Abstract
We previously demonstrated the active contribution of orienting to preference decision making (Shimojo et al, 2003) in the “gaze cascade effect”, a continually increasing likelihood that subjects' gaze was directed to the stimulus eventually chosen. The effect was robust across a wide range of stimuli and conditions (VSS 04), thus we suspected that whenever a preference decision needs to be made the gaze cascade accompanies it. We here show an extreme case where gaze cascade effect was observed even when the stimuli were no longer visually present. Unlike our previous studies, the observation duration was controlled and randomized by the experimenter while subjects were trying to decide the preferred one. In roughly half of the trials the presentation time was long enough for a decision, mimicking our previous experiments. However, in the other half, a decision had to be made after the stimuli were taken off the screen. Testing whether visual input is required for the cascade effect was one the motivations of this study. We used eye-tracking and our gaze likelihood analysis (VSS 02).
First, as expected, we show the gaze cascade effect before decision in the trials in which observers had enough time to choose the preferred stimulus. Moreover, the bias slowly decreases in the next second after decision, when the stimuli were still presented on the screen, confirming that the cascade is linked to the decision process and not to observers' already-made preference. Second and intriguingly, in the trials where a decision came after the stimuli were removed from the screen, the cascade was still present. Thus, gaze is participating in the decision process even when the decision is made purely in memory. Observers made fixations in the approximate regions previously occupied by faces, and their gaze pattern was still correlated with their decision. Thus our claim that gaze cascade is intrinsically involved in the decision making process is extended beyond perceptual domain.