Memory and perception seem to be completely different experiences, and neuroscientists were once confident that the brain creates them differently, too. But in the 1990s, neuroimaging studies revealed that parts of the brain that were thought to be active only during sensory perception were also active during memory recall.
“It starts to raise the question of whether a memory representation is really different from a perceptual representation,” he said. Sam Ling, associate professor of neuroscience and director of the Visual Neuroscience Laboratory at Boston University. Could our memory of a beautiful savanna forest, for example, be just a reconstruction of the neural activity that enabled us to see it before?
“The debate has moved from debate about whether there is any sensory cortex involvement to saying ‘Oh, wait a minute, is there any difference?'” Christopher Baker, an investigator at the National Institute of Mental Health who runs the learning and resilience unit. “The pendulum swung from side to side, but it swung too far.”
Even if there is a very strong neural similarity between memory and experience, we know that they cannot be exactly the same. “Don’t confuse them,” said Serra Favilaa postdoctoral scientist at Columbia University and the lead author of a recent study natural communication research. Her team’s work has identified at least one of the ways in which visual memories and perceptions are assembled differently at the neural level.
Blurred spots
As we look at the world, visual information about it travels through the photoreceptors of the retina and into the visual cortex, where it is processed sequentially in different groups of neurons. Each group adds new levels of complexity to the image: Simple highlights turn into lines and edges, then outlines, then shapes, then complete scenes that represent what we’re seeing.
In the new study, the researchers focused on a visual processing feature that’s important in early groups of neurons: the position of things in space. The pixels and contours that make up an image need to be in the right place, or else the brain will create a disturbing, imperceptible distortion of what we’re seeing.
The researchers trained participants to memorize the positions of four different patterns on a background that resembles a dartboard. Each pattern is placed in a very specific position on the board and is associated with a color in the center of the board. Each participant was checked to make sure they had memorized this information correctly—for example, if they saw a green dot, they knew the star was on the far left. left. Then, as the participants perceived and memorized the locations of the patterns, the researchers recorded their brain activity.
Brain scans allow researchers to map how neurons record the location of something, as well as how they remember it later. Each neuron participates in a space, or “receptive field,” in your field of vision, such as the lower left corner. A neuron “will only work when you put something on that little spot,” says Favila. Neurons tuned to a certain point in space tend to cluster together, making their activity easier to detect during brain scans.
Previous studies on visual perception have determined that neurons in the lower, early processing levels have small receptive fields, and neurons in the higher, later levels have larger receptive fields. This makes sense because higher-level neurons are synthesizing signals from many lower-level neurons, gathering information over a wider array of the visual field. But a larger receptive field also means lower spatial accuracy, creating an effect like dotting a large ink dot over North America on a map to represent New Jersey. In fact, visual processing in perception is a matter of sharp little dots growing into larger, dimmer but more meaningful blobs.
