Representation of CV-sounds in cat primary auditory cortex: intensity dependence

Abstract

The level-dependent representation of simple speech sounds in cat primary auditory cortex (AI) is explored in naive cats and in animals that have been exposed to these sounds in behavioral detection and discrimination tasks. Population analyses of multiple unit responses in the form of post-stimulus time histograms (PSTHs), neurograms, and spatial distribution were made for synthetic consonant–vowel sounds across AI. The temporal profile of cortical responses was robust across neurons, characterized by brief phasic responses at the onset of consonantal burst and voicing. The spectral profile of the sounds, i.e., the formant structure, was only weakly expressed in the response magnitude across characteristic frequency. The spatial response distribution across AI was discontinuous, and consisted of several patches of activation. Intensity-dependence in the spatial activity distribution was more strongly expressed than in population PSTHs and neurograms. Differences attributable to behavioral training were observed for rate-encoding and temporal encoding of speech sounds.