Summary
Perceptual constancy describes the ability to represent objects in the world across variation in sensory input such as recognizing a person from different angles or a spoken word across talkers. This ability requires neural representations that are sensitive to some aspects of a stimulus (such as the spectral envelope of a sound) while tolerant to other variations in stimuli (such periodicity). In hearing, such representations have been observed in auditory cortex but never in combination with behavioural testing, which is essential in order to link neural codes to perceptual constancy. By testing ferrets in a vowel discrimination task which they perform across multiple stimulus dimensions and recording neuronal activity in auditory cortex we directly correlate neural tolerance with perceptual constancy. Subjects reported vowel identity across variations in fundamental frequency, sound location, and sound level, but failed to consistently generalize across voicing from voiced to whispered sounds. We decoded the responses of simultaneously recorded units in auditory cortex to identity units informative about vowel identity across each of these task-orthogonal variations in acoustic input. Significant proportions of units were vowel informative across each of these conditions, although fewer units were informative about vowel identity across voicing. For about half of vowel informative units, information about vowel identity was conserved across multiple orthogonal variables. The time of best decoding was also used to identify the relative timing and temporal multiplexing of sound features. Our results show that neural tolerance can be observed within single units in auditory cortex in animals demonstrating perceptual constancy.
