Search PubMed⌕ Search

Biomedical subjects

Lori L Holt

Publications and source records attributed to Lori L Holt.

17 recordsLinked to original sources
PubMed2006

Are there interactive processes in speech perception?

Lexical information facilitates speech perception, especially when sounds are ambiguous or degraded. The interactive approach to understanding this effect posits that this facilitation is accomplished through bi-directional flow of information, allowing lexical knowledge to influence pre-lexical processes. Alternative autonomous theories posit feed-forward processing with lexical influence restricted to post-perceptual decision processes. We review evidence supporting the prediction of interactive models that lexical influences can affect pre-lexical mechanisms, triggering compensation, adaptation and retuning of phonological processes generally taken to be pre-lexical. We argue that these and other findings point to interactive processing as a fundamental principle for perception of speech and other modalities.

Humans↗
PubMed2006

Cue weighting in auditory categorization: implications for first and second language acquisition.

The ability to integrate and weight information across dimensions is central to perception and is particularly important for speech categorization. The present experiments investigate cue weighting by training participants to categorize sounds drawn from a two-dimensional acoustic space defined by the center frequency (CF) and modulation frequency (MF) of frequency-modulated sine waves. These dimensions were psychophysically matched to be equally discriminable and, in the first experiment, were equally informative for accurate categorization. Nevertheless, listeners' category responses reflected a bias for use of CF. This bias remained even when the informativeness of CF was decreased by shifting distributions to create more overlap in CF. A reversal of weighting (MF over CF) was obtained when distribution variance was increased for CF. These results demonstrate that even when equally informative and discriminable, acoustic cues are not necessarily equally weighted in categorization; listeners exhibit biases when integrating multiple acoustic dimensions. Moreover, changes in weighting strategies can be affected by changes in input distribution parameters. This methodology provides potential insights into acquisition of speech sound categories, particularly second language categories. One implication is that ineffective cue weighting strategies for phonetic categories may be alleviated by manipulating variance of uninformative dimensions in training stimuli.

Cues↗
PubMed2006

Speech categorization in context: joint effects of nonspeech and speech precursors.

The extent to which context influences speech categorization can inform theories of pre-lexical speech perception. Across three conditions, listeners categorized speech targets preceded by speech context syllables. These syllables were presented as the sole context or paired with nonspeech tone contexts previously shown to affect speech categorization. Listeners' context-dependent categorization across these conditions provides evidence that speech and nonspeech context stimuli jointly influence speech processing. Specifically, when the spectral characteristics of speech and nonspeech context stimuli are mismatched such that they are expected to produce opposing effects on speech categorization the influence of nonspeech contexts may undermine, or even reverse, the expected effect of adjacent speech context. Likewise, when spectrally matched, the cross-class contexts may collaborate to increase effects of context. Similar effects are observed even when natural speech syllables, matched in source to the speech categorization targets, serve as the speech contexts. Results are well-predicted by spectral characteristics of the context stimuli.

Adult↗
PubMed2006

The mean matters: effects of statistically defined nonspeech spectral distributions on speech categorization.

Adjacent speech, and even nonspeech, contexts influence phonetic categorization. Four experiments investigated how preceding sequences of sine-wave tones influence phonetic categorization. This experimental paradigm provides a means of investigating the statistical regularities of acoustic events that influence online speech categorization and, reciprocally, reveals regularities of the sound environment tracked by auditory processing. The tones comprising the sequences were drawn from distributions sampling different acoustic frequencies. Results indicate that whereas the mean of the distributions predicts contrastive shifts in speech categorization, variability of the distributions has little effect. Moreover, speech categorization is influenced by the global mean of the tone sequence, without significant influence of local statistical regularities within the tone sequence. Further arguing that the effect is strongly related to the average spectrum of the sequence, notched noise spectral complements of the tone sequences produce a complementary effect on speech categorization. Lastly, these effects are modulated by the number of tones in the acoustic history and the overall duration of the sequence, but not by the density with which the distribution defining the sequence is sampled. Results are discussed in light of stimulus-specific adaptation to statistical regularity in the acoustic input and a speculative link to talker normalization is postulated.

Acoustic Stimulation↗
PubMed2006

Putting phonetic context effects into context: a commentary on Fowler (2006).

On the basis of a review of the literature and three new experiments, Fowler (2006) concludes that a contrast account for phonetic context effects is not tenable and is inferior to a gestural account. We believe that this conclusion is premature and that it is based on a restricted set of assumptions about a general perceptual account. Here, we briefly address the criticisms of Fowler (2006), with the intent of clarifying what a general auditory and learning approach to speech perception entails.

