University of Arizona doctoral degree candidate Jay Sanguinetti has authored a new study, published online in the journal Psychological Science, that indicates that the brain processes and understands visusal input that we may never consciously perceive. The finding challenges currently accepted models about how the brain processes visual information.
A doctoral candidate in the UA’s Department of Psychology in the College of Science, Sanguinetti showed study participants a series of black silhouettes, some of which contained meaningful, real-world objects hidden in the white spaces on the outsides. Saguinetti worked with his adviser Mary Peterson, a professor of psychology and director of the UA’s Cognitive Science Program, and with John Allen, a UA Distinguished Professor of psychology, cognitive science and neuroscience, to monitor subjects’ brainwaves with an electroencephalogram, or EEG, while they viewed the objects.
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?”
The answer, Sanguinetti’s data indicates, is yes.
Study participants’ brainwaves indicated that even if a person never consciously recognized the shapes on the outside of the image, their brains still processed those shapes to the level of understanding their meaning.
“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.”
The presence of the N400 peak indicates that subjects’ brains 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.”
The N400 waveform does not appear on the EEG of subjects when they are seeing truly novel silhouettes, without images of any real-world objects, indicating that the brain does not recognize 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.”
The finding leads to the question of why the brain would process the meaning of a shape when a person is ultimately not going to perceive it, Sanguinetti said.
“The traditional opinion in vision research is that this would be wasteful in terms of resources,” he 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?”