Pupillary dilation response as an indicator of auditory discrimination in the barn owl |
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Authors: | A D S Bala T T Takahashi |
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Institution: | (1) Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA e-mail: avinash@uoneuro.uoregon.edu Tel.: +1-541-346-4544; Fax: +1-541-346-4548, US |
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Abstract: | The pupil of an awake, untrained, head-restrained barn owl was found to dilate in response to sounds with a latency of about
25 ms. The magnitude of the dilation scaled with signal-to-noise ratio. The dilation response habituated when a sound was
repeated, but recovered when stimulus frequency or location was changed. The magnitude of the recovered response was related
to the degree to which habituating and novel stimuli differed and was therefore exploited to measure frequency and spatial
discrimination. Frequency discrimination was examined by habituating the response to a reference tone at 3 kHz or 6 kHz and
determining the minimum change in frequency required to induce recovery. We observed frequency discrimination of 125 Hz at
3 kHz and 250 Hz at 6 kHz – values comparable to those reported by others using an operant task. Spatial discrimination was
assessed by habituating the response to a stimulus from one location and determining the minimum horizontal speaker separation
required for recovery. This yielded the first measure of the minimum audible angle in the barn owl: 3° for broadband noise
and 4.5° for narrowband noise. The acoustically evoked pupillary dilation is thus a promising indicator of auditory discrimination
requiring neither training nor aversive stimuli.
Accepted: 28 February 2000 |
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Keywords: | Habituation Frequency discrimination Minimum audible angle Sound localization Psychoacoustics |
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