Decoding rapidly presented visual stimuli from prefrontal ensembles without report nor post-perceptual processing.

Summary

Neuronal activity in the macaque prefrontal cortex (PFC) reliably encodes visual stimuli even when perception and post-perceptual processing are challenged by rapid serial visual presentation (RSVP). Stimulus identity could be decoded from PFC population activity, with first signals at 60 ms and peak information at 150 ms after stimulus onset. In RSVP, decoding accuracy dropped to chance by 200 ms, and the next stimulus became decodable. Decoding in ventrolateral PFC was stronger than in posterior parietal cortex. The findings show PFC encodes stimuli under conditions that reduce conscious perception and post-perceptual processing in humans.

Study at a glance

Abstract

The role of the primate prefrontal cortex (PFC) in conscious perception is debated. The global neuronal workspace theory of consciousness predicts that PFC neurons should contain a detailed code of the current conscious contents. Previous research showed that PFC is indeed activated in paradigms of conscious visual perception, including no-report paradigms where no voluntary behavioral report of the percept is given, thus avoiding a conflation of signals related to visual consciousness with signals related to the report. Still, it has been argued that prefrontal modulation could reflect post-perceptual processes that may be present even in the absence of report, such as thinking about the perceived stimulus, therefore reflecting a consequence rather than a direct correlate of conscious experience. Here, we investigate these issues by recording neuronal ensemble activity from the macaque ventrolateral PFC during briefly presented visual stimuli, either in isolated trials in which stimuli were clearly perceived or in sequences of rapid serial visual presentation (RSVP) in which perception and post-perceptual processing were challenged. We report that the identity of each stimulus could be decoded from PFC population activity even in the RSVP condition. The first visual signals could be detected at 60 ms after stimulus onset and information was maximal at 150 ms. However, in the RSVP condition, 200 ms after the onset of a stimulus, the decoding accuracy quickly dropped to chance level and the next stimulus started to be decodable. Interestingly, decoding in the ventrolateral PFC was stronger compared to posterior parietal cortex for both isolated and RSVP stimuli. These results indicate that neuronal populations in the macaque PFC reliably encode visual stimuli even under conditions that have been shown to challenge conscious perception and/or substantially reduce the probability of post-perceptual processing in humans. We discuss whether the observed activation reflects conscious access, phenomenal consciousness, or merely a preconscious bottom-up wave.

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