Abstract
Two experiments examined plasticity induced by context in a simple target localization task. The context was represented by interleaved localization trials with the target preceded by a distractor. In a previous study, the context induced large response shifts when the target and distractor stimuli were identical 2-ms-noise clicks [Kopčo, Best, and Shinn-Cunningham (2007). J. Acoust. Soc. Am. 121, 420-432]. Here, the temporal characteristics of the contextual effect were examined for the same stimuli. Experiment 1 manipulated the context presentation rate and the distractor-target inter-stimulus interval (ISI). Experiment 2 manipulated the temporal structure of the context stimulus, replacing the one-click distractor either by a distractor consisting of eight sequentially presented clicks or by a noise burst with total energy and duration identical to the eight-click distractor. In experiment 1, the contextual shift size increased with increasing context rate while being largely independent of ISI. In experiment 2, the eight-click-distractor induced a stronger shift than the one-click-distractor context, while the noise-distractor context induced a very small shift. These results suggest that contextual plasticity is an adaptation driven both by low-level factors like spatiotemporal context distribution and higher-level factors like perceptual similarity between the stimuli, possibly related to precedence buildup.
Highlights
Acoustic scenes often contain multiple sources emitting sounds in an arbitrary temporal sequence
The current study showed a complex effect of the temporal characteristics of context on sound localization, likely driven by processing at multiple stages in the auditory pathway
A noise distractor that has the same spectrum, overall energy, and duration as an eightclick distractor induces a much smaller contextual plasticity (CP), presumably because it contains fewer onsets and offsets. (Note that the analysis of CP in this study is limited by the chosen response method that introduced response biases even in the baseline and had a relatively large response standard deviation of up to 6; Kopco et al, 2015.)
Summary
Acoustic scenes often contain multiple sources emitting sounds in an arbitrary temporal sequence. The listener’s ability to localize a sound of interest in such scenes is influenced by many factors, including the temporal distribution of the stimuli (Simpson et al, 2007) and their perceptual similarity (Best et al, 2007). Which factors are the most important is not well understood, especially when the sounds are presented without temporal overlap, i.e., when nonenergetic factors dominate how the preceding stimuli influence target localization. In Kopco et al (2007), CP was observed as biases of up to 10 in localization of single-click targets, induced by contextual stimuli preceding the targets on the time scale of seconds to tens of seconds. The contextual stimuli were distractor-target click pairs, randomly interleaved with the single-click target-alone trials. Each distractor-target click pair consisted of clicks identical to the single-click target. The distractor click location was fixed within a block while the target location varied, and the distractor preceded the target by up to 400 ms
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