Competing Sound Sources Reveal Spatial Effects in Cortical Processing
Figure 4
Spike additions and subtractions affect performance differently.
For three spatial configurations (left to right: target ipsilateral, masker contralateral; target front, masker front; target contralateral, masker ipsilateral), (A) clean target rate, (B) masked rate, and (C) the difference between masked and clean rates are shown, averaged across all sites. Red peaks show where the masker added spikes, and blue depths show masker subtractions. The large initial peaks have been clipped to increase the dynamic range of the rates that follow. (D) Using these rates, we modeled spike trains that had additions and subtractions, subtractions only, or additions only (“modeled,” which includes additions and subtractions, “sub-only,” and “add-only,” respectively). We calculated percents correct for these generated spike trains for each unit and plotted them against the actual masked performance. (E) The subtractions-only performance for each site (blue circles) and the centroid (black cross, branches are 1 SEM in each direction). Centroids are close to the diagonal, indicating similar subtractions-only and masked performances. (F) Additions-only performances, in the same manner as (E). Centroids are far from the diagonal, indicating a smaller detrimental effect on performance from spike additions. (G) The average (±1 SEM) performance. Additions-only performance does not differ significantly from clean performance for any configuration. Subtractions-only performance is significantly worse than clean performance. As the target moves from ipsilateral to contralateral (and the masker oppositely), subtractions account for an increasing proportion of the masking performance hit, completely accounting for it in the target contralateral, masker ipsilateral configuration. Gray brackets indicate significant differences of p<.05.