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Spatial representation and parietal cortex
Marlene Behrmann Department of Psychology,
CMU and CNBC
Contact: [email protected]
•URL: http://www.cnbc.cmu.edu/~behrmann
Division of labour in human visual cortical system
Mishkin and Ungerleider
The parietal lobes:• “crossroads of the brain”
(Critchley, 1953)
• well situated
topographically
• multimodal
• requisite cortical and subcortical connectivity
• Distribution of MCA, little collateral supply
InferiorParietal lobule
Supramarginalgyrus
Angulargyrus
Neglect
Federico Fellini (1920-1993)
*
• Asymmetry in incidence: RH (66%) in humans not monkeys
• Inferior parietal lobule– Areas 39 and 40;
– non-human primate analog: IPL (7) vs STS
– bimodal: short-lived vs persistent
• Affects different sensory modalities
• Not sensory deficit
*
Neglect
Not just parietal
• Distributed network: (Mesulam; Heilman)– dorsolateral prefrontal, medial frontal (cingulate, thalamus,
basal ganglia, white matter).– Same network activated in eye movement studies
• Close relationship between attention and eye movements(Corbetta et al.)
• Other terminology– Extinction– Allesthesia– anosagnosia
Extent of effect
• Other sensory modalities– Auditory– Olfactory– Tactile
• Mental imagery– Piazza del Duomo (Bisiach and Luzzatti)
• Affects output: not surprisingly
Vision and eye movements(Behrmann et al.)
• 45 x 36 degrees visual angle
• magnetic scleral coil in right eye
• indicate number of As in display
Lesions: neglect patients
Lesions: BD controls
with hemianopia
Location and duration of fixations
Eye movements reflect left-sided neglect
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
What can we learn about parietal cortex?
• What determines what information is neglected?
• What gives rise to neglect?
• What happens to the information that is neglected?
What can we learn about parietal cortex?
• What determines what information is neglected?
• What gives rise to neglect?
• What happens to the information that is neglected?
Possible frames of reference: what defines ‘left’?
Egocentric: retino? head? trunk?
Allocentric:
Environmentor Scene
Object
Visual neglect in allocentric coordinates
midline of environment midline of environment
(a) (b)
midline of environment midline of environment
UPRIGHT ROTATED
Depiction of environmental neglect
Visual neglect in allocentric and egocentric coordinatesmidline of environment midline of environment
(a) (b)
midline of environment midline of environment
UPRIGHT ROTATED
Tactile and visual neglectMoscovitch and Behrmann
Tactile neglect in allocentric co-ordinates
Range of possible frames of reference
Egocentric: retino? head? trunk?
Allocentric:
Environmentor Scene
Object
Neglect with respect to object midline
• Target
• Copy
Behrmann and Tipper
right objectright space
left object
right space
Object-based neglect: inhibition for right and facilitation for left targets
Directional selectivity of neuronsOlson and Gettner (1995, 1998)
Fixation spot: 200 msecA
Sample bar: 500 msecB
Cue: 300 msecC
Delay: 400-600 msecD
Fixation spot offTarget bar on
E
ResponseF
L/R of barL/R eye movement
Neurons fire for left or right of bar independent of direction of movement
Eye MovementCue on
500 msec
Left with Respect to Bar
Eye MovementCue on
500 msec
Right with Respect to Bar
Paradigm: object and environ- neglect
square
circle
Simultaneous object- and environ-based neglect
Multiple reference frames in eye movements too
FARMFEVER
CAGE
TEAR
FLAP
WHIP
TREADFLAME
BLOCK
BRAIN
SLEDGE
HOLDER
DEJECT
HEIGHT
BRIGHT
Normal: no errors in reading
Neglect: errors and eye movements
Another example
FARMFEVER
CAGE
TEAR
FLAP
WHIP
TREADFLAME
BLOCK
BRAIN
SLEDGE
HOLDER
DEJECT
HEIGHT
BRIGHTXX X
X
right
Hemianopic: no reading errors
Frames of reference
• Egocentric (dependent on viewer)
• But also allocentric (independent on viewer)– Not only in vision, also in tactile
• Multiple coordinate frame– Also evident in eye movements
What can we learn about parietal cortex?
• What determines what information is neglected?
• What gives rise to neglect?
• What happens to the information that is neglected?
What gives rise to neglect?
gradient
Gradient consistent with neuronal distribution: 68 bilateral, 29 contra, 3 ipsi
Suggests competition too:bad on left, too good on right
Visual search paradigm
I. ‘Pop-out’ Task.Target defined by a distinctive feature:specifically, an intersecting line.
II. ‘Serial’ Task.Target defined by the lackof a distinctive feature.
Normal subjectsFeature search Conjunction search
1 6 12 1 6 12
Patients with LHD
Patients with
RHD
So:
• Spatial deficit apparent in visual search
• Generally scaled with severity of neglect– But more in RHD than LHD
– Some competition: better on right side as neglect severe in conjunction
What can we learn about parietal cortex?
• What determines what information is neglected?
• What gives rise to neglect?
• What happens to the information that is neglected?
Fate of neglected information
• Do patients process unattended information normally?
– failure to reach consciousness?– degraded processing?
Volpe, Ledoux and Gazzaniga (1979)
Same or different? Name the objects
Response: different Response: A star
Unconscious processing/ failure to explicitly report information that is available
Priming paradigmMcGlinchey Berroth et al.
Normal subjects: faster lexical decision time if related than unrelated
related unrelated
GOSE THIP
Results
• Patients faster to say ‘yes’ when semantic related pic on right (eye-nose) compared to eye-ship
• Patients faster to say ‘yes’ when semantic related pic on left
• SAME AMOUNT OF PRIMING/FACILITATION FROM BOTH SIDES! Even though report the information.
• Patients process neglected info normally.
Results … Continued
• BUT: normals show double priming on left than right
• Cannot conclude processing is normal!
• Priming not as demanding as explicit report.
What can we learn about parietal cortex?
• What determines what information is neglected? – Multiple reference frames, demands of task
• What gives rise to neglect?– Competition between residual activated neurons, spatial and temporal factors
relevant
• What happens to the information that is neglected?– Seems to be activated to some extent, not fully
Alternative view of parietal cortex:“how” not “where”
• Milner and Goodale– Parietal cortex involved in on-line ballistic
movements
Where the action is!
Grasping
matching
What can we learn about parietal cortex?
• What determines what information is neglected? – Multiple reference frames, demands of task
• What gives rise to neglect?– Competition between residual activated neurons, spatial and temporal factors
relevant
• What happens to the information that is neglected?– Seems to be activated to some extent, not fully
