Abstract
This study tested the hypothesis that object-based attention modulates the discrimination of level increments in stop-consonant noise bursts. With consonant-vowel-consonant (CvC) words consisting of an ≈80-dB vowel (v), a pre-vocalic (Cv) and a post-vocalic (vC) stop-consonant noise burst (≈60-dB SPL), we measured discrimination thresholds (LDTs) for level increments (ΔL) in the noise bursts presented either in CvC context or in isolation. In the 2-interval 2-alternative forced-choice task, each observation interval presented a CvC word (e.g., /pæk/ /pæk/), and normal-hearing participants had to discern ΔL in the Cv or vC burst. Based on the linguistic word labels, the auditory events of each trial were perceived as two auditory objects (Cv-v-vC and Cv-v-vC) that group together the bursts and vowels, hindering selective attention to ΔL. To discern ΔL in Cv or vC, the events must be reorganized into three auditory objects: the to-be-attended pre-vocalic (Cv–Cv) or post-vocalic burst pair (vC–vC), and the to-be-ignored vowel pair (v–v). Our results suggest that instead of being automatic this reorganization requires training, in spite of using familiar CvC words. Relative to bursts in isolation, bursts in context always produced inferior ΔL discrimination accuracy (a context effect), which depended strongly on the acoustic separation between the bursts and the vowel, being much keener for the object apart from (post-vocalic) than for the object adjoining (pre-vocalic) the vowel (a temporal-position effect). Variability in CvC dimensions that did not alter the noise-burst perceptual grouping had minor effects on discrimination accuracy. In addition to being robust and persistent, these effects are relatively general, evincing in forced-choice tasks with one or two observation intervals, with or without variability in the temporal position of ΔL, and with either fixed or roving CvC standards. The results lend support to the hypothesis.
Highlights
In the perception of speech, the sensitivity to level differences in stop-consonant noise bursts plays an important role because such differences facilitate categorization along place of articulation [1], voicing [2, 3], and other phonetic continua
To estimate level discrimination thresholds (LDTs), maximum-likelihood probits were fit to the data relating correct probability, P(C), to ΔL in dB; each data point is based on 80 trials or more
Neither the LDT predicted from the SI-2AFC task nor the one measured was significantly different from the LDT observed in the 2I-2AFC task, F(1, 2) = .046, MSE = 0.283, p = .851, and F(1, 2) = 3.006, MSE = .410, p =
Summary
In the perception of speech, the sensitivity to level differences in stop-consonant noise bursts plays an important role because such differences facilitate categorization along place of articulation [1], voicing [2, 3], and other phonetic continua. Determining perceptual significance is important because, by being much briefer and lower in level than the immediately preceding or following vowels, the stop-consonant noise bursts are less audible and vulnerable to intra-speech or context interference such as temporal masking [7] that degrades the bursts perceptual analysis. Owing to this interference, the perceptual significance of burst-level differences is not equivalent to the acoustic one, and the discordance between perceptual and acoustic magnitude is not fully understood. Among these variables is whether the burst is pre- or post-vocalic, the duration of silences preceding or following the consonant-release burst, the vowel level, the uncertainty about which burst conveys a level increment, and others; few studies have investigated how these variables modulate the perceptual effect
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