The control of movement can be studied with the countermanding (stop signal) task success error

Inhibition function RT distributions of non-cancelled and no stop signal trials

Stop Signal Reaction Time (SSRT) – time needed to cancel a previously planned movement Race model can explain behavior GO WINS! non-cancelled trial STOP WINS! cancelled trial

Frontal Eye Field Controls when gaze shifts Time from stimulus (sec) 0.0 Activation (as part of a network!) Hanes, D.P. and J.D. Schall (1996) Neural control of voluntary movement initiation. Science 274:

SSRTStop Signal No Stop Signal Trials Non-canceled Trials No difference SSRTStop Signal SSRTStop Signal No Stop Signal Trials Canceled Trials Sig. difference before SSRT. SSRT Stop Signal movement neurons No Stop Signal Trials Canceled Trials Sig. difference before SSRT SSRTStop SignalSSRTStop Signal fixation neurons FEF SC

GO process STOP process Movement Neuron Fixation Neuron

1 - The race model of countermanding performance assumes that the GO and the STOP processes have independent finish times (Logan & Cowan, 1984). Mapping the race model onto neural processes 2 – Saccades are produced by a network of interacting neurons. Paradox – How can a network of interacting neurons produce behavior that looks like the outcome of race between independent processes?

Explore properties of simple network of GO and STOP units. Mapping the race model onto neural processes L.Boucher, G.D.Logan, T.J.Palmeri, J.D.Schall. An interactive race model of countermanding saccades. Program No Abstract Viewer/Itinerary Planner. Constrain by the properties of countermanding behavior and by the form of activation of neurons

GO activation = (GO growth rate – STOP inhibition) + noise STOP activation = (STOP growth rate – GO inhibition) + noise Time from stimulus (ms) STOP process GO process GO,GO STOP STOPGO     ß GO ß STOP STOP,

GO,GO STOP STOPGO     STOP, Independent Race Model

Non-cancelled and no stop signal GO,GO STOP STOPGO     STOP, Independent Race Model

GO,GO STOP STOPGO     ß GO ß STOP STOP, Interactive Race Model

Non-cancelled and no stop signal Cancelled and no stop signal ObservedModel Predictions GO,GO STOP STOPGO     ß GO ß STOP STOP, Interactive Race Model