Quantifying Variability in Oculomotor and Manual Choice Response Times

Abstract

Response times (RTs) of various motor systems have traditionally been used to characterize aspects of human performance (e.g., fatigue, disease states). However, the properties and sensitivity of different motor systems to detect changes in neural states across multiple timescales remain an open question. In this thesis, we attempt to characterize the difference in sensitivity of the pursuit, saccadic, and manual systems to detect changes in stimulus strength. In Experiment 1, we used a modified Yes-No task to test the effects of contrast (5, 10, 20, 40, 80, 100%) on three pursuit, saccadic, and manual RT's for three observers. In Experiment 2, we used a 2-AFC task to test the effects of luminance (0-10 d' above background noise) on saccadic and manual RT for five observers. We observed: 1) saccadic RT are better correlated with changes in stimulus strength, 2) manual responses are more variable, 3) trial-by-trial variability is greater than variability across sessions, and 4) each pair of motor systems shows significant shared variability. We conclude that oculomotor and manual responses have different signal processing and RT characteristics, and may have different levels of utility to detect physiological factors that affect performance (e.g., Dinges & Powell, 1985), with the saccadic system being more sensitive to changes in stimulus strength and less variable in the timing of the response.