NEW EVIDENCE AGAINST A PERCEPTUAL-MOTOR DISSOCIATION

Andrei Gorea & Pedro Cardoso-Leite

collaborator:

Florian Waszak

Laboratoire Psychologie de la PerceptionCNRS & Paris Descartes University

Biomédicale des Saints Pères45 rue des Saints Pères, 75006 Paris, France

Sensory Input

A. The layman’s view

Action

with perceptual awareness

PerceptualDecision

Verbal reportaware / not aware

However… since Goodale & Milner (1992), a whole line of

research leans in favor of this other view:

Sensory Input

Action

with or withoutperceptual awareness

Verbal report

aware / not aware

B. The two pathways view

Lateral Interactions(implicit)

ventral

dorsal

Percept. Criterion

Decision rule not specified

?

The experimental paradigms used to test this dissociation in stroke patients (blind sight, ataxia/agnosia…) and normals (size illusions, congruent / incongruent subliminar priming + masking, comparison of perceptual and motor

latencies…) present a number of methodological problems

and / or

reject this dissociation.

Two variants of a liminar perturbation paradigm (versions of standard priming + mask technique) coupled with perceptual and motor (RT) responses test negatively the perceptual-action dissociation hypothesis:

• Yes/No variant;

• 2AFC variant [a recast of Klotz & Neumann’s (1999) subliminar priming].

Gorea & Waszak (2004); Waszak & Gorea (2004)Waszak, Cardoso-Leite & Gorea (2007).

T I M E

S1

prime/targetp variable

S2

Impératif stim.p = 1

S1: Yes/No?

HitsFAMissesCR

≈

S2S1

7° NOT Masked

S2

22.5°

Masked(metacontrast)

S2S1

7°

Yes/No (SDT) liminar perturbation + Response Times

RT

Waszak, Cardoso-Leite & Gorea (2007)

S1

“prime”

S2

“mask”

t

SOA

13 ms 36 ms

52 ms

-50

-40

-30

-20

-10

0

10

RT

Gai

n r

el.

to C

R (

ms)

S1

S2

NOT Masked

0 1 2 3 4

Not (or weakly) Masked(6 Obs)

d’S1

RTHIT – RTCR

d’S1

S1

Masked(metacontrast)

S2

0 1 2 3 4

Strong Masking conditions(6 Obs)

RTHIT – RTCR

RTMISS – RTCR

RTMISS – RTCR Perceptual-motor

dissociation?

Ye

s/N

o L

imin

ar

per

turb

ati

on

+ R

Ts

One path – Two decisions/criteria race modelwith variable reference noise levels.

The motor system reacts only if

the stimulus is present and

observers are “aware” of it (i.e. only for Hits).

The difference between RTs for Hits and Misses pleads against a sensory-motor dissociation.

a recast of Klotz & Neumann (1999)

A congruent/incongruent priming + backward masking RT task with a ‘0’ d’ prime

Methodological problems:0 d’ assessment

unreliable (theoretically & statistically impossible);

2AFC Liminar perturbation + RTs

Stimulation complexity entailing problematic data (d’) analysis

Non-matched sensory & motor assessments;

Dismissal of the decisional behavior (response criteria);

Stimuli & Paradigm(one trial)

A recast of Klotz & Neumann (1999) into a 2AFC format: No d’=0 requirement: target/’prime’ set at

d’1.5 No congruent/incongruent manipulation;

2A

FC

Lim

inar

pe

rtu

rbat

ion

+ R

Ts

2AFC perceptual task: Specify target location (L/R)

Motor tasks: Simple RT press a key as soon

as either S1 or S2 is seen;

Choice RT equivalent to the 2AFC perceptual task but performed in a speeded mode.

The motor dissociation stand predicts that RTs should be independent of whether or not perceptual responses are correct.

As expected from our previous data (and model), RT-drop is larger under not-masked than under masked conditions.

