Individual differences in the use of top-down versus bottom-up cues to resolve phonetic ambiguity.

How listeners weight a wide variety of information to interpret ambiguities in the speech signal is a question of interest in speech perception, particularly when understanding how listeners process speech in the context of phrases or sentences. Dominant views of cue use for language comprehension posit that listeners integrate multiple sources of information to interpret ambiguities in the speech signal. Here, we study how semantic context, sentence rate, and vowel length all influence identification of word-final stops. We find that while at the group level all sources of information appear to influence how listeners interpret ambiguities in speech, at the level of the individual listener, we observe systematic differences in cue reliance, such that some individual listeners favor certain cues (e.g., speech rate and vowel length) to the exclusion of others (e.g., semantic context). While listeners exhibit a range of cue preferences, across participants we find a negative relationship between individuals' weighting of semantic and acoustic-phonetic (sentence rate, vowel length) cues. Additionally, we find that these weightings are stable within individuals over a period of 1 month. Taken as a whole, these findings suggest that theories of cue integration and speech processing may fail to capture the rich individual differences that exist between listeners, which could arise due to mechanistic differences between individuals in speech perception.

Impaired perceptual phonetic plasticity in Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative condition primarily associated with its motor consequences. Although much of the focus within the speech domain has focused on PD's consequences for production, people with PD have been shown to differ in the perception of emotional prosody, loudness, and speech rate from age-matched controls. The current study targeted the effect of PD on perceptual phonetic plasticity, defined as the ability to learn and adjust to novel phonetic input, both in second language and native language contexts. People with PD were compared to age-matched controls (and, for three of the studies, a younger control population) in tasks of explicit non-native speech learning and adaptation to variation in native speech (compressed rate, accent, and the use of timing information within a sentence to parse ambiguities). The participants with PD showed significantly worse performance on the task of compressed rate and used the duration of an ambiguous fricative to segment speech to a lesser degree than age-matched controls, indicating impaired speech perceptual abilities. Exploratory comparisons also showed people with PD who were on medication performed significantly worse than their peers off medication on those two tasks and the task of explicit non-native learning.

Reliability and validity for perceptual flexibility in speech.

The study of perceptual flexibility in speech depends on a variety of tasks that feature a large degree of variability between participants. Of critical interest is whether measures are consistent within an individual or across stimulus contexts. This is particularly key for individual difference designs that aredeployed to examine the neural basis or clinical consequences of perceptual flexibility. In the present set of experiments, we assess the split-half reliability and construct validity of five measures of perceptual flexibility: three of learning in a native language context (e.g., understanding someone with a foreign accent) and two of learning in a non-native context (e.g., learning to categorize non-native speech sounds). We find that most of these tasks show an appreciable level of split-half reliability, although construct validity was sometimes weak. This provides good evidence for reliability for these tasks, while highlighting possible upper limits on expected effect sizes involving each measure.

Accuracy and cue use in word segmentation for cochlear-implant listeners and normal-hearing listeners presented vocoded speech.

Cochlear-implant (CI) listeners experience signal degradation, which leads to poorer speech perception than normal-hearing (NH) listeners. In the present study, difficulty with word segmentation, the process of perceptually parsing the speech stream into separate words, is considered as a possible contributor to this decrease in performance. CI listeners were compared to a group of NH listeners (presented with unprocessed speech and eight-channel noise-vocoded speech) in their ability to segment phrases with word segmentation ambiguities (e.g., "an iceman" vs "a nice man"). The results showed that CI listeners and NH listeners were worse at segmenting words when hearing processed speech than NH listeners were when presented with unprocessed speech. When viewed at a broad level, all of the groups used cues to word segmentation in similar ways. Detailed analyses, however, indicated that the two processed speech groups weighted top-down knowledge cues to word boundaries more and weighted acoustic cues to word boundaries less relative to NH listeners presented with unprocessed speech.

Individual Differences in Phonetic Plasticity Across Native and Nonnative Contexts.

