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Elizabeth Huber, Jessica Thomas, Geoffrey Boynton, Ione Fine; Frequency tuning in auditory but not occipital cortex predicts frequency discrimination in early blind individuals.. Journal of Vision 2015;15(12):919. doi: 10.1167/15.12.919.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Early onset blindness is associated with enhanced auditory abilities, which may be supported by plasticity within auditory and/or occipital cortex. We previously reported auditory frequency selectivity within occipital cortex of early blind subjects, accompanied by significantly narrower tuning bandwidths within auditory cortex. To assess the functional role of these group differences, we now examine whether it is possible to predict individual auditory frequency discrimination thresholds based on estimates of frequency tuning within auditory and/or occipital cortex. Method: Tonotopic mapping was carried out in auditory and occipital cortex in 4 early blind and 4 sighted controls using fMRI. Stimuli were pure tones ranging from 88 to 8000 Hz, presented in pseudo-randomized sequences. Using methods developed by Thomas et al. (2014), we estimated a one dimensional Gaussian sensitivity profile on a log auditory frequency axis for each voxel within anatomically defined regions of interest. We next measured auditory frequency discrimination thresholds for the same subjects in a separate session using 6 pure tones with baseline frequencies ranging between 200 and 6400 Hz. Frequency discrimination thresholds were then estimated for each of these baseline frequencies by finding the increment in frequency that produced a criterion change in expected BOLD response across voxels. This allowed us to predict psychophysical frequency discrimination performance for each subject based on cortical responses with a single free parameter. Results: For both blind and sighted subjects, discrimination thresholds as a function of baseline frequency were well predicted from estimated frequency tuning within auditory cortex. In contrast, frequency tuning within occipital regions (found only in the blind group) did not predict behavioral performance well, either alone or in combination with auditory cortex. Our findings suggest that, despite showing frequency tuning, auditory responses within occipital cortex may support auditory tasks more complex than simple frequency discrimination.
Meeting abstract presented at VSS 2015
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