Tanya Kraljic

Generalization in perceptual learning for speech

Lexical context strongly influences listeners’ identification of ambiguous sounds. For example, a sound midway between /f/ and /s/ is reported as /f/ in “sheri_’” but as /s/ in “Pari_.” Norris, McQueen, and Cutler (2003) have demonstrated that after hearing such lexically determined phonemes, listeners expand their phonemic categories to include more ambiguous tokens than before. We tested whether listeners adjust their phonemic categories for a specific speaker: Do listeners learn a particular speaker’s “accent”? Similarly, we examined whether perceptual learning is specific to the particular ambiguous phonemes that listeners hear, or whether the adjustments generalize to related sounds. Participants heard ambiguous /d/ or /t/ phonemes during a lexical decision task. They then categorized sounds on /d/-/t/ and /b/-/p/ continua, either in the same voice that they had heard for lexical decision, or in a different voice. Perceptual learning generalized across both speaker and test continua: Changes in perceptual representations are robust and broadly tuned.

Perceptual learning for speech

Adult language users have an enormous amount of experience with speech in their native language. As a result, they have very well-developed processes for categorizing the sounds of speech that they hear. Despite this very high level of experience, recent research has shown that listeners are capable of redeveloping their speech categorization to bring it into alignment with new variation in their speech input. This reorganization of phonetic space is a type of perceptual learning, or recalibration, of speech processes. In this article, we review several recent lines of research on perceptual learning for speech.

Accommodating variation: Dialects, idiolects, and speech processing

Listeners are faced with enormous variation in pronunciation, yet they rarely have difficulty understanding speech. Although much research has been devoted to figuring out how listeners deal with variability, virtually none (outside of sociolinguistics) has focused on the source of the variation itself. The current experiments explore whether different kinds of variation lead to different cognitive and behavioral adjustments. Specifically, we compare adjustments to the same acoustic consequence when it is due to context-independent variation (resulting from articulatory properties unique to a speaker) versus context-conditioned variation (resulting from common articulatory properties of speakers who share a dialect). The contrasting results for these two cases show that the source of a particular acoustic-phonetic variation affects how that variation is handled by the perceptual system. We also show that changes in perceptual representations do not necessarily lead to changes in production.

First Impressions and Last Resorts How Listeners Adjust to Speaker Variability

Perceptual theories must explain how perceivers extract meaningful information from a continuously variable physical signal. In the case of speech, the puzzle is that little reliable acoustic invariance seems to exist. We tested the hypothesis that speech-perception processes recover invariants not about the signal, but rather about the source that produced the signal. Findings from two manipulations suggest that the system learns those properties of speech that result from idiosyncratic characteristics of the speaker; the same properties are not learned when they can be attributed to incidental factors. We also found evidence for how the system determines what is characteristic: In the absence of other information about the speaker, the system relies on episodic order, representing those properties present during early experience as characteristic of the speaker. This “first-impressions” bias can be overridden, however, when variation is an incidental consequence of a temporary state (a pen in the speakers mouth), rather than characteristic of the speaker.

How listeners represent dialectal variation.

Successful speech recognition requires that listeners map acoustically variant pronunciations onto the same meaningful interpretation. As listeners are exposed to a talker’s speech, they learn the relevant mapping, and their perception shifts to accommodate the talker’s pronunciations. Recent work on the perceptual learning of idiolectal variation has made it possible to investigate precisely what it is that changes in perceptual processing as listeners adapt to speakers. These studies suggest that phonemic representations themselves are rapidly modified to reflect the idiolectal variants produced by a talker. However, dialectal variation appears to be handled differently. Several studies will be presented that address the representation of dialectal forms, including a recent experiment that directly compared learning of a dialectal variant to learning of an idiolectal variant with the same acoustic properties. Listeners adjust to talkers’ dialects, but unlike with idiolectal variation, such adjustments d...