FREQUENCY RESOLUTION AND SPECTRAL INTEGRATION (CRITICAL BAND ANALYSIS) IN SINGLE UNITS OF THE CAT PRIMARY AUDITORY-CORTEX

Frequency resolution and spectral filtering in the cat primary auditor y cortex (AI) were mapped by extracellular recordings of tone response s in white noise of various bandwidths. Single-tone excitatory tuning curves, critical bandwidths, and critical ratios were determined as a function of neuronal characteristic frequency and tone level. Single-t one excitatory tuning curves are inadequate measures of frequency reso lution and spectral filtering in the AI, because their shapes (in most neurons) deviated substantially from the shapes of ''tuning curves fo r complex sound analysis'', the cut-yes determined by the band limits of the critical bandwidths. Perceptual characteristics of spectral fil tering (intensity independence and frequency dependence) were found in average critical bandwidths of neurons from the central and ventral A I. The highest frequency resolution (smallest critical bandwidths) rea ched by neurons in the central and ventral AI equaled the psychophysic al frequency resolution. The dorsal AI is special, since most neurons there had response properties incompatible with psychophysical feature s of frequency resolution. Perceptual characteristics of critical rati os were not found in the average neuronal responses in any area of the AI. It seems that spectral integration in the way proposed to be the basis for the perception of tones in noise is not present at the level of the AI.