Search PubMed⌕ Search

Biomedical subjects

A S Bregman

Publications and source records attributed to A S Bregman.

At least 19 recordsLinked to original sources
PubMed1994

Resetting the pitch-analysis system. 2. Role of sudden onsets and offsets in the perception of individual components in a cluster of overlapping tones.

Experiments on young adults studied the effects of suddenness of onset or offset on the discrimination of the order of pitches of individual tones in a 1-s, 4-tone cluster of overlapping pure tones. In experiment 1, the tones, all within a critical band, went on asynchronously. Each rose and decayed linearly in amplitude. Faster onsets, within the range 10 to 640 ms as measured on the first tone, increased the accuracy of the discrimination of the order of onsets, but 10-ms onsets were slightly worse than 40-ms onsets in early sessions. Experiment 2 found similar effects for the abruptness of offsets of tones in clusters whose components came on synchronously but went off asynchronously. Onset order was very much easier to detect than offset order. The auditory system may use neural onset and offset responses to reset itself and carry out new analyses at frequency-by-amplitude points of sudden amplitude change, thereby contributing to auditory scene analysis.

Acoustic Stimulation↗
PubMed1994

Organization in audition by similarity in rate of change: evidence from tracking individual frequency glides in mixtures.

In audition, sound energy is assigned to separate auditory "streams" following principles of organization that closely parallel the visual gestalt principles that guide the perception of distinct forms or objects. Metzger (1934) provided evidence for organization in vision based on similarity in the velocity of moving forms. If two dots approach one another along one spatial dimension, they may appear to cross and continue beyond their meeting point if their velocities differ; otherwise, they usually appear to change direction abruptly and retrace their movements. If an analogous auditory principle exists, with rate of change in frequency substituted for velocity of movement, two frequency glides that sweep through the same frequency range in opposite directions should be able to perceptually cross if their rates of change differ; otherwise, they should usually appear to change direction and retrace the same frequency region. Four experiments provided data in support of this hypothesis, and the results were consistent across experiments with varying stimuli and methods of presentation. When properties of the stimuli favored organization according to a principle of frequency proximity, the effect of a principle of rate similarity was attenuated but still evident.

Acoustic Stimulation↗
PubMed1994

Allocating attention to frequency regions.

Three experiments were conducted to determine whether attention may be allocated to a specific frequency region. On each trial, a frequency cue was presented and was followed by a target tone. The cue indicated the most likely frequency of the forthcoming target about which the listeners were required to make a duration judgment. It was reasoned that if listeners are able to allocate attention to the cued frequency region, then judgments of any characteristic of a tone of the cued frequency should be facilitated relative to tones of different frequencies. Results indicated that duration judgements were made more quickly and accurately when the cue provided accurate frequency information than when it did not. In addition, performance generally declined as the frequency separation between cue and target increased. These effects are interpreted as an indication that listeners may use a frequency cue to allocate attention to a specific frequency region and that, under these conditions, the shape of the attentional focus conforms to a gradient. The possible similarities of covert orienting mechanisms in vision and audition are discussed.

Acoustic Stimulation↗
PubMed1994

Resetting the pitch-analysis system: 1. Effects of rise times of tones in noise backgrounds or of harmonics in a complex tone.

The question of whether sudden increases in the amplitude of pure-tone components would perceptually isolate them from a more complex spectrum was investigated in two experiments. In Experiment 1, a 3.5-sec noise was played as a masker. During the noise, two pure-tone components of different frequencies appeared in succession. Subjects were asked to judge whether the pitch sequence went up or down. The rise time of these components had only a small and inconsistent effect on discrimination. In Experiment 2, the 3.5-sec background signal was a complex tone. The amplitudes of two of its components were incremented in succession. Again, subjects judged whether the pitch pattern went up or down. This time there was a sizable, monotonic effect of the rise time of the increments, with more rapid increments leading to better discrimination. The difference between the two results is interpreted in terms of the auditory system's response to changing and unchanging signals and the role of its "sudden-change" responses in attracting perceptual processing to certain spectral regions.

Adult↗
PubMed1993

The perceptual segregation of simultaneous vowels with harmonic, shifted, or random components.

