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

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

3. 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

4. Frontal Eye Field Controls when gaze shifts Time from stimulus (sec) 0.0 Activation 0.10.2 (as part of a network!) Hanes, D.P. and J.D. Schall (1996) Neural control of voluntary movement initiation. Science 274:427-430.

5. 200 100 0 0 200 400 SSRTStop Signal No Stop Signal Trials Non-canceled Trials No difference. 100 4000200 SSRTStop Signal 0 200 400 200 100 0 SSRTStop Signal No Stop Signal Trials Canceled Trials Sig. difference before SSRT. SSRT 400200 0 100 Stop Signal movement neurons No Stop Signal Trials Canceled Trials Sig. difference before SSRT. 100 50 0 0 200 400 SSRTStop SignalSSRTStop Signal 400200 0 100 fixation neurons FEF SC

6. GO process STOP process Movement Neuron Fixation Neuron

7. 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?

8. 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. 72.10. 2003 Abstract Viewer/Itinerary Planner. Constrain by the properties of countermanding behavior and by the form of activation of neurons

9. GO activation = (GO growth rate – STOP inhibition) + noise STOP activation = (STOP growth rate – GO inhibition) + noise 0100200300 0.0 0.5 1.0 Time from stimulus (ms) STOP process GO process GO,GO STOP STOPGO     ß GO ß STOP STOP,

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

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

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

13. 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