Slides

Evidence for Relative Position Coding in the Posterior Fusiform

GyrusMark D. Lescroart, Kenneth Hayworth, Irving Biederman

Neuroscience ProgramUniversity of Southern California

Presented at the Society for Neuroscience ConferenceNovember 6, 2007

Relations are easy and fast

“This Way” by Robert Hague

“This Way” by Robert Hague

Intro Shape Demo

Unlabeled Feature Hierarchy

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V1V1 Anterior Infero-temporal Cortex / Anterior Infero-temporal Cortex / Posterior Fusiform GyrusPosterior Fusiform Gyrus

Ventral stream hierarchyVentral stream hierarchy

New Object

S1

S2

Identical

Translated

Relation

Translated + Relation

or... or… or…

Trial Types:Experiment 1

First Trial Demo3.3˚

3.3˚

Original airplane position

(200 ms S1)(200 ms S2)(500 ms ISI)

~5˚ of Visual Angle

Possible S1 ArrangementsEight possible starting (S1) arrangements:

Example Trial - Trans+Rel

Translation + Relation Translation + Relation Change TrialChange Trial

4.6˚

Original airplane position

Example Trial - Ident

Baseline: Baseline: Identical TrialIdentical Trial

Example Trial - New Object

Task: Detect Task: Detect New Object TrialNew Object Trial

Relation (swap)Relation (swap)

Participation1 - Trans

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Participation2 - Ident

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Participation3 - Trans

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Participation4 - NewObj

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Participation5 - Rel

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New Object

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S2

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Translated

Relation


or... or… or…

Trial Types:Experiment 1

(S1)

Predictions of various models:Predictions of various models:

Large receptive fields, Large receptive fields, unlabeled feature list unlabeled feature list (e.g. the MIT (e.g. the MIT “Standard Model”)“Standard Model”) 0

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Identical Translated Relation New Object


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Smaller, Smaller, retinotopically-specific retinotopically-specific receptive fields receptive fields

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Explicitly encoded Explicitly encoded relations / labeled relations / labeled feature listfeature list



Behavorial Responses

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Identical Translation Relation Trans +Relation

New Object

% Error Rate

Behavioral Results: Experiment 1

false alarms misses

Region of Interest: BilateralRegion of Interest: BilateralPosterior Fusiform GyrusPosterior Fusiform Gyrus

Defined by a Defined by a

standard localizer:standard localizer: -- ==

We took the most significant voxels (PWe took the most significant voxels (Pbonfbonf<.01) in the most <.01) in the most

anterior portion of the posterior fusiform gyrusanterior portion of the posterior fusiform gyrus

MRI Results: Experiment 1

Posterior Fusiform

Gyrus


% Release over Identical Condition (pFs)

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Translate Relation Trans +Relation

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% Release

Relation > Translate p<.03Trans+ Relation > Translated p<.01Trans+ Relation > Retinotopic Prediction p<.01Relation > Trans+ Relation n.s.

Posterior Fusiform

Gyrus

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Example T1 trial (in 45 degrees reference frame)

Other Changes: Other Changes:

o Shortened stimulus duration (100 ms)Shortened stimulus duration (100 ms)

o White-on-black line drawing instead of grayscale imagesWhite-on-black line drawing instead of grayscale images

T2

T1

T2+R

T1+R

A New Object trial can be any of these rearrangements with one of the objects changed.

Trial Types: Experiment 2 Ident

Prediction from Cortical Prediction from Cortical Magnification:Magnification:

Foveal over-Foveal over-representation representation (Cortical (Cortical Magnification)Magnification)

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T1 + Relation > T1 p<.01T2 + Relation > T2 p<.01T1 + Relation > T2 + Relation n.s.Note: Trend of T1 > T2 and T1+R > T2+R is close to significant

**

Posterior Fusiform

Gyrus

Inter-object

Scene outline

low spatial frequency

global shape

Could relations be explained by global or inter-object features?