230

250

270

290

310

330

350

370

390

410

430

Incorrect Correct

Perceptual (non-speeded) Responses

RT

(m

s)

sRT - no S1

sRT, nM

sRT, M

cRT, nM

cRT, M

6 Obs

Reference sRT to S2 in the absence of S1

All 6 Obs show identical trends: when S1 is not seen (incorrect perceptual responses), sRT

are about the same as in the absence of S1;

when S1 is seen (correct perceptual responses), sRT are shortened by about 15 ms and cRT by about 28 ms;

2A

FC

Lim

inar

pe

rtu

rbat

ion

+ R

Ts

One (unreasonable) prediction of the sensory-motor dissociation stand is that speeded (‘Motor’) and delayed (‘Perceptual’) decisions should not correlate.

In short, the present simplified recast of a main pro-dissociation priming experiment yields data entirely compatible with the non-dissociation view.

2A

FC

Lim

inar

pe

rtu

rbat

ion

+ R

Ts Not surprisingly (as predicted by any one-pathway race model), they

strongly do.

y = 0.76x + 0.42

r² = 0.45

0.0

0.5

1.0

0.0 0.5 1.0

p(Mot = Correct) (arcsin)

p(P

erc

= C

orr

ect)

(ar

csin

)

nM

M

These and previous data (Cardoso-Leite, Gorea & Mamassian, 2007;

Cardoso-Leite, Mamassian & Gorea, submitted) suggest that Perception and Action use the same input pathway and relate as follows:

One pathway-two decisions SDT race model with variable reference noises

Simple RT Choice RT

Detection Discrimination

Internal noise Mask noise

Sensory

Input

Perceptual Criterion

Action

Motor Criterion

with or withoutawareness

Perceptionaware / not aware

Speed-Accuracy trade-off

Perceptual Criterion:Detection without Mask

Speed-Accuracy trade-off

Motor Criterion:Simple (detection) RT

Perceptual Detection (in non-Masking condition) + Simple RT

PARTIAL “N

ON-DIS

SOCIATIO

N”

Internal noise Mask noise

Perceptual Misses do not exceed the motor criterion and do not contribute (or contribute little) to simple

RTs.

Speed-Accuracy trade-off

Perceptual Detection (in non-Masking condition) + Choice RT

Perceptual Criterion:Detection without Mask

Motor Criterion:Choice (discrimination) RT

FULL “NON-D

ISSOCIA

TION”

Internal noise Mask noise

Perceptual Misses do not exceed the motor criterion and do not contribute (at

all) to choice RTs.

Perceptual Discrimination (in Masking condition) + Simple RT

Speed-Accuracy trade-off

Perceptual Misses exceed the motor criterion and do contribute to simple RTs.

Motor Criterion:Simple (detection) RT

Perceptual Criterion:Discrimination with Mask

FULL “DIS

SOCIATIO

N”

Internal noise Mask noise

Speed-Accuracy trade-off

Perceptual Discrimination (in Masking condition) + Choice RT

Motor Criterion:Choice (discrimination) RT

Perceptual Misses partially exceed the motor criterion and do (partially) contribute to choice RTs.

Perceptual Criterion:Discrimination with Mask

PARTIAL “D

ISSOCIA

TION”

Internal noise Mask noise

In CONCLUSION

The Perceptual-Action dissociation / non-dissociation issue is resolved by assuming a unique processing stream with distinct perceptual and motor decision criteria whose relationship is modulated by

the stimulation conditions (with or without masking)

and by

the perceptual (detection vs. discrimination) and motor (simple vs. choice RTs) tasks.

THANK YOU

One (unreasonable) prediction of the sensory-motor dissociation stand is that speeded (‘Motor’; cRT) and delayed (‘Perceptual’) decisions should not correlate.

In short, the present simplified recast of a main pro-dissociation priming experiment yields data entirely compatible with the non-dissociation view.

Not surprisingly (as predicted by any one-pathway race model), they strongly do.

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0p(Perc = Correct \ Mot = Incorrect )

p(P

erc

= C

orr

ec

t \

Mo

t =

Co

rre

ct)

not Masked

Masked

Conditional probabilities

2A

FC

Lim

inar

pe

rtu

rbat

ion

+ R

Ts