Biomedical subjects

J A Stillman

Publications and source records attributed to J A Stillman.

7 recordsLinked to original sources

PubMed1993

Intensity just-noticeable differences at equal-loudness levels in normal and pathological ears.

The relationship between loudness level and intensity discrimination was investigated in the frequency range 0.5-6.5 kHz by comparing the intensity just-noticeable differences (jnd's) at a number of equal-loudness levels in the better and poorer ears of eight individuals with essentially unilateral hearing loss of cochlear origin. Such hearing loss usually produces loudness recruitment, altering the relationships among the loudness, sound-pressure level (SPL), and sensation-level (SL) variables, so that their effects can be separated. In these experiments, the jnd's were correlated with loudness level, not SPL or SL. Although, in some listeners, there were significant differences between jnd's in the two ears at some binaurally equal-loudness levels, they were not systematic over the group of listeners. Statistically, there was no significant difference between equal-loudness jnd's in the two ears, whereas the corresponding SLs and SPLs were significantly different. The rate of loudness growth had no effect on the jnd's. As expected from the near-miss to Weber's law, the mean jnd's decreased with sound intensity. The corresponding decrease in the mean Weber fraction, delta I/I, was accompanied by a decrement in its intrasubject standard deviation. The latter was correlated with the mean, independent of its relationship to SPL or SL.

Acoustic Stimulation↗

PubMed1993

Response selection, sensitivity, and taste-test performance.

Tasters selected the odd stimulus from among sets of three samples of party dip. Two samples came from one batch, and one sample came from another batch. The physicochemical difference between the batches consisted of the presence or absence of added salt. Two different tests of discriminability were undertaken by the same subjects with the same stimuli: the triangle test and the three-alternative forced-choice (3-AFC) method. Although different numbers of correct selections were obtained in the two tasks, an index of discriminability, d', had the same value when the data were analyzed in accordance with the Thurstone-Ura and signal-detection models, respectively. The average data support Frijters's (1979b) contention that different models of the discrimination process are appropriate to the results of the triangular and the 3-AFC procedures. Further analysis of the data revealed that discrimination was poorer for trios containing one physicochemically weak stimulus and two stronger stimuli than it was for trios containing one stronger stimulus and two weak stimuli. A two-signal 3-AFC task was undertaken by some subjects, and d' estimates from this task were lower than expected on the basis of performance in the other tasks.

Adult↗

PubMed1993

Context effects in judging taste intensity: a comparison of variable line and category rating methods.

The effect of stimulus range and stimulus spacing was examined when subjects registered the perceived intensity of sweet liquids using either a matching procedure (Experiment 1) or category rating (Experiment 2). The matching procedure is conceptually similar to absolute magnitude estimation, whereby subjects match their impression of number size to their impression of the subjective magnitude of a stimulus. In Experiment 1, subjects matched their impression of the stimulus to their impression of the magnitude of the length of a continuously variable line under their control. In Experiment 2, subjects rated perceived sweetness on a vertical 13-point scale with five equally spaced verbal labels. In both experiments, three sets of four sucrose concentrations were employed. In two of these sets, a set of weaker solutions and a set of stronger solutions, concentrations were separated by 0.25 log units. In a third set, which spanned the range of concentrations used in the other two sets (0.87 to 27.36% w/v), solutions were separated by 0.5 log units. An examination of both individual and group data showed the matching procedure to be less susceptible to a range bias than the rating procedure. In particular, a single intensity function accommodated data from individual ranges better when the matching procedure was used than when the rating procedure was used. No effect of stimulus spacing was evident in the data from either procedure.

Attention↗

PubMed1990

Signal detectability in the presence of monotic or dichotic noise bands of equal or unequal levels.

