Thomas joined the lab in 2010 as graduate student in the BME PhD program, after completing a BS in Aerospace Engineering from Virginia Tech, and Post-bachelorette in Mathematics from University of Zaragoza, Spain.
He was awarded a National Science Foundation Graduate Fellowship, and he is also a Fulbright Scholar.
A common aspect of individuality is our subjective preferences in evaluation of reward and effort. The neural circuits that evaluate these commodities influence circuits that control our movements, raising the possibility that vigor differences between individuals may also be a trait of individuality, reflecting a willingness to expend effort. In contrast, classic theories in motor-control suggest that vigor differences reflect a speed-accuracy trade-off, predicting that those who move fast are sacrificing accuracy for speed. Tom tested these contrasting hypotheses by measuring motion of the eyes, head, and arm during various elementary movements (saccades, head-free gaze shifts, and reaching). He found that some moved with low vigor, while others moved with high vigor. Those with high vigor tended to react sooner to a visual stimulus, moving both their eyes and arm with a shorter reaction-time. Arm and head vigor were tightly linked: individuals who moved their head with high vigor also moved their arm with high vigor. In all modalities, vigor had no impact on endpoint accuracy, demonstrating that differences in vigor were not due to a speed-accuracy tradeoff. Our results suggest that movement vigor may be a trait of individuality, not reflecting a willingness to accept inaccuracy, but demonstrating a propensity to expend effort.
Tom's research moved the lab into the area of neuro-economics and its influence on human motor control. He discovered that during a decison-making task involving monetary options, saccadic movements of the eyes carried a vigor signal that reflected the subjective value that the brain assigned to each option. That is, saccade vigor was higher as the eyes moved toward the option that currently had the higher subjective value. Importantly, the vigor changes occurred before the decision was reached, demonstrating that vigor was potentially a real-time indicator of the decision-making process.
He completed his thesis in August 2016, focusing on the shared control of vigor across eye, head, and arm movements. He is currently an Asst. Prof. of Neuroscience at Sewanee University.
Movement vigor as a trait-like attribute of individuality. Thomas R. Reppert, Ioannis Rigas, David J. Herzfeld, Ehsan Sedaghat-Nejad, Oleg Komogortsev, and Reza Shadmehr (2018) Journal of Neurophysiology.
Movement vigor: consistency, conservation, and modulation. Thomas R. Reppert (2016) PhD Thesis, Johns Hopkins University
Modulation of saccade vigor during value-based decision making. TR Reppert, KM Lempert, PW Glimcher, and R Shadmehr (2015) Journal of Neuroscience 35:15369-15378.
Evidence for hyperbolic temporal discounting of reward in control of movements. AM Haith, TR Reppert, and R Shadmehr (2012) Journal of Neuroscience 32:11727-11736.
Changes in saccade kinematics associated with the value and novelty of a stimulus. TR Reppert, JES Choi, AM Haith, and R Shadmehr (2012) Conference on Information Sciences and Systems 46:1-5.
Publications
Publications
Thomas Reppert
Thomas Reppert
