Biomedical subjects

J Zera

Publications and source records attributed to J Zera.

4 recordsLinked to original sources

PubMed1995

Effect of signal component phase on asynchrony discrimination.

The ability of listeners to detect the temporal asynchrony of a single harmonic in complex sounds was measured. The listeners discriminated an asynchronous complex from one in which all harmonics were synchronous (standard). The asynchrony was created either at the onset or offset of the complex. In the asynchronous complex, one component either began or ended after all other components in the complex, or it began or ended prior to all other components in the complex. The phase of the signal component was systematically varied in the range from 0 degrees to 180 degrees. All nonsignal components had the same sine phase. The results show that detecting the asynchrony at the onset is superior when all components are in sine phase. Altering the phase of the signal component increased thresholds by as much as a factor of 50, with the largest thresholds obtained when the signal component was inverted in phase. For offset conditions, the phase of the signal component had a much smaller and less consistent effect. Some of the observed effects of phase on the asynchrony thresholds can be understood by considering the response of the Roex filter [Patterson et al., J. Acoust. Soc. Am. 72, 1788-1803 (1982)] centered at the signal frequency.

Auditory Perception↗

PubMed1993

Detecting temporal onset and offset asynchrony in multicomponent complexes.

The ability of listeners to detect asynchrony in either the temporal onset or offset of components in multicomponent complexes was measured. The listener discriminated a standard complex, one in which all components were synchronous, from an asynchronous complex. In the initial experiments, asynchrony was created by starting (onset experiments) or ending (offset experiments) the harmonics at times drawn from a Gaussian distribution. In later experiments, asynchrony was created by starting or terminating only certain components before or after the other components in the complex. One complex consisted of 20 harmonic components with a fundamental of 200 Hz. Another multicomponent complex used components spaced at equal intervals in logarithmic frequency (200 to 4000 Hz). The parameters investigated were rise or decay time of components, duration of a complex, and frequency position of displaced components. The obtained thresholds were different for onset and offset asynchrony. For onset asynchrony in harmonic complexes, the thresholds were a nonmonotonic function of rise time with a minimum of 0.2 ms obtained for a rise time of 1 ms. For offset asynchrony, thresholds were generally monotonic with increases in decay time and ranged from 0.45-1.3 ms. Experiments with a much shorter signal duration demonstrated that forward and backward masking played little role in the observed differences in thresholds. Onset thresholds for harmonic stimuli measured as a function of the frequency region of the asynchronous component(s) showed a minimum of 0.2 ms at about 2000 Hz. The thresholds for offset were about ten times larger. For logarithmic complexes, in some conditions, thresholds were larger by nearly two orders of magnitude. Experiments in which the listeners discriminated changes either in the onset or offset envelope of the wideband stimulus suggest that detection of temporal asynchrony depends on comparison between frequency channels rather than on differences in the temporal onset or offset of the overall energy of the sounds.

Acoustic Stimulation↗

PubMed1993

Auditory profile analysis of harmonic signals.

Spectral shape discrimination for harmonic complexes with 100-, 200-, or 400-Hz fundamental was investigated in two sets of experiments. In the first set, the signal was an increment in a single component of an otherwise equal-amplitude complex. The results of these experiments showed nearly a 30-dB increase in thresholds as the signal frequencies increased from 1000 to 5000 Hz. A transformation of data based on the assumption that the critical detection quantity is the change in the level in a critical band centered at the signal frequency was applied to remove the effects of the nonsignal components. The corrected thresholds have a bowl-like shape similar to that seen in studies of spectral shape discrimination of stimuli with components equally spaced on a logarithmic frequency scale. Additional experiments examined the effects of the number of components in the complex and the relative phase of the components of the harmonic complex. In the second set of experiments, the effects of local masking were examined either by increasing the level of several adjacent components, or by removing nonsignal components near a single signal component. Again, the results with harmonic signals are similar to those obtained with components spaced at equal intervals on a logarithmic frequency scale, if one calculates the increment in the level produced in a critical band centered at the signal frequency.

Acoustic Stimulation↗

PubMed1993

Detecting temporal asynchrony with asynchronous standards.

The ability of listeners to detect asynchrony in either the temporal onset or offset of individual components in a multicomponent complex was investigated. A standard stimulus was created having a simple kind of asynchrony by linearly delaying successive components of a complex stimulus. Additional asynchrony (the signal) was created by altering the temporal position of a single component of the complex relative to its temporal position in the standard. Asynchrony discrimination was measured for harmonic signals (experiment I) and for complexes in which the components were logarithmically spaced in frequency (experiment II). For the onset condition, asynchrony in either the harmonic or logarithmic complex greatly increased the difficulty in detecting the temporal asynchrony of a single component. For the offset condition, asynchrony discrimination was not greatly affected by asynchrony in the standard.

Acoustic Stimulation↗