Temporal characteristics of contextual effects in sound localization

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.

Timescales of adaptation to context in horizontal sound localization

“…The analysis of the spatial properties of CP showed that 1) CP is observed as a repulsion of responses away from the adaptor location that decreases with separation between target and adaptor, and that 2) the effect is stronger in the variable context condition where the overall adaptor click rate is higher. These results are consistent with previous studies (Hládek et al, 2017; Kopčo et al, 2015) but extends the finding to lateral as well as frontal adaptors. Additionally, we find that variable and fixed context effects are similar both in their strength and spatial extent for the frontal and lateral adaptor when expressed as a function of distance from the adaptor, suggesting that the spatial representation in which CP is induced is approximately uniform, even though auditory spatial resolution decreases with azimuth (Hartmann & Rakerd, 1989).…”

“…The additional adaptation in the variable context showed either a constant or an approximately linear growth, uniform over the whole duration of the current runs. This again shows that the variable context, randomly switching between a 1-click and an 8-click adaptor, causes the adaptation to have a very slow component, much slower than those observed in our previous studies (e.g., (Hládek et al, 2017)) and resulting in a stronger CP. Note that the additional adaptation would likely have reached an asymptotic value if the runs were sufficiently long.…”

“…Specifically, increasing the average number of adaptor clicks (variable context) resulted in a stronger CP, while both varying the number of clicks from trial to trial and an exposure to reverberation resulted in a slower temporal profile of the adaptation. Strikingly, the variable context resulted in adaptation that grew over time in both environments, resulting in the strongest CP we have observed to date, even stronger than that induced by a fixed 8-click context (9° observed in (Hládek et al, 2017)). These effects of context type and environment are likely due to some non-linear interaction of multiple adaptive processes that depend on the adaptor presentation rate, its variability, and the presence of reflections.…”

“…We addressed several questions related to the time course of CP. First, while we expected that CP would be stronger in the variable context condition as the average number of context clicks is higher in this condition (Hládek et al, 2017), we tested the hypothesis that it might also be slower to asymptote as the context varies from trial to trial. We also hypothesized that CP may be weaker and/or slower in the reverberant environment, as reverberation tends to make the spatio-temporal distribution of stimuli more uniform, which may reduce the strength of adaptation.…”

Formation of three-dimensional auditory space

“…To estimate the distance of a source, listeners have access to a broad variety of acoustic cues like sound intensity, reverberation characteristics (often quantified by the direct-to-reverberant energy ratio), near-field ILDs, the shape of the stimulus spectrum, and others (for review, see Kolarik et al, 2016). The relative perceptual relevance of these cues and their underlying neural codes are the subject of debate and are most probably dependent on the context (for a review, see Hládek et al, 2017). Recent studies suggest that the amount of temporal ILD fluctuations and amplitude modulation depth likely represent reverberation-related cues (Catic et al, 2015).…”