This experiment was an investigation of the ability of listeners to identify the constituents of double vowels (pairs of synthetic vowels, presented concurrently and binaurally). Three variables were manipulated: (1) the size of the difference in F0 between the constituents (0, 1/2, and 6 semitones); (2) the frequency relations among the sinusoids making up the constituents: harmonic, shifted (spaced equally in frequency but not integer multiples of the F0), and random; and (3) the relationship between the F0 contours imposed on the constituents: steady state, gliding in parallel, or gliding in opposite directions. It was assumed that, in the case of the gliding contours, the harmonics of each vowel would "trace out" their spectral envelope and potentially improve the definition of the formant locations. It was also assumed that the application of different F0 contours would introduce differences in the direction of harmonic movement (common fate), thus aiding the perceptual segregation of the two vowels. The major findings were the following: (1) For harmonic constituents, a difference in F0 leads to improved identification performance. Neither tracing nor common-fate differences add to the effect of pitch differences. (2) For shifted constituents, a difference between the spacing of the constituents also leads to improved performance. Formant tracing and common fate contribute some further improvement. (3) For random constituents, tracing does not contribute, but common fate does.

Adult↗
PubMed1993

An experimental evaluation of three theories of auditory stream segregation.

Three theories of auditory stream segregation were evaluated. In two-part trials, subjects heard an induction sequence, whose effects upon an immediately subsequent test sequence were measured. The rhythm and total duration of Induction Sequence tones were varied in two experiments. The similarity between induction and test sequences aided segregation, but rhythmic predictability and longer tone durations did not. Frequency alternation during the induction sequence was not necessary to induce segregation in the test sequence. Furthermore, peripheral processes inadequately account for the segregation effects found. The data suggest that, once a distinct percept emerges from an auditory scene, properties derived from the percept (particularly changes) are fed back to control the ongoing analysis of that auditory scene. A neural adaptation to stimuli with constant properties may form part of this analysis.

Adult↗
PubMed1992

The phonetic integration of speech and non-speech sounds: effects of perceived location.

The third-formant (F3) transition of a three-formant /da/ or /ga/ syllable was extracted and replaced by sine-wave transitions that followed the F3 centre frequency. The syllable without the F3 transition (base) was always presented at the left ear, and a /da/ (falling) or /ga/ (rising) sine-wave transition could be presented at either the left, the right, or both ears. The listeners perceived the base as a syllable, and the sine-wave transition as a non-speech whistle, which was lateralized near the left ear, the right ear, or the middle of the head, respectively. In Experiment 1, the sine-wave transition strongly influenced the identity of the syllable only when it was lateralized at the same ear as the base (left ear). Phonetic integration between the base and the transitions became weak, but was not completely eliminated, when the latter was perceived near the middle of the head or at the opposite ear as the base (right ear). The second experiment replicated these findings by using duplex stimuli in which the level of the sine-wave transitions was such that the subjects could not reliably tell whether a /da/ or a /ga/ transition was present at the same ear as the base. This condition was introduced in order to control for the possibility that the subjects could have identified the syallables by associating a rising or falling transition presented at the left ear with a /da/ or /ga/ percept. Alternative suggestions about the relation between speech and non-speech perceptual processes are discussed on the basis of these results.

Acoustic Stimulation↗
PubMed1990

Auditory grouping based on fundamental frequency and formant peak frequency.

The perceptual grouping of a four-tone cycle was studied as a function of differences in fundamental frequencies and the frequencies of spectral peaks. Each tone had a single formant and at least 13 harmonics. In Experiment 1 the formant was created by filtering a flat spectrum and in Experiment 2 by adding harmonics. Fundamental frequency was found to be capable of controlling grouping even when the spectra spanned exactly the same frequency range. Formant peak separation became more effective as the sharpness (amplitude of the peak relative to a spectral pedestal) increased. The effect of each type of acoustic difference depended on the task. Listeners could group the tones by either sort of difference but were also capable of resisting the disruptive effect of the other one. This was taken as evidence for the presence of a schema-based process of perceptual grouping and the relative weakness of primitive segregation.

Adult↗
PubMed1990

Auditory streaming and the continuity illusion.

In the present experiment, auditory stream organization was investigated in the presence of perceptually restored continuity. It was found that auditory streaming processes tend to yield the same perceptual organization independently of the presence or absence of perceptual restoration. Other observations include the dominance of frequency proximity over trajectory as a perceptual organization principle, and the effect of harmonic enrichment on perceptual grouping.

Adult↗
PubMed1990

Fusion of auditory components: effects of the frequency of amplitude modulation.

