Localization of a 2-ms-click target was previously shown to be influenced by interleaved localization trials in which the target was preceded by an identical distractor [Kopčo, Best, and Shinn-Cunningham (2007). J. Acoust. Soc. Am. 121, 420–432]. Here, two experiments were conducted to explore this contextual effect. Results show that context-related bias is not eliminated (1) when the response method is changed so that vision is available or that no hand-pointing is required; or (2) when the distractor-target order is reversed. Additionally, a keyboard-based localization response method is introduced and shown to be more accurate than traditional pointer-based methods.

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.

Auditory perception of distance is not well understood (Zahorik et al, 2005) For familiar sounds, overall received sound pressure level (loudness) considered to be the main distance cue (Warren, 1999) In rooms, reverberation provides distance information. Candidate cue Direct-to-Reverberant energy ratio, D/R (Bronkhorst and Houtgast, 1999).

Abstract-An experiment was performed to measure how dynamic changes in a target talker location affect speech perception in a complex multi-talker environment. The listener's task was to report a number sequence spoken by the target talker, masked by four distractor talkers differing in their voices and spatial locations. The location of the target was either fixed during a trial (static condition) or randomly changing from one number to the next one (dynamic condition). The distractor talker locations were always randomized between numbers. A cue word sequence spoken by the target speaker with no distractors preceded each trial. The cue indicated the voice (dynamic condition) or the voice and location (static condition) of the target. A large decrease in performance was observed in the dynamic condition compared to the static condition. The position of the target number in a sequence, as well as the inter-word interval, only had a small effect on performance. The decrease in performance in the dynamic condition is either due to a cost of switching attention from one location to another, which can be large when attention is controlled by audition, or due to a change in listeners' strategy from selective focusing to one location (in static condition) to attempting to process all stimuli concurrently (in the dynamic condition).

A previous study of visual and auditory hemispheric cuing in horizontal sound localization found modalitydependent effects of cuing resulting in biases in responses [Kopco, Tomoriova, Andoga, J. Acoust. Soc. Am. 121, 3094, 2007]. The previous study also suggested that some of the effects might be due to eye movements as eye fixation was not controlled. The goal of the current study was to isolate the attentional effects from the eye movement effects. An experiment identical to the previous one was performed, with the exception that the subjects were fixating the center of the audiovisual display. Localization performance was measured for transient auditory stimuli originating in the frontal horizontal plane. In most runs, a cue preceded the stimulus and indicated (correctly or incorrectly) the hemisphere (left vs. right) from which the subsequent target arrived. The cues differed by modality and the cue-to-target onset asynchrony. The listeners were instructed to focus their attention to the cued side. Compared to the previous study, a reduction in some effects was observed. However, modality-dependent biases in performance persisted, confirming that auditory spatial attentional control is modality dependent and operating on time scale of seconds. [Supported by the Slovak Science Grant Agency.]