Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, C16

Oral Communications

Probing the physiology of perception: Invariant neural responses in ferret auditory cortex during vowel discrimination

S. Town1, K. Wood1, H. Atilan1, J. Bizley1

1. Ear Institute, University College London, London, UK, United Kingdom.


Perceptual invariance is the ability to recognize an object despite variation in sensory input. For example when listening to a violin solo, the instrument has a constant identity despite variations in sound waveform as different notes are played. Likewise in speech we can recognize phonetic components, such as the vowel "u", across talkers with different voice pitches. However, it is unclear how the brain supports perceptual invariance and specifically whether neurons in auditory cortex extract invariant representations of vowel identity across pitch.Here we study an animal model of perceptual invariance in which ferrets (n=4) were trained in a two-alternative forced choice task to discriminate artificial vowel sounds. On each trial of the task, the subject was presented with two vowel sounds and required to respond at a particular location depending on vowel identity. Across trials vowel pitch was varied and ferrets were required to generalize discrimination across pitch variation. During task performance, multi-unit activity was recorded from microelectrodes positioned in auditory cortex. We recorded 104 responsive units - units whose firing rate during vowel presentation differed by ≥ 2 standard deviations from mean spontaneous activity. For each responsive unit, we asked if it was possible to decode vowel identity from the spiking responses observed across all pitches. Using a bootstrap procedure to test significance (100 iterations, p<0.05), the majority of units (n = 72) were found to encode information about vowel identity across pitches. In a large number of units (n = 90) vowel pitch was successfully decoded across vowel identities. Many units provided information about both vowel pitch and identity (n = 66).Our results show that auditory cortical neurons may offer a physiological substrate for invariant perceptual representations of sound. Our findings also indicate that information about multiple sound features may be represented in auditory cortex during behavior, even when such features are irrelevant for task performance.

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