Study Shows Brain Processes Input That May Not Be Perceived
November 14, 2013

Now You See It, Even If You Don’t

Alan McStravick for – Your Universe Online

Freudian and Behavioral scientists have long been at odds regarding the validity of each school of thought. Freudians champion the idea that human perception is separated into three distinct compartments: the conscious, unconscious and pre-conscious. Behaviorists reject these constructs for their inability to be subjected to rigorous scientific testing. However, University of Arizona (UA) doctoral degree candidate Jay Sanguinetti may have just found a way to ruffle the feathers of the Behaviorist community.

Sanguinetti’s study, published online in the journal Psychological Science, indicates the brain can understand and process visual input, even when that input isn’t consciously perceived. This revelation is a challenge to the currently accepted models regarding how the brain processes visual information.

Sanguinetti, performing his research in UA’s Department of Psychology in the College of Science, presented a series of black silhouettes to his study participants. Embedded into the white outsides of some of the silhouettes were meaningful, real-world objects. Along with his doctoral adviser Mary Peterson, professor of psychology and director of UA’s Cognitive Science Program, and John Allen, UA Distinguished Professor of psychology, cognitive science and neuroscience, Sanguinetti employed the used of electroencephalograms (EEG) to monitor the subjects’ brainwaves while they observed the series of silhouettes.

“We were asking the question of whether the brain was processing the meaning of the objects that are on the outside of these silhouettes,” Sanguinetti said. “The specific question was, ‘Does the brain process those hidden shapes to the level of meaning, even when the subject doesn't consciously see them?’”

As it turns out, data collected from Sanguinetti’s study definitively says yes.

According to the team, the brains of study participants processed the shapes on the silhouettes to the level of understanding their meaning, judging from their brainwaves. This was true even in instances when the participant never made a conscious recognition of the shape outside of the silhouetted image.

“There's a brain signature for meaningful processing,” Sanguinetti said. A peak in the averaged brainwaves called N400 indicates that the brain has recognized an object and associated it with a particular meaning.

"It happens about 400 milliseconds after the image is shown, less than a half a second," said Peterson. "As one looks at brainwaves, they're undulating above a baseline axis and below that axis. The negative ones below the axis are called N and positive ones above the axis are called P, so N400 means it's a negative waveform that happens approximately 400 milliseconds after the image is shown."

Had there been no N400 peaks, the team would be unable to make the claim that participants’ brains could recognize the meaning of the shapes on the outside of the figure.

"The participants in our experiments don't see those shapes on the outside; nonetheless, the brain signature tells us that they have processed the meaning of those shapes," said Peterson. "But the brain rejects them as interpretations, and if it rejects the shapes from conscious perception, then you won't have any awareness of them."

"We also have novel silhouettes as experimental controls," Sanguinetti said. "These are novel black shapes in the middle and nothing meaningful on the outside."

In this second style of silhouettes in the series, the N400 waveform was absent from the EEG of the subjects. This means the brain, consciously or unconsciously, was unable to detect a meaningful object in the image.

"This is huge," Peterson said. "We have neural evidence that the brain is processing the shape and its meaning of the hidden images in the silhouettes we showed to participants in our study."

Of course, the finding leads to more questions that will need to be addressed with further study. Chief among them: Why would the brain take the time to process the meaning of a shape when a person is ultimately not going to perceive it?

"The traditional opinion in vision research is that this would be wasteful in terms of resources," Sanguinetti explained. "If you're not going to ultimately see the object on the outside why would the brain waste all these processing resources and process that image up to the level of meaning?"

"Many, many theorists assume that because it takes a lot of energy for brain processing, that the brain is only going to spend time processing what you're ultimately going to perceive," added Peterson. "But in fact the brain is deciding what you're going to perceive, and it's processing all of the information and then it's determining what's the best interpretation.

"This is a window into what the brain is doing all the time," Peterson said. "It's always sifting through a variety of possibilities and finding the best interpretation for what's out there. And the best interpretation may vary with the situation."

The team theorizes the march through time and evolution may have given our brains the ability to sift through the barrage of visual input we receive and ultimately identify only those things most important for us to perceive consciously, such as threats or resources like food.

Future study for the team will focus on the specific regions in the brain responsible for the processing of meaning.

"We're trying to look at exactly what brain regions are involved," said Peterson. "The EEG tells us this processing is happening and it tells us when it's happening, but it doesn't tell us where it's occurring in the brain.

"We want to look inside the brain to understand where and how this meaning is processed," said Peterson.

Each image presented to the study’s participants was viewable for only 170 milliseconds. Despite this drastically abbreviated time, the subject’s brains were able to complete the complex processes necessary to interpret the meaning of the hidden objects contained in the silhouettes.

"There are a lot of processes that happen in the brain to help us interpret all the complexity that hits our eyeballs," Sanguinetti said. "The brain is able to process and interpret this information very quickly."

Sanguinetti’s study, funded by a grant to Peterson from the National Science Foundation, suggests our brains are working overtime all the time. As we walk down the street, our brains may recognize many meaningful objects in the visual scene, but our consciousness of those many objects is filtered down to merely a handful of what our brain recognizes. Our brain is taking in and shuffling massive amounts of information and releasing to us what it believes to be the best and most useful interpretation of the visual world.