Acoustic feature analysis in the perception of voicing contrasts

Various types of acoustic cues have been shown to signal voicing contrasts in initial prestressed stop consonants. Two of the most important of these cues are the time interval between the release burst and the onset of voicing (voice onset time) and the duration of voiced transitions. In the present experiment, a selective adaptation procedure was used to investigate possible feature extraction mechanisms which underlie the perception of voicing. Subjects first identified either of two series of test stimuli, [ba-p^ha) or [ga-k^ha]. Next they listened to repeated presentations of an adapting stimulus and then again identified the original test series. Adapting stimuli having the same value of voice onset time but different voiced transition durations produced differential (and sometimes opposite) effects on the identification of the test stimuli. In every case, the adapting stimulus with the greater duration of voiced transitions led to larger reduction in voiced responses or to a smaller increase in voiceless responses. These results are incompatible with models of voicing perception based strictly on detectors for voice onset time. The results also suggest that the adaptation effect occurs at a point in the system prior to the actual phonetic decision.     

Speech perception development in children with dyslexia

Several studies have indicated that dyslexics show a deficit in speech perception (SP). The main purpose of this research is to determine the development of SP in dyslexics and normal readers paired by grades from 2nd to 6th grade of primary school and to know whether the phonetic contrasts that are relevant for SP change during development, taking into account the individual differences. The achievement of both groups was compared in the phonetic tasks: voicing contrast, place of articulation contrast and manner of articulation contrast. The results showed that the dyslexic performed poorer than the normal readers in SP. In place of articulation contrast, the developmental pattern is similar in both groups but not in voicing and manner of articulation. Manner of articulation has more influence on SP, and its development is higher than the other contrast tasks in both groups.     

Identification of time-compressed sentential stimuli by good vs poor readers

Ability of eight good and eight poor readers (in Grade 1, ages ranging from 6.7 to 7.4 yr.) to discriminate phonemic contrasts presented in 50% time-compressed sentential stimuli (Subtest 13 of the Carrow-Auditory Visual Abilities Test) was measured. Good readers exhibited a significantly higher over-all mean performance than poor readers on the time-compressed task. Effects of time-compression on the perception of manner, place, voicing and frequency contrasts showed a similar pattern of errors for both groups of readers. Implications of the effects of auditory discrimination on reading abilities are discussed.     

Tracking the time course of phonetic cue integration during spoken word recognition

Speech perception requires listeners to integrate multiple cues that each contribute to judgments about a phonetic category. Classic studies of trading relations assessed the weights attached to each cue but did not explore the time course of cue integration. Here, we provide the first direct evidence that asynchronous cues to voicing (/b/ vs. /p/) and manner (/b/ vs. /w/) contrasts become available to the listener at different times during spoken word recognition. Using the visual world paradigm, we show that the probability of eye movements to pictures of target and of competitor objects diverge at different points in time after the onset of the target word. These points of divergence correspond to the availability of early (voice onset time or formant transition slope) and late (vowel length) cues to voicing and manner contrasts. These results support a model of cue integration in which phonetic cues are used for lexical access as soon as they are available.     

Some effects of laboratory training on identification and discrimination of voicing contrasts in stop consonants

For many years there has been a consensus that early linguistic experience exerts a profound and often permanent effect on the perceptual abilities underlying the identification and discrimination of stop consonants. It has also been concluded that selective modification of the perception of stop consonants cannot be accomplished easily and quickly in the laboratory with simple discrimination training techniques. In the present article we report the results of three experiments that examined the perception of a three-way voicing contrast by naive monolingual speakers of English. Laboratory training procedures were implemented with a small computer in a real-time environment to examine the perception of voiced, voiceless unaspirated, and voiceless aspirated stops differing in voice onset time. Three perceptual categories were present for most subjects after only a few minutes of exposure to the novel contrast. Subsequent perceptual tests revealed reliable and consistent labeling and categorical-like discrimination functions for all three voicing categories, even though one of the contrasts is not phonologically distinctive in English. The present results demonstrate that the perceptual mechanisms used by adults in categorizing stop consonants can be modified easily with simple laboratory techniques in a short period of time.     