Purpose Individuals vary in their ability to learn the sound categories of nonnative languages (nonnative phonetic learning) and to adapt to systematic differences, such as accent or talker differences, in the sounds of their native language (native phonetic learning). Difficulties with both native and nonnative learning are well attested in people with speech and language disorders relative to healthy controls, but substantial variability in these skills is also present in the typical population. This study examines whether this individual variability can be organized around a common ability that we label "phonetic plasticity." Method A group of healthy young adult participants (N = 80), who attested they had no history of speech, language, neurological, or hearing deficits, completed two tasks of nonnative phonetic category learning, two tasks of learning to cope with variation in their native language, and seven tasks of other cognitive functions, distributed across two sessions. Performance on these 11 tasks was compared, and exploratory factor analysis was used to assess the extent to which performance on each task was related to the others. Results Performance on both tasks of native learning and an explicit task of nonnative learning patterned together, suggesting that native and nonnative phonetic learning tasks rely on a shared underlying capacity, which is termed "phonetic plasticity." Phonetic plasticity was also associated with vocabulary, comprehension of words in background noise, and, more weakly, working memory. Conclusions Nonnative sound learning and native language speech perception may rely on shared phonetic plasticity. The results suggest that good learners of native language phonetic variation are also good learners of nonnative phonetic contrasts. Supplemental Material https://doi.org/10.23641/asha.16606778.

Action at a distance: Long-distance rate adaptation in event perception.

Viewers' perception of actions is coloured by the context in which those actions are found. An action that seems uncomfortably sudden in one context might seem expeditious in another. In this study, we examined the influence of one type of context: the rate at which an action is being performed. Based on parallel findings in other modalities, we anticipated that viewers would adapt to the rate at which actions were displayed at. Viewers watched a series of actions performed on a touchscreen that could end in actions that were ambiguous to their number (e.g., two separate "tap" actions versus a single "double tap" action) or identity (e.g., a "swipe" action versus a slower "drag"). In Experiment 1, the rate of actions themselves was manipulated; participants used the rate of the actions to distinguish between two similar, related actions. In Experiment 2, the rate of the actions that preceded the ambiguous one was sped up or slowed down. In line with our hypotheses, viewers perceived the identity of those final actions with reference to the rate of the preceding actions. This was true even in Experiment 3, when the action immediately before the ambiguous one was left unmodified. Ambiguous actions embedded in a fast context were seen as relatively long, while ambiguous actions embedded in a slow context were seen as relatively short. This shows that viewers adapt to the rate of actions when perceiving visual events.

Constraints on learning disjunctive, unidimensional auditory and phonetic categories.

Phonetic categories must be learned, but the processes that allow that learning to unfold are still under debate. The current study investigates constraints on the structure of categories that can be learned and whether these constraints are speech-specific. Category structure constraints are a key difference between theories of category learning, which can roughly be divided into instance-based learning (i.e., exemplar only) and abstractionist learning (i.e., at least partly rule-based or prototype-based) theories. Abstractionist theories can relatively easily accommodate constraints on the structure of categories that can be learned, whereas instance-based theories cannot easily include such constraints. The current study included three groups to investigate these possible constraints as well as their speech specificity: English speakers learning German speech categories, German speakers learning German speech categories, and English speakers learning musical instrument categories, with each group including participants who learned different sets of categories. Both speech groups had greater difficulty learning disjunctive categories (ones that require an "or" statement) than nondisjunctive categories, which suggests that instance-based learning alone is insufficient to explain the learning of the participants learning phonetic categories. This fact was true for both novices (English speakers) and experts (German speakers), which implies that expertise with the materials used cannot explain the patterns observed. However, the same was not true for the musical instrument categories, suggesting a degree of domain-specificity in these constraints that cannot be explained through recourse to expertise alone.

Support for context effects on segmentation and segments depends on the context.

