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About the Authors:
James P. Herman
* E-mail: [email protected]
Current address: Laboratory of Sensorimotor Research, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States of America
Affiliations Department of Biology, The City College of New York, New York, New York, United States of America, PhD Program in Biology, The Graduate Center, The City University of New York, New York, NY, United States of America
C. Phillip Cloud
Affiliations Department of Biology, The City College of New York, New York, New York, United States of America, PhD Program in Psychology, The Graduate Center, The City University of New York, New York, New York, United States of America
Josh Wallman
Affiliations Department of Biology, The City College of New York, New York, New York, United States of America, PhD Program in Biology, The Graduate Center, The City University of New York, New York, NY, United States of America
Introduction
Because a small (roughly 1° in diameter), central region of the human retina (the fovea) has the greatest receptor density, the best view of an environmental stimulus is achieved by accurately orienting gaze towards it. We move our gaze from point-to-point using rapid movements called saccades. Somewhat surprisingly, the accuracy of saccades changes little with age [1], [2], suggesting that movement accuracy is actively monitored and maintained. Indeed, experiments on humans with extraocular muscle paresis [3]–[5] and tenectomized monkeys [6], [7] demonstrated an impressive endogenous ability to restore normal saccade amplitudes in a relatively brief period (on the order of days). Meanwhile, McLaughlin noted that modification of saccade amplitude can be achieved by an intrasaccadic step (ISS) paradigm, applying experimentally arranged, primary-saccade-triggered secondary target shifts in a series of successive saccade trials [8].
This maintenance, restoration, or manipulation of saccade size is termed “saccade adaptation.” Since it was recognized that the adaptive changes achieved by the ISS paradigm are the same as those resulting from tenectomy [9], the majority of adaptation studies have relied on the ISS paradigm to extensively explore and document the multiplicity of subtle ways that saccade adaptation can display sensitivity [10], [11].
There are two major classes of ISS paradigm. The first is identical to the method used by McLaughlin: the amplitude of the ISS is fixed (in degrees of visual...