The effect of talker variability on word recognition in preschool children.

In a series of experiments, the authors investigated the effects of talker variability on children's word recognition. In Experiment 1, when stimuli were presented in the clear, 3- and 5-year-olds were less accurate at identifying words spoken by multiple talkers than those spoken by a single talker when the multiple-talker list was presented first. In Experiment 2, when words were presented in noise. 3-, 4-, and 5-year-olds again performed worse in the multiple-talker condition than in the single-talker condition, this time regardless of order; processing multiple talkers became easier with age. Experiment 3 showed that both children and adults were slower to repeat words from multiple-talker than those from single-talker lists. More important, children (but not adults) matched acoustic properties of the stimuli (specifically, duration). These results provide important new information about the development of talker normalization in speech perception and spoken word recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory-phonetic projection and lexical structure in the recognition of sine-wave words.

Speech remains intelligible despite the elimination of canonical acoustic correlates of phonemes from the spectrum. A portion of this perceptual flexibility can be attributed to modulation sensitivity in the auditory-to-phonetic projection, although signal-independent properties of lexical neighborhoods also affect intelligibility in utterances composed of words. Three tests were conducted to estimate the effects of exposure to natural and sine-wave samples of speech in this kind of perceptual versatility. First, sine-wave versions of the easy and hard word sets were created, modeled on the speech samples of a single talker. The performance difference in recognition of easy and hard words was used to index the perceptual reliance on signal-independent properties of lexical contrasts. Second, several kinds of exposure produced familiarity with an aspect of sine-wave speech: (a) sine-wave sentences modeled on the same talker; (b) sine-wave sentences modeled on a different talker, to create familiarity with a sine-wave carrier; and (c) natural sentences spoken by the same talker, to create familiarity with the idiolect expressed in the sine-wave words. Recognition performance with both easy and hard sine-wave words improved after exposure only to sine-wave sentences modeled on the same talker. Third, a control test showed that signal-independent uncertainty is a plausible cause of differences in recognition of easy and hard sine-wave words. The conditions of beneficial exposure reveal the specificity of attention underlying versatility in speech perception. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Acoustic differences, listener expectations, and the perceptual accommodation of talker variability.

Two talkers' productions of the same phoneme may be quite different acoustically, whereas their productions of different speech sounds may be virtually identical. Despite this lack of invariance in the relationship between the speech signal and linguistic categories, listeners experience phonetic constancy across a wide range of talkers, speaking styles, linguistic contexts, and acoustic environments. The authors present evidence that perceptual sensitivity to talker variability involves an active cognitive mechanism: Listeners expecting to hear 2 different talkers differing only slightly in average pitch showed performance costs typical of adjusting to talker variability, whereas listeners hearing the same materials but expecting a single talker or given no special instructions did not show these performance costs. The authors discuss the implications for understanding phonetic constancy despite variability between talkers (and other sources of variability) and for theories of speech perception. The results provide further evidence for active, controlled processing in real-time speech perception and are consistent with a model of talker normalization that involves contextual tuning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intelligibility of tracheoesophageal speech among naive listeners

Tracheoesophageal (TE) speech is now the most common method of voice rehabilitation after total laryngectomy. The speech intelligibility of laryngectomees who use TE speech as their primary mode of communication was evaluated by 20 "naive" listeners. Two speech intelligibility tests were administered using phonetically balanced rhyming words or lists of spondee words. The overall intelligibility for the group of laryngectomees was 76%, with a wide range of variability among the individual TE speakers. We concluded that TE speech is significantly less intelligible to naive listeners than normal laryngeal speech; further refinement of voice rehabilitation for laryngectomees is needed.     

Speaking clearly for the hard of hearing IV: Further studies of the role of speaking rate

The contribution of reduced speaking rate to the intelligibility of "clear" speech (Picheny, Durlach, & Braida, 1985) was evaluated by adjusting the durations of speech segments (a) via nonuniform signal time-scaling, (b) by deleting and inserting pauses, and (c) by eliciting materials from a professional speaker at a wide range of speaking rates. Key words in clearly spoken nonsense sentences were substantially more intelligible than those spoken conversationally (15 points) when presented in quiet for listeners with sensorineural impairments and when presented in a noise background to listeners with normal hearing. Repeated presentation of conversational materials also improved scores (6 points). However, degradations introduced by segment-by-segment time-scaling rendered this time-scaling technique problematic as a means of converting speaking styles. Scores for key words excised from these materials and presented in isolation generally exhibited the same trends as in sentence contexts. Manipulation of pause structure reduced scores both when additional pauses were introduced into conversational sentences and when pauses were deleted from clear sentences. Key-word scores for materials produced by a professional talker were inversely correlated with speaking rate, but conversational rate scores did not approach those of clear speech for other talkers. In all experiments, listeners with normal hearing exposed to flat-spectrum background noise performed similarly to listeners with hearing loss.     