The application of the power-spectrum model of masking to the detectability of a signal masked by dichotic noise was investigated in three experiments. In each experiment, the signal was a 2-kHz sinusoid of 400-msec duration, masked by either one or two 800-Hz wide bands of noise presented singly or in pairs. In Experiment 1, we compared the detectability of a diotic signal masked by dichotic noise with the detectability of a monaural signal masked by each of the noises separately. The spectrum level of the noise was 35 dB SPL. For dichotic presentations, the signal was sent to both ears while pairs of noise bands, one below and one above the signal frequency, were presented together, one band to each ear. Threshold levels with the dichotic stimuli were lower than or equal to the thresholds with either ear's stimulus on its own. Similar dichotic stimuli were used in Experiment 2, except that the signal frequency was nearer to one or the other of the bands of masking noise, and the noise had a spectrum level of 50 dB SPL. In Experiment 3, thresholds were obtained with two sets of symmetrically and asymmetrically placed notched-noise maskers. For one of these sets, the spectrum level of both noise bands was 35 dB SPL; for the other set, interaural intensity differences were introduced in the form of an inequality in the levels of the noise bands on either side of the signal. In one ear, the spectrum level of the lower frequency noise band was 35 dB SPL and the spectrum level of the higher frequency noise band was 25 dB SPL, whereas in the other ear, the allocation of noise level to noise band was reversed. The dichotic thresholds obtained with the unequal noise maskers could be predicted from the shapes of the auditory filters derived with equal noise maskers. The data from all three experiments suggest that threshold signal levels in the presence of interaural differences in masker intensity depend principally on the ear with the higher signal-to-masker ratio at the output of its auditory filter, a finding consistent with the power-spectrum model of masking.

Adult↗

PubMed1989

A comparison of three adaptive psychophysical procedures using inexperienced listeners.

Thresholds for a masked 1-kHz tone were obtained in single sessions from 60 inexperienced listeners. A two-alternative forced-choice procedure was used in conjunction with one of three adaptive psychophysical techniques. These techniques comprised two staircase techniques targeting either 70.7% or 79.4% correct detection (Staircase-71 and Staircase-79), and parameter estimation by sequential testing (PEST), targeting 80% correct detection. Listeners were provided with a rationale for maintaining concentration at weak signal levels. Similar threshold values were obtained from the Staircase-79 and PEST groups in equal numbers of trials. The degree of oscillation in the level of the signal around the value finally chosen as the threshold was comparable for both staircase techniques. Subsequent fixed-level testing did not provide a true indication of the subjects' capabilities. The amount by which percent correct in fixed-level testing differed from expectations based on adaptive testing varied among the techniques. Additional thresholds were obtained in a second session from 30 of the original subjects. Thresholds with both staircase techniques improved by about 1 dB on retest, while thresholds with PEST were constant across sessions. The variability of the data compared well with that from studies involving experienced listeners.

Adult↗

PubMed1986

The width of the auditory filter in children.

Because young children have poorer auditory temporal resolution than older children, they ought to have, according to the inverse relation between temporal and frequency resolution, narrower auditory filters than older children. Therefore, the auditory filters of two 6-year-olds, two 10-year-olds, and two adults were measured by having them detect a 400-ms sinusoid (500, 1000, or 3000 Hz) centered in a spectral notch in a band of noise. The signal power for 71% correct was determined as a function of notch width with the two-alternative, forced-choice procedure. The principal results showed a significant decrease in signal power with age and a significant interaction between age and notch width. The best-fitting parameters of a model of the auditory filter showed that the filter was significantly wider for the 6-year-olds than for the 10-year-olds or the adults.

Adult↗

PubMed1985

The development of auditory temporal acuity in children.

The development of auditory temporal acuity was studied in 56 children aged 6-12 years and compared with that of 8 adults. Acuity was measured by determining the minimum detectable duration of a brief cessation in a noise band with the 2-alternative forced-choice method. For detection of gaps in a broadband noise, acuity improved significantly with age and reached adult values by 11 years. The minimum detectable duration was significantly shorter at higher levels of the noise. For narrow-band noises, acuity also improved significantly with age and depended on the center frequency of the band. The improvement in temporal acuity with age was attributed to the development of sensory processes and not to age-related changes in nonsensory factors.

Adult↗