Categorical perception for voicing contrasts in normal and lead-treated rhesus monkeys: electrophysiological indices

Categorical perception of voicing contrasts was evaluated in rhesus monkeys. The monkeys had been chronically exposed to subclinical levels of lead either from conception to birth, or for approximately 6 months postnatally beginning at birth, or were never exposed to lead. Auditory evoked responses were recorded at 1 year of age from scalp electrodes placed over the left and right hemispheres during stimulus presentation. A late component of the brain responses recorded from the right temporal region of all monkeys discriminated between stimuli in a categorical manner. This pattern of responses was noted to be similar to that previously reported for humans. Categorical discriminations were also noted earlier in the waveforms for control monkeys and for monkeys exposed to lead prenatally, although this discrimination pattern shifted to the left hemisphere of the latter group. No such effects were noted for monkeys exposed to lead postnatally. These results suggest that the neurocortical mechanisms associated with categorical perception for voicing information may be similar across human and nonhuman primates. However, early exposure to lead appears to alter these processes.     

Noise on, voicing off: Speech perception deficits in children with specific language impairment

Speech perception of four phonetic categories (voicing, place, manner, and nasality) was investigated in children with specific language impairment (SLI) (n = 20) and age-matched controls (n = 19) in quiet and various noise conditions using an AXB two-alternative forced-choice paradigm. Children with SLI exhibited robust speech perception deficits in silence, stationary noise, and amplitude-modulated noise. Comparable deficits were obtained for fast, intermediate, and slow modulation rates, and this speaks against the various temporal processing accounts of SLI. Children with SLI exhibited normal “masking release” effects (i.e., better performance in fluctuating noise than in stationary noise), again suggesting relatively spared spectral and temporal auditory resolution. In terms of phonetic categories, voicing was more affected than place, manner, or nasality. The specific nature of this voicing deficit is hard to explain with general processing impairments in attention or memory. Finally, speech perception in noise correlated with an oral language component but not with either a memory or IQ component, and it accounted for unique variance beyond IQ and low-level auditory perception. In sum, poor speech perception seems to be one of the primary deficits in children with SLI that might explain poor phonological development, impaired word production, and poor word comprehension.     

Phonetic disintegration in aphasia: Acoustic analysis of spectral characteristics for place of articulation

In this study, we attempted to determine whether phonetic disintegration of speech in Broca's aphasia affects the spectral characteristics of speech sounds as has been shown for the temporal characteristics of speech. To this end, we investigated the production of place of articulation in Broca's aphasics. Acoustic analysis of the spectral characteristics for stop consonants were conducted. Results indicated that the static aspects of speech production were preserved, as Broca's aphasics seemed to be able to reach the articulatory configuration for the appropriate place of articulation. However, the dynamic aspects of speech production seemed to be impaired, as their productions reflected problems with the source characteristics of speech sounds and with the integration of articulatory movements in the vocal tract. Listener perceptions of the aphasics' productions were compared with acoustic analyses for these same productions. The two measures were related; that is, the spectral characteristics of the utterances provided salient cues for place of articulation perception. An analysis of the occurrences of errors along the dimensions of voicing and place showed that aphasics rarely produce utterances containing both voice and place substitutions.     

Measuring the difference limen for identification of order of onset for complex auditory stimuli

The approximately 20-msec perceptual threshold for identifying order of onset for components of auditory stimuli has been considered both as a possible factor contributing to the perception of voicing contrasts in speech and as no more than a methodological artifact. In the present research, we investigate the identification of the temporal order of onset of spectral components in terms of the first of a sequence of thresholds for complex stimuli (modeled after consonant-vowel [CV] syllables) that vary in degree of onset. The results provide clear evidence that the difference limen (DL) for discriminating differences in onset time follows predictions based on a fixed perceptual threshold or limit at relatively short onset differences. Furthermore, the DL seems to be a function of context coding of stimulus information, with both the DL and absolute threshold probably reflecting limits on the effective perception and coding of the short-term stimulus spectrum.     

