Abstract
The amplitude of the event-related N1 wave decreases with repeated stimulation. This repetition-attenuation has not previously been investigated in response to variable auditory stimuli, nor has the relative impact of acoustic vs. perceptual category repetition been studied. In the present study, N1 repetition-attenuation was investigated for speech and spectrally rotated speech with varying degrees of acoustic and perceptual category variation. In the speech condition, participants (n = 19) listened to stimulus trains consisting of either the same vowel exemplar (no variability condition), different exemplars of the same vowel (low variability condition), or different exemplars of two different vowels (high variability condition). In the rotated speech condition, the spectrally rotated counterparts of the vowels were presented. Findings show N1 repetition-attenuation in the face of acoustic and perceptual category variability, but no impact of the degree of variability on the degree of N1 attenuation. Speech stimuli resulted in less attenuation than the acoustically matched non-speech stimuli, which is in line with previous findings. It remains unclear if the attenuation of the N1 wave is reduced as a result of stimuli being perceived as belonging to perceptual categories or as a result of some other characteristic of speech.
Highlights
The amplitude of the N1 wave1 of the event-related potential (ERP) decreases with repeated stimulation (Näätänen and Picton, 1987)
If N1 repetition-attenuation is at least partly caused by neural refractoriness, more attenuation in response to speech stimuli than in response to non-speech stimuli could be an indication of neuronal populations tuned to specific speech sound categories, which with repeated stimulation are depleted of neurotransmitters in a similar way as those sensitive to specific acoustic features
The averaged ERPs show prominent N1s at expected latencies (Figure 1) and scalp locations (Figure 2) in all speech type and variability conditions
Summary
The amplitude of the N1 wave of the event-related potential (ERP) decreases with repeated stimulation (Näätänen and Picton, 1987). If N1 repetition-attenuation is at least partly caused by neural refractoriness, more attenuation in response to speech stimuli than in response to non-speech stimuli could be an indication of neuronal populations tuned to specific speech sound categories (or characteristics thereof), which with repeated stimulation are depleted of neurotransmitters in a similar way as those sensitive to specific acoustic features. Indicating that this may be the case, mismatch negativity (MMN) has been reported for speech sound category deviations despite the enormous acoustical variation, constituted by 450 vowel tokens uttered by different speakers and no exemplar repetition (Shestakova et al, 2002).
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