The response of single units in the auditory cortex of rhesus monkeys to predicted and to unpredicted sound stimuli.
Rhesus monkeys were trained to predict the nature of short auditory signals of two different types, to which they responded differentially. Prediction was based on visual signals that preceded the auditory ones. The monkey's use of the visual signals as predictors was assessed through two behavioural criteria. (1) performance in trials in which the visual signals was followed by the correct auditory signal (true conditioning) vs performance in trials in which the visual signal was followed by the wrong auditory signal (false conditioning). (2) Reaction time in trials with different types of conditioning. The response of single auditory cortex units to correctly and to incorrectly predicted auditory signals was recorded. The unconditioned response of every unit to each type of auditory stimulus was also obtained. Of 92 units that were analysed in detail, the response of about half was affected by the predictability of the stimulus. Units were affected in two different ways. One involved facilitation of the response to correctly predicted signals and inhibition of the response to incorrectly predicted signals. The other involved facilitation of the response to incorrectly predicted signals and base line response to correctly predicted signals. These findings were discussed in terms of neural mechanisms that relate to prediction.