Expressing gratitude to a partner leads to more relationship maintenance behavior

We proposed that expressing gratitude would increase positive perception of a relationship partner, thereby increasing comfort in expressing relationship concerns, which is a form of relationship maintenance. Study 1 (n = 159) showed a relationship between naturally occurring expressions of gratitude and comfort in voicing relationship concerns. Study 2 (n = 178) provided longitudinal evidence for direction of effects because Time 1 gratitude expression predicted Time 2 comfort in voicing relationship concerns, controlling for baseline comfort in voicing relationship concerns. Study 3 (n = 225) showed that expressing gratitude to a friend did increase voicing relationship concerns, compared with positive thought and neutral control conditions. In Study 4 (n = 74), we explored the mechanism through a longitudinal, experimental design and found that participants assigned to express gratitude reported higher comfort voicing concerns and more positive perception of partner than did control participants. Moreover, positive perception of partner mediated the relationship between condition and comfort in voicing relationship concerns.     

The fragile nature of the speech-perception deficit in dyslexia: natural vs synthetic speech

A number of studies reported that developmental dyslexics are impaired in speech perception, especially for speech signals consisting of rapid auditory transitions. These studies mostly made use of a categorical-perception task with synthetic-speech samples. In this study, we show that deficits in the perception of synthetic speech do not generalise to the perception of more naturally sounding speech, even if the same experimental paradigm is used. This contrasts with the assumption that dyslexics are impaired in the perception of rapid auditory transitions.     

Analysis of voice impairment in aphasia after stroke-underlying neuroanatomical substrates

Phonation is a fundamental feature of human communication. Control of phonation in the context of speech-language disturbances has traditionally been considered a characteristic of lesions to subcortical structures and pathways. Evidence suggests however, that cortical lesions may also implicate phonation. We carried out acoustic and perceptual analyses of the phonation of /a/ in 60 males with aphasia (20 Wernicke's, 20 Broca's, 20 subcortical aphasia) and 20 males matched in age with no neurological or speech-language disturbances. All groups with aphasia were significantly more impaired on the majority of acoustic and perceptual measures as compared with the control speakers. Within the subjects with aphasia, subjects with subcortical aphasia were more impaired on most measures compared to subjects with Broca's aphasia, and they, in turn, more impaired than those with Wernicke's aphasia. Lesions in regions involved in sound production-perception result in dysfunction of the entire neurocognitive system of articulation-phonological language processing.     

Right hemisphere EEG sensitivity to speech

Recent speech perception work with normals and aphasics suggests that the right hemisphere may be more adept than the left at making the voicing discrimination, and the reverse for place of articulation. We examined this right hemisphere voicing effect with natural speech stimuli: stop consonants in pre-, mid-, and postvocalic contexts. Using a neuroelectric event-related potential paradigm, we found numerous effects indicating bilateral components reflecting the voicing and place contrast and unique right hemisphere discrimination of both voicing and place of articulation.     

Cerebral hemispheric involvement in the acquisition of new phonetic categories

This study was concerned with the involvement of the cerebral hemispheres in the acquisition of perceptual skill with novel speech sounds. Two groups of eight subjects rated on three occasions the dissimilarity of pairs of Mandarin Chinese speech sounds varying on voicing and aspiration, presented to the left or right ear with contralateral noise. The experimental group received listening experience with long passages of Mandarin containing the target sounds. Multidimensional scaling analysis of dissimilarity ratings indicated that listening experience leads to increased perceptual differentiation of phonetic categories drawn from a language unfamiliar to the listener. This improvement occurred sooner with presentation of the target sounds to the right hemisphere than to the left if the phonological contrast was along the voicing dimension. Improvement in the perception of stimuli varying on aspiration occurred in right ear presentations only. This finding supports the position that speech perception mechanisms at the feature level may be distributed asymmetrically across the hemispheres.     

A modern assessment of the basic forms of aphasia

A brief survey of the field of aphasia is presented. Many of the facts described in the neurological classics remain valid, but the interpretation of these facts must be altered. The basic principles of aphasia are reassessed in the light of neuropsychology. Neuropsychological analysis shows sensory (acoustico-gnostic) aphasia to be based upon an impairment in phonemic hearing. Motor aphasia breaks down into afferent (kinesthetic) and efferent (kinetic) aphasia. The former is based upon an impaired kinesthetic input into the speech functions, which results in a special type of oral apraxia. Efferent (kinetic) aphasia is based upon a breakdown in the kinetic organization of speech motor acts. Nominative (amnestic) aphasia consists of a number of forms, each based on either a weakness of visual or auditory analysis or difficulty in selection between evoked memory traces. “Transcortical motor aphasia” proves to be either perseverative aphasia, i.e., aphasia in which the dynamics of plasticity are impaired, or the result of the impairment of internal speech. The basic defect underlying “conduction” aphasia is beginning to be understood as a weakened acoustico-gnostic function or difficulties in retarding sideline associations.     

