Mechanisms of long-term adaptation in visual cortex

The brain has a remarkable ability to change its own function. In the visual system, such plasticity is evident when children learn to read, when the elderly adjust to impaired vision, and when new drivers master navigating traffic. The mechanisms that produce long-lasting plasticity in the visual brain remain unclear, however. With support from the National Science Foundation, Dr. Stephen Engel of the University of Minnesota is carrying out research to elucidate mechanisms of long-term visual plasticity. The work builds upon effects of short-term plasticity that are relatively well-understood. For example, when observers view a bright pattern of stripes for a few minutes, their visual systems adapt, and fairly dramatic consequences can result: Faint patterns of similar stripes that were previously apparent can be briefly rendered completely invisible. But few laboratory studies have examined perceptual adaptation over the long term, primarily due to methodological limitations. This project uses recently developed technology to overcome those roadblocks. Participants view video on a head-mounted display that originates in a head-mounted camera and is image-processed by a lap-top computer. The system allows participants to live in a visual world that has been digitally altered. Four experiments use this system to test hypotheses about long-lasting plasticity in the visual system. The first hypothesis is that longer duration adaptation will produce longer lasting plasticity. Participants are placed for up to five days in environments similar to those that produce short-term perceptual adaptation effects. The persistence of adaptation is measured using traditional tests of perceptual abilities. The second hypothesis is that the visual system adapts to discount noisy, uninformative visual input, as suggested by preliminary results. Experiments in this project measure the strength of this novel form of adaptation over the long term. The third hypothesis is that both kinds of adaptation effects arise in early visual cerebral cortex. To test this, the neural bases of long-term adaptation is measured with functional magnetic resonance imaging (fMRI). Together, these experiments can strongly constrain both empirical and theoretical accounts of long-lasting visual plasticity.

This research is advancing understanding of how the human visual system can modify its own operation. This ability, visual plasticity, underlies the acquisition a wide array of human skills, from learning to read, to learning to hit a baseball, to learning to see patterns in satellite imagery. The project uses novel technology to place observers in a digitally altered world for up to 5 days, and measures how their visual perception and their visual cortex adapt to this challenge. Results can help identify specific factors, for example the length and kind of visual stimulation, which lead to long-lasting changes in visual performance. These in turn should have important applications in a diverse array of fields where visual plasticity is critical, from education to the military to public health.