Abstract:
The model [N. Todd, ``A theory of the principal monaural pathway. I. Pitch and time perception,'' J. Acoust. Soc. Am. (these proceedings)] proposes to account for auditory streaming by a cross-correlation mechanism modeled as an array of cortical columns. A column contains excilatory and inhibitory interneurons and pyramidal cells which receive input from both the thalamus and from neighboring columns. For columns with coherent thalamic inputs, the outputs of the pyramids sum across frequency because local interneurons compute a correlation between the AM transform of the inputs of the local and remote columns, and selectively gate the input to the pyramidal cell. (1) Grouping by frequency proximity---for columns separated by less than a critical band, thalamic inputs are unresolved. (2) Grouping by temporal proximity---at repetition rates below the mean of the AM distribution, AM fundamentals are less well represented; at higher repetition rates the AM harmonics are more separated. (3) Temporal development---where the AM spectra take time to develop. The AM coherence mechanism also gates the inputs to disjoint subpopulations of a low-pass mechanism, and thus also accounts for comodulation masking release, since backward masking will only take place within a single subpopulation.