When Your Brain Is Overstimulated, It Can Forget Things You Just Saw

The human brain is pretty efficient at taking in a ton of information and quickly making sense of the world around us—it can process up to 70 images per second, and identify images that the eye sees for as little as 13 milliseconds.

But sometimes our brains can’t keep up with processing everything, and we wind up not realizing we saw certain details we did, in fact, see. Now, a group of neuroscientists have figured out why people experience this so-called “crash in visual processing.”

According to the study, published in the Journal of Vision Wednesday: When our brains take in too much information back-to-back (i.e., we see one image, then immediately see another), a bottleneck—or jam—of signals causes us to not be consciously aware of certain visual stimuli that our brains actually recognized.

The researchers conducted behavioral and electroencephalography (EEG) experiments, which entailed showing participants various nature scenes in quick, short bursts of 12 images per second. After, the participants were asked questions such as how many images contained animals and what kind of animals they saw, while the researchers studied the EEG responses to map out the brain’s visual signals. The team found that whenever two images were shown within about 400 milliseconds or less of one another, people struggled with recalling certain details in the images they saw. Interestingly, when subsequent images were shown in a different hemifield, or field of vision, the participants had a much higher chance (by about 72 percent) of recalling exactly what they had seen.

These visual crashes boil down to a glitch in the “feedback wave”—the way our brains recognize and understand images. When we detect something, a visual signal runs along a pathway that starts at the back of the brain and moves up toward the frontal cortex—this is known as “feed forward.” Then, when the signals reach the frontal cortex, they’re sent right back to the base of the brain where the came from—a process called “feedback” in which we become conscious of whatever it is we saw. If we see another image before the visual signal completes that entire loop, a crash takes place, causing us to not recognize details we saw.

This can all slow down how quickly humans learn and process new information. But understanding how this loops works could ultimately help facilitate learning and cognitive processing by reducing interference between the feedforward and feedback signals and giving our brains a moment to breathe, according to the researchers. “We can reduce neural interference and improve people's ability to recognize images even when they are presented at a rate of 12 per second by alternating which side of the visual field we show subsequent stimuli to,” said the study’s senior investigator Maximilian Riesenhuber, PhD, a professor of neuroscience at Georgetown. Cutting down on that "noise" could improve our ability to actually hold on to what we see.

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