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An Information Flow Perspective on Access Consciousness Michael C. Mozer Donald W. Mathis Jennifer Finger Michael Colagrosso Institute of Cognitive Science and Department of Computer Science University of Colorado, Boulder Consciousness Course Spring 2004

An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

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Page 1: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

An Information Flow Perspective on Access Consciousness

Michael C. MozerDonald W. MathisJennifer Finger

Michael ColagrossoInstitute of Cognitive Science andDepartment of Computer ScienceUniversity of Colorado, Boulder

Consciousness CourseSpring 2004

Page 2: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Cognitive Architecture

Cortical computation can be characterized by coarse-scale, functionally specialized pathways.

E.g., visual word-form recognitionidentification of semantic features of visual objectsauditory word recognitioncomputation of spatial relationshipsconstruction of motor plans

Cognition requires coordination of multiple pathways.

Pathways act as associative memories.E.g., visual word recognition

input: visual featuresoutput: letter strings

Past experience imposes well-formedness constraintson the output.

Letter strings must be consistent with English orthography.

Output is the best-fitting interpretation of the input.

pathway

input domain

output domain

Page 3: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Cognitive Architecture

Pathway operation shows a speed-accuracy trade off.Initial output appears rapidly, but is inaccurate.

Pathway asymptotically converges on the best interpretation.

With each experience, pathway tends to produce its response more rapidly.

80 100 120 140 160 180 200 2200

0.2

0.4

0.6

0.8

1

processing time

probability ofcorrect output

Page 4: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Pathway Operation

Implementation using two standard connectionist components:

input domain output domain(e.g., semantic)(e.g., visual)

dogcat

cow rat

neutral

output

input

attractor network

feedforward network

Page 5: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Pathway Implementation

Speed-accuracy trade off due to• inaccuracies in feedforward mapping• Gaussian noise added to unit activities

Common connectionist architecture• Hinton & Shallice (1991); Plaut & Shallice (1993); Mozer

& Behrmann (1990)• Cascaded attractor net models incorporate feedforward

mappings (e.g., McClelland & Rumelhart, 1981).• Feedforward net models implicitly assume attractor net

for read out (e.g., Sejnowski & Rosenberg, 1987).

Page 6: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Pathway Dynamics

attractor unit update equation:

state unit update equation:

attractorunits state

units

externalinput

a(t)

s(t)

e(t)

: center of attractor j: width of attractor j

µj

βjaj t( ) s t( ) µj–

2 βj⁄–( )exp=

aj t( ) aj t( ) ai t( )∑⁄=

si t( ) h si t 1–( ) ωext+ ei t( ) ωattr aj t 1–( )µjij∑ ηi t σ;( )+ +=

freeparameters

Page 7: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Cascaded Pathways

Sequential operation?• biologically implausible

• computationally inefficient

pathway A

pathway B

classificationresponse

semantics

visual input

Page 8: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Information Flow

What sort of representation in the output of pathway A will support a response from pathway B?

Sufficient condition: familiar and temporally persistent representation

0.940.95

0.960.97

0.980.99

1

50

100

150

200

250

3000

0.2

0.4

0.6

0.8

1

duration of pathwayA representation

familiarity of pathwayA representation

A

Bprobabilityof correct

pathway Boutput

Page 9: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Information Flow

Familiar and persistent representationattained when pathway reaches attractor

Page 10: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Information Flow

Familiar and persistent representationattained when pathway reaches attractor

At attractor, representation is stable.

Stability defined to occur if ,where ,

,, and

d t( ) ζ<d t( ) αd t 1–( ) 1 α–( )d t( )+=d t( ) s t( ) s t 1–( )–=ζ 0.25= α 0.9=

100 120 140 160 180 200 220 240 260

100

120

140

160

180

200

220

240

260

cycles tocorrect

pathway Bresponse

cycles to pathway A stability

Page 11: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Level of Expertise

Stability required to initiate underlearned responses.

