Transcript Receptive Fields - Villanova University

Vision: Outline
• Eye
– Color vision
– Receptive Field
– Edge Detection
• Visual Path
– thalamus (LGN)
– primary visual cortex
• Orientation sensitive; Spatial frequency
– Ventral Pathways
• Area MT (motion), Object Recognition, Area V4 (color)
• synesthesia
– Dorsal Pathway
• Spatial Attention
• Hemispatial Neglect
Dorsal Pathway
Dorsal
Dorsal
Visual Cortex
Ventral
Retina
LGN
V1
(Color,
Form)
(Shape,
Object
Recognition)
V4
Inferotemporal
Cortex
(Relay Station)
(Detects Edges)
Parietal
Cortex
(Location,
How to reach or
act upon)
hemispatial neglect syndrome
- Line-bisection task
- Drawing
- Extinction
- Line cancellation
Memory/Attention Task
(fMRI / ERP)
time
Regions of Interest
Right
Visual
Field
Left
Visual
Field
Single-Unit Recording
Receptive Field
(Macaque monkey)
Signal
Analysis
“spike” = single neuron’s action potential
Stim 1
Stim 2
Attention Effects in
Single Neuron Responses
Attended bar
Frequency
of
spikes
Unattended bar
100 msec
(Robert Desimone, NIH)
Attention contributes to object
perceptual awareness
• move your eyes (& your attention)
• you ‘see’ the change -- you are
‘perceptually aware’-- at the attended
location
• You are unaware at the unattended
locations.
Try to find the difference between these two
pictures
‘look for blue horizontal line”
• Inattentional blindness (here)
http://viscog.beckman.uiuc.edu/grafs/demos/15.html
Count how many passes the ‘white’ team makes
• Continuity errors (Terminator 2)
Atypical Alzheimer’s Disease
• Also known as Posterior Cortical Atrophy (PCA)
• Similar pathology to AD, but:
– Localized in Parietal cortex
• Some clinical similarities to:
– Right parietal stroke
(hemispatial neglect)
– Bi-parietal stroke
(Balint’s syndrome)
Hemispatial neglect
Atypical AD Patient
• 68 y-old male
• Local bias
cc ccc
c
c
c
c
c
• Impaired drawing
• Left visual field extinction
• bilateral posterior parieto-temporal atrophy, most pronounced in
right hemisphere
• ‘Perception’ Tasks:
• Can the patient ‘discriminate’ two simultaneous shapes? (circle,
square)
• Can the patient ‘see’ two simultaneous shapes?
Shape Discrimination Task: same / different
Display:
Sequential
Simultaneous
T1
(duration tailored
for each subject)
Buffer
Mask
Interval
T2
88% correct
Ts 1 & 2
50% correct
Buffer
Mask
Buffer
Mask
Count Task: one / two
Accuracy
R.D. (right TPJ)
50 %
(400 ms)
Conclusion:
- R.D. cannot ‘see’ two objects
Follow-up study
- Single Figure
Accuracy
Control study: Single complex figure
61%
46%
90% accuracy
Interactions between Dorsal and Ventral
Pathways
Objects exist in space