Cognition↗
PubMed2005

Temporally nonadjacent nonlinguistic sounds affect speech categorization.

Speech perception is an ecologically important example of the highly context-dependent nature of perception; adjacent speech, and even nonspeech, sounds influence how listeners categorize speech. Some theories emphasize linguistic or articulation-based processes in speech-elicited context effects and peripheral (cochlear) auditory perceptual interactions in non-speech-elicited context effects. The present studies challenge this division. Results of three experiments indicate that acoustic histories composed of sine-wave tones drawn from spectral distributions with different mean frequencies robustly affect speech categorization. These context effects were observed even when the acoustic context temporally adjacent to the speech stimulus was held constant and when more than a second of silence or multiple intervening sounds separated the nonlinguistic acoustic context and speech targets. These experiments indicate that speech categorization is sensitive to statistical distributions of spectral information, even if the distributions are composed of nonlinguistic elements. Acoustic context need be neither linguistic nor local to influence speech perception.

Adult↗
PubMed2005

Effects of later-occurring nonlinguistic sounds on speech categorization.

Nonspeech stimuli influence phonetic categorization, but effects observed so far have been limited to precursors' influence on perception of following speech. However, both preceding and following speech affect phonetic categorization. This asymmetry raises questions about whether general auditory processes play a role in context-dependent speech perception. This study tested whether the asymmetry stems from methodological issues or genuine mechanistic limitations. To determine whether and how backward effects of nonspeech context on speech may occur, one experiment examined perception of CVC words with [ga]-[da] series onsets followed by one of two possible embedded tones and one of two possible final consonants. When the tone was separated from the target onset by 100 ms, contrastive effects of tone frequency similar to those of previous studies were observed; however, when the tone was moved closer to the target segment assimilative effects were observed. In another experiment, contrastive effects of a following tone were observed in both CVC words and CV nonwords, although the size of the effects depended on syllable structure. Results are discussed with respect to contrastive mechanisms not speech-specific but operating at a relatively high level, taking into account spectrotemporal patterns occurring over extended periods before and after target events.

Acoustic Stimulation↗
PubMed2005

Incidental categorization of spectrally complex non-invariant auditory stimuli in a computer game task.

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.

Acoustic Stimulation↗
PubMed2005

Perceptual effects of preceding nonspeech rate on temporal properties of speech categories.

The rate of context speech can influence phonetic perception. This study investigated the bounds of rate dependence by observing the influence of nonspeech precursor rate on speech categorization. Three experiments tested the effects of pure-tone precursor presentation rate on the perception of a [ba]-[wa] series defined by duration-varying formant transitions that shared critical temporal and spectral characteristics with the tones. Results showed small but consistent shifts in the stop-continuant boundary distinguishing [ba] and [wa] syllables as a function of the rate of precursor tones, across various manipulations in the amplitude of the tones. The effect of the tone precursors extended to the entire graded structure of the [w] category, as estimated by category goodness judgments. These results suggest a role for durational contrast in rate-dependent speech categorization.

Humans↗
PubMed2005

A critical evaluation of visually moderated phonetic context effects.

Fowler, Brown, and Mann (2000) have reported a visually moderated phonetic context effect in which a video disambiguates an acoustically ambiguous precursor syllable, which, in turn, influences perception of a subsequent syllable. In the present experiments, we explored this finding and the claims that stem from it. Experiment 1 failed to replicate Fowler et al. with novel materials modeled after the original study, but Experiment 2 successfully replicated the effect, using Fowler et al.'s stimulus materials. This discrepancy was investigated in Experiments 3 and 4, which demonstrate that variation in visual information concurrent with the test syllable is sufficient to account for the original results. Fowler et al.'s visually moderated phonetic context effect appears to have been a demonstration of audiovisual interaction between concurrent stimuli, and not an effect whereby preceding visual information elicits changes in the perception of subsequent speech sounds.

Cues↗
PubMed2004

Hemispheric asymmetries in children's perception of nonlinguistic human affective sounds.