Listeners must adapt to differences in speech rate across talkers and situations. Speech rate adaptation effects are strong for adjacent syllables (i.e., proximal syllables). For studies that have assessed adaptation effects on speech rate information more than one syllable removed from a point of ambiguity in speech (i.e., distal syllables), the difference in strength between different types of ambiguity is stark. Studies of word segmentation have shown large shifts in perception as a result of distal rate manipulations, while studies of segmental perception have shown only weak, or even nonexistent, effects. However, no study has standardized methods and materials to study context effects for both types of ambiguity simultaneously. Here, a set of sentences was created that differed as minimally as possible except for whether the sentences were ambiguous to the voicing of a consonant or ambiguous to the location of a word boundary. The sentences were then rate-modified to slow down the distal context speech rate to various extents, dependent on three different definitions of distal context that were adapted from previous experiments, along with a manipulation of proximal context to assess whether proximal effects were comparable across ambiguity types. The results indicate that the definition of distal influenced the extent of distal rate effects strongly for both segments and segmentation. They also establish the presence of distal rate effects on word-final segments for the first time. These results were replicated, with some caveats regarding the perception of individual segments, in an Internet-based sample recruited from Mechanical Turk.

The Electrophysiology of Basic Phrase Building.

A defining trait of linguistic competence is the ability to combine elements into increasingly complex structures to denote, and to comprehend, a potentially infinite number of meanings. Recent magnetoencephalography (MEG) work has investigated these processes by comparing the response to nouns in combinatorial (blue car) and non-combinatorial (rnsh car) contexts. In the current study we extended this paradigm using electroencephalography (EEG) to dissociate the role of semantic content from phonological well-formedness (yerl car). We used event-related potential (ERP) recordings in order to better relate the observed neurophysiological correlates of basic combinatorial operations to prior ERP work on comprehension. We found that nouns in combinatorial contexts (blue car) elicited a greater centro-parietal negativity between 180-400ms, independent of the phonological well-formedness of the context word. We discuss the potential relationship between this 'combinatorial' effect and classic N400 effects. We also report preliminary evidence for an early anterior negative deflection immediately preceding the critical noun in combinatorial contexts, which we tentatively interpret as an electrophysiological reflex of syntactic structure initialization.

Age-Related Differences in Speech Rate Perception Do Not Necessarily Entail Age-Related Differences in Speech Rate Use.

PURPOSE: A new literature has suggested that speech rate can influence the parsing of words quite strongly in speech. The purpose of this study was to investigate differences between younger adults and older adults in the use of context speech rate in word segmentation, given that older adults perceive timing information differently from younger ones. METHOD: Younger (18-25 years) and older (55-65 years) adults performed a sentence transcription task for sentences that varied in speech rate context (i.e., distal speech rate) and a syntactic cue to the presence of a word boundary. RESULTS: There were no differences between younger and older adults in their use of the distal speech rate cue to word segmentation. CONCLUSIONS: The differences previously documented between younger and older adults in their perception of speech rate cues do not necessarily translate to older adults' use of those cues. Older adults' difficulties with compressed speech may arise from problems broader than just speech rate alone.

Prosodic Structure as a Parallel to Musical Structure.

What structural properties do language and music share? Although early speculation identified a wide variety of possibilities, the literature has largely focused on the parallels between musical structure and syntactic structure. Here, we argue that parallels between musical structure and prosodic structure deserve more attention. We review the evidence for a link between musical and prosodic structure and find it to be strong. In fact, certain elements of prosodic structure may provide a parsimonious comparison with musical structure without sacrificing empirical findings related to the parallels between language and music. We then develop several predictions related to such a hypothesis.

Long-term temporal tracking of speech rate affects spoken-word recognition.

Humans unconsciously track a wide array of distributional characteristics in their sensory environment. Recent research in spoken-language processing has demonstrated that the speech rate surrounding a target region within an utterance influences which words, and how many words, listeners hear later in that utterance. On the basis of hypotheses that listeners track timing information in speech over long timescales, we investigated the possibility that the perception of words is sensitive to speech rate over such a timescale (e.g., an extended conversation). Results demonstrated that listeners tracked variation in the overall pace of speech over an extended duration (analogous to that of a conversation that listeners might have outside the lab) and that this global speech rate influenced which words listeners reported hearing. The effects of speech rate became stronger over time. Our findings are consistent with the hypothesis that neural entrainment by speech occurs on multiple timescales, some lasting more than an hour.