Finally, Ramla Msheik ran model simulations based on a leaky evidence accumulation process and reproduced the results observed in the ventral visual cortex, indicating that this regions might be implementing leaky evidence accumulation for perceptual experience!

Decoders in the ventral visual cortex also reflected non-veridical percepts, when participants reported seeing a face when none was presented or reported seeing more than one face when only one was presented.

To assess if the same neural code underlies all these responses, we tested if a multivariate decoder trained on immediate detection could reflect evidence accumulation, delayed detection and confidence, and passive perception. We found such signatures in the ventral visual cortex.

Additionally, we asked participants to report confidence in their detection in the delayed-response experiment. In several regions including the ventral visual cortex, the HGA was modulated by perceptual confidence independent of stimulus intensity.

The results at the region level seemed to be mostly driven by channels located in the mid-fusiform gyrus, consistent with the location of the fusiform face area.

Looking at pre-registered regions of interest, the ventral visual cortex was the only region that was found to (1) accumulate evidence, (2) reflect detection and (3) respond to stimulus intensity during passive perception.

Populations of neurons involved in conscious access should respond more strongly to suprathreshold than threshold stimuli, as the former were perceived consciously more often. The HGA of some channels displayed this effect, mirroring the effect of detection in experiment 2.

In a second experiment, participants waited for the end of the trial to provide a delayed response. We found HGA signatures of detection irrespective of (1) motor preparation and (2) stimulus intensity (threshold vs suprathreshold faces).

In a first experiment, participants pressed on a button as soon as they saw a face. Looking at the slope of high gamma activity (HGA), we found signatures of evidence accumulation in the ventral visual, insular and inferior cortices amongst other regions.

Our new sEEG study is out on BioRxiv: tinyurl.com/4afh3b9n! Using 3 face detection experiments and recording from >3000 channels, we found a neural code that reflected evidence accumulation for conscious perception and perceptual confidence! 👇