Biomedical subjects

K W Grant

Publications and source records attributed to K W Grant.

8 recordsLinked to original sources

PubMed1991

Single band amplitude envelope cues as an aid to speechreading.

Amplitude envelopes derived from speech have been shown to facilitate speech-reading to varying degrees, depending on how the envelope signals were extracted and presented and on the amount of training given to the subjects. In this study, three parameters related to envelope extraction and presentation were examined using both easy and difficult sentence materials: (1) the bandwidth and centre frequency of the filtered speech signal used to obtain the envelope; (2) the bandwidth of the envelope signal determined by the lowpass filter cutoff frequency used to "smooth" the envelope fluctuations; and (3) the carrier signal used to convey the envelope cues. Results for normal hearing subjects following a brief visual and auditory-visual familiarization/training period showed that (1) the envelope derived from wideband speech does not provide the greatest benefit to speechreading when compared to envelopes derived from selected octave bands of speech; (2) as the bandwidth centred around the carrier frequency increased from 12.5 to 1600 Hz, auditory-visual (AV) performance obtained with difficult sentence materials improved, especially for envelopes derived from high-frequency speech energy; (3) envelope bandwidths below 25 Hz resulted in AV scores that were sometimes equal to or worse than speechreading alone; (4) for each filtering condition tested, there was at least one bandwidth and carrier condition that produced AV scores that were significantly greater than speechreading alone; (5) low-frequency carriers were better than high-frequency or wideband carriers for envelopes derived from an octave band of speech centred at 500 Hz; and (6) low-frequency carriers were worse than high-frequency or wideband carriers for envelopes derived from an octave band centred at 3150 Hz. These results suggest that amplitude envelope cues can provide a substantial benefit to speechreading for both easy and difficult sentence materials, but that frequency transposition of these signals to regions remote from their "natural" spectral locations may result in reduced performance.

Adult↗

PubMed1991

Evaluating the articulation index for auditory-visual input.

An investigation of the auditory-visual (AV) articulation index (AI) correction procedure outlined in the ANSI standard [ANSI S3.5-1969 (R1986)] was made by evaluating auditory (A), visual (V), and auditory-visual sentence identification for both wideband speech degraded by additive noise and a variety of bandpass-filtered speech conditions presented in quiet and in noise. When the data for each of the different listening conditions were averaged across talkers and subjects, the procedure outlined in the standard was fairly well supported, although deviations from the predicted AV score were noted for individual subjects as well as individual talkers. For filtered speech signals with AIA less than 0.25, there was a tendency for the standard to underpredict AV scores. Conversely, for signals with AIA greater than 0.25, the standard consistently overpredicted AV scores. Additionally, synergistic effects, where the AIA obtained from the combination of different bandpass-filtered conditions was greater than the sum of the individual AIA's, were observed for all nonadjacent filter-band combinations (e.g., the addition of a low-pass band with a 630-Hz cutoff and a high-pass band with a 3150-Hz cutoff). These latter deviations from the standard violate the basic assumption of additivity stated by Articulation Theory, but are consistent with earlier reports by Pollack [I. Pollack, J. Acoust. Soc. Am. 20, 259-266 (1948)], Licklider [J. C. R. Licklider, Psychology: A Study of a Science, Vol. 1, edited by S. Koch (McGraw-Hill, New York, 1959), pp. 41-144], and Kryter [K. D. Kryter, J. Acoust. Soc. Am. 32, 547-556 (1960)].

Adult↗

PubMed1990

Studies in auditory timing: 1. Simple patterns.

Listeners' accuracy in discriminating one temporal pattern from another was measured in three psychophysical experiments. When the standard pattern consisted of equally timed (isochronic) brief tones, whose interonset intervals (IOIs) were 50, 100, or 200 msec, the accuracy in detecting an asynchrony or deviation of one tone in the sequence was about as would be predicted from older research on the discrimination of single time intervals (6%-8% at an IOI of 200 msec, 11%-12% at an IOI of 100 msec, and almost 20% at an IOI of 50 msec). In a series of 6 or 10 tones, this accuracy was independent of position of delay for IOIs of 100 and 200 msec. At 50 msec, however, accuracy depended on position, being worst in initial positions and best in final positions. When one tone in a series of six has a frequency different from the others, there is some evidence (at IOI = 200 msec) that interval discrimination is relatively poorer for the tone with the different frequency. Similarly, even if all tones have the same frequency but one interval in the series is made twice as long as the others, temporal discrimination is poorer for the tones bordering the longer interval, although this result is dependent on tempo or IOI. Results with these temporally more complex patterns may be interpreted in part by applying the relative Weber ratio to the intervals before and after the delayed tone. Alternatively, these experiments may show the influence of accent on the temporal discrimination of individual tones.

Adult↗

PubMed1987

Frequency modulation detection by normally hearing and profoundly hearing-impaired listeners.

