The most robust finding on infants' listening preferences has been widely characterized as a preference for baby talk (BT) over adult-directed speech (ADS). Although prosodic modifications characteristic of BT also convey positive affect, differences in affect across BT and ADS speech registers have not been controlled in previous studies. This set of experiments sought to elucidate the basis for 6-month-olds' listening preference by independently manipulating affect and speech register. When affect was held constant, no preference for any speech register was observed. Moreover, when ADS stimuli presented more positive affect than BT stimuli, infants' preferences followed the positive affect. Higher and more variable pitch was neither necessary nor sufficient for determining infants' preferences, although pitch characteristics may modulate affect-based preferences. The BT preference is thus attributable to a more general preference for speech that imparts relatively positive affect, a preference perhaps ascribable to a preexisting generalpurpose mechanism opportunistically exploited by language.From birth onward, infants display a range of preferences for auditory stimuli. As early as the first month of life, infants prefer to listen to speech rather than nonspeech (Cooper & Aslin, 1994), mothers' speech rather than other females' speech (DeCasper

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Although infants begin to encode and track novel words in fluent speech by 7.5 months, their ability to recognize words is somewhat limited at this stage. In particular, when the surface form of a word is altered, by changing the gender or affective prosody of the speaker, infants begin to falter at spoken word recognition. Given that natural speech is replete with variability, only some of which determines the meaning of a word, it remains unclear how infants might ever overcome the effects of surface variability without appealing to meaning. In the current set of experiments, consequences of high and low variability are examined in preverbal infants. The source of variability, vocal affect, is a common property of infant-directed speech with which young learners have to contend. Across a series of four experiments, infants' abilities to recognize repeated encounters of words, as well as to reject similar-sounding words, are investigated in the context of high and low affective variation. Results point to positive consequences of affective variation, both in creating generalizable memory representations for words, but also in establishing phonologically precise memories for words. Conversely, low variability appears to degrade word recognition on both fronts, compromising infants' abilities to generalize across different affective forms of a word and to detect similar-sounding items. Findings are discussed in the context of principles of categorization that may potentiate the early growth of a lexicon.

To learn words, infants must be sensitive to native phonological contrast. While lexical tone predominates as a source of phonemic contrast in human languages, there has been little investigation of the influences of lexical tone on word learning. The present study investigates infants' sensitivity to tone mispronunciations in two groups of infants. For one group (Chinese learners), tone is phonemic in their native language, and for the second group (English learners), tone is non-phonemic and constituted suprasegmental variation. In Experiment 1, English learners were trained on novel word-object pairings and tested on their recognition of correct pronunciations, tone and vowel mispronunciations of these words at 18 and 24 months. In Experiment 2a, bilingual English-Chinese learners were tested on a similar task translated into Chinese at the same age intervals. Results demonstrate that non-tonal learners treated tonal and vowel substitutions alike as mispronunciations at 18 months but only treated vowel substitutions as mispronunciations at 24 months. Tonal learners treated both tonal and vowel substitutions as mispronunciations at both ages. In Experiment 2b, bilingual non-tone language learners were tested on the same set of tasks replicating a similar set of results as monolingual non-tone language learners (Experiment 1). Findings point to an early predisposition to treat tone as a defining characteristic of words regardless of its lexical relevance at 18 months. Between 18 and 24 months, learners appear to ascribe lexical relevance to tone in a language-specific manner. The current study identifies the influences of tone variation on memories for newly learned words and the time period during which lexical tone - a highly frequent constituent of human languages - actually becomes lexical for early learners. Findings are contextualized with prevailing models of the developing lexicon.

Conversation is a primary area of difficultly for individuals with high-functioning autism (HFA) although they have unimpaired formal language abilities. This likely stems from the unstructured nature of face-to-face conversation as well as the need to coordinate other modes of communication (e.g. eye gaze) with speech. We conducted a quantitative analysis of both verbal exchange and gaze data obtained from conversations between children with HFA and an adult, compared with those of typically-developing children matched on language level. We examined a new question: How does speaking about a topic of interest affect reciprocity of verbal exchange and eye gaze? Conversations on generic topics were compared with those on individuals’ circumscribed interests, particularly intense interests characteristic of HFA. Two opposing hypotheses were evaluated. Speaking about a topic of interest may improve reciprocity in conversation by increasing participants’ motivation and engagement. Alternatively, it could engender more one-sided interaction, given the engrossing nature of circumscribed interests. In their verbal exchanges HFA participants demonstrated decreased reciprocity during the interest topic, evidenced by fewer contingent utterances and more monologue-style speech. Moreover, a measure of stereotyped behaviour and restricted interest symptoms was inversely related to reciprocal verbal exchange. However, both the HFA and comparison groups looked significantly more to their partner’s face during the interest than generic topic. Our interpretation of results across modalities is that circumscribed interests led HFA participants to be less adaptive to their partner verbally, but speaking about a highly practiced topic allowed for increased gaze to the partner. The function of this increased gaze to partner may differ for the HFA and comparison groups.