Temporal Constraints on Saccadic Eye Movements

Although we are rarely aware of it, our ability to visually perceive and successfully interact with the world depends on a rapid and carefully orchestrated sequence of eye movements. Roughly three times a second, large high-velocity movements known as saccades drastically alter the spatial and temporal stream of visual input. To investigate the temporal constraints on saccadic eye movements and identify biases in oculomotor behavior, I developed a simple but novel task: rapid alternating saccades (RAS). Human participants are asked to make a series of eye movements back and forth between stationary targets as quickly as possible.In Chapter 2, I investigate the characteristics of one of the most prominent and well-known biases in eye guidance, inhibition of return. Participants made RAS between two targets or following an “hourglass” pattern in which the same location is only sampled every fourth eye movement. The experiments revealed that both saccade dwell times and secondary saccade characteristics were dramatically altered when the eye returned directly to a previously viewed location. The effects depended on the direction of movement and the angular difference between subsequent saccades. The results further explicate the inhibition of return phenomenon and provide novel insight into motor and attentional constraints governing the rate of sequential eye movements.Chapter 3 explores interactions between the eye and the hand. Findings indicate that the maximum rate of RAS increases when concurrent and directionally compatible hand movements accompany the eye movements. The increase is the result of shorter dwell times, higher saccade peak velocity, and a decrease in secondary saccade occurrence. The findings occur independently of changes in saccade amplitude or direction. Hand movements in the opposite direction of the eye result in longer dwell times and more frequent secondary saccades. The experiments illustrate the tight temporal coordination between saccades and arm motor systems during sequential movements.