Cognitive Processing During Saccadic Eye Movements

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People make rapid eye movements called saccades in order to examine the world around them. The still periods between saccades are called fixations. It is well known that vision is suppressed during saccades; therefore, visual information about the world is acquired only during fixations. Recent findings have shown that saccades also interfere with particular cognitive processes. This research will determine why this occurs while also exploring the fundamental characteristics and generality of the phenomenon of cognitive saccadic suppression. Four hypotheses about the possible mechanisms underlying suppression will be investigated in a series of experiments drawn from the areas of working memory, mathematical cognition, stimulus novelty, and retrieval from semantic memory. In general, the experiments will examine whether cognitive processes that are set in motion during an eye fixation continue to operate while the eyes are moving to a new position in space or whether these processes pause during the eye movement. People will be presented with a simple mental task that they will begin to perform while they are fixating one position in space and will then make either a short or a long saccade to a different position in space while attempting to continue performing the task. If cognitive processing is suppressed during eye movements, then long saccades (which take longer to execute) should disrupt performance more than short saccades (which take less time to execute). Performance will also be measured in another condition, in which the eyes do not move. Performance in the eye-movement conditions should be equivalent to performance in the no-eye-movement condition if eye movements do not interfere with cognition. The effects of cognitive processing on saccadic behavior (e.g., saccade latency, duration, accuracy, and peak velocity) will be examined as well to determine the reciprocity of the interference.The average person makes about three saccades per second (hence, about 172,800 saccades per 16-hour working day) and the average saccade lasts about 30 ms; thus, if suppression occurs during saccades, it would mean that cognition is disrupted for approximately 90 minutes each day. Determining why this occurs is of fundamental importance to the understanding of human cognition, particularly for activities such as scene perception and scene navigation that require many eye movements. The research also has practical implications for the design of visual displays and control panels that may require users to make saccades.