Abstract 1019, Date 1:00 pm, Monday, February 16, 2009 (24 hours) Session K11: Poster
Temporal Characteristics of Task-Dependent Contextual Shifts in Sound Localization
*Norbert Kopco, Beata Tomoriová, Rudolf Andoga, Michal Barto
A previous study of sound localization with a preceding distractor found that the responses were biased away from the distractor location even on the interleaved baseline trials on which the target was preceded by no distractor [Kopco et al., JASA, 121, 420-432, 2007]. The current study measured the temporal characteristics of this contextual plasticity. Subjects localized 2-ms frozen noise bursts presented either in the left (-11° to -79°) or the right (11° to 79°) hemifield of the frontal horizontal plane, preceded on some trials by an identical distractor coming from directly ahead of the listener (0°). Each 189-trial block used one randomly chosen combination of the target presentation hemifield (left or right), the percentage of non-distractor trials (50%, 25%, or 10%), and the distractor-to-target stimulus onset asynchrony (SOA of 25, 100, or 400 ms). Performance was compared to baseline blocks that only contained no-distractor trials. Contextual shifts up to 4° away from the distractor location were observed in all conditions, with only small decreases at the longest SOA or when the percentage of distractor trials was the lowest. The contextual shifts were observed at all target speaker locations and the build-up of the shifts was fast, reaching the maximum (or disappearing) within the first 40 trials after the onset (or the offset) of the distractor trials. The general character and the quick build-up of the effect suggest that the task-specific context is a top-down factor and that it can influence localization performance in a variety of experimental and everyday conditions. [Supported by NIH #1R03TW007640 and VEGA #1/3134/06]