Current Biology
Volume 26, Issue 17, 12 September 2016, Pages 2280-2290
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Article
Encoding of Stimulus Probability in Macaque Inferior Temporal Cortex

https://doi.org/10.1016/j.cub.2016.07.007Get rights and content
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Highlights

  • Inferior temporal cortex encodes prediction errors and long-term probabilities

  • These effects persist even after local stimulus repetition has been accounted for

  • Probability signals are observed throughout the entire trial duration

  • Activity evoked at the time of behavioral response is also modulated by expectations

Summary

Optimal perceptual decisions require sensory signals to be combined with prior information about stimulus probability. Although several theories propose that probabilistic information about stimulus occurrence is encoded in sensory cortex, evidence from neuronal recordings has not yet fully supported this view. We recorded activity from single neurons in inferior temporal cortex (IT) while monkeys performed a task that involved discriminating degraded images of faces and fruit. The relative probability of the cue being a face versus a fruit was manipulated by a latent variable that was not revealed to the monkeys and that changed unpredictably over the course of each recording session. In addition to responding to stimulus identity (face or fruit), population responses in IT encoded the long-term stimulus probability of whether a face or a fruit stimulus was more likely to occur. Face-responsive neurons showed reduced firing rates to expected faces, an effect consistent with “expectation suppression,” but expected stimuli were decoded from multivariate population signals with greater accuracy. These findings support “predictive coding” theories, whereby neural signals in the mammalian visual system actively encode and update predictions about the local sensory environment.

Keywords

decision making
expectation suppression
monkey
neuron
predictive coding

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