Optimality in saccade planning
The visual system is more accurate at the center of the eye -- the fovea, than in the periphery. Does the observer have any knowledge, explicit or implicit, of this acuity function? We have asked this question using an oculomotor economical game based on visual search. In this task subjects could maximize their reward only if they took into account their acuity when planning the next saccade. The paper is in preparation, meanwhile, you can find some more details in our cosyne abstract.
Visuo-motor coordination
Hand movement planning is highly constrained by vision and vice versa. Psychophysical research has focused on skilled behaviors requiring tight eye-hand coordination. However, many activities (driving, reading, typing, playing music, etc.) require the hand and eye motor systems to work separately. The eyes move quickly and very precisely in a ballistic manner. In contrast, the hand's movement is much slower and can be adjusted during an action. The eyes and hands are two systems with different dynamics that often interact. Do those systems interact coherently in an optimal fashion over time? Our results seem to show that it is not the case.
Compensation for smooth pursuit eye movements
When we move our eyes, for instance to follow a moving object, the background slips on the retina with a velocity opposite-and-equal to that of the eyes. In order to perceive the real position and speed of objects in space, this retinal slip must be compensated for. The classical model of compensation states that an extraretinal signal encodes the eye velocity and is substracted to the retinal image. This linear model has been widely used and is considered as a reference. In Morvan & Wexler (2009) we show that this model does not explain compensation for movement non colinear to the pursuit. More details here.
Do we perceive motion on the retina or in the world?
Motion pops-out and it is good because moving objects are potential threats. Given the rapidity of this detection one could think that it occurs at a low level of processing -- like the retina or V1 -- but the motion at those steps of processing is not compensated yet (ie, non corrected for the eye movement -- see here for more details). Where does pop-out occur: at low level -- uncompensated motion -- or high-level -- motion in the world? In Morvan & Wexler (2005) by coupling object motion to eye motion, we created stimuli that moved fast on the retina but slowly in an eye-independent reference frame, or vice versa. In the 100 ms after stimulus onset, motion detection is dominated by retinal motion, uncompensated for eye movements. As early as 130 ms, compensated signals become available: objects that move slowly on the retina but fast in an eye-independent frame are detected as easily as those that move fast on the retina.
Stopping rules in visual search
One major challenge of visual search tasks is to decide when to quit if the target has not yet been found. In a study in collaboration with Jeremy wolfe's Visual Attention Lab we asked whether observers stop searching at an optimal point. We used a classical visual search task as well as a cognitive equivalent in which subjects has to click on object to sample the environement. We found that subjects have on average a tendency to undersample and therefore do not maximize expected gain.