150 200 250 300

100

150

200

250

300

“novice”

“intermediate”

“expert”

cycles tocorrect

pathway Bresponse

cycles to pathway A stability

Page 12: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Task Difficulty

Stability required for tasks relying on finer granularity of information.

80 100 120 140

60

80

100

120

140

cycles tocorrect

pathway Bresponse

cycles to pathway A stability

complex

simple

(slope = .72)

(slope = –.03)

Page 13: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Number of Response Alternatives

Stability required for discriminations involving a large number of alternatives.

cycles tocorrect

pathway Bresponse

cycles to pathway A stability

200 alternatives(slope = .91)

50 alternatives(slope = .83)

10 alternatives(slope = .52)

2 alternatives(slope = .10)

100 150 200

50

100

150

200

250

Page 14: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Role of Stability

Stability of a pathway’s output is sufficient to induce the correct response from pathways to which it is connected.

Stability of a pathway’s output is necessary when

• decision making with limited domain expertise

• responses are arbitrary or complex

• responses involve discrimination among many alternatives

Stable representations are the most accessible — they allow for the flexible control of behavior (including verbal report).

A

B C D E

Page 15: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Neurobiological Correlate of Stability?

0.940.95

0.960.97

0.980.99

1

50

100

150

200

250

3000

0.2

0.4

0.6

0.8

1

Page 16: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Similar Properties for Belief Net Implementation

00.2

0.40.6

0.81

0

50

100

150

2000

0.2

0.4

0.6

0.8

1

familiarity of pathwayA representation

duration of pathwayA representation

probabilityof correct

pathway Boutput

20

40

60

80

100

120

140

160

180

200

220

70 80 90 100 110 120 130 140 150

Tim

e fo

r se

cond

pat

hway

to r

each

crit

erio

n

Time for first pathway to reach criterion

0

50

100

150

200

250

300

200 250 300 350 400 450 500

Tim

e fo

r se

cond

pat

hway

to r

each

crit

erio

n

Time for first pathway to reach criterion

120

140

160

180

200

220

240

260

280

120 130 140 150 160 170 180 190T

ime

for

seco

nd p

athw

ay to

rea

ch c

riter

ion

Time for first pathway to reach criterion

2 actions

10 actions

50 actions

Page 17: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Relation to Other Stories about Consciousness 1

Conscious states are interpretationsGregory: ambiguous objectsCrick & Koch: high frequency flicker not perceivedLogothetis, Lumer: rivalrous displaysMarcel: subliminal semantic priming

Attractor state is an interpretation.

Page 18: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Relation to Other Stories about Consciousness 2

Conscious states require high quality representations

Farah, O’Reilly, & Vecera: prosopagnosia modelMunakata

Any attractor state is a high quality representation, in the sense that adding noise moves away from attractor and also lowers quality of a representation.

Probably makes more sense to focus on familiarity than quality:Familiarity a natural way of explaining how pathway A can have an effect on pathway B.

Page 19: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Relation to Other Stories about Consciousness 3

Conscious states require temporal persistence

O’Brien & Opie: “stability” is a characteristic of phenomenal awarenessCrick & Koch: “coalitions” that are sustained in time; “snapshots” that must cross a threshold in timeDehaene & Naccache: “information must be maintained over a sufficient duration”

My story is about access consciousness.

Crick & Koch coalitions are probably coarser scale (front vs. back)

Page 20: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Relation to Other Stories about Consciousness 4

Conscious states require explicit representationsCrick & Koch, O’Brien & Opie

Page 21: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Relation to Other Stories about Consciousness 5

Conscious states are attractors

Rumelhart & McClelland, Smolensky: cited in Farah et al.Crick & Koch: dynamic competition among coalitions

Page 22: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Relation to Other Stories about Consciousness 6

Consciousness entails global availability of information to to widespread brain sources

Baars, Dehaene & Naccache: global workspace framework

My story requires functional connectivity between perceptual and response pathways for access to occur.

