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Biomedical subjects

D W Grantham

Publications and source records attributed to D W Grantham.

28 records · Page 2Linked to original sources
PubMed1986

Detection and discrimination of simulated motion of auditory targets in the horizontal plane.

Three experiments investigated subjects' ability to detect and discriminate the simulated horizontal motion of auditory targets in an anechoic environment. "Moving" stimuli were produced by dynamic application of stereophonic balancing algorithms to a two-loudspeaker system with a 30 degree separation. All stimuli were 500-Hz tones. In experiment 1, subjects had to discriminate a left-to-right moving stimulus from a stationary stimulus pulsed for the same duration (300 or 600 ms). For both durations, minimum audible "movement" angles ("MAMA's") were on the order of 5 degrees for stimuli presented at 0 degrees azimuth (straight ahead), and increased to greater than 30 degrees for stimuli presented at +/- 90 degrees azimuth. Experiment 2 further investigated MAMA's at 0 degrees azimuth, employing two different procedures to track threshold: holding stimulus duration constant (at 100-600 ms) while varying velocity; or holding the velocity constant (at 22 degrees-360 degrees/s) while varying duration. Results from the two procedures agreed with each other and with the MAMA's determined by Perrott and Musicant for actually moving sound sources [J. Acoust. Soc. Am. 62, 1463-1466 (1977b)]: As stimulus duration decreased below 100-150 ms, the MAMA's increased sharply from 5 degrees-20 degrees or more, indicating that there is some minimum integration time required for subjects to perform optimally in an auditory spatial resolution task. Experiment 3 determined differential "velocity" thresholds employing simulated reference velocities of 0 degrees-150 degrees/s and stimulus durations of 150-600 ms. As with experiments 1 and 2, the data are more easily summarized by considering angular distance than velocity: For a given "extent of movement" of a reference target, about 4 degrees-10 degrees additional extent is required for threshold discrimination between two "moving" targets, more or less independently of stimulus duration or reference velocity. These data suggest that for the range of simulated velocities employed in these experiments, subjects respond to spatial changes--not velocity per se--when presented with a "motion" detection or discrimination task.

Acoustic Stimulation↗
PubMed1984

Interaural intensity discrimination: insensitivity at 1000 Hz.

Recent data from three laboratories have replicated Mills' [J. Acoust. Soc. Am. 32, 132-134 (1960)] finding that interaural intensity discrimination is relatively poorer for tones of 1000 Hz than for tones of either higher or lower frequencies. To get a finer look at this frequency effect, interaural intensity difference thresholds were obtained from four subjects for tones of several frequencies around 1000 Hz. An adaptive two-interval forced-choice procedure was employed, in which the overall intensity of the signals was varied randomly in order to prevent subjects from listening to monaural loudness changes. Despite large intersubject differences in overall sensitivity to interaural intensity differences, all four subjects showed a local peak in their threshold functions at or near 1000 Hz. This curious "1000-Hz effect" might be explained by imagining that an interaural intensity comparator operates more efficiently as frequency increases, but that a peripheral interaural intensity difference to interaural-time difference conversion contributes to laterality judgments for low-frequency tones, thus acting to lower thresholds again for frequencies below 1000 Hz.

Auditory Threshold↗
PubMed1984

Discrimination of dynamic interaural intensity differences.

An experiment was conducted to measure observers' ability to detect time-varying interaural intensity differences (IIDs). In a two-interval forced-choice task, observers discriminated a binaural amplitude modulated (AM) noise in which the modulating sinusoid was interaurally in-phase from the same AM noise in which the modulator was interaurally phase-reversed. The latter stimulus produces a sinusoidally varying IID whose rate and peak IID depend on the frequency (fm) and depth (m) of modulation. The carrier was a narrow-band noise, interaurally uncorrelated, centered at 500, 1000, or 4000 Hz. Presentation level was 75 dB SPL; duration was 1.0 s. For a given fm, m was varied in an adaptive procedure to estimate the depth required for 71% discriminability (mthr). Three of the four observers displayed "low-pass" modulation functions: at 500 Hz, as fm increased from 0-50 Hz, mthr increased from 0.08 (IID = 1.3 dB) to 0.50 (peak IID = 9.5 dB). At 1000 and 4000 Hz observers were more sensitive to IID and the functions (mthr vs fm) were flatter than at 500 Hz. Comparison of these data to previously published data indicates that the binaural system can follow fluctuations in IID more efficiently than it can follow fluctuations in interaural time difference, although there are large individual differences in subjects' capacity to process these two types of binaural cues.

Auditory Threshold↗
PubMed1982

The phase angle of addition in temporal masking for diotic and dichotic listening conditions.

The phase angle, alpha, between a tonal signal and a tonal masker was varied from 0 degrees to 135 degrees in simultaneous masking, forward masking, and pulsation-threshold paradigms. In all conditions the frequency of the signal and masker was 500 Hz. For forward masking both diotic (MOSO) and dichotic (MOS pi) listening conditions were investigated. Only the dichotic case was studied using the pulsation threshold method. In simultaneous masking, thresholds varied as a function of alpha in both diotic and dichotic conditions. Thresholds in the diotic conditions were consistently different from those in the dichotic conditions -- i.e., there were masking-level differences (MLDs) at most values of alpha tested. In forward masking and pulsation-threshold, however, thresholds were independent of alpha in the dichotic conditions; and thresholds were independent of alpha in the diotic, forward masking conditions. Nevertheless, for forward masking the dichotic thresholds remained below the diotic thresholds, yielding MLDs of 3-6 dB. Thus, in nonsimultaneous masking, there is a clear effect of the interaural signal phase, but not of the masker-signal phase relationship, on signal detectability. These results imply that masker-signal phase information is either not preserved or not used by subjects in nonsimultaneous tone-on-tone masking experiments.

