Despite the tremendous amount of phonetic variability in speech across talkers, listeners seem to effortlessly process acoustic signals while attending to both the linguistic content and talker-specific information. Previous studies have explained this phenomenon by providing evidence for talker normalization, a process in which our perceptual system strips away information about a talker so that the abstract, canonical linguistic units are all that remain for further linguistic analysis. However, it is currently unknown whether or how talker normalization is facilitated by familiar talkers. In this study, we investigated whether talker familiarity had an impact on the speed in which listeners perceived highly confusable words under varying contexts. Over the course of three days, listeners were explicitly trained on the voices of four talkers. Baseline and post-test measures were administered to determine the effect of talker training and to see whether this effect was impacted by the presence of a carrier phrase as well as the variability of talker presentation. The results demonstrated that listeners adapted to the talker regardless of familiarity. Having immediate information about a talker from preceding speech appeared to play a larger role in managing talker variability than a long-term familiarity with the talker’s voice. Our findings suggest that talker normalization is a feedforward process that does not rely on prior memory traces.

Purpose: The aim of this study was to examine whether a verb-focused language intervention was effective in increasing children’s verb-vocabulary. In particular, this study investigated whether the treatment resulted in changes to children’s production of target words compared to control words for children who are late talkers. Method: The study utilised a single-subject, multiple baseline across behaviours design. Four children, aged 26-to-39 months who exhibited delayed expressive language development participated in the study. At the beginning of the study, all children had poor expressive language performance indicated by a mean length of utterance two standard deviations below the mean expected for their age and limited vocabulary measured by the New Zealand Communicative Development Inventory: Words and Sentences. New verb-vocabulary items were randomly assigned to intervention and untreated control conditions and probed at regular intervals over a period of eight weeks. Results: All the participants showed increased use of the target verbs compared to the control verbs during the intervention and post-intervention phase. Conclusion: The findings suggest that a verb-focused language intervention was effective in increasing the verb-vocabulary of late talkers. Further research is warranted to determine whether similar results can be found with a larger cohort and whether these gains are sustained over time.

Three experiments examined normal-hearing and cochlear-implant listeners' abilities to perceive and use talker-specific information in the speech signal. In Experiment 1 voice similarity judgments were gathered from normal-hearing listeners to maximize variability across talkers used in Experiment 2. These judgments were submitted to a multidimensional scaling (MDS) analysis; this solution was used to select the talkers of Experiment 2. Experiment 2 was an approximate replication of Nygaard and Pisoni's (1998) work. In this study cochlear-implant and normal-hearing listeners were trained to recognize 6 different voices. The cochlear-implant users recognized the voices with 59.31% accuracy and the normal-hearing listeners achieved 92.64% accuracy. After training the listeners completed a sentence recognition task in noise. In the task 6 familiar talkers spoken half of the sentences and 6 novel talkers spoke the other half. It was predicted that sentences spoken by the familiar talkers would be more accurately perceived than those spoken by the novel talkers. However, there was no difference in accuracy, nor was there a difference in performance across the groups of listeners. The factors contributing to these null results were discussed at length. Experiment 3 gathered voice similarity judgments from the normal-hearing and cochlear-implant listeners of Experiment 2. These data were submitted to both classical and weighted MDS analyses. The voice maps showed notable differences in the perceptual spaces of the two groups of listeners. The participant space yielded from the weighted MDS showed great variation across all of the participants' judgments, but no clear trend supporting the listeners' group membership. In conclusion, despite listening via a constrained, electric signal, the cochlear-implant users were trained to recognize voices with notable accuracy (as were the normal-hearing listeners). Nevertheless, Experiment 2 failed to provide insight into talker familiarity's effect on the sentence recognition skills of cochlear-implant and normal-hearing listeners. These results are contrary to research with normal-hearing listeners that suggests talker familiarity facilitates speech processing in noise. The present studies did show, though, that cochlear-implant users appear to perceive and use talker-specific information differently than normal-hearing listeners.

One of the fundamental challenges for communication by speech is the variability in speech production/acoustics. Talkers vary in the size and shape of their vocal tract, in dialect, and in speaking mannerisms. These differences all impact the acoustic output. Despite this lack of invariance in the acoustic signal, listeners can correctly perceive the speech of many different talkers. This ability to adapt one's perception to the particular acoustic structure of a talker has been investigated for over fifty years. The prevailing explanation for this phenomenon is that listeners construct talker-specific representations that can serve as referents for subsequent speech sounds. Specifically, it is thought that listeners may either be creating mappings between acoustics and phonemes or extracting the vocal tract anatomy and shape for each individual talker. This research focuses on an alternative explanation. A separate line of work has demonstrated that much of the variance between talkers' productions can be captured in their neutral vocal tract shape (that is, the average shape of their vocal tract across multiple vowel productions). The current model tested is that listeners compute an average spectrum (long term average spectrum - LTAS) of a talker's speech and use it as a referent. If this LTAS resembles the acoustic output of the neutral vocal tract shape - the neutral vowel - then it could accommodate some of the talker based variability. The LTAS model results in four main hypotheses: 1) during carrier phrases, listeners compute an LTAS for the talker; 2) this LTAS resembles the spectrum of the neutral vowel; 3) listeners represent subsequent targets relative to this LTAS referent; 4) such a representation reduces talker-specific acoustic variability. The goal of this project was to further develop and test the predictions arising from these hypotheses. Results suggest that the LTAS model needs to be further investigated, as the simple model proposed does not explain the effects found across all studies.

