Abstract
Neural discrimination of auditory contrasts is usually studied via the mismatch negativity (MMN) component of the event-related potentials (ERPs). In the processing of speech contrasts, the magnitude of MMN is determined by both the acoustic as well as the phonological distance between stimuli. Also, the MMN can be modulated by the order in which the stimuli are presented, thus indexing perceptual asymmetries in speech sound processing. Here we assessed the MMN elicited by two types of phonological contrasts, namely vowel quality and vowel length, assuming that both will elicit a comparably strong MMN as both are phonemic in the listeners’ native language (Czech) and perceptually salient. Furthermore, we tested whether these phonemic contrasts are processed asymmetrically, and whether the asymmetries are acoustically or linguistically conditioned. The MMN elicited by the spectral change between /a/ and /ε/ was comparable to the MMN elicited by the durational change between /ε/ and /ε:/, suggesting that both types of contrasts are perceptually important for Czech listeners. The spectral change in vowels yielded an asymmetrical pattern manifested by a larger MMN response to the change from /ε/ to /a/ than from /a/ to /ε/. The lack of such an asymmetry in the MMN to the same spectral change in comparable non-speech stimuli spoke against an acoustically-based explanation, indicating that it may instead have been the phonological properties of the vowels that triggered the asymmetry. The potential phonological origins of the asymmetry are discussed within the featurally underspecified lexicon (FUL) framework, and conclusions are drawn about the perceptual relevance of the place and height features for the Czech /ε/-/a/ contrast.
Highlights
Speech perception is a cognitive process which transforms the acoustic signal into respective neural representations in the human brain
The first question addressed by this experiment was whether the neural processing of phonemic vowel quality differs from the neural processing of phonemic vowel length
We assessed the neural mismatch response (MMN) in adult speakers of Czech listening to changes between [fε] and [fa] and to changes between [fε] and [fε:] syllables, where both types of change represent a phonological vowel contrast
Summary
Speech perception is a cognitive process which transforms the acoustic signal into respective neural representations in the human brain. One of the most fundamental properties of human speech perception is the ability to detect phonetic and phonological contrasts. Sensitivity to such contrasts has been examined by the means of behavioral tests (discrimination or categorization tasks) (Repp and Crowder, 1990; Polka and Bohn, 2003; Johnson, 2015) as well as via techniques that monitor brain activity, such as event-related potentials (ERPs) measured with electroencephalography (EEG; Eulitz and Lahiri, 2004; De Jonge and Boersma, 2015) or their magnetic equivalents measured with magnetoencephalography (Scharinger et al, 2016; Højlund et al, 2019). The MMN can be used to estimate the linguistic importance and relevance of phonetic differences between stimuli for speech perception
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