Neuroelectrical correlates of categorical speech perception in adults

Auditory evoked potentials were recorded from the left and right hemispheres of 16 adults during a phoneme identification task. The use of multivariate statistics enabled researchers to identify a number of cortical processes related to categorical speech perception which were common to both hemispheres, as well as several which disinguished between the two hemispheres.     

Conditions on rate normalization in speech perception

Recent work by Summerfield (1975) and others indicates that a listener’s phonemic judgments may vary with the utterance rate of prior context. In particular, if a phonemic distinction is signaled by a temporal cue such as voice onset time (VOT), faster utterance rates tend to shift the phoneme boundary toward smaller values of that cue. The listener thus appears to “normalize” temporal cues according to utterance rate. In the present experiment, subjects identified syllables varying in VOT ([ga]-[k^ha]) following either a slow or a fast version of the phrase “Teddy hears_ _ _ _ .” Typical normalization effects were observed when the precursor phrase and target syllable had formant frequencies corresponding to an adult male vocal tract. However, a reversal of the typical pattern (i.e., a shift in the perceived voicing boundary towardlarger values of VOT with an increased utterance rate) occurred when the precursor and target had formant frequencies corresponding to an adult female vocal tract. Both normalization and “reverse” normalization effects were reduced or eliminated under several conditions of source change between precursor and target. These conditions included a change in fundamental frequency, a change in implied vocal-tract size (as reflected in an upward or downward scaling of formant frequencies), or both.     

An experimental investigation of the modifiability of the temporal structure of spontaneous speech

This study attempted to test the hypothesis that the temporal structure of spontaneous speech is modifiable by reinforcing and punishing pauses, of a certain duration, in an operant conditioning situation. Pause rate was significantly affected by these contingencies: moreover, rate of change was rapid, indicating a prepared association between pausing and such contingencies. This study also attempted to test the hypothesis that there is a class of noncognitive pauses in monologue by punishing UPs to determine if UPs can be eliminated without affecting speech content. Although this manipulation did lead to a decline in pause rate, a significant increase in the amount of filled hesitation, particularly in repetition, resulted. This suggests that the overall amount of hesitation is fixed by the cognitive demands of the task but that a speaker is able to adapt to different interactional contexts by varying the category of hesitation used for cognitive planning.     

The perception of speech rate from the sound-silence patterns of monologues

Two experiments asked whether listeners can judge word rate from a speech signal that has been degraded in various ways. In the first, the rates of spontaneous speech were increased by 42% and further transformed to produce tone-silence sequences. The tonesilence sequences were presented to listeners who judged the rate of each sequence. Results clearly indicated that listeners could differentiate the rates of the tone-silence sequences, suggesting that minimal nonlinguistic information may be sufficient to make grossly accurate estimates of speech rates. In the second study, listeners were presented with speech sequences involving three naturally produced rates (slow, moderate, and fast) in three conditions (clear, frequency-inverted, and tone-silence) such that different listeners participated in the three conditions, but heard all rates in each condition. Listeners in the clear and frequency-inverted conditions distinguished all three rates, but those in the tone-silence condition differentiated only the slow and moderate rates. Contrary to expectation, the gender and extroversion scores of the listeners did not affect their judgments.     

Gender and speech rate in the perception of competence and social attractiveness

The authors' hypotheses were that (a) listeners regard speakers whose global speech rates they judge to be similar to their own as more competent and more socially attractive than speakers whose rates are different from their own and (b) gender influences those perceptions. Participants were 17 male and 28 female listeners; they judged each of 3 male and 3 female speakers in terms of 10 unipolar adjective scales. The authors used 8 of the scales to derive 2 scores describing the extent to which the listener viewed a speaker as competent and socially attractive. The 2 scores were related by trend analyses (a) to the listeners' perceptions of the speakers' speech rates as compared with their own and (b) to comparisons of the actual speech rates of the speakers and listeners. The authors examined trend components of the data by split-plot multiple regression analyses. In general, the results supported both hypotheses. The participants judged speakers with speech rates similar to their own as more competent and socially attractive than speakers with speech rates slower or faster than their own. However, the ratings of competence were significantly influenced by the gender of the listeners, and those of social attractiveness were influenced by the gender of the listeners and the speakers.     

An analysis of speech perception in word deafness

A patient with a rather pure word deafness showed extreme suppression of right ear signals under dichotic conditions, suggesting that speech signals were being processed in the right hemisphere. Systematic errors in the identification and discrimination of natural and synthetic stop consonants further indicated that speech sounds were not being processed in the normal manner. Auditory comprehension improved considerably however, when the range of speech stimuli was limited by contextual constraints. Possible implications for the mechanism of word deafness are discussed.     

