Fig. 7.

Plasticity of sound localization depends on the auditory cortex. A: percent correct scores (averaged across all speaker locations) measured every day over a 10-day period. The performance is shown 1 day before (Pre) and on each of the 8 days after insertion of an earplug in the left ear (Left ear plugged), as well as on the day on which the earplug was removed (Post). The stimuli were 1,000-ms noise bursts. The gray bars depict the range of values obtained from 3 other ferrets with an intact auditory cortex. In these control animals, the percentage of correct responses falls dramatically when the ear is first plugged but recovers toward preplug levels with daily behavioral training. The different symbols correspond to the ferrets with cortical lesions, with the open symbols showing the data from the ferrets with restricted cortical lesions (the dashed line represents the mean scores for this group) and the filled symbols showing the data from 2 of the ferrets with extensive cortical lesions (the solid black line indicates the mean performance; the third animal in this group could not do the task with the earplug in place). In contrast to the controls, the localization abilities of the animals with cortical lesions did not improve during the period of time over which the earplug was worn. B: stimulus-response plots showing the approach-to-target performance before (Pre Plug) and after plugging the left ear (Plugged days 1–3 and Plugged days 7–9) and after removal of the earplug (Post Plug). The size of the dots indicates, for each of the 12 target locations, the proportion of responses to different loudspeaker/reward-spout locations, and the corresponding percent correct scores are given to the right of each panel. Monaural occlusion disrupted sound localization accuracy at all locations tested, but particularly on the side of the earplug. No improvement in performance was seen with daily localization training (middle panels). After earplug removal, sound localization accuracy returned to preplug levels.