Frontal areas could provide this functional connectivity, so global workspace ideas complement my story.

Page 23: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Relation to Other Stories about Consciousness 7

Attention is a prerequisite for consciousness

Dehaene & Naccache; Crick & Koch

In my story, attention is not necessary, but it makes awareness more likely: Standard notion of attention is to amplify some representations. Attractor corresponding to amplified representation more likely to be chosen.

Page 24: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Semantic Priming Paradigm

Task: lexical decision to target word following prime word

Congruent conditionprime LEAF

target TREE

Unrelated conditionprime AUTO

target TREE

Facilitation on lexical decision RT for targets congruent with prime.

Page 25: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Modeling Semantic Priming

Presentation of stimulus strengthens attractors that are visited (McClelland & Rumelhart, 1986; Becker et al., 1997)

Nearby (similar) attractors are also strengthened.

Priming depends on state space trajectory.

Priming can occur without stability (awareness).

extendedpresentation

neutral neutral

leaf

tree

briefpresentation

neutralneutral neutral

Page 26: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Semantic Priming with Polysemous Words(Marcel, 1980; Swinney, 1979; Tanenhaus & Leiman, 1979)

Task: lexical decision to target

Modeling semantic primingTwo pathway architecture

Decision pathway responds “yes” if perceptualpathway obtains a well-formed state, “no”otherwise.

congruent incongruent unassociatedcontext LEAF HAND HANDprime PALM PALM RACEtarget TREE TREE TREE

decision

perceptual

orthography

semantics

lexical decision

pathway

pathway

Page 27: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Simulation with extended presentation of prime

After model has stabilized on PALM:• one interpretation has been selected• facilitation for targets congruent with that meaning• awareness of prime

congruent incongruent unassociatedhuman data (Marcel, 1980) 499 ms 547 ms 541 ms

simulation 224 cycles 252 cycles 257 cycles

palm1

palm2

leaf

tree

palm1

palm2

leaf

tree

palm1

palm2

leaf

tree

palm1

palm2

leaf

tree

2. present PALM1. present LEAF

wrist wrist wrist wrist

= facilitation

Page 28: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Simulation with brief presentation of prime

Before model has settled on PALM:• no interpretation has been selected• facilitation for targets congruent with either meaning• no awareness of prime

Human data showed correlation between onset of awareness and selection.

Model suggests further that selection is a necessary precursor to awareness.

congruent incongruent unassociatedhuman data (Marcel, 1980) 511 ms 520 ms 548 ms

simulation 238 cycles 242 cycles 254 cycles

palm1

palm2

leaf

tree

palm1

palm2

leaf

tree

palm1

palm2

leaf

tree

palm1

palm2

leaf

tree

2. present PALM1. present LEAF

wristwrist wrist wrist

Page 29: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Primed Stem Completion(Debner & Jacoby, 1994)

ProcedureMasked prime (e.g., TABLE)

Followed by stem to be completed (e.g., TAB_ _)

Inclusion condition: Ss instructed to complete stem with prime if possible.Exclusion condition: Ss instructed to complete stem with any word but prime.

Short (mostly unconscious) and long (mostly conscious) exposure conditions

Dependent measure: probability that stem completed with prime

Page 30: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Simulation

Presentation of prime (TABLE)• Perceptual pathway produces lexical representation.• Priming mechanism operates inside perceptual pathway.• If input is sustained and perceptual pathway stabilizes, lexical

representation copied to working memory.

Presentation of stem (TAB_ _ )• Stem representation: average of three similar orthographic representations• Perceptual pathway finds best-fitting completion of visual input consistent

with lexicon.• Perceptual processing modulated by contents of working memory

naming

orthography

lexical rep.

name

pathway

workingmemory

perceptualpathway

Page 31: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Results

Debner and Jacoby analysis of data suggests a dissociation between conscious and unconscious processes.

No such distinction in our model: awareness is an emergent property of representations, not processes or pathways.

