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.     

Stimulus dominance and ear dominance in the perception of dichotic voicing contrasts

Two studies were conducted to determine the effect of variations in voice onset time (VOT) on the perception of dichotic stop-consonant-vowel syllables contrasting in the voicing feature. The dichotic stimuli were partially fused, so that only a single response was required. Variations in VOT had a systematic effect on the probability of hearing the fused stimuli as voiced or voiceless. Changing the VOT of a voiceless stimulus had a larger effect than changing the VOT of a voiced stimulus. Unless one of the competing stimuli was close to the category boundary, the perceptual integration of their VOTs seemed to be roughly additive. The relative phase of the periodic portions of the stimuli had an unexpected effect on perception that remains to be explained. A number of subjects showed very strong right-ear dominance in these tests. The range and reliability of the laterality effects obtained, as well as certain other methodological features, make the present tests promising as tools for assessing individual differences in ear dominance.     

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.     

Memory strategies with brain damage

The ability of anterograde amnesics with and without a history of alcoholism and patients with frontal lobe damage to think about memory, memorizing, and remembering was assessed. Alcoholic Korsakoffs' and frontal lobe patients' knowledge and use of memory strategies was deficient when compared with controls whereas nonalcoholic amnesics' was not. The use of the categorization mnemonic was assessed in a verbal learning experiment. Frontal lobe patients failed to spontaneously categorize a categorizable word list when trying to memorize it. Nevertheless, when forced to categorize the list, they benefited from the imposed structure. Nonalcoholic amnesics spontaneously categorized the list and benefited from the resulting organization.     

The nature of speech production impairments in anterior aphasics: an acoustic analysis of voicing in fricative consonants

This study investigated the acoustic characteristics of voicing in English fricative consonants produced by anterior aphasics and the effects of phonetic context on these characteristics. Three patients produced voiced and voiceless fricative-vowel syllables in isolation, following a voiced velar stop, and following a voiceless velar stop. Acoustic analyses were conducted of the amplitude and patterning of glottal excitation, as well as fricative noise duration. Results showed that, although the patients are able to coordinate the articulatory gestures for voicing in fricative consonants, they demonstrated abnormal patterns of glottal excitation in the amplitude measures, owing to weaker amplitudes of glottal excitation in voiced fricatives. Context effects failed to emerge because of dysfluent speech. These results suggest that the locus of the speech production deficit of anterior aphasics is not at the higher stages of phoneme selection or planning but rather in articulatory implementation, one related to laryngeal control.     

Disfluent speech associated with brain damage

The frequency and type of disfluencies in the spontaneous speech of 15 people with Broca's aphasia and right hemiplegia was studied. Two aged-matched control groups (15 nonaphasic stroke patients with left hemiplegia and 15 normals) were also studied. The frequency of disfluencies in the speech of aphasics was three times greater than that in the speech of either control group. However, most of the disfluencies uttered by aphasics were of the types commonly found in speech of normals.     

Extracommunicative functions of language: Verbal interference causes selective categorization impairments

In addition to its communicative functions, language has been argued to have a variety of extracommunicative functions, as assessed by its causal involvement in putatively nonlinguistic tasks. In the present work, I argue that language may be critically involved in the ability of human adults to categorize objects on a specific dimension (e.g., color) while abstracting over other dimensions (e.g., size). This ability is frequently impaired in aphasic patients. The present work demonstrates that normal participants placed under conditions of verbal interference show a pattern of deficits strikingly similar to that of aphasic patients: impaired taxonomic categorization along perceptual dimensions, and preserved thematic categorization. A control experiment using a visuospatial-interference task failed to find this selective pattern of deficits. The present work has implications for understanding the online role of language in normal cognition and supports the claim that language is causally involved in nonverbal cognition.     

Stuttering following brain damage

This paper describes the neurological, language, and speech status of seven brain-damaged patients with symptoms of cortical stuttering. We compare data from our seven patients to data presented on other brain-damaged stutterers, review theories of cortical stuttering's etiology, advance alternative hypotheses about mechanisms underlying such dy sfluencies, and compare cortical stuttering to stuttering in childhood.     

Cluttering after brain damage

On the basis of published cases and of observations made in two patients, a syndrome of acquired cluttering after brain damage in adults is delineated, and a hypothesis is presented regarding the patho-physiology of the disorder.     

Perceptual anomalies in schizophrenia co-occur with selective impairments in the gamma frequency component of midlatency auditory ERPs

This study aimed to establish concordance between phenomenological and psychophysiological indices of sensory gating disturbance in schizophrenia. Perceptually normal and deviant subgroups of schizophrenia (SZ) and healthy comparison (HC) participants were empirically determined on the basis of self-rated Sensory Gating Inventory scores. Contrasts by diagnosis and subgroup classification were conducted on event-related brain potential (ERP) response attenuation to paired auditory stimuli, measured in time (P50 ERP) and frequency (low frequency, 1-20 Hz; gamma band, 20-50 Hz) domains. The SZ sample evidenced significantly less low-frequency response attenuation than did HC but comparable P50 and gamma responses. The low-frequency response, however, appeared insensitive to variation in perceptual experience between SZ subgroups. Conversely, smaller P50 amplitude and weaker gamma response attenuation distinguished deviant SZ (n=17) from normal SZ (n=9) and normal HC (n=29) subgroups. Perceptually normal SZ and normal HC subgroups were statistically equivalent across all comparisons. These findings support hypotheses relating perceptual disturbance in schizophrenia to an early sensory input dysfunction, which is thought to involve gamma-mediated thalamocortical integration of sensory stimuli.     

Relating computer-associated stress to computerphobia

The associations of computer-related stress, somatic complaints, and computerphobia were studied by administering questionnaires covering demographic data, exposure to computer information, computer-related stress, as measured by the Computer Technology Hassles Scale, somatic complaint items of the Hopkins Symptom Checklist, and Rosen, Sears, and Weil's measures of computerphobia: Computer Anxiety Rating Scale, Attitudes Toward Computers Scale, and Computer Thoughts Scale to 109 students. Correlations indicated scores on the Computer Technology Hassles Scale were significantly correlated .35 with somatic complaints, .27 with years used a computer, and .28 with self-rated computer knowledge. The Computer Technology Hassles Scale was not significantly correlated (.18, -.08, and -.05) with the three measures of computerphobia. Computer-related stress appears to be distinct from computerphobia.     

Electroconvulsive treatment of psychotic patients with organic brain damage

It is reported about 2 patients in whom the decision on electroconvulsive therapy was rendered more problematic by proven organic defects of the brain or a seizure disease. In our opinion, the electroconvulsive therapy is, in exceptional cases, also practicable under these conditions after an exact risk-benefit analysis.