Neural mechanisms of value bias in the human visual cortex (12/26/2008)

New research demonstrates that bias toward a potentially more valuable outcome can influence how visual information is processed in the human brain. The study, published by Cell Press in the December 26th issue of the journal Neuron, provides insight into how the visual centers encode more valuable stimuli at the expense of less valuable alternatives.

Acquisition and evaluation of incoming sensory information is absolutely critical for guiding interactions with the environment. There is no doubt that prior rewards have a strong influence on decision making and that the value of a stimulus modulates the activity of neurons involved in initiating movements towards the more favorable of alternatives.

However, although recent studies have suggested that value also influences areas of the brain involved in processing sensory input, many questions remain. "Little is known about how value influences the acquisition and representation of incoming sensory information, or about the neural mechanisms that track the relative value of different objects to guide behavior," explains senior study author, Dr. John Serences from the Department of Psychology at the University of California, San Diego.

To examine how value impacts visual processing, Dr. Serences used functional magnetic resonance imaging to estimate changes in neural activity as human subjects selected one of two spatially separated targets (red or green) that varied in value across the course of the experiment. His experimental paradigm was carefully designed so as to measure value-related modulations within areas of the visual cortex and to dissociate the influence of prior rewards and subjective value.

The study revealed value-related modifications in many different areas of the human visual system. Interestingly, value influenced activation of early regions of visual cortex that are thought to play a key role in representing features of objects in the environment (shapes, colors, etc.). In addition, these modifications of neural activity were primarily driven by the reward history of each stimulus and not to self-reported estimates of stimulus value. "This result raises the intriguing possibility that these value related changes in brain activity operate largely via an implicit mechanism that is not necessarily accessible to the observer," offers Dr. Serences.

Dr. Serences also observed activation in regions of frontal and parietal cortex that were associated with representing the difference between the value of the two objects; these areas were very active when one choice was much more valuable than the other, and less active when the choices were of approximately equal value. Interestingly, these cortical areas have been previously implicated in the process of anticipating and tracking rewards. "These findings suggest that these brain regions may provide signals to bias visual processing in favor of more valuable stimuli, perhaps so that valuable objects are processed more efficiently and have more of an impact on decision making and behavior," concludes Dr. Serences.

Note: This story has been adapted from a news release issued by the Cell Press

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