Search PubMed⌕ Search

Biomedical subjects

C R Mason

Publications and source records attributed to C R Mason.

29 records · Page 2Linked to original sources
PubMed1989

Roving-level tone-in-noise detection.

The detectability of tones, or of intensity increments to tones, in bands of random noise was measured for conditions in which the overall level was fixed or was randomly roved from interval to interval of every experimental trial. The purpose of the within-trial rove was to limit the usefulness of a detection strategy based on overall level or level within a single "critical band." At "supracritical" bandwidths, the functions relating masked threshold to noise bandwidth for the roved conditions were similar to those obtained when no rove was employed. At "subcritical" bandwidths, thresholds were higher in some roved conditions, but, for the largest rove, were still lower than would be predicted from arguments based purely on level detection--with one exception. A comparison of observer performance relative to the statistical limits imposed by the roving-level procedure indicated that the traditional critical-band energy-detector model could not account for the results, which are attributed to discrimination based on spectral shape or on waveshape.

Adult↗
PubMed1988

Evidence for sensory-trace comparisons in spectral shape discrimination.

The ability of experienced observers to discriminate changes in the shapes of complex sound spectra was studied for three conditions. In one condition, the reference spectrum or "background" was fixed in spectral shape across each block of trials; in a second condition, the reference spectrum differed in spectral shape from trial to trial within each block of trials but was the same for the two presentations within a trial; and, in a third condition, the reference spectrum differed in spectral shape on every stimulus presentation. The variation in the reference spectrum was a random perturbation in the amplitudes of the tonal components comprising the complex sounds. The signal was an intensity increment to the center component (1000 Hz) of the complex and was present in one interval of each two-interval, two-alternative, forced-choice trial. The principal experimental manipulations were the degree of amplitude perturbation of the reference spectrum and the interval of time between the two stimulus presentations of each trial (interstimulus interval, ISI). The theory proposed by Durlach and Braida [J. Acoust. Soc. Am. 46, 372-383 (1969)] describing memory processes involved in the perception of sound intensity was used to explain the experimental results. As that theory was applied in this study, only the condition in which the stimuli were perturbed between trials showed evidence for comparisons based on "sensory traces," while the conditions in which the stimuli were fixed or were perturbed within trials were best explained by comparisons based on judgments relative to the stimulus context.

Acoustic Stimulation↗
PubMed1987

Level discrimination as a function of level for tones from 0.25 to 16 kHz.

Difference limens for level (delta L in dB = 20 log [(p + delta p)/p], where p is pressure) were measured as a function of level for tones at 0.25, 0.5, 1, 2, 4, 8, 10, 12, 14, and 16 kHz. At each frequency, test levels encompassed the range from near threshold to 95 dB SPL in steps of 10 dB or smaller. The stimulus duration was 500 ms and the interstimulus interval was 250 ms. An adaptive two-alternative forced-choice procedure with feedback was used. Results for six normal listeners show individual differences among listeners, but the general trends seen in the average data clearly are present in the individual data and show the following. First, the delta Ls at all but the highest frequencies are generally smaller at high levels than at low levels. Second, the delta Ls at equal SPLs are largely independent of frequency up to about 4 kHz, but increase with frequency above 4 kHz. Third, at 8 and 10 kHz, the delta Ls are clearly nonmonotonic functions of level, showing consistent deterioration in the mid-level delta Ls relative to the low- and high-level delta Ls. The present data are discussed qualitatively in terms of current models of level discrimination.

Acoustic Stimulation↗
PubMed1986

Auditory profile analysis of irregular sound spectra.

The discrimination of changes in the shapes of sound spectra is reported. The change was always an intensity increment to the 948-Hz component of a multitone complex. First, the ability of naive listeners to learn to discriminate a change in a "regular" background or reference spectrum (equal-level tones equally spaced in logarithmic frequency) was measured as a function of the number of trials. On the average, threshold improved about 10 dB over 3000 trials, with about 50% of the decrease in threshold occurring during the first 750 trials. In a subsequent series of experiments, the overall pattern of spectral shape of the background was varied randomly. Two kinds of perturbations in spectral shape were employed: Randomly choosing the frequencies of the reference spectra and randomly choosing the amplitudes of the components of the reference spectra. The experimental manipulations involved fixing the random spectra across a block of trials, varying the reference spectra from interval to interval of each trial, and providing extensive practice in discriminating specific randomly perturbed reference spectra. The results of the spectrum-learning and random perturbation experiments provide insight into the roles of critical band filtering, sensory variability, and short-term and long-term memory representations in auditory profile analysis. Further, the appropriateness of the generalization of a simple energy detection model is discussed.

Acoustic Stimulation↗
PubMed1985

One method for assessing the effectiveness of fast brushing.

The purposes of this study were to determine if fast brushing of the skin overlying a muscle is effective in increasing the sensitivity of the stretch reflex of that muscle and to detect the optimal rate and duration of brushing to elicit this effect in healthy adults. The stretch sensitivity of the right lateral gastrocnemius muscle was measured by EMG activity and force produced by the abrupt tap of the Achilles tendon before and after fast brushing. Peak-to-peak EMG and force from 10 taps were established. Eight different conditions (two control and six experimental brushing) were applied to 10 healthy adult subjects (age range, 30 to 46 years). The experimental conditions included rotary brushing at 5 Hz, 180 Hz, or 360 Hz for 5 seconds or at 5 Hz, 180 Hz, or 360 Hz for 30 seconds. Postbrushing taps began 30 seconds after the brush was turned off and continued every 5 minutes for 30 minutes. This method of fast brushing did not increase the stretch sensitivity of the muscle in healthy adults. Possible factors influencing the results of the study and recommendations for future studies are presented.