Some properties of linguistic feature detectors

A series of experiments, using a selective adaptation procedure, investigated some of the properties of the linguistic feature detectors that mediate the perception of the voiced and voiceless stop consonants. The first experiment showed that these detectors are centrally rather than peripherally located, in that monotic presentation of the adapting stimulus and test stimuli to different ears resulted in large and reliable shifts in the locus of the phonetic boundary. The second experiment revealed that the detectors are part of the specialized speech processor, inasmuch as adaptation of a voicing detector (as measured by a shift in the phonetic boundary) occurred only when the voicing information was presented in a speech context. In the third experiment, the detector mediating perception of the voiced stops was shown to be more resistant to adaptation than the detector mediating perception of the voiceless stops.     

Interruption of phonological coding in conduction aphasia

A case study of conduction aphasia, investigating single word repetition, phonological coding, and short-term memory, is reported. Evidence from intact adults suggests that repetition can occur through either a lexical route or a direct auditory-articulatory link. For this conduction aphasic, E.A., the direct link was impaired, although the lexical route could be used to produce accurate single word repetition. Several experiments demonstrated a significant impairment in the generation and maintenance of an abstract phonological code. The consequences of a disruption of phonological coding on speech perception and on verbal short-term memory are discussed.     

Perception Abilities of L1 Cypriot Greek Listeners - Types of Errors Involving Plosive Consonants in L2 English

This paper investigates the difficulties adult second language (L2) users of English encounter with plosive consonants in the L2. It presents the results of a task examining the acquisition of plosive voicing contrasts by college students with Cypriot Greek (CG) linguistic background. The task focused on the types of errors involving plosive consonants indicating that performance was significantly better in the voiceless plosive category. Participants were able to perceive voiced plosives but they treated such instances as a /nasal + voiced plosive/ sequence. Therefore, the question raised concerns different phonological contrasts realised through similar phonetic cues. The patterns observed suggested that this gap between phonetic cues and phonological contrast might explain why CG users have difficulties perceiving voiced English plosives. In this context, voice onset time (VOT) differences between the L1 and L2 are of crucial importance. In English, voiced plosives are characterised by short lag VOT while their voiceless counterparts fall within the long lag VOT continuum. The same phonetic contrast is used in CG to differentiate between single and geminate voiceless plosives. The results are discussed in relation to the frameworks of second language phonology and speech perception suggesting that the difficulties faced by the L2 listeners support the operation of a phonetic-phonological challenge.     

Extending formant transitions may not improve aphasics'' perception of stop consonant place of articulation

Synthetic speech stimuli were used to investigate whether aphasics' ability to perceive stop consonant place of articulation was enhanced by the extension of initial formant transitions in CV syllables. Phoneme identification and discrimination tests were administered to 12 aphasic patients, 5 fluent and 7 nonfluent. There were no significant differences in performance due to the extended transitions, and no systematic pattern of performance due to aphasia type. In both groups, discrimination was generally high and significantly better than identification, demonstrating that auditory capacity was retained, while phonetic perception was impaired; this result is consistent with repeated demonstrations that auditory and phonetic processes may be dissociated in normal listeners. Moreover, significant rank order correlations between performances on the Token Test and on both perceptual tasks suggest that impairment on these tests may reflect a general cognitive rather than a language-specific deficit.     

The perception of stop consonants by children

Kindergarten and second-grade children's perception of voicing distinctions among the stop consonants was investigated by assessing their ability to identify and discriminate a series of synthetic speech stimuli varying in voice onset time (VOT). Perception of these sounds was found to be nearly categorical. No differences between the two age groups in either identification or discrimination performance were found; furthermore, the children's performance was comparable to adult performance in other studies using these stimuli. When considered in the context of data on the perception of VOT by infants as well as adults, the results suggest that the differential discriminability of stimuli along the VOT continuum has a biological basis.