Poster #: 124
Topic: Speech and language (incl. deficits)
Wednesday, Sep 9, 2015
Finding the origin of directionality effects in MMNs to phonetic contrasts
Amsterdam Centre for Language and Communication, University of Amsterdam, Amsterdam, Netherlands
Different MMN amplitudes depending on deviance direction are reported for speech sound contrasts and are argued to support abstract phonological representations (e.g. Eulitz & Lahiri, 2004). This study set out to establish whether the directionality effect in the MMN to the vowel contrast [o]-[ø] could be replicated and whether it could be explained by spectral properties of the vowels rather than abstract phonological concepts.
In this experiment, the vowels differed only in frequency of the second formant, 793 Hz for [o] versus 1417 Hz for [ø]. Two types of control stimuli were created: sinusoids matching the formant frequencies, and non-speech sounds matching the spectral envelope of the vowels but containing only harmonics within the spectral band of the critical formant. For each stimulus type (sinusoid, spectral band, vowel), two oddball blocks were created using either the high or the low F2 stimulus as a deviant (probability 0.09). EEG was recorded from 64 scalp locations while participants watched a silent subtitled film. MMN amplitudes at Fz were calculated in a 40 ms window centered around the grand average minimum of the difference waves in all 6 conditions.
Preliminary inspection of the data of the first 10 participants suggests that high F2 vowels evoke larger MMNs than low F2 vowels, replicating the original pattern. A similar pattern appears for the spectral band stimuli, but not for the sinusoids. Testing the statistical significance of the MMN data will only be carried out once the planned sample of 24 participants is completed.