Our visual perception of the world is usually regarded as relatively stable. Nonetheless, like all of our cognitive functions, visual processing is formed by our experiences. During each development and maturity, learning can alter visual perception. For instance, improved visual discrimination of comparable patterns is a learned skill critical for reading. In a recent research study published in Current Biology, scientists have now discovered the neuronal changes that occur during learning to enhance discrimination of closely related visual images.

This study, led by first creator Dr. Joseph Schumacher and senior creator Dr. David Fitzpatrick on the Max Planck Florida Institute for Neuroscience, establishes a transformative approach to studying perceptual learning within the brain. Researchers imaged the activity of huge numbers of single neurons over days to trace the changes that occur while a visible discrimination task is learned, performing these experiments in a novel animal model, the tree shrew.

The tree shrew is a small mammal with visual properties akin to the human, including a high degree of visual acuity and an identical orderly spatial arrangement of visually responsive neurons within the brain. Because the researchers show, these animals may learn complex behavioral tasks, making them ideal for understanding how experience shapes visual perception. On this study, tree shrews were trained to discriminate between highly similar visual images: an identical black lines that differed only by a small change in orientation (22.5 degrees). In the duty, the presentation of the lines at one orientation was rewarded with a drop of juice. Over days, tree shrews learned to discriminate between the 2 similar visual images, licking only in response to the lines on the rewarded orientation and withholding licking to the lines on the non-rewarded orientation.

The scientists combined this behavioral task with measurements of neural activity in V1, an area of the brain essential for visual processing. The neurons on this area are activated by specific features of visual input, equivalent to the orientation of light-dark edges. Individual neurons show ‘preference’ for specific edge orientations, responding with the very best activity to those orientations and with progressively lower activity or no activity to edges orientated farther from the popular orientation. In this manner, a visible scene that has edges with different orientations prompts particular subsets of neurons to generate a neural activity pattern that encodes the data needed for visual perception.

Schumacher and colleagues found that visual discrimination learning within the tree shrew was accompanied by enhancement of the difference within the patterns of neural activity evoked by the 2 visual images. This was primarily because of a rise in the quantity of neural activity in response to the presentation of the rewarded stimulus orientation relative to the non-rewarded orientation. But this was not only a general increase in neuronal responses to the rewarded stimulus. When the scientists examined the changes more closely, they found that this was mediated by changes within the activity of a remarkably specific subset of neurons: those whose orientation preference was optimal for distinguishing the orientation of the rewarded stimulus from the non-rewarded stimulus.

To completely understand the effect of learning on visual perception, the authors next investigated whether the changes in neuronal activity that improved visual discrimination persevered outside of the learned task context. Interestingly, they found that the neuronal changes not only persevered but were accompanied by changes within the trained tree shrew’s abilities to perform other discriminations. This included each enhancements for some stimulus orientations and impairments for others-; behavioral changes that were exactly what can be expected given the changes within the responses of this specific subset of neurons.

“This work demonstrates specific experience-driven changes within the activity of neurons that impact the perception of visual stimuli, enhancing discriminations relevant to task performance on the expense of other related discriminations,” explains first creator Joe Schumacher. Now the lab has set its sights on combining this approach with recent technologies to unlock the sequence and changes that occur in multiple forms of neurons as a way to mediate perceptual learning. By probing these questions within the visual system of the tree shrew, scientists within the Fitzpatrick lab are discovering fundamental recent insights about perceptual learning that might impact our understanding of a broad range of learning disorders.

Source:

Max Planck Florida Institute for Neuroscience

Journal reference:

10.1016/j.cub.2022.06.009