fMRI Reveals a Dissociation Between Object Grasping and

Object Recognition

Culham et al. (submitted)

Overview

• Background

• Methods

• Results

• Conclusions

• Discussion– Contrasts & baselines

Background

• Visual systems

Dual Stream Theory

“ACTION” (grasping)

“PERCEPTION”

(1-back recognition)

fMRI Studies

• LO = lateral occipital complex– Recognition area in ventral stream

• AIP = anterior intraparietal complex– Grasping area in dorsal stream

Methods

• Participants– N=7, age 23-33, R-handed, fMRI experienced

• Design– 1 scan session of grasping task– 1 scan session of recognition task

Grasping Task

Grasparatus

Recognition Task

• Intact Objects– Grayscale– Line Drawings– Familiar and Novel

• Scrambled

Event-Related fMRI

• Removed motion-related artifact

• Blocked response types– Grasp, Reach, (No response)

• ITI = 14 s

Imaging & Analyses

• 4-Tesla system, head coil

• 13 T*-2 slices every 2 s– Parallel to calcarine sulcus

• T1 structural images

• Cortical surface-based analysis

Results

1) Functionally define ROIs

2) Reverse comparisons

AIP in Grasping (fig2a)

AIP Grasping: Time Course(fig4a - Left IPS time course)

AIP Grasping: Representative Individual (fig3b)

LO in Object Recognition (fig2b)

LO Recognition(fig4d – Left time course)

Intact

Scrambled

LO Recognition: Object Type(fig5a)

Cross Comparisons

1) AIP in Recognition

2)LO in Grasping

AIP in Recognition(fig4b – Right IPS data)

Intact

Scrambled

AIP Recognition: Object Type (fig5b)

Recognition: LO vs AIP (fig3c)

Grasp & Reach vs ITI (fig3a)

LO: Grasping = Reaching(fig4c – Left data)

Grasping

Reaching

Comparison Map (fig3d)

Discussion

• Is AIP activated by Intact-Scrambled?

• Is LO activated by Grasping-Reaching?

• Results support hypotheses

• How much do they specify the processes unique to AIP and LO?

AIP: Contrasts in Grasping Task

• Grasp -Reach– G requires info to preshape hand– More goal directed(?)

• G&R – dark ITI– Both above baseline– Why this baseline?

• What happened to the ‘no response’ condition (Blue LED)?

LO: Contrasts in 1-Back Task• Intact-Scrambled

– ID and meaning– Recognition – a misnomer?

• Novel > Familiar; Adaptation of LO

• I&S – fixation on dot– Only I greater– Alternative baselines – role of 1-back?

• Scrambled-Intact– Rationale? Interpretation?

Task Comparisons

“AIP is activated more strongly by grasping, when object information is required to preshape the hand, but does not respond to images of objects in the absence of action”

“LO is activated more strongly by objects than scrambled control images, but shows no enhanced activity when real objects are the targets for grasping compared to reaching”

“Real” vs Images

• Potential for grasping a requirement of AIP?

• Different stimulus types complicate direct comparisons

• Recognition of ‘real’ rectangles– LO adaptation

• Grasping of complex objects (e.g., tools)– AIP in viewing of graspable objects

AIP: Scrambled-Intact

• Attentional and spatial demands– S>I?– I>S? (Kourtzi & Kanwisher, 2000)

• Is G-R accounted for by attentional demands?– Overlap of G-R and S-C?

Conclusions• Was the study objective addressed?

• Did results support hypotheses?

• How conclusive are the findings?

• How/why might additional and/or alternative contrast analyses be valuable?