The fusion of two amplitude-modulated (AM) tones presented simultaneously was studied. Subjects were presented with an AM tone (A) followed by a copy of itself (B) which was accompanied by another AM tone (C). In different experiments, the subjects were asked either to rate how clearly they could hear Tone B in the BC mixture or whether Tone B was present or not. The stronger the fusion of Tones B and C, the harder it was to "hear out" Tone B. It was found that fusion was strongest when Tones B and C were modulated at the same rate; segregation curves were obtained for the degree of mismatch of modulation frequency.

Adult↗
PubMed1989

Role of predictability of sequence in auditory stream segregation.

This study evaluates the role of item predictability in auditory temporal coherence. Thirteen normal-hearing subjects were required to hold together long tonal sequences as single strings of notes. Temporal and spectral predictability of successive notes in a sequence varied as a function of experimental condition. As the frequency separation of the notes in the sequence increased, the subjects found it more difficult to hold the sequence together as a single stream. There was no significant difference in subjects' abilities in performing this task as a function of experimental condition. That is, the predictability of successive notes appeared not to have a role in temporal coherence.

Attention↗
PubMed1989

The effects of auditory streaming on duplex perception.

When a formant transition and the remainder of a syllable are presented to subjects' opposite ears, most subjects perceive two simultaneous sounds: a syllable and a nonspeech chirp. It has been demonstrated that, when the remainder of the syllable (base) is kept unchanged, the identity of the perceived syllable will depend on the kind of transition presented at the opposite ear. This phenomenon, called duplex perception, has been interpreted as the result of the independent operation of two perceptual systems or modes, the phonetic and the auditory mode. In the present experiments, listeners were required to identify and discriminate such duplex syllables. In some conditions, the isolated transition was embedded in a temporal sequence of capturing transitions sent to the same ear. This streaming procedure significantly weakened the contribution of the transition to the perceived phonetic identity of the syllable. It is likely that the sequential integration of the isolated transition into a sequence of capturing transitions affected its fusion with the contralateral base. This finding contrasts with the idea that the auditory and phonetic processes are operating independently of each other. The capturing effect seems to be more consistent with the hypothesis that duplex perception occurs in the presence of conflicting cues for the segregation and the integration of the isolated transition with the base.

Attention↗
PubMed1989

The perceptual segregation of simultaneous auditory signals: pulse train segregation and vowel segregation.

In the experiments reported here, we attempted to find out more about how the auditory system is able to separate two simultaneous harmonic sounds. Previous research (Halikia & Bregman, 1984a, 1984b; Scheffers, 1983a) had indicated that a difference in fundamental frequency (F0) between two simultaneous vowel sounds improves their separate identification. In the present experiments, we looked at the effect of F0s that changed as a function of time. In Experiment 1, pairs of unfiltered or filtered pulse trains were used. Some were steady-state, and others had gliding F0s; different F0 separations were also used. The subjects had to indicate whether they had heard one or two sounds. The results showed that increased F0 differences and gliding F0s facilitated the perceptual separation of simultaneous sounds. In Experiments 2 and 3, simultaneous synthesized vowels were used on frequency contours that were steady-state, gliding in parallel (parallel glides), or gliding in opposite directions (crossing glides). The results showed that crossing glides led to significantly better vowel identification than did steady-state F0s. Also, in certain cases, crossing glides were more effective than parallel glides. The superior effect of the crossing glides could be due to the common frequency modulation of the harmonics within each component of the vowel pair and the consequent decorrelation of the harmonics between the two simultaneous vowels.

Attention↗
PubMed1985

Speech processing ability in alcoholics: a transient impairment and its relation to field dependence.

Alcoholic and non-alcoholic subjects received a test of the ability to identify speech presented against competing speech (Synthetic Sentence Identification) and a test of field dependence (Embedded-Figures Test (EFT). Performance on the speech task (which involved auditory figure-ground differentiation) bore no special relationship to performance on the field-dependence test. However, cross-sectional and longitudinal data suggested that recently-drinking alcoholics are temporarily impaired in their speech-processing ability, recovering this ability after several months of alcohol-abstinence. A relationship between chronicity of alcoholism and field dependence was also observed. The latter relationship, along with findings on auditory tests, were discussed in terms of their relevance to the issue of whether field dependence is an antecedent to or a consequence of alcoholism.

Adult↗