The responses of single neurons in the primary (AI) and secondary (AII) auditory cortical fields of waking cats were recorded during presentation of sequences of five iso-intensity tones. Tonal contour was varied by employing sequences that either increased or decreased monotonically in frequency, or in which contour was non-monotonic. The vast majority of neurons in both auditory fields (84%) exhibited sensitivity to tonal contour, that is, the response to at least one frequency (usually more) in a sequence differed significantly between two or more types of contour. Although all of the mechanisms involved have not been identified, the serial position of a tone within a sequence could explain some of the findings. Responsivity may also depend upon the magnitude of the interval difference between two consecutive tones. Additionally, contour per se could be effective even for neurons that were not sensitive to differences in type of contour; for example, responses to the same tones could be facilitated when presented in sequences of different frequencies compared to sequences of the same frequency. Further, the range of frequency response and the best frequency of a neuron may depend upon whether these parameters are determined using isolated tones or contoured sequences. Finally, omission of one tone within a sequence produced significant modification of response to other tones in most (87%) cells, with effects extending up to 3 sec following the the gap. Neurons in both primary and secondary auditory cortical fields displayed all effects, the only difference was that neurons in All were more likely to exhibit sensitivity to tone omission than those in AI. The findings are discussed with reference to neurophysiological and psychophysical data. We conclude that the effects of contour and other aspects of tonal sequences are detectable at the level of single neurons in auditory cortex of waking animals and that the use of dynamic stimuli is likely to be critical for a neurophysiological account of music perception and the perception of other complex acoustic stimuli.

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