In the present work, we developed a database of nonlinguistic sounds that mirror prosodic characteristics typical of language and thus carry affective information, but do not convey linguistic information. In a dichotic-listening task, we used these novel stimuli as a means of disambiguating the relative contributions of linguistic and affective processing across the hemispheres. This method was applied to both children and adults with the goal of investigating the role of developing cognitive resource capacity on affective processing. Results suggest that children's limited computational resources influence how they process affective information and rule out attentional biases as a factor in children's perceptual asymmetries for nonlinguistic affective sounds. These data further suggest that investigation of perception of nonlinguistic affective sounds is a valuable tool in assessing interhemispheric asymmetries in affective processing, especially in parceling out linguistic contributions to hemispheric differences.

Acoustic Stimulation↗
PubMed2004

Categorization and discrimination of nonspeech sounds: differences between steady-state and rapidly-changing acoustic cues.

Different patterns of performance across vowels and consonants in tests of categorization and discrimination indicate that vowels tend to be perceived more continuously, or less categorically, than consonants. The present experiments examined whether analogous differences in perception would arise in nonspeech sounds that share critical transient acoustic cues of consonants and steady-state spectral cues of simplified synthetic vowels. Listeners were trained to categorize novel nonspeech sounds varying along a continuum defined by a steady-state cue, a rapidly-changing cue, or both cues. Listeners' categorization of stimuli varying on the rapidly changing cue showed a sharp category boundary and posttraining discrimination was well predicted from the assumption of categorical perception. Listeners more accurately discriminated but less accurately categorized steady-state nonspeech stimuli. When listeners categorized stimuli defined by both rapidly-changing and steady-state cues, discrimination performance was accurate and the categorization function exhibited a sharp boundary. These data are similar to those found in experiments with dynamic vowels, which are defined by both steady-state and rapidly-changing acoustic cues. A general account for the speech and nonspeech patterns is proposed based on the supposition that the perceptual trace of rapidly-changing sounds decays faster than the trace of steady-state sounds.

Acoustic Stimulation↗
PubMed2004

Auditory discontinuities interact with categorization: implications for speech perception.

Behavioral experiments with infants, adults, and nonhuman animals converge with neurophysiological findings to suggest that there is a discontinuity in auditory processing of stimulus components differing in onset time by about 20 ms. This discontinuity has been implicated as a basis for boundaries between speech categories distinguished by voice onset time (VOT). Here, it is investigated how this discontinuity interacts with the learning of novel perceptual categories. Adult listeners were trained to categorize nonspeech stimuli that mimicked certain temporal properties of VOT stimuli. One group of listeners learned categories with a boundary coincident with the perceptual discontinuity. Another group learned categories defined such that the perceptual discontinuity fell within a category. Listeners in the latter group required significantly more experience to reach criterion categorization performance. Evidence of interactions between the perceptual discontinuity and the learned categories extended to generalization tests as well. It has been hypothesized that languages make use of perceptual discontinuities to promote distinctiveness among sounds within a language inventory. The present data suggest that discontinuities interact with category learning. As such, "learnability" may play a predictive role in selection of language sound inventories.

Adult↗
PubMed2004

Speech perception.

This chapter focuses on one of the first steps in comprehending spoken language: How do listeners extract the most fundamental linguistic elements-consonants and vowels, or the distinctive features which compose them-from the acoustic signal? We begin by describing three major theoretical perspectives on the perception of speech. Then we review several lines of research that are relevant to distinguishing these perspectives. The research topics surveyed include categorical perception, phonetic context effects, learning of speech and related nonspeech categories, and the relation between speech perception and production. Finally, we describe challenges facing each of the major theoretical perspectives on speech perception.

Humans↗
PubMed2002

Behavioral examinations of the level of auditory processing of speech context effects.

One of the central findings of speech perception is that identical acoustic signals can be perceived as different speech sounds depending on adjacent speech context. Although these phonetic context effects are ubiquitous in speech perception, their neural mechanisms remain largely unknown. The present work presents a review of recent data suggesting that spectral content of speech mediates phonetic context effects and argues that these effects are likely to be governed by general auditory processes. A descriptive framework known as spectral contrast is presented as a means of interpreting these findings. Finally, and most centrally, four behavioral experiments that begin to delineate the level of the auditory system at which interactions among stimulus components occur are described. Two of these experiments investigate the influence of diotic versus dichotic presentation upon two phonetic context effects. Results indicate that context effects remain even when context is presented to the ear contralateral to that of the target syllable. The other two experiments examine the time course of phonetic context effects by manipulating the silent interval between context and target syllables. These studies reveal that phonetic context effects persist for hundreds of milliseconds. Results are interpreted in terms of auditory mechanism with particular attention to the putative link between auditory enhancement and phonetic context effects.

Acoustic Stimulation↗