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

Ventral Dorsal Visual Cortex Dorsal Dorsal Pathway

RetinaLGNV1 V4 Parietal Cortex Inferotemporal Cortex (Relay Station) (Detects Edges) (Color, Form) (Shape, Object Recognition) (Location, How to reach or act upon)

- Line-bisection task - Extinction hemispatial neglect syndrome - Drawing - Line cancellation

time Memory/Attention Task (fMRI / ERP)

Regions of Interest Right Visual Field Left Visual Field

Stim 1Stim 2 Single-Unit Recording “spike” = single neuron’s action potential (Macaque monkey) Signal Analysis Receptive Field

Attention Effects in Single Neuron Responses 100 msec Frequency of spikes Attended bar Unattended bar ( Robert Desimone, NIH)

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 Attention contributes to object perceptual awareness

‘look for blue horizontal line”

Inattentional blindness (here)here 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 ccc c c c c c c c Impaired drawing bilateral posterior parieto-temporal atrophy, most pronounced in right hemisphere Left visual field extinction

‘Perception’ Tasks: Can the patient ‘discriminate’ two simultaneous shapes? (circle, square) Can the patient ‘see’ two simultaneous shapes?

Buffer Shape Discrimination Task: same / different Display: Sequential (duration tailored for each subject) T 1 Ts 1 & 2 Mask Interval T 2 Simultaneous Buffer Mask Buffer Mask 88% correct 50% correct

Count Task: one / two Follow-up study - Single Figure Accuracy 61%46% Conclusion: - R.D. cannot ‘see’ two objects Control study: Single complex figure 90% accuracy

© 2000 Charly Herscovici, Brussels / Artists Rights Society (ARS), New York Reproduction, including downloading of Magritte works is prohibited by copyright laws and international conventions without the express written permission of Artists Rights Society (ARS), New York. Interactions between Dorsal and Ventral Pathways Objects exist in space