This study examined perceptual learning of spectrally complex nonspeech auditory categories in an interactive multi-modal training paradigm. Participants played a computer game in which they navigated through a three-dimensional space while responding to animated characters encountered along the way. Characters' appearances in the game correlated with distinctive sound category distributions, exemplars of which repeated each time the characters were encountered. As the game progressed, the speed and difficulty of required tasks increased and characters became harder to identify visually, so quick identification of approaching characters by sound patterns was, although never required or encouraged, of gradually increasing benefit. After 30 min of play, participants performed a categorization task, matching sounds to characters. Despite not being informed of audio-visual correlations, participants exhibited reliable learning of these patterns at posttest. Categorization accuracy was related to several measures of game performance and category learning was sensitive to category distribution differences modeling acoustic structures of speech categories. Category knowledge resulting from the game was qualitatively different from that gained from an explicit unsupervised categorization task involving the same stimuli. Results are discussed with respect to information sources and mechanisms involved in acquiring complex, context-dependent auditory categories, including phonetic categories, and to multi-modal statistical learning.

Speakers can adopt a speaking style that allows them to be understood more easily in difficult communication situations, but few studies have examined the acoustic properties of clearly produced consonants in detail. This study attempts to characterize the adaptations in the clear production of American English fricatives in a carefully controlled range of communication situations. Ten female and ten male talkers produced fricatives in vowel-fricative-vowel contexts in both a conversational and a clear style that was elicited by means of simulated recognition errors in feedback received from an interactive computer program. Acoustic measurements were taken for spectral, amplitudinal, and temporal properties known to influence fricative recognition. Results illustrate that ͑1͒ there were consistent overall style effects, several of which ͑consonant duration, spectral peak frequency, and spectral moments͒ were consistent with previous findings and a few ͑notably consonant-to-vowel intensity ratio͒ of which were not; ͑2͒ specific acoustic modifications in clear productions of fricatives were influenced by the nature of the recognition errors that prompted the productions and were consistent with efforts to emphasize potentially misperceived contrasts both within the English fricative inventory and based on feedback from the simulated listener; and ͑3͒ talkers differed widely in the types and magnitude of all modifications.

This study addressed whether acoustic variability and category overlap in non-native speech contribute to difficulty in its recognition, and more generally whether the benefits of exposure to acoustic variability during categorization training are stable across differences in category confusability. Three experiments considered a set of Spanish-accented English productions. The set was seen to pose learning and recognition difficulty (experiment 1) and was more variable and confusable than a parallel set of native productions (experiment 2). A training study (experiment 3) probed the relative contributions of category central tendency and variability to difficulty in vowel identification using derived inventories in which these dimensions were manipulated based on the results of experiments 1 and 2. Training and test difficulty related straightforwardly to category confusability but not to location in the vowel space. Benefits of high-variability exposure also varied across vowel categories, and seemed to be diminished for highly confusable vowels. Overall, variability was implicated in perception and learning difficulty in ways that warrant further investigation.

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