Functional and Structural Implications of Non-Separability of Spectral and Temporal Responses in AI
Abstract
Units in primary auditory cortex (AI) are well characterized by their responses to moving ripples; specifically the two-dimensional transfer function T(w,) measured over a range of ripple velocities w and densities. A Fourier transformation of the transfer function (TF) gives the Spectro-Temporal Reponse Field of the unit, STRF(t,x) where x=log(frequency). An important property of a TF is its separability, i.e., whether it can be decomposed into the product of two one-dimensional functions (T=T_x*T_). A separable TF is one whose temporal T(w.,) and spectral T(.,)TF are independent of each other. A fully separable TF is reducible to a single product, independent of the direction of travel of a sound (i.e. upward or downward); a quadrant separable TF is separable only within each direction, i.e. within a quadrant of the two dimensional TF. We shall discuss three important aspects of separability: (1) Separability can be assessed in a graded fashion as we illustrate using singular-value-decomposition methods; (2) Quadrant separable TF imply highly constrained temporal and spectral interactions, reflecting underlying functional and organizational principles; (3) Transfer function inseparability and quadrant separability are fundamentally due to asymmetries in the responses to upward vs downward moving sound envelopes. [Simon, J. et al. 2000, Assoc. Res. Otolaryngol. Abs: 5335.]
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 23, 2000
- Accession Number
- ADA484245
Entities
People
- David J. Klein
- Didier A. Depireux
- Jonathan Z. Simon
- Shihab A. Shamma
Organizations
- University of Maryland