The ability of normally hearing and profoundly hearing-impaired subjects to detect frequency modulations was evaluated under conditions where the amplitudes of the test signals were either constant (CA), sinusoidally modulated (SAM), or randomly modulated (RAM). Results for hearing-impaired listeners showed larger frequency difference limens (DLFM) than those for normally hearing listeners for all test frequencies (100 to 1000 Hz) and for all amplitude conditions. For both normal-hearing and hearing-impaired subjects, the DFLM was smallest for the constant amplitude condition and largest for the randomly modulated condition. Differences in performance between the RAM and CA conditions were generally much larger for impaired listeners than for normally hearing listeners. With random amplitude modulation, DLFMs for the hearing-impaired subjects were approximately 36 times larger than those for normally hearing subjects.

Adult↗

PubMed1987

Identification of intonation contours by normally hearing and profoundly hearing-impaired listeners.

Fundamental frequency (F0) information extracted from low-pass-filtered speech and aurally presented as frequency-modulated sinusoids can greatly improve speechreading performance [Grant et al., J. Acoust. Soc. Am. 77, 671-677 (1985)]. To use this source of information, listeners must be able to detect the presence or absence of F0 (i.e., voicing), discriminate changes in frequency, and make judgments about the linguistic meaning of perceived variations in F0. In the present study, normally hearing and hearing-impaired subjects were required to locate the stressed peak of an intonation contour according to the extent of frequency transition at the primary peak. The results showed that listeners with profound hearing impairments required frequency transitions that were 1.5-6 times greater than those required by normally hearing subjects. These results were consistent with the subjects' identification performance for intonation and stress patterns in natural speech, and suggest that natural variations in F0 may be too small for some impaired listeners to perceive and follow accurately.

Auditory Threshold↗

PubMed1987

Encoding voice pitch for profoundly hearing-impaired listeners.

The ability of five profoundly hearing-impaired subjects to "track" connected speech and to make judgments about the intonation and stress in spoken sentences was evaluated under a variety of auditory-visual conditions. These included speechreading alone, speechreading plus speech (low-pass filtered at 4 kHz), and speechreading plus a tone whose frequency, intensity, and temporal characteristics were matched to the speaker's fundamental frequency (F0). In addition, several frequency transfer functions were applied to the normal F0 range resulting in new ranges that were both transposed and expanded with respect to the original F0 range. Three of the five subjects were able to use several of the tonal representations of F0 nearly as well as speech to improve their speechreading rates and to make appropriate judgments concerning sentence intonation and stress. The remaining two subjects greatly improved their identification performance for intonation and stress patterns when expanded F0 signals were presented alone (i.e., without speechreading), but had difficulty integrating visual and auditory information at the connected discourse level, despite intensive training in the connected discourse tracking procedure lasting from 27.8-33.8 h.

Adult↗

PubMed1986

The transmission of prosodic information via an electrotactile speechreading aid.

Variations in voice fundamental frequency were extracted from naturally produced speech samples and transmitted to an electrocutaneous display consisting of 10 electrodes arranged in a linear array along the forearm. Changes in fundamental frequency were encoded as changes in stimulus location. Speechreading performance, with and without the electrocutaneous aid, was examined for both sentence and connected discourse materials with one profoundly hearing-impaired listener and one normally hearing listener whose hearing was masked. After 20 hours of speechreading training in connected discourse tracking procedure, both subjects showed higher tracking rates and faster learning rates with the aid than without the aid. Results from closed-set sentence-identification tests showed that patterns of intonation, stress, and phrase structure, which are not easily speechread, are readily available with the aid.

Adult↗

PubMed1985

The contribution of fundamental frequency, amplitude envelope, and voicing duration cues to speechreading in normal-hearing subjects.

The ability to combine speechreading (i.e., lipreading) with prosodic information extracted from the low-frequency regions of speech was evaluated with three normally hearing subjects. The subjects were tested in a connected discourse tracking procedure which measures the rate at which spoken text can be repeated back without any errors. Receptive conditions included speechreading alone (SA), speechreading plus amplitude envelope cues (AM), speechreading plus fundamental frequency cues (FM), and speechreading plus intensity-modulated fundamental frequency cues (AM + FM). In a second experiment, one subject was further tested in a speechreading plus voicing duration cue condition (DUR). Speechreading performance was best in the AM + FM condition (83.6 words per minute,) and worst in the SA condition (41.1 words per minute). Tracking levels in the AM, FM, and DUR conditions were 73.7, 73.6, and 65.4 words per minute, respectively. The average tracking rate obtained when subjects were allowed to listen to the talker's normal (unfiltered) speech (NS condition) was 108.3 words per minute. These results demonstrate that speechreaders can use information related to the rhythm, stress, and intonation patterns of speech to improve their speechreading performance.

Adult↗