhauer & Connolly 2008; Martin et al. 2007).
Phonological Mapping Negativity (PMN) – A negative- going waveform peaking between ms after stimulus onset. Thought to reflect phonological processing of speech (Connolly & Phillips 1994). Sensitive to coarticulatory mismatches (Archibald & Joanisse 2011; Arbour 2012).
Conclusion
We found effects of coarticulatory violations on all three components studied. This suggests that the N100 and P200 are not solely perceptual responses, but may also be taken to reflect early steps in phonological processing. Furthermore, the PMN was shown to be modulated by the type of coarticulatory violation, indicating that it is not an all-or-nothing response as first suggested by Newman et al. (2003), and that it too reflects the processing, not just of broad phonemic information, but of fine-grained phonetic detail.
Experimental Methods
N100: Main effect of incongruity type (F = , p = 2.27e-09). Apparent additive effect of
coarticulatory violations in backness and height (Fig. 1 a). Effect was maximal over left-
hemisphere centro-parietal sites (Fig. 3, 4)
Main effects of backness and height of original vowel (Fig. 2 a, b) and spliced vowel
(Fig. 2 c, d)
P200: Main effect of incongruity type (F = , p = 1.03e-15). Coarticulatory violations in
backness and height attenuate P200 less than violations in both features (Fig. 1 b).
Main effect of original vowel height (Fig. 2 e).
PMN: Main effect of incongruity type (F = , p = 1.96e-09). Apparent additive effect of
coarticulatory violations in backness and height (Fig. 1 c)
Main effect of backness of spliced vowel (Fig. 2 f).
References
Twenty-two native English-speaking undergraduates (14 female) saw single-syllable CVC words presented on a computer screen for 1500ms. Immediately following presentation of the visual prime, participants heard a spoken word either matching (580 trials) or not matching (76 trials) the previously seen word. Of the matching trials, 184 were subphonemically congruent, while 396 were incongruent. Participants were asked to indicate with a mouse-click whether or not the spoken word matched the word they had read.
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