The effect of onset asynchrony on profile analysis by normal-hearing and hearing-impaired listeners

Abstract

The effect of onset asynchrony on discrimination of spectral shape was evaluated for hearing-impaired and normal-hearing listeners. Stimuli were the sum of four tones equally spaced on a logarithmic frequency scale. The standard stimulus had tones of equal amplitude, and the signal stimulus had two adjacent components increased in level, and the other two components decreased in level. Thresholds for discrimination between the standard and signal stimuli were measured as a function of an onset asynchrony among the components of 0, 50, and 200 ms. Hearing-impaired and normal-hearing listeners had similar thresholds when the stimulus components were widely spaced in frequency, but hearing-impaired listeners had much higher thresholds for narrowly spaced components. Excitation pattern analyses indicated that listeners may use spectral peaks in the stimulus rather than the change in excitation across the full stimulus bandwidth for spectral shape discrimination tasks. Increasing temporal asynchrony of components resulted in increased thresholds for both groups of listeners to a greater extent in the wide span than the narrow span. Reduced effects of onset asynchrony in the narrow span suggest that spectral resolvability of components plays an important role in the processing of onset asynchrony across frequency.

The effect of onset asynchrony on relative weights in profile analysis

“…In contrast, the effect of onset asynchrony was significant ͓F͑2,6͒ = 92, p Ͻ 0.0005͔. These data are in accord with past results, except that in the current experiment the change in thresholds with number of components is somewhat smaller than in the past ͑Green and Dai, 1992;Hill and Bailey, 1997;Lentz et al, 2004;Berg, 2004͒. Figure 1 shows the values of relative weights for level randomization averaged across subjects for the six conditions tested ͑from left to right: 5-tone and 15-tone simultaneous, 5-tone and 15-tone leading-100, and 5-tone and 15-tone leading-300͒.…”

“…Consider, for example, the detection of an increment to the level of the central component ͑signal component͒ of several equalamplitude tones ͑nonsignal components͒. Thresholds increase when the onset of the signal components is changed from synchronous to asynchronous relative to the nonsignal components ͑Green and Dai, 1992;Hill and Bailey, 1997;Lentz et al, 2004͒. One potential account for this result is the segregation hypothesis: the onset asynchrony between the signal and nonsignal components results in the segregation of the signal from the nonsignal components.…”

Envelope Processing and Sound-Source Perception

“…The asynchronous component was also more likely to be perceived as part of a rhythmic sequence with the alternating pure tone. As in the profile-analysis work of Lentz et al (2004), effects diminished with reduction in the frequency spacing between stimulus components.…”

“…Green and Dai (1992) showed that either a 50-ms onset or offset asynchrony between target and nontarget components significantly elevated thresholds, with the effect increasing with gating disparity up to at least 250 ms. Subsequent work demonstrated that the deleterious effect of target asynchrony can be reduced by either reducing the frequency separation between stimulus components (Lentz et al 2004) or adding captor tones concurrent with the leading temporal fringe of the target (Hill and Bailey 1997). The intent of the latter manipulation was to minimize target segregation from nontarget components by encouraging a perceptual organization in which the target fringe combines with the captor tones to result in two sequential events: target-fringe plus captors followed by target plus nontarget components.…”

“…Results from a number of studies show that the ability to detect change in a target component of a complex is at times either unaffected or impaired by gating asynchrony. These include studies of identification thresholds of masked signals (Gordon 2000), pitch processing (Carlyon 1994;Brunstrom and Roberts 2001), and profile analysis (Green and Dai 1992;Hill and Bailey 1997;Lentz et al 2004). Though the independent variable in all cases was some characteristic of the target component, task performance was influenced by cross-spectral processing between the target and remaining (nontarget) stimulus components.…”