The Taub Faculty of Computer Science Events and Talks

Why do we perceive some elements in a visual scene, while others remain undetected? We compared fixations on detected vs. undetected items in the Identity Search Task (Jacob & Hochstein, 2009). Using a gaze-contingent technique, we further controlled the number of fixations on the target (Jacob & Hochstein, 2010). Results show that detected targets were fixated at a greater extent, and a backward dynamics alignment revealed a bifurcation point where the differential characteristics begin. Moreover, the greater the number of target fixations, the better the recognition, as manifested in a decrease in response time, increases in hit-rate and detectability, d', and increase in reported response confidence. The results suggest that target fixations lead to an early implicit recognition which in turn leads to more fixations, and ultimately to full explicit recognition. We constructed a model (Jacob & Hochstein, 2011) which simulates the relative information that is available to the observer for each scene unit, at any given moment. Depending on the eye movement scan-path, the available information is incremented by the fixations as well as affected by memory decay. The model results reflect the experimental conclusion that several target fixations are needed for processing visual information in order to achieve recognition.