Berkeley and Princeton: macaque neurons alternate between seen and suppressed 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.comZME Sciencezmescience.comOpen source ↗ The work used two rhesus macaques and has not yet passed peer review.

The authors argue that conscious access depends not only on where information is processed but also on when neurons fire. 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.

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. When a second face was flashed to one eye, the first dropped out of awareness although both images stayed in front of the eyes. 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.

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

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. Averaged over a full second, the decoded output was a blurred merger of both faces. 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.

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

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