Do neurons see what we tell them to see?

Perception of a face's identity predicts whether a specific neuron will fire when presented with an image of blended faces
September 30, 2014

Which U.S. president do you see in this merged image? (Credit: Q. Quiroga et al./Neuron)

Neurons programmed to fire at specific faces may have more affect on conscious recognition of faces than the images themselves, neuroscientists have found.

Subjects presented with a blended face, such as an amalgamation of Bill Clinton and George W. Bush, had significantly more firing of such face-specific neurons when they recognized the blended or morphed face as one person or the other.

Results of the study led by Christof Koch at the Allen Institute for Brain Science were published (open access) online in the journal Neuron.

Some neurons in the region of the brain known as the medial temporal lobe are observed to be extremely selective in the stimuli they respond to. A cell may only fire in response to different pictures of a particular person who is very familiar to the subject (such as loved one or a celebrity, as in the famous “Jennifer Aniston neuron“), the person’s written or spoken name, or recalling the person from memory.

“These highly specific cells are an entry point to investigate how the brain makes meaning out of visual information,” explains Christof Koch, Chief Scientific Officer at the Allen Institute for Brain Science and senior author on the paper*. “We wanted to know how these cells responded not just to a simple image of a person’s face, but to a more ambiguous image of that face averaged or morphed with another person’s face.”

For the trials, subjects were first shown the “adaptor” image of the face of individuals such as Bill Clinton or George W. Bush, and then an ambiguous face that was a blend of both faces. Primed with the Clinton image, subjects tended to recognize Bush’s face in the blended image, while subjects who saw Bush’s face first recognized the blended face as Clinton. That is, even though the blended images were identical, subjects tended to consciously perceive the identity of face to which they were not adapted.

So do the selective neurons respond to the actual image on the screen, or more to the perception that the image causes in your brain? The researchers tested that and found that when subjects recognized the ambiguous face as belonging to Clinton, their Clinton-specific neurons fired.

However, when subjects recognized that same face as Bush, the “Clinton neurons” fired significantly less. These results indicated that conscious recognition of the face played a crucial role in whether the neurons fired, rather than the raw visual stimulus.

“This distinction may help us glean insight into how the brain takes raw visual information and transforms it into something meaningful, which can be further modulated by other aspects of experience in the brain,” explains Koch.

Or as comedian Richard Pryor put it, “Who are you going to believe, me or your lying eyes?”

Which raises a broader question: How do our past experiences bias our perception of abstract events (like climate change), based on our own different experiences?

* The study was carried out by neuroscientists Rodrigo Quian Quiroga at the University of Leicester, Alexander Kraskov at University College London, and Florian Mormann at the University of Bonn, under the clinical supervision of neurosurgeon Itzhak Fried at the University of California at Los Angeles Medical School.