Previous studies have shown that multiple talkers help learners make more robust word representations when the learner is not very experienced with the language (Richtsmeier et al., 2009; Rost & McMurray, 2009, 2010). This is likely because exposure to variation allows the learner to observe which acoustic dimensions vary unpredictably across talkers, and which acoustic dimensions vary predictably. However, this predicts that only learners who are less experienced with a language will benefit from multiple talkers, as more experienced learners should be able to use their previous knowledge about the language's speech sounds. Three word-learning experiments, with participants who were expected to have different levels of experience in the language, were performed to test this prediction. In the first experiment, English-acquiring children did benefit from multiple talker in the production but not perception of newly learned words. In the second experiment, native English-speaking adults did not benefit from learning from multiple talkers in either the perception or production of new words. Finally, second language-learning adults benefited from multiple talkers if they were less proficient speakers, but not if they were more proficient. Collectively, these results suggest that learning from multiple talkers is only beneficial for less experienced language learners.

Phonotactics are the restrictions on sound sequences within a word or syllable. They are an important cue for speech segmentation and a guiding force in the creation of new words. By studying phonotactics, we stand to gain a better understanding of why languages and speakers have phonologies. Through a series of four experiments, I will present data that sharpen our theoretical and empirical perspectives of what phonotactics are and how they are acquired.The methodology is similar to that used in studies of infant perception: children are familiarized with a set of words that contain either a few or many examples of a phonotactic sequence. The participants here are four-year-olds, and the test involves producing a target phonotactic sequence in a new word. Because the test words have not been encountered before, children must generalize what they learned in the familiarization phase and apply it to their own speech. By manipulating the phonetic and phonological characteristics of the familiarization items, we can determine which factors are relevant to phonotactic learning. In these experiments, the phonetic manipulation was the number of talkers who children heard produce a familiarization word. The phonological manipulation was the number of familiarization words that shared a phonotactic pattern.The findings include instances where learning occurs and instances where it does not. First, the data show that the well-studied correlation between phonotactic probability and production accuracy in child speech can be attributed, at least partly to perceptual learning, rather than a practice effect attributable to repeated articulation. Second, the data show that perceptual learning is a process of abstraction and learning about those abstractions. It is not about making connections between stored, unelaborated exemplars because learning from the phonetic manipulation alone was insufficient for a phonotactic pattern to generalize. Furthermore, perceptual learning is not about reorganizing pre-existing symbolic knowledge, because learning from words alone is insufficient. I argue that a model which learns abstract word-forms from direct phonetic experience, then learns phonotatics from the abstract word-forms, is the most parsimonious explanation of phonotactic learning.

Little is known about infants’ ability to deal with commonly encountered situations in which speech from one individual occurs simultaneously with that of others. Previous research has shown that while age of the infant and intensity of the background matter, so does the number of background speakers. The read-aloud multi-talker speech used in previous studies is perceptually different from conversational speech typically encountered by infants. To test generalizability, this study used a background of ecologically valid multi-talker speech. Using the head-turn preference procedure, infants were presented with passages of background noise with and without target infant-directed speech at a 10 dB SNR. Results show that while 9-month-olds prefer passages containing target speech with a white noise background, both 9- and 12-month-olds failed to show a preference with a multi-talker background. This inability to segregate speech streams under ecologically valid conditions demonstrates the adversity infants face to learn their community’s language.

Adult listeners more accurately identify talkers speaking a known language than a foreign language (Thompson, 1987), a phenomenon known as the language-familiarity effect (Perrachione & Wong, 2007). Two experiments explored how knowledge of a language facilitates talker identification. In Experiment 1, participants identified talkers in three conditions: (a) a foreign-language speech condition featuring unfamiliar sound patterns and no known words; (b) a nonsense speech condition featuring all the familiar sound patterns of their native language, such as familiar phonemes, prosody, and syllable structure, but no actual words; and (c) a native-language condition with all the familiar components of a language, including words. In Experiment 2, participants again identified speakers in familiar and unfamiliar languages. In both languages, listeners identified speakers in a condition in which no word was ever repeated, and in a condition featuring repeated words. The results suggest that access to familiar, meaningful spoken words confers an advantage beyond access to familiar sounds, syllables, and prosody, particularly when words are repeated. Together, Experiments 1 and 2 support integrated models of voice and language processing systems, and indicate that access to meaningful words is a crucial component of the language-familiarity effect in talker identification.

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<p>In many earlier investigations a recall advantage of auditory lists spoken in a single voice has been found over recall of lists spoken in two alternating voices. One explanation proposed is an organization strategy which makes recall of alternating-voice lists so difficult. The strategy implies sorting same-voice words into same-voice groups at encoding. Based on this proposition, it was assumed that voice-by-voice recall would be better than recall in order of presentation, as then the recall instruction and the organization of items in memory would be in concordance. The present experiment tested and was unable to support this hypothesis. However, an intriguing interaction between recall instruction and the sex of the participants was found, indicating that males perform worse in the voice-by-voice recall instruction than in serial recall while females’ performance did not differ between the two recall instructions. Implications of these results are discussed.</p>