Ehud Zohary

Visual perception, memory & eye movements

Active vision, visual remapping and integration across saccades

The visual image is heavily blurred in the periphery (the fovea, a region with highest visual acuity, is limited to the central ~2 degrees of the visual field). One of our means to compensate for this limitation is to constantly scan the visual scene, making about 3 saccades in a second. This in turn generates another problem, since the retinal image is changing with every new eye movement we make. Still, our brain seamlessly generates a stable representation of the visual scene. This perceptual stability is so robust that we live in an illusion that we see everything at the highest precision all at once.

Perception and action form a tightly coupled loop. On the one hand, action is driven by perception: our eyes are drawn to salient features (or objects) in the scene. See an example of a typical pattern of eye movements (shown in arrows and circles) during natural scene viewing. But on the other hand, perception is also governed by action: We can only resolve fine visual details in the parts of the scene that are mapped on our fovea (try recognizing the animals in the scene without fixating on them). In our lab we (Ayelet McKyton, Yoni Pertzov) are using both behavioral procedures and MRI scanning techniques to study the following issues in active vision:

Visual remapping

Where in the visual pathways does remapping take place (i.e. a change from a retinotopic representation to a representation independent of eye/head/ or body position)? 

What is the representation in the ventral and dorsal pathways? The coordinates of the map may well depend on the function of the cortical region.  This may lead to a use of different coordinate systems in the two pathways. 

When does this remapping occur?  This can be probed using various behavioral techniques, in which the timing between the image presentation and saccade onset is variable. 

Active vision, attention and memory

What's the source of the remapping signal (visual, motor, proprioceptive)? What are the underlying principles of connectivity between the cortical eye-movement areas (FEF, SEF, LIP) and the visual cortex. 

What  information is  accumulated across saccades. How do we build a reliable representation of a scene.

What guides our eye movements: Feature salience vs. attentive guidance. The role of an implicit search template.