Time management: An experimental investigation

Four groups of preservice teachers participating in student teaching seminars were randomly assigned to one of three conditions to test the effectiveness of brief training in time-management techniques. A control group received no training. Experimental Group 2 received basic training in time management, whereas Experimental Group 1 received the same training and, in addition, implemented two specific time- management procedures (written planning and self-monitoring) under the supervision of the experimenters. Significant differences among the groups were observed in the expected direction on measures of promptness in completing tasks during student teaching and on self-ratings of proficiency in time management.     

An investigation of overlap in children's speech

The simultaneous speech of six 4-year-old girls was investigated within three-party conversation. The data reveal two major types of overlap, one providing instances of turn completion projections and the other reflecting tension for the turn at speaking. The data are discussed in terms of the Sacks, Schegloff, and Jefferson (1974) model of conversational interaction.     

Qualitative influences on the perception of movement: An experimental study

One of the most puzzling features of “hyperactivity” in children is the importance of activity itself. Generalized overactivity has not been found to be a valid diagnostic marker. Could some qualitative features of activity be important determinants of the perceived quantity of activity? The analogue study reported here derives from a social-psychological hypothesis that anything that makes a behavior more noticeable or distracting can create an illusion of increased movement. Subjects performed a simple cognitive task while watching short films of adult actors. Two variables were manipulated: (a) The sound level was either loud or quiet, and (b) instructions to subjects were varied so that the behaviors shown were perceived as either appropriate or inappropriate. Results strongly supported the hypothesis. Loudness and contextual inappropriateness made the films more distracting, produced higher ratings of the amount of movement observed, and led to more negative evaluations of the behaviors seen. Implications for assessment and intervention are discussed.     

Functional anatomy of speech perception and speech production: psycholinguistic implications

This paper presents evidence for a new model of the functional anatomy of speech/language (Hickok & Poeppel, 2000) which has, at its core, three central claims: (1) Neural systems supporting the perception of sublexical aspects of speech are essentially bilaterally organized in posterior superior temporal lobe regions; (2) neural systems supporting the production of phonemic aspects of speech comprise a network of predominately left hemisphere systems which includes not only frontal regions, but also superior temporal lobe regions; and (3) the neural systems supporting speech perception and production partially overlap in left superior temporal lobe. This model, which postulates nonidentical but partially overlapping systems involved in the perception and production of speech, explains why psycho- and neurolinguistic evidence is mixed regarding the question of whether input and output phonological systems involve a common network or distinct networks.     

The effect of discrimination training on speech perception: Noncategorical perception

Three subjects were given extensive practice in discriminating syllables which differed in voice onset time. For these subjects, there were two major findings. First, discrimination of speech follows normal psychophysical laws: long-onset-time stimuli require larger differences than shorter ones for comparable discrimination. Second, the shape of the discrimination function for experienced subjects is more like a leaning W than an inverted V, the usual shape for naive subjects. The data support a model of speech perception with both an acoustic and a phonetic component. The phonetic component is best characterized as a prototype matching process, with the prototype including information on the simultaneity of formant onset.     

An investigation of the interaural time difference threshold for speech

The interaural time difference threshold for speech has been reported to be approximately 35 μsec (Cherry & Sayers, 1956), a value substantially larger than the 6 ~sec reported for broadband noise signals by other experimenters (e.g., Tobias & Zerlin, 1959). In the two studies just mentioned, however, different subjects and psychoacoustical methods were employed; thus, it is unclear whether larger interaural time differences are needed to lateralize speech signals. The purpose of this experiment, therefore, was to compare lateralization performance for speech and nonspeech stimuli. Interaural time difference thresholds were obtained for speech, speech spectrum noise, speech multiplied noise, and 200-, 500-, and 1,000-Hz sinusoids for the same subjects using a 2 IFC experimental paradigm. Under these conditions, speech and speech-multiplied noise yielded essentially the same interaural time difference thresholds.     

Thinking the voice: neural correlates of voice perception

The human voice is the carrier of speech, but also an "auditory face" that conveys important affective and identity information. Little is known about the neural bases of our abilities to perceive such paralinguistic information in voice. Results from recent neuroimaging studies suggest that the different types of vocal information could be processed in partially dissociated functional pathways, and support a neurocognitive model of voice perception largely similar to that proposed for face perception.