L−I L−E S−I S−E CTL0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

L−I L−E S−I S−E CTL0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

= inclusion= exclusion= inclusion= exclusion= control (no prime)

modeldata

p(re

spon

se =

prim

e)

} longexpos.

} shortexpos.

orthography

lexical rep.

name

workingmemory

namingpathway

perceptualpathway

Page 32: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Semantic Priming and Response Windows(Draine & Greenwald, 1996; Greenwald, Draine, & Abrams, 1996)

Masked prime word followed by target word

Semantic classification task: Is target pleasant/unpleasant?

Conditions• congruent (FUN-PLAY) vs. incongruent (SICK-PLAY)

• short vs. long prime exposure (“subliminal” vs. “supraliminal”)

• RT to target constrained to fall within temporal response window vs. unconstrained

SimulationDecision pathway makes two-alternativeforced-choice classification

At brief exposure, prime is subliminal

Response window simulated by forcing decisionpathway to closest attractor at time response is required.

decision

perceptual

orthography

semantics

classification

pathway

pathway

Page 33: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

PredictionMagnitude of priming effect is larger near center of speed-accuracy curve than near the extremes.

When a forced response is made at a time near the center of the curve, accuracy priming effects will be largest.

100 150 200 250 300 350 4000

0.2

0.4

0.6

0.8

1

cycle

% c

orre

ct

supralim primesublim primenot primed

100 150 200 250 300 350 4000

0.1

0.2

0.3

cycle of forced response

prim

ing

effe

ct

Page 34: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Results

L−C L−I S−C S−I0

0.2

0.4

0.6

0.8

1

L−C L−I S−C S−I0

0.2

0.4

0.6

0.8

1

L−C L−I S−C S−I0

0.2

0.4

0.6

0.8

1

L−C L−I S−C S−I0

0.2

0.4

0.6

0.8

1

no window response windowdata model data model

= long exposure, congruent= long exposure, incongruent

= short exposure, congruent= short exposure, incongruent

accu

racy

L−C L−I B−C B−I570

580

590

600

610

620

L−C L−I B−C B−I200

210

220

230

240

250

260

reac

tion

time

data model

Page 35: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Automatization and Multistep Tasks

Trained network to add two 2-digit numbers in three steps

Each digit represented by pool of units.

4 86 2

1 1 0

1

+

14 86 2

? 1 0

1

+

14 86 2

? ? 0

1

+

?4 86 2

? ? ?

?

+

?step 1 step 2 step 3

hidden units

attractor network

feedforward mapping

copy

result3

result2

result1

carry1

op2-1

op1-2

op1-1

op2-2

carry2

result3

result2

result1

carry1

carry2

result3

result2

result1

carry1

carry2

Page 36: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Sequence of stable states reach awareness; correspond to results of computation

Benefit of attractor net clean up (“projection”)

training set size(% of all problems)

10 20 40 5030

20

40

60

80

100 ProjectionNo projection

Overall performance comparison

Page 37: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Prediction from the Theory: Automatization

Conscious awareness can drop out simply by speeding up processing; doesn’t require a qualitative reorganization of knowledge

Might expect to find evidence for the application of intermediate steps, even without awareness.

E.g., Crutcher (1992) doronico – door – leopard

Page 38: An Information Flow Perspective on Access Consciousnessmozer/Research...Consciousness Course Spring 2004. Cognitive Architecture Cortical computation can be characterized by coarse-scale,

Explaining Unitary Nature of Consciousness

Often claimed that people can only be aware of one thing at a time.

According to framework, strictly speaking this is false.

Within the output domain of a pathway, a single, coherent representation is selected.

Across pathways, no explicit competition; e.g., stable patterns can be achieved in somatosensory and visual modules simultaneously. But strongly linked domains require mutual consistency.

The subjective impression of unity also arises due to the equating of awareness with verbalization. If we assume there is a module responsible for the verbal expression of ideas, then it is limited to one expression at a time.