Poor visual search performance affects the quality of life for many people with vision impairments, visual field
loss (foveal or peripheral) and other low vision issues. Search involves multiple underlying neural processes
including the guidance of attention to and subsequent categorization of stimuli, which necessarily rely on
peripheral and foveal vision respectively. Our central hypothesis is that differences between central and
peripheral vision will result in systematic disassociations between categorical search guidance (directing
attention) and categorization. In recent years, the search literature has begun to explore categorical search,
however, this work is still in its infancy. By bridging the search and categorization literatures, we can begin to
characterize how the underlying category representation affects search performance.
A prominent categorization theory, called COVIS (for COmpetition between Verbal and Implicit Systems)
posits that explicit (verbalizable) category rule learning is mediated by the prefrontal cortex, while implicit
(nonverbalizable) rule learning is mediated by subcortical structures related to associative learning. Most
categorical search has historically utilized natural categories, which likely engage both systems to varying
degrees. We will utilize simple perceptual stimuli common to the categorization literature to isolate categorical
search performance mediated by explicit and implicit systems. In addition, we will also characterize decisional
influences like base-rates and payoffs on categorical search performance. This research in healthy young
controls is a necessary first step to develop new avenues to train individuals suffering from low vision, visual
field loss (i.e. central or peripheral vision loss) and those with various visual cognitive deficits. For example,
training people with an explicit verbalizable rule (when appropriate, such as pointing out specific features that
are easily attended in peripheral vision), may result in easier and faster visual search training. However, much
of the classification in daily life is likely learned via implicit (nonverbal) means and thus performance based
feedback training and gradual associative learning through repeated exposure may improve search and
classification outcomes.
In the proposed experiments, participants will perform implicit or explicit category rule learning followed by
search in which eye movements will be monitored. The eye movements allow us to distinguish between
changes in the ability to direct spatial attention to search targets (guidance) and categorization processes. By
examining the contribution of separate learning systems in the brain to determine category membership, the
effects of categorical variability, and decisional influences (base-rates and payoffs), we will systematically
characterize what makes explicit and implicit categorical search inefficient.