Stimulus variability and spoken word recognition. II. The effects of age and hearing impairment

Three experiments were conducted to investigate the effects of variations in talker characteristics, speaking rate, and overall amplitude on perceptual identification in normal-hearing young (NHY), normal-hearing elderly (NHE), and hearing-impaired elderly (HIE) listeners. The three dimensions were selected because variations in voice characteristics and speaking rate affect features of speech signals that are important for word recognition while overall amplitude changes do not alter stimulus parameters that have direct effects on phonetic identification. Thus, the studies were designed to examine how variations in both phonetically relevant and irrelevant stimulus dimensions affect speech processing in a number of different populations. Age differences, as indicated by greater effects of variability for the NHE compared with the NHY listeners, were observed for mixed-talker and mixed-amplitude word lists. Effects of age-related hearing impairment, as indicated by reduced scores for the HIE compared with the NHE group, were observed for variations in speaking rate and talker characteristics. Considered together, the findings suggest that age-related changes in perceptual normalization and selective attention may contribute to the reduced speech understanding that is often reported for older adults.     

Differential neural contributions to native- and foreign-language talker identification.

Humans are remarkably adept at identifying individuals by the sound of their voice, a behavior supported by the nervous system’s ability to integrate information from voice and speech perception. Talker-identification abilities are significantly impaired when listeners are unfamiliar with the language being spoken. Recent behavioral studies describing the language-familiarity effect implicate functionally integrated neural systems for speech and voice perception, yet specific neuroscientific evidence demonstrating the basis for such integration has not yet been shown. Listeners in the present study learned to identify voices speaking a familiar (native) or unfamiliar (foreign) language. The talker-identification performance of neural circuitry in each cerebral hemisphere was assessed using dichotic listening. To determine the relative contribution of circuitry in each hemisphere to ecological (binaural) talker identification abilities, we compared the predictive capacity of dichotic performance on binaural performance across languages. Listeners’ right-ear (left hemisphere) performance was a better predictor of binaural accuracy in their native language than a foreign one. This enhanced role of the classically language-dominant left hemisphere in listeners’ native language demonstrates functionally integrated neural systems for speech and voice perception during talker identification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spoken word recognition in individuals with dementia of the Alzheimer's type: Changes in talker normalization and lexical discrimination.

Four experiments were conducted to examine the effects of dementia of the Alzheimer's type (DAT) on talker normalization and lexical discrimination. Talker normalization has been proposed as the principal mechanism underlying listeners' ability to maintain perceptual constancy for speech signals. Lexical discrimination refers to the ability to distinguish individual words from phonetically similar items stored in the mental lexicon. Healthy older adults served as controls. Comparisons of controls and very mildly impaired patients with DAT revealed no significant change in either lexical discrimination or talker normalization. In contrast, individuals with more advanced DAT (mildly demented) exhibited significant declines in both abilities. The results are discussed with respect to the possible roles of general slowing and inhibitory declines as factors affecting speech perception in DAT. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Examining the Time Course of Indexical Specificity Effects in Spoken Word Recognition.

Variability in talker identity and speaking rate, commonly referred to as indexical variation, has demonstrable effects on the speed and accuracy of spoken word recognition. The present study examines the time course of indexical specificity effects to evaluate the hypothesis that such effects occur relatively late in the perceptual processing of spoken words. In 3 long-term repetition priming experiments, the authors examined reaction times to targets that were primed by stimuli that matched or mismatched on the indexical variable of interest (either talker identity or speaking rate). Each experiment was designed to manipulate the speed with which participants processed the stimuli. The results demonstrate that indexical variability affects participants' perception of spoken words only when processing is relatively slow and effortful. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of talker-specific information in word segmentation by infants.

Infants' representations of the sound patterns of words were explored by examining the effects of talker variability on the recognition of words in fluent speech. Infants were familiarized with isolated words (e.g., cup and dog) from 1 talker and then heard 4 passages produced by another talker, 2 of which included the familiarized words. At 7.5 months of age, infants attended longer to passages with the familiar words for materials produced by 2 female talkers or 2 male talkers but not for materials by a male and a female talker. These findings suggest a strong role for talker-voice similarity in infants' ability to generalize word tokens. By 10.5 months, infants could generalize different instances of the same word across talkers of the opposite sex. One implication of the present results is that infants' initial representations of the sound structure of words not only include phonetic information but also indexical properties relating to the vocal characteristics of particular talkers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibitory processes and spoken word recognition in young and older adults: The interaction of lexical competition and semantic context.

Two experiments were conducted to examine the importance of inhibitory abilities and semantic context to spoken word recognition in older and young adults. In Experiment 1, identification scores were obtained in 3 contexts: single words, low-predictability sentences, and high-predictability sentences. Additionally, identification performance was examined as a function of neighborhood density (number of items phonetically similar to a target word). Older adults had greater difficulty than young adults recognizing words with many neighbors (hard words). However, older adults also exhibited greater benefits as a result of adding contextual information. Individual differences in inhibitory abilities contributed significantly to recognition performance for lexically hard words but not for lexically easy words. The roles of inhibitory abilities and linguistic knowledge in explaining age-related impairments in spoken word recognition are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Review of research on the intelligibility and comprehension of accelerated speech.

