Higher Order Visual Processing in the primate brain

Projection of the visual field on the retina Retina

Οπτικό νεύρο περιέχει ίνες που προέρχονται από ένα μάτι Οπτικό χίασμα αλλά μεταφέρουν πληροφορία και από τα δύο οπτικά ημιπεδία Οπτική ταινία: περιέχει ίνες που προέρχονται και από τα δύο μάτια αλλά μεταφέρουν πληροφορία από το ετερόπλευρο οπτικό ημιπεδίο

Υποθάλαμος Έξω γονατώδες σώμα Προτετραδιμυκός πυρήνας (pretectum) Άνω διδύμιο

Visual deficits from damage at different points along the primary visual pathway

Visual deficits from damage at different points along the primary visual pathway Bitemporal (heteronomous) hemianopsia

Visual deficits from damage at different points along the primary visual pathway Bitemporal (heteronomous) hemianopsia Left homonymous hemianopsia

Course of the optic radiation to the striate cortex

Visual deficits from damage at different points along the primary visual pathway Bitemporal (heteronomous) hemianopsia Left homonymous hemianopsia Left superior quadrantanopsia

Organizational Principles of Visual Projections Retinotopy Neighboring cells in the retina feed information to neighboring places in their target structures

Visual field representation in V1 Retinotopy but..: Distortion (e.g. central vs peripheral representation) When the retina is stimulated by a point of light the activity in striate cortex is a broad distribution with a peak at the corresponding retinotopic location

Φυσιολογία V1 Διοφθάλμια υποδεκτικά πεδία κύτταρα αποκρίνονται σε ερεθισμό και των δύο ματιών. Επιλεκτικότητα για προσανατολισμό ερεθίσματος. Επιλεκτικότητα για κατεύθυνση κίνησης. Απλά και Πολύπλοκα υποδεκτικά πεδία (simple and complex) Ανάλυση χρώματος blobs Οργάνωση σε στήλες (οφθαλμικής επικράτησης, προσανατολισμού)

Cytoarchitectonic subdivisions of the cerebral cortex motor cortex primary somatosensory cortex early 1900s Brodmann primary visual cortex

Macaque Cortex CORTEX: 52% visual, 10% somatosensory, 3% auditory, 8% motor, 1% olfactory) Van Essen, The Visual Neurosciences, Chapter 32, 2004

Human Cortex CORTEX: 27% visual, 7% somatosensory, 8% auditory, 7% motor)

Felleman and Van Essen 1991 Van Essen, Anderson and Felleman Science 1992

Too many visual areas (24, 32, 10-12) WHY?

Color Shape Depth Motion

Two visual pathways Dorsal and Ventral

Two visual pathways Dorsal and Ventral Posterior Parietal MST MT V3 V2 V1 Inferior Temporal (IT) V4

Posterior Parietal MST MT V3 V2 V1 Inferior Temporal (IT) V4

PRIMARY VISUAL CORTEX (V1) (cytochrome oxidase histology) blobs: color processing interblobs: high spatial resolution form processing layer 4B: direction-selectivity interblob blob

Parallel streams of visual processing V1 V2 blob Layer 4B thin stripe interblob interstripe thick stripe

Parallel streams of visual processing V1 V2 V4, MT blob Layer 4B thin stripe interblob interstripe thick stripe V4 MT

Parallel streams of visual processing

Ventral Pathway Parallel streams of visual processing Dorsal Pathway Posterior Parietal Lobe

Mixing of K, P and M pathways within V1 and origins of projections to higher areas Shipp Vis Neurosci 2005

The dorsal and ventral cortical streams cannot be viewed as an extension of the M and P retinogeniculate pathways Predominance of M or P input in the dorsal and ventral pathways, respectively. Experiment?????

WHERE spatial localization Ungerleider and Mishkin (1982) WHAT object recognition

identity vs location Mishkin, Ungerleider and Macko Trends Neurosci 1983

HOW Vision for action WHAT Vision for perception Milner and Goodale 1992

Goodale and Milner Nature 1991

V1 V2 V3 MT V4 Ραχιαία Οδός: ΠΟΥ, ΟΠΤΙΚΗ ΠΛΗΡΟΦΟΡΙΑ ΓΙΑ ΡΑΣΗ Οπίσθιος βρεγματικός λοβός Κάτω κροταφικός λοβός (ΙΤ) Κοιλιακή Οδός: ΤΙ, ΑΝΑΓΝΩΡΙΣΗ ΑΝΤΙΚΕΙΜΕΝΩΝ

Visual Illusions Muller-Lyer illusion Kanizsa triangle

Responses of V2 cells to illusory contours

MT Middle Temporal area (V5) 95% of the neurons selective for the direction of motion Receives input from layer 4B of V1 as well as from the thick stripes of V2 RFs ten times wider than those of cells in V1 directional specificity organized into vertical columns

The aperture problem

Microstimulation of ΜΤ affects perception of motion

Two techniques that can assess causal relationship between brain activity and behavior lesions (necessary) microstimulation (sufficient)

V4 Receives input from the blob and interblob regions of striate cortex via a relay in V2 RFs are larger than those in V1 and V2 Cells display orientation and color selectivity => shape and color perception Lesions in the human analogue of V4 result in achromatopsia

IT No clear retinotopic organization Very large RFs covering both visual hemifields => position invariance Sensitive to shape and color Cells respond to abstract shapes and complex stimuli (e.g. hands, faces) Damage in IT results in prosopagnosia

Face selective cells in IT

Fusiform Face Area (FFA) in humans

How does visual perception come about from the concerted action of individual neurons? Which neurons in which areas determine what we perceive? How and where does integration take place?

Going higher in the visual hierarchy we encounter larger RFs and processing of more complex stimuli Rolls, ET, Visual Neurosciences 1992

A hierarchy of visual areas in the macaque based on laminar patterns of anatomical connections Van Essen, Anderson and Felleman Science 1992

Multiple visual areas defined on the basis of anatomy and function Two visual pathways with different properties and functions but with extensive crossconnections. Parallel processing throughout the visual system=> division of labor for perception: within a given cortical area many broadly tuned cells may serve to represent features of objects

Contralateral (hemispatial) neglect syndrome Inability to report or respond to stimuli presented on the side opposite to the lesion. Usually a result of damage to the RIGHT parietal lobe

Optic ataxia