Achilles Tendon↗
PubMed1985

Auditory profile analysis: frequency, phase, and Weber's law.

This paper reports three separate experiments on different aspects of performance in auditory profile analysis. The first experiment deals with the effects of the frequency and position of an increment in a single component of a multitonal complex. The general results indicate that detection of the signal is easier for components in the mid-frequency range (around 1000 Hz) independent of signal position within the complex. The second experiment investigates the effects of relative phase of the individual components of the complex. Regardless of the number of components, our results indicate that phase has very little effect, even when different phases are selected for each presentation. The third experiment compares the detection of an increment in intensity of a single component, the traditional Weber fraction experiment, and conditions where additional components are present, a profile experiment. The detection of the increment is measured as a function of the level of the standard. The single-tone condition shows the usual near miss to Weber's law whereas the multitone condition does not. In addition, threshold for the increment is better for the multitone condition than for the single tone condition for levels of the standard up to 70 dB SPL. This last result is investigated for ten observers, five of whom were experienced in profile tasks and five of whom were not. Using a low level standard, the five experienced observers replicate the results described above. The inexperienced observers show the opposite result. On average, they are better able to detect the increment in the single-component condition.

Auditory Threshold↗
PubMed1984

Profile analysis and level variation.

This study examines the effects of random level variation, a method used in studies of profile analysis [3-6,14,15]. Presentation levels for a complex of sinusoids are varied randomly on each interval of a two-interval, forced-choice detection task in which subjects are required to detect an increment on one of the sinusoidal components of the complex. Three experiments are reported. The first experiment examines the effect of the range of level variation. The second is concerned with the effects of the median level about which the presentation levels vary. The third experiment is designed to provide a within-trial analysis of the effect of the differences in presentation levels. As the range of level variation is increased, ability to detect the increment decreases. The results indicate that detection performance is best at moderate intensity levels and decreases at lower and higher levels. Finally, the difference in levels within a single trial has little if any effect.

Acoustic Stimulation↗
PubMed1984

Temporal integration of forward masking in listeners having sensorineural hearing loss.

Findings are described from three experiments that were designed to contrast estimates of auditory time and frequency analysis in highly practiced, young adult subjects having sensorineural hearing loss of cochlear origin with subjects having normal hearing. In one experiment, pure-tone detection threshold was measured for two durations of tones. For the hearing-impaired subjects, smaller differences were found between thresholds for the two durations of tones than were found for the normally hearing subjects at test frequencies where the sensitivity loss was greatest. In a subsequent forward masking experiment, masked thresholds were obtained at 3 kHz as a function of masker level at several masker durations. The results indicated that, for the range of values tested, masked probe thresholds changed less as a function of masker duration for the hearing-impaired subjects than for normally hearing subjects. However, forward masking grew as a function of masker level more steeply for the hearing-impaired listeners than for the normally hearing listeners. We believe that this result indicates abnormal temporal processing of sequential sounds. In a third experiment, psychophysical tuning curves were measured in a forward masking procedure for two maskers that differed in duration by approximately an order of magnitude. Again, the hearing-impaired subjects demonstrated less change in forward masking as a function of masker duration than normally hearing subjects. Further, the sharpness of the tuning curves from the hearing-impaired listeners was markedly reduced as compared to normal. It is believed that the results reflect a disruption of the normal temporal and spectral representation of sounds in the hearing-impaired subjects.

Auditory Threshold↗
PubMed1984

Profile analysis: critical bands and duration.

The detection of an increment in the intensity of the central component of a multi-component complex was measured as a function of the frequency spacing of the components and the duration of the presentation. The overall intensity of the complex was randomly varied on each presentation of the stimulus. Curiously, the increment becomes easier to hear as the range and density of the surrounding complex is increased. This increase in range and density is also effective in improving the detectability of the increment when there is no random variation in intensity, i.e., a conventional Weber fraction experiment. This is unlike the results obtained in many other critical-band experiments where energy remote from the signal frequency has little or no effect. Measurement of the effects of signal duration showed that when presentations were shorter than about 100 msec a greater increment in intensity was required than for longer durations. These results with duration are similar to those obtained in other intensity-discrimination tasks.

Discrimination Learning↗
PubMed1984

Relation of feedlot performance and certain physiological responses to the metabolizable protein and urea content of cattle diets.

An experiment was conducted to test the accuracy of the metabolizable protein system in predicting the amount of urea that would be useful in a corn-based cattle diet. Treatment diets included a basal, low-protein (7.8% CP) negative control (NC) with no supplemental N and a positive control (PC) that contained soybean meal. Urea was added to the NC diet in quantities calculated to be either 25% deficient (LU), equal to (MU) or 25% in excess (HU) of the urea fermentation potential ( UFP ). In vitro rumen fermentation studies were used to determine sequential ammonia production and digestible dry matter content of the diets. In a growth trial, 12 individually-fed Angus, Hereford and Angus X Hereford steers weighing an average of 213 kg were assigned randomly to each treatment diet. At the conclusion of the 112-d trial, rumen ammonia and jugular blood urea N (BUN) concentrations were determined on two steers from each treatment before feeding and at 1, 2, 3, 4 and 5 h postfeeding. In vitro ammonia concentrations of the NC and PC treatments were lower (P less than .05) than that of urea containing diets. In vivo rumen ammonia concentrations at 1 h postfeeding and BUN levels at 3 h postfeeding were low for both the NC and PC diets compared with urea-containing diets. Both of these values increased with each successive increase of added urea to the NC diet. During the initial 70 d of the growth trial, daily gains were improved (P less than .05) by addition of urea up to the MU level, which fulfilled the calculated UFP .(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