A computational model of serial and parallel processing in visual search

The following is a dissertation aimed at understanding what the various phenomena in visual search teach us about the nature of human visual representations and processes. I first review some of the major empirical findings in the study of visual search. I next present a theory of visual search in terms of what I believe these findings suggest about the representations and processes underlying ventral visual processing. These principles are instantiated in a computational model called CASPER (Concurrent Attention: Serial and Parallel Evaluation with Relations), originally developed by Hummel, that I have adapted to account for a range of phenomena in visual search. I then describe an extension of the CASPER model to account for our ability to search for visual items defined not simply by the features composing those items but by the spatial relations among those features. Seven experiments (four main experiments and three replications) are described that test CASPER's predictions about relational search. Finally, I evaluate the fit between CASPER's predictions and the empirical findings and show with three additional simulations that CASPER can account for negative acceleration in search functions for relational stimuli if one postulates that the visual system is leveraging an emergent feature that bypasses relational processing.