Auditory spatial resolution in the barn owl under echoic and anechoic conditions

Abstract

Experiments were designed to allow direct comparison of auditory spatial resolution, measured behaviorally, with that of single space‐specific neurons in the barn owl’s midbrain. Behavioral measurements of spatial discrimination were obtained using habituation and recovery of the pupillary dilation response (PDR). The acoustically evoked PDR habituates to repeated presentation of a sound, and recovers if the location changes. Thus, the difference in magnitudes of PDRs evoked by a sequence of test and habituating stimuli can be quantified using signal detection theory to provide a measure of discrimination [‘‘p(c),’’ computed from empirical ROC curves]. The minimum audible angles (MAAs) for single sound sources separated in azimuth and elevation were 3° and 9°, respectively. Under simulated echoic conditions, MAAs increased by a factor of 2 for direct sources, and 4 for simulated reflections. Neuronal discrimination was similarly quantified using ROC curves to calculate p(c) for spike discharges evoked by sources at different virtual locations. Preliminary analysis of neuronal data from anesthetized owls suggests that MAAs of the most sensitive neurons are similar to behavioral MAAs. Simultaneous measurement of neuronal and behavioral performance in awake owls is currently underway. [Work supported by the McKnight Foundation, NIH DC03925 and DC00448.]