The visual world contains more information than we can perceive in a single glance. To compensate for this state of affairs, we make eye and head movements to look at objects of interest, and we gradually construct a mental representation of the environment from these successive views. Our eyes scan the world by means of rapid movements, called saccades, that are separated by brief periods of time, called fixations, during which the eyes are still. One might logically expect this pattern of eye movement activity to produce a terribly disruptive pattern of visual input for perception, a sequence of stationary, clear images of the world, alternating with violent sweeps of information during the saccades. Our perceptual experience, of course, does not correspond to such an alternating sequence at all. Rather, it consists of clear, continuous, panoramic views of large sections of the visual environment, with objects remaining stable in space. This mismatch between the nature of the visual input and the nature of our phenomenal experience is one of the great mysteries in the study of perception, a mystery that is still largely unsolved. This research project will investigate the characteristics of the memory or memories responsible for integrating information across eye movements to yield the coherent perception of the visual world that we ordinarily experience. In particular, the research will focus on the capacity, time-course, and representational format of these memories. People will view visual displays while their eye movements are monitored. When an eye movement is detected, the visual display will disappear and the observer's memory for that display will be assessed. For example, the observer may indicate whether a second display is identical to or different from the first display, or may attempt to report some particular information that was present in the display. These responses will reveal what aspects of the original view are stored in memory and maintained across an eye movement. By varying the amount and the visual characteristics of the information in the display and by varying the timing and the nature of the memory test following the eye movement, the research will reveal how much information is retained across eye movements, how long it persists in memory, and how detailed is its memory representation. The perception of a stable and continuous visual environment across changes in eye position has puzzled and intrigued scientists for over a century. The research will allow us to make progress in solving this puzzle. In addition, the research will provide important information about spatial representation and spatial cognition in general, with possible relevance to the study of reading and to the study of oculomotor disorders that are sometimes accompanied by perceptual instability.
