Page 50 - Volume 12, Issue 2 - Spring 2012

Fig. 7. Direction of acoustic-motion discrimination (mean performance from four cats) performance in the left hemifield, right hemifield, and positions that traverse the midline (both hemifields) prior to, and following, cooling deactivation (Pre/Post, red), during bilateral cooling of the anterior auditory field (AAF) (dark blue), during bilat- eral cooling of the primary auditory field (A1) (light blue), and during bilateral cooling of posterior auditory field (PAF) (green). Single asterisk indicates performance sig- nificantly different (p<0.01) from pre/post cooling levels, and double asterisks indicate performance significantly different (p<0.01) from both pre/post cooling levels and from bilateral A1 cooling deactivation performance. Dashed line=chance performance of 50% correct.
sequential noise bursts (78 dB SPL) emitted from five speak- ers across 60° of arc. The cat then made a correct response by approaching a left or right 30° LED to indicate leftward or rightward motion, respectively. Both rightward and leftward motion were examined in three different zones of the audito- ry field: positions confined to the left hemifield; positions that crossed the midline; and positions that were confined to the left hemifield (Fig. 7). Performance prior to, and follow- ing, cooling deactivation was in excess of 80% correct. During bilateral deactivation of AAF cortex, discrimination of acoustic-motion direction was unimpaired and not signif- icantly different from control levels (Fig. 7). Bilateral deacti- vation (i.e., cooling) of A1 resulted in an acoustic-motion discrimination impairment throughout the entire field exam- ined, with performance falling to ~65% correct (p<0.01; Fig. 7). In contrast, bilateral deactivation of PAF performance fell to chance levels during bilateral cooling of PAF. Therefore, as with the static-localization task, deficits were most profound during bilateral deactivation of PAF, moderate during bilater- al deactivation of A1, and absent during bilateral AAF deac- tivation.
Overall, the results show that areas involved in acoustic- motion processing are also involved in static acoustic spatial localization. An area that is uniquely involved in acoustic- motion processing was not identified. These results suggest that spatial-localization functions may be a prerequisite for acoustic-motion processing in auditory cortex, and do not support the possibility of the existence of an auditory equiv- alent of the visual field MT.AT
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