Auditory Perception↗
PubMed1982

Measures of intensity discrimination.

Several different measures have been employed in the literature to describe performance by human observers in intensity discrimination tasks. These measures include the difference limen (DL) or "delta I in dB," the Weber fraction (delta I/I), and signal-to-masker ratio (Ps/Pm). This article describes the mathematical relationship among these measures for conditions in which masker and signal are (1) sinusoids of the same frequency; (2) sinusoids of different frequencies; and (3) noise waveforms. We provide a table which contains values of each of these measures, describing equivalent performance over the typical range obtained in most intensity discrimination experiments. We express some cautions that should be observed in choosing and reporting particular measures of intensity discrimination.

Humans↗
PubMed1982

Detectability of time-varying interaural correlation in narrow-band noise stimuli.

In a two-interval, forced-choice task, observers discriminated a binaural noise whose interaural correlation r varied according to the function r(t) = m cos 2 pi fmt from an interaurally uncorrelated noise [NU; r(t) = 0.0]. The former stimulus produces a perceptual binaural "flutter," where the flutter rate is equal to the modulation frequency fm, and the amount of flutter corresponds to m. The stimuli were 0.4-octave-wide Gaussian noises with center frequencies of 500, 1000, 2000, or 4000 Hz. Presentation levels were 70-75 dB SPL; duration was 1.0 s. For a given modulation frequency, the peak interaural correlation m was varied in a blocked procedure, and thresholds were estimated as that value of m required for 75% discriminability. Plotting thresholds as a function of fm yields a modulation function, which can be interpreted as an "attenuation characteristic" of the binaural system. For the 500-Hz stimulus, thresholds increased from m - 0.28 at fm = 1 Hz to m - 0.80 at fm - 50 Hz. For higher frequency stimuli, discrimination was generally poorer and the modulation functions were flatter: thus, for 2000 Hz, m = 0.54 at fm = 1 Hz and m = 0.71 at fm = 20 Hz; for 4000 Hz, m = 0.71 at fm = 1 Hz and m = 0.81 at fm = 10 Hz. The modulation function from an "ideal observer" (at 500 Hz) differed in both form and absolute level from those of real observers. The data are discussed in relation to previous work on dynamic binaural processing.

Auditory Perception↗
PubMed1979

Detectability of a pulsed tone in the presence of a masker with time-varying interaural correlation.

Detectability of a filtered probe tone (250, 500, or 1000 Hz) was measured in the presence of a narrow-band Gaussian masker centered at the signal frequency. The signal was interaurally phase-reversed (Spi), and the masker's interaural correlation varied sinusoidally between +1.00 (NO) and -1.00 (Npi) at a varaible rate (fm = 0--4 Hz). The signal was presented at various points on the masker's modulation cycle. For 0-Hz modulation (fixed interaural correlation) signal threshold decreased monotonically as the masker's interaural correlation was changed from -1.00 to +1.00 (by a total of about 20, 16, and 8 dB, respectively, for 250-, 500-, and 1000-Hz signals). For fm greater than 0 the function relating signal threshold to the masker's interaural correlation at the moment of signal presentation became progressively flatter with increasing fm for all signal frequencies. For fm = 4 Hz the function was flat; there was no measurable effect of masker interaural correlation on signal detectability. Estimates of minimum binaural integration time based on these data ranged from 44--243 ms, supporting previous studies which have noted the binaural system's relative insensitivity to dynamic stimulation. Additionally, the estimated time constants were approximately twice as large at 250 Hz as at 500 Hz, indicating observers could follow binaural fluctuations better at 500 Hz. The time-constant estimates at 1000 Hz were not suggiciently reliable to permit comparisons with the lower-frequency data.

Acoustic Impedance Tests↗
PubMed1978

Detectability of varying interaural temporal differences.

Detectability and salience of time-varying interaural temporal differences (IATD's) were measured in three experiments by determining observers' ability to follow the temporal fluctuations of a "moving stimulus"--a 3000-Hz low-pass computer-generated noise presented binaurally with a sinusoidally varying IATD. In the first two experiments the peak IATD (deltat the "extent of movement") was manipulated to determine, for different rates of interaural variation (fm), threshold discriminability of the "moving" stimulus from a reference (two-interval forced-choice paradigm). The nonmoving reference was either a dichotic noise stimulus (experiment 1) or a dichotic noise stimulus whose "image width" matched that of the excursions traced by the "moving stimulus" (experiment 2). Threshold deltat's in the two experiments were similar, increasing from 30 microns at fm = 0 Hz to 90 microns at fm = 20 Hz, indicating a "low-pass characteristic" for the binaural system. Thresholds decreased again for fm = 50 Hz, apparently because at these high rates of "movement" observers used other cues than the varying IATD's to perform the task. The third experiment measured the threshold of a binaural click in the presence of a "moving noise" masker as a function of fm and of the instantaneous IATD of the masker when the click was presented. As fm increased, click threshold gradually became independent of the masker's instantaneous IATD, again suggesting a "low-pass" characteristic for the binaural system; additionally, there was some evidence for a lag in the system's response for fm greater than 5 Hz. The data from the three experiments are discussed in terms of results from other studies which have investigated temporal aspects of the binaural system. The possible existence of movement detectors in the auditory system is discussed.

Acoustic Stimulation↗