Cognitive and cortical mechanisms of trans-saccadic motion perception

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My research program investigates the underlying mechanisms of a fundamental everyday conscious visual experience: the perception of a stable and continuous visual world despite dramatic changes to the location of objects in a visual scene every time we move our eyes. We scan our surroundings using rapid eye movements called saccades. We typically make about 3-5 saccades per second. During each saccade the entire image of the world shifts across our retina and objects in our surroundings shift to different retinal locations. However, rather than perceiving these objects as jumping around as our eyes move they are normally perceived as spatially stable in the world. This is an example of perceptual continuity in so-called trans-saccadic perception, and suggests that the visual system has mechanisms for keeping track of where objects are in space by taking into account the change in gaze during saccades. Most research on perceptual continuity in trans-saccadic perception has been focused on how the brain keeps track of the locations of static visual stimuli in a scene. But what happens in a dynamic scene with moving objects like what we experience in the real world? For example, when driving we often make a series of saccades to look at other vehicles or pedestrians moving about our visual field. To interact with them effectively, our brain has to integrate their motion from one glance to another to perceive continuous spatial motion over the saccade. The objective of this research program is to gain a more complete understanding of the cognitive and cortical mechanisms of trans-saccadic object motion tracking. In the proposed research program, participants will be tested in a variety of different visual motion judgement tasks, some including a form of non-invasive brain stimulation called transcranial magnetic stimulation, to examine the following questions: 1) To what extent and under what conditions does the brain rely on internal information of the eyes' own movements compared to environmental cues to keep track of an object's movements over a saccade? 2) How many objects can we track across saccades? 3) How accurately can we make spatial judgments of a moving object's future position over a saccade in a inferred motion paradigm? 4) To what extent do different brain areas involved in programming eye movements, memory, or visual motion processing play a role in trans-saccadic motion tracking? The findings from this research program will have important implications for current theories of perceptual continuity across eye movements and offer new insight into the underlying mechanisms of a fundamental conscious visual experience.