Vowel categorization induces departure of M100 latency from acoustic prediction.
MEG studies have shown that the timing (latency) of the evoked response that peaks approximately 100 ms post-stimulus onset (M100) decreases as frequency increases for sinusoidal tones. We investigated M100 latency using a continuum of synthesized vowel stimuli in which the dominant formant frequency increases from 250 Hz (perceived /u/) to 750 Hz (perceived /a/) in 50 Hz steps. While M100 latency did vary inversely with formant frequency overall, frequency modulation was flattened within each vowel category. However, for mid-continuum ambiguous tokens (i.e. those with increased reaction time/decreased accuracy in the concurrent behavioral identification task), M100 reverted to formant frequency differences, agreeing with previous findings of frequency-dependence. A theory is proposed in which phonological categorization emerges from specific spatial distribution of frequency-tuned neurons.
Roberts
Timothy P L
TP
Department of Medical Imaging, University of Toronto, 150 College Street, Toronto, Ontario M5S 3E2, Canada.
Flagg
Elissa J
EJ
Gage
Nicole M
NM
D000161:Acoustic Stimulation / Q000379:methods; D001307:Auditory Perception / Q000502:physiology* / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007802:Language; D015225:Magnetoencephalography; D008960:Models, Psychological; D011930:Reaction Time / Q000502:physiology*; D013997:Time Factors