A signature of neural coding at human perceptual limits.
Simple visual features, such as orientation, are thought to be represented in the spiking of visual neurons using population codes. I show that optimal decoding of such activity predicts characteristic deviations from the normal distribution of errors at low gains. Examining human perception of orientation stimuli, I show that these predicted deviations are present at near-threshold levels of contrast. The findings may provide a neural-level explanation for the appearance of a threshold in perceptual awareness whereby stimuli are categorized as seen or unseen. As well as varying in error magnitude, perceptual judgments differ in certainty about what was observed. I demonstrate that variations in the total spiking activity of a neural population can account for the empirical relationship between subjective confidence and precision. These results establish population coding and decoding as the neural basis of perception and perceptual confidence.
Paul M
PM
Bays
D000328:Adult; D001364:Awareness; D001921:Brain / Q000166:cytology*; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D009474:Neurons / Q000502:physiology*; D009949:Orientation / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult