Visual search requires sequences of saccades. Many studies have focused on spatial aspects of saccadic decisions, while relatively few (e.g., Hooge & Erkelens, 1999) consider timing. We studied saccadic timing during search for targets (thin circles containing tilted lines) located among nontargets (thicker circles). Tasks required either (a) estimating the mean tilt of the lines, or (b) looking at targets without a concurrent psychophysical task. The visual similarity of targets and nontargets affected both the probability of hitting a target and the saccade rate in both tasks. Saccadic timing also depended on immediate conditions, specifically, (a) the type of currently fixated location (dwell time was longer on targets than nontargets), (b) the type of goal (dwell time was shorter prior to saccades that hit targets), and (c) the ordinal position of the saccade in the sequence. The results show that timing decisions take into account the difficulty of finding targets, as well as the cost of delays. Timing strategies may be a compromise between the attempt to find and locate targets, or other suitable landing locations, using eccentric vision (at the cost of increased dwell times) versus a strategy of exploring less selectively at a rapid rate.

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BackgroundPrior studies of oculomotor function in Parkinson’s disease (PD) have either focused on saccades without considering smooth pursuit, or tested smooth pursuit while excluding saccades. The present study investigated the control of saccadic eye movements during pursuit tasksand assessed the quality of binocular coordinationas potential sensitive markers of PD.MethodsObservers fixated on a central cross while a target moved toward it. Once the target reached the fixation cross, observers began to pursue the moving target. To further investigate binocular coordination, the moving target was presented on both eyes (binocular condition), or on one eye only (dichoptic condition).ResultsThe PD group made more saccades than age-matched normal control adults (NC) both during fixation and pursuit. The difference between left and right gaze positions increased over time during the pursuit period for PD but not for NC. The findings were not related to age, as NC and young-adult control group (YC) performed similarly on most of the eye movement measures, and were not correlated with classical measures of PD severity (e.g., Unified Parkinson’s Disease Rating Scale (UPDRS) score).DiscussionOur results suggest that PD may be associated with impairment not only in saccade inhibition, but also in binocular coordination during pursuit, and these aspects of dysfunction may be useful in PD diagnosis or tracking of disease course.

The interpretation of other agents as intentional actors equipped with mental states has been connected to the attribution of rationality to their behavior. But a workable definition of "rationality" is difficult to formulate in complex situations, where standard normative definitions are difficult to apply. In this study, we explore a notion of rationality based on the idea of evolutionary fitness. We ask whether agents that are more adapted to their environment are, consequently, perceived as more rational and intentional. We created a 2-D virtual environment populated with autonomous virtual agents, each of which behaves according to a built-in program equipped with simulated perception, memory, and decision making. We then introduced a process of simulated evolution that pressured the agents' programs toward behavior more adapted to the simulated environment. We showed these agents to human subjects in 2 experiments, in which we respectively asked them to judge their intelligence and to dynamically estimate their "mental states." The results confirm that subjects construed evolved agents as more intelligent, and judged evolved agents' mental states more accurately, relative to nonevolved agents. These results corroborate a view that the interpretation of agent behavior is connected to a concept of rationality based on the apparent fit between an agent's actions and its environment.