Ident+GFTrans+GFRelT+RNewObj

One of above trial types where one object changes identity

S1 S2

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Identical + ΔGF

Translated + ΔGF

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Trial TypesTrial Types:Experiment 3

HMAX BOLD Release Predictions

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Ident+GF Trans+GF Rel Trans+Rel New Object

C2 correlation

Standard Model Predictions

HMAX BOLD Release Predictions(Without Backgrounds)

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Ident Trans Rel Trans+Rel New Object

C2 correlation

• C2 Correlation taken as a measure of similarity of representation

• The model comes close to predicting the initial results (though the translation condition is probably too high)

HMAX BOLD Release Predictions

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C2 correlation

Standard Model Predictions

HMAX BOLD Release Predictions(Without Backgrounds)

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HMAX BOLD Release Predictions(With Backgrounds)

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C2 correlation

• C2 Correlation taken as a measure of similarity of representation

• The model comes close to predicting the initial results (though the translation condition is probably too high)

• But with the addition of the texture backgrounds, the OPPOSITE effect is predicted. Thus if global features are driving the BOLD response, the changes in Experiment 3 ought to drastically change the results

BOLD Response in pFs (N=6)

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Identical+GF Translate+GF Relation Trans +Relation

New Object

%BOLD

Relation > Translate+GF p<.01Trans+ Relation > Translate+GF p=.01Relation > Trans+ Relation n.s.


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Posterior Fusiform

Gyrus

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Conclusions• Relative position changes have more of

an effect on the neural representation in the posterior fusiform gyrus than absolute position changes

• This effect can not be explained by eccentricity, eye movements, or global features

AcknowledgementsCo-AuthorsCo-Authors::

Ken HayworthKen Hayworth

Dr. Irving BiedermanDr. Irving Biederman

Special Thanks to: Special Thanks to:

Dr. Xiaomin YueDr. Xiaomin Yue

Jiye KimJiye Kim

Xiaokun XuXiaokun Xu

Dave BergDave Berg

Funded byFunded by::

NSF Grants BCS NSF Grants BCS

04-20794, 05-31177, 04-20794, 05-31177,

and 06-17699 to I.B.and 06-17699 to I.B.

Extra Slides

Low-frequency / Low-frequency / global shape global shape featuresfeatures

Inter-Inter-object object featuresfeatures

(nothing)

Scene Scene outlineoutline(nothing)

Could global features explain the greater Could global features explain the greater release from adaptation in the relation- release from adaptation in the relation-

change conditions?change conditions?

(nothing)

Experiment 3: Adding Global Experiment 3: Adding Global Feature ChangesFeature Changes

Measuring Similarity of Representation in the Brain

Response to two different stimuli, presented close together in time

Response to two of the same stimuli, presented close together in time

(S1)


Attention Shifts: Attention Shifts: Saliency drivenSaliency driven

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Attention Shifts: Attention Shifts: Position order drivenPosition order driven

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(A-B-B-A)(A-B-B-A)(A-B-A-B)(A-B-A-B)

(A-B-A-B)(A-B-A-B) (A-B-A-B)(A-B-A-B)

Subject presses key when ready to start trial

33ms scene presentation

100ms mask

Variable blank delay (0ms to 133ms)

Subject writes down the names of both objects and their relative spatial relation

Fast Two-Object Naming Experiment

Fast Naming Results

Stimulus33ms

Mask100ms

SOA

Behavioral ResultsS1 = 33ms, Effective Mask =

0102030405060708090

100

33 67 100 133 167

SOA (ms)

% correct

Two object (both correct)

(Chance)

d primes

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Identical Translation Relation Trans+Relation

d Prime



Error Rates

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Ident T1 T2 T1+R T2+R NO

Ident

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d prime

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Behavorial Responses (N=6)

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Stimulus Parameters

2.1 ˚

3.3˚

2.3˚

2.3˚

3.3˚S1Pos

S1Pos

4.6˚

Example T1 trial (in 0 degrees reference frame)Example T1 trial (in 0 degrees reference frame)

Example T2 trial (in 45 degrees reference frame)

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