Time-compressed or accelerated speech is speech which has been reproduced in less than the original production time. Such speech may prove to be useful in a variety of situations in which people must rely upon listening to obtain the information specified by language. It may also prove to be a useful tool in studying the temporal requirements of the listener as he processes spoken language. Methods for the generation of time compressed speech are reviewed. Methods for the assessment of the effect of compression on word intelligibility and listening comprehension are discussed. Experiments dealing with the effect of time compression upon word intelligibility and upon the comprehensibility of connected discourse, and experiments concerned with the influence of stimulus variables, such as signal distortion, and organismic variables such as intelligence, are reviewed. The general finding that compression in time has a different effect upon the comprehensibility of connected discourse than upon word intelligibility is discussed, and a tentative explanation of this difference is offered. (63 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phonological ambiguity and lexical ambiguity: Effects on visual and auditory word recognition.

Three experiments in Serbo-Croatian were conducted on the effects of phonological ambiguity and lexical ambiguity on printed word recognition. Subjects decided rapidly if a printed and a spoken word matched or not. Printed words were either phonologically ambiguous (two possible pronunciations) or unambiguous. If phonologically ambiguous, either both pronunciations were real words or only one was, the other being a nonword. Spoken words were necessarily unambiguous. Half the spoken words were auditorily degraded. In addition, the relative onsets of speech and print were varied. Speed of matching print to speech was slowed by phonological ambiguity, and the effect was amplified when the stimulus was also lexically ambiguous. Auditory degradation did not interact with print ambiguity, suggesting the perception of the spoken word was independent of the printed word. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Episodic encoding of voice attributes and recognition memory for spoken words.

Recognition memory for spoken words was investigated with a continuous recognition memory task. Independent variables were number of intervening words (lag) between initial and subsequent presentations of a word, total number of talkers in the stimulus set, and whether words were repeated in the same voice or a different voice. In Exp 1, recognition judgments were based on word identity alone. Same-voice repetitions were recognized more quickly and accurately than different-voice repetitions at all values of lag and at all levels of talker variability. In Exp 2, recognition judgments were based on both word identity and voice identity. Ss recognized repeated voices quite accurately. Gender of the talker affected voice recognition but not item recognition. These results suggest that detailed information about a talker's voice is retained in long-term memory representations of spoken words. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Generalizing linguistic structures under high attention demands.

We explored whether the generalization of rules based on simple structures depends on attention. Participants were exposed to a stream of artificial words that followed a simple syllabic structure (ABA or AAB), overlaid on a sequence of familiar noises. After passively listening, participants successfully recognized the individual words present in the stream among foils, and they were able to generalize the underlying word structure to new exemplars. Yet, when attention was diverted from the speech stream (by requiring participants to monitor the sequence of noises), recognition of the individual words fell dramatically irrespective of word structure, whereas generalization depended on stimulus structure. For structures based on vowel repetitions across nonadjacent syllables (ABA; Experiment 1), generalization was affected by attention. In contrast, for structures based on adjacent repetitions (AAB; Experiment 2), generalization capacity was unaffected by attention. This pattern of results was replicated under favorable conditions for generalization, such as increased token variability and the implementation of the rule over whole syllables (Experiments 3 and 4). These results suggest a differential effect of attention on rule learning and generalization depending on stimulus structure. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Renal and hepatic 1 alpha-hydroxylation of 25-hydroxyvitamin D3 in piglets suffering from pseudo vitamin D-deficiency rickets, type I

Research has shown that speech articulated in a clear manner is easier to understand than conversationally spoken speech in both the auditory-only (A-only) and auditory-visual (AV) domains. Because this research has been conducted using younger adults, it is unknown whether age-related changes in auditory and/or visual processing affect older adults' ability to benefit when a talker speaks clearly. The present study examined how speaking mode (clear vs conversational) and presentation mode (A-only vs AV) influenced nonsense sentence recognition by older listeners. Results showed that neither age nor hearing loss limited the amount of benefit that older adults obtained from a talker speaking clearly. However, age was inversely correlated with identification of AV (but not A-only) conversational speech, even when pure-tone thresholds were controlled statistically.     

Effects of speech intelligibility level on concurrent visual task performance

Four experiments were performed to determine if changes in the level of speech intelligibility in an auditory task have an impact on performance in concurrent visual tasks. The auditory task used in each experiment was a memory search task in which subjects memorized a set of words and then decided whether auditorily presented probe items were members of the memorized set. The visual tasks used were an unstable tracking task, a spatial decision-making task, a mathematical reasoning task, and a probability monitoring task. Results showed that performance on the unstable tracking and probability monitoring tasks was unaffected by the level of speech intelligibility on the auditory task, whereas accuracy in the spatial decision-making and mathematical processing tasks was significantly worse at low speech intelligibility levels. The findings are interpreted within the framework of multiple resource theory.