The control of movement can be studiedwith the countermanding (stop signal) task

NO STOP SIGNAL Trials

Reaction Time

STOP SIGNAL Trials

Stop Signal Delay

CANCELLED

NON-CANCELLED

success

success

error

Inhibition function

Stop signal delay ( ms)

Pro

ba

bili

ty (

no

nca

nce

lled

)

50 100 150 200 2500.0

0.5

1.0

RT distributions of non-cancelled and no stop signal trials

Reaction time (ms)200 300 400

0%

50%

100%

116 ms168 ms216 msno stop signal

STOPGO

STOP processGO process

Stop Signal Reaction Time (SSRT) – time needed to cancel a previously planned movement

Race model can explain behavior

Time from stimulus (ms)

Act

iva

tion

0.0

0.5

1.0

0 100 200 300

GO WINS!non-cancelled trial

Time from stimulus (ms)

Act

iva

tion

0.0

0.5

1.0

0 100 200 300

STOP WINS!cancelled trial

Frontal Eye FieldControls when gaze shifts

Time from stimulus (sec)0.0

Act

ivat

ion

0.1 0.2

(as part of a network!)

Hanes, D.P. and J.D. Schall (1996) Neural control of voluntary movement initiation. Science 274:427-430.

200

100

00 200 400

SSRTStop SignalNo Stop Signal Trials

Non-canceled Trials

No difference.

100

4000 200

SSRT Stop Signal

0 200 400

200

100

0

SSRT Stop SignalNo Stop Signal Trials

Canceled Trials

Sig. differencebefore SSRT.

SSRT

4002000

100

Stop Signal

mov

emen

t neu

rons

No Stop Signal Trials

Canceled Trials

Sig. differencebefore SSRT.

100

50

0

0 200 400

SSRTStop SignalSSRT Stop Signal

4002000

100

fixa

tion

neu

ronsFEF SC

GOprocess

STOPprocess

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. 72.10. 2003 Abstract Viewer/Itinerary Planner.

Time from stimulus (ms)

Act

iva

tio

n

0.0

0.5

1.0

0 100 200 300

STOPGO

Constrain by the properties of countermanding behavior and by the form of activation of neurons

GOSTOPSTOPGOGO

dta

dtda

STOPGOGOSTOPSTOP

dta

dtda

GO activation = (GO growth rate – STOP inhibition) + noise

STOP activation = (STOP growth rate – GO inhibition) + noise

0 100 200 3000.0

0.5

1.0

Time from stimulus (ms)

STOP processGO process

GO, GO STOP

STOPGO

ß GO

ßSTOP

STOP,

GO, GO STOP

STOPGO

STOP,

Time from stimulus (ms)

Act

iva

tion

GO process

0.0

0.5

1.0

0 100 200 300

STOP process

Stop signal delay ( ms)

Pro

ba

bili

ty (

no

nca

nce

lled

)

50 100 150 200 2500.0

0.5

1.0ObservedModel

Reaction time (ms)200 300 400

0%

50%

100%

Independent Race Model

Non-cancelled and no stop signal

0 100 200 3000.0

0.5

1.0

Time from stimulus (ms)

Act

ivat

ion

Time from stimulus (ms)

Act

iva

tion

GO process

0.0

0.5

1.0

0 100 200 300

STOP process

GO, GO STOP

STOPGO

STOP,

Independent Race Model

GO, GO STOP

STOPGO

ß GO

ßSTOP

STOP, 0 100 200 3000.0

0.5

1.0

Time from stimulus (ms)

Act

iva

tion

STOP processGO process

Stop signal delay (ms)

Pro

bab

ility

(n

on

ca

nc

ell

ed

)

50 100 150 200 2500.0

0.5

1.0ObservedModel

Reaction time (ms)200 300 400

0%

100%

50%

Interactive Race Model

0 100 200 300

Act

iva

tion

Time from stimulus (ms)

0.0

1.0

0.5

0 100 200 300A

ctiv

atio

n0.0

1.0

0.5

Time from stimulus (ms)0 100 200 300

0.0

0.5

1.0

Time from stimulus (ms)

Act

ivat

ion

0 100 200 3000.0

0.5

1.0

Time from stimulus (ms)

Act

ivat

ion

Non-cancelled and no stop signal

Cancelled and no stop signal

Observed Model PredictionsGO, GO STOP

STOPGO

ß GO

ß STOP

STOP,

Interactive Race Model