Publisher Summary
This chapter introduces the methodology used in a series of papers by Richmond and Optican exploring temporal encoding in a primate visual area. They used principal components analysis and information theory to argue that a temporal code provided more information about the stimulus than a rate code did. Richmond and Optican studied pattern discrimination in a primate visual area, the inferior temporal (IT) cortex. They addressed the question of temporal coding in IT in a well-known series of papers in the Journal of Neurophysiology. They found that the firing rate of IT neurons modulated in response to the presentation of one of 64 two-dimensional visual stimuli. They also saw evidence of temporal modulation that was not captured by the firing rate. To quantify the relevance of this temporal modulation, Richmond and Optican converted the raster plot for each trial into a spike density function. They then computed principal components (PCs) of these functions. They computed the mutual information between the stimulus and either the firing rates (rate code) or the first three PCs (temporal code). Their results indicated that the temporal code carried on average twice the information as the rate code.