Regressive spectral assimilation bias in speech perception

The Temporal Dynamics of Stop Consonant Perception: Evidence from Context Effects

Empirical evidence and theoretical models suggest that phonetic category perception involves two stages of auditory and phonetic processing. However, few studies examined the time course of these two processing stages. With brief stop consonant segments as context stimuli, this study examined the temporal dynamics of stop consonant perception by varying the inter-stimulus interval between context and target stimuli. The results suggest that phonetic category activation of stop consonants may appear before 100 ms of processing time. Furthermore, the activation of phonetic categories resulted in contrast context effects on identifying the target stop continuum; the auditory processing of stop consonants resulted in a different context effect from those caused by phonetic category activation. The findings provide further evidence for the two-stage model of speech perception and reveal the time course of auditory and phonetic processing.

The influences of forward context on stop-consonant perception: The combined effects of contrast and acoustic cue activation?

The perception of the /da/-/ga/ series, distinguished primarily by the third formant (F3) transition, is affected by many nonspeech and speech sounds. Previous studies mainly investigated the influences of context stimuli with frequency bands located in the F3 region and proposed the account of spectral contrast effects. This study examined the effects of context stimuli with bands not in the F3 region. The results revealed that these non-F3-region stimuli (whether with bands higher or lower than the F3 region) mainly facilitated the identification of /ga/; for example, the stimuli (including frequency-modulated glides, sine-wave tones, filtered sentences, and natural vowels) in the low-frequency band (500-1500 Hz) led to more /ga/ responses than those in the low-F3 region (1500-2500 Hz). It is suggested that in the F3 region, context stimuli may act through spectral contrast effects, while in non-F3 regions, context stimuli might activate the acoustic cues of /g/ and further facilitate the identification of /ga/. The combination of contrast and acoustic cue effects can explain more results concerning the forward context influences on the perception of the /da/-/ga/ series, including the effects of non-F3-region stimuli and the imbalanced influences of context stimuli on /da/ and /ga/ perception.

Integral perception, but separate processing: The perceptual normalization of lexical tones and vowels

In tonal languages, speech variability arises in both lexical tone (i.e., suprasegmentally) and vowel quality (segmentally). Listeners can use surrounding speech context to overcome variability in both speech cues, a process known as extrinsic normalization. Although vowels are the main carriers of tones, it is still unknown whether the combined percept (lexical tone and vowel quality) is normalized integrally or in partly separate processes. Here we used electroencephalography (EEG) to investigate the time course of lexical tone normalization and vowel normalization to answer this question. Cantonese adults listened to synthesized three-syllable stimuli in which the identity of a target syllable - ambiguous between high vs. mid-tone (Tone condition) or between /o/ vs. /u/ (Vowel condition) - was dependent on either the tone range (Tone condition) or the formant range (Vowel condition) of the first two syllables. It was observed that the ambiguous tone was more often interpreted as a high-level tone when the context had a relatively low pitch than when it had a high pitch (Tone condition). Similarly, the ambiguous vowel was more often interpreted as /o/ when the context had a relatively low formant range than when it had a relatively high formant range (Vowel condition). These findings show the typical pattern of extrinsic tone and vowel normalization. Importantly, the EEG results of participants showing the contrastive normalization effect demonstrated that the effects of vowel normalization could already be observed within the N2 time window (190-350 ms), while the first reliable effect of lexical tone normalization on cortical processing was observable only from the P3 time window (220-500 ms) onwards. The ERP patterns demonstrate that the contrastive perceptual normalization of lexical tones and that of vowels occur at least in partially separate time windows. This suggests that the extrinsic normalization can operate at the level of phonemes and tonemes separately instead of operating on the whole syllable at once.

Stop Laryngeal Distinctions Driven by Contrastive Effects of Neighboring Tones

This study examined contrastive effects of neighboring tones that give rise to a systematic asymmetry in stop perception. Korean-speaking learners of Mandarin Chinese and naïve listeners labeled voiceless unaspirated stops preceded or followed by low or high extrinsic tonal context (e.g., ma^LO.pa vs. ma^HI.pa) either as lenis (associated with a low F0 at the vowel onset) or as fortis stops (with a high F0). Further, the target tone itself varied between level and rising (e.g., ma^LO.pa^LEV vs. ma^LO.pa^RIS). Both groups of listeners showed significant contrastive effects of extrinsic context. Specifically, more lenis responses were elicited in a high tone context than in a low one, and vice versa. This indicates that the onset F0 of a stop is perceived lower in a high tone context, which, in turn, provides positive evidence for lenis stops. This effect was more clearly pronounced for the level than for the contour tone target and also for the preceding than for the following context irrespective of linguistic experience. Despite qualitative similarities, learners showed larger effects for all F0 variables, indicating that the degree of context effects may be enhanced by one's phonetic knowledge, namely sensitivity to F0 cues along with the processing of consecutive tones acquired through learning a tone language.

Acoustic context effects in speech perception

The extreme acoustic variability of speech is well established, which makes the proficiency of human speech perception all the more impressive. Speech perception, like perception in any modality, is relative to context, and this provides a means to normalize the acoustic variability in the speech signal. Acoustic context effects in speech perception have been widely documented, but a clear understanding of how these effects relate to each other across stimuli, timescales, and acoustic domains is lacking. Here we review the influences that spectral context, temporal context, and spectrotemporal context have on speech perception. Studies are organized in terms of whether the context precedes the target (forward effects) or follows it (backward effects), and whether the context is adjacent to the target (proximal) or temporally removed from it (distal). Special cases where proximal and distal contexts have competing influences on perception are also considered. Across studies, a common theme emerges: acoustic differences between contexts and targets are perceptually magnified, producing contrast effects that facilitate perception of target sounds and words. This indicates enhanced sensitivity to changes in the acoustic environment, which maximizes the amount of potential information that can be transmitted to the perceiver. This article is categorized under: Linguistics > Language in Mind and Brain Psychology > Perception and Psychophysics.