Macaque neurons switch between seen and hidden faces 15 times a second

Neuroscientists at the University of California, Berkeley, and Princeton University, led by Janis K. Hesse and Doris Y. Tsao, report that the primate brain alternates between a consciously seen image and a suppressed one about 15 times per second, according to a bioRxiv preprint covered by ZME Science. zmescience.com The work used two rhesus macaques and has not yet passed peer review. zmescience.com

The authors argue that conscious access depends not only on where information is processed but also on when neurons fire. zmescience.com Earlier recordings, including the 2025 COGITATE Consortium study in Nature, did not reveal a pure neural representation of conscious perception in any recorded region during rivalry. zmescience.com

Binocular flash suppression and recordings

The team used binocular flash suppression. Each macaque wore red-and-cyan 3D glasses, so each eye received a different face. zmescience.com When a second face was flashed to one eye, the first dropped out of awareness although both images stayed in front of the eyes. zmescience.com To validate the effect, 14 human volunteers viewed the same display and reported that the second face dominated their awareness 82 percent of the time. zmescience.com

The researchers then inserted Neuropixels probes and recorded hundreds of neurons at once across 1,500 face presentations. zmescience.com The targets were face-selective areas of the inferotemporal cortex and the prefrontal cortex. zmescience.com

Decoding faces in 60-millisecond windows

First, the monkeys viewed 1,500 faces without rivalry. An algorithm learned to translate the spikes of 3,501 neurons into 50 measurements of facial shape and appearance. zmescience.com Averaged over a full second, the decoded output was a blurred merger of both faces. zmescience.com Split into alternating 60-millisecond states, it gave sharp reconstructions of the consciously seen face in one state and of the suppressed face in the other. zmescience.com

The same neurons produced both portraits, rather than two separate groups of cells. zmescience.com During conscious windows, neurons were about 21 percent more sensitive to facial features than during suppressed windows. zmescience.com The authors say the suppressed stimulus is not a weak residual trace but occupies the same face space. zmescience.com

The study covered specific visual and frontal areas in only two monkeys. zmescience.com What drives the 15-hertz rhythm, and why only some time segments reach awareness, remains unknown. zmescience.com

Berkeley and Princeton: macaque neurons alternate between seen and suppressed faces 15 times a second

Binocular flash suppression and recordings

Decoding faces in 60-millisecond windows

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