55-101 Lecture Notes - Retinotopy, Optical Flow, Visual System
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1 Feb 2013
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Outline of Lecture 66 (03-27 A; Connor)
Visual System III – Dorsal Pathway
I. Introduction to the dorsal pathway
- The dorsal pathway processes depth and motion
- Components of the dorsal pathway are V1, V2, V3, middle temporal (MT), medial superior
temporal (MST), intraparietal regions (lat., vent., med., ant.), and area 7a
- Lesions in the human parietal cortex can cause
- Attentional hemineglect: neglect of contralateral space, also manifested in memory
- Constructional apraxia: inability to reproduce complex objects
II. V1, V2: lower level processing of stereoscopic vision
- 3D depth perception is achieved by stereopsis: there is a slight disparity between the images on
the two retinas
- Both V1 and V2 are tuned to binocular image disparity and motion direction
III. MT: intermediate level processing
- MT cells respond to motion direction and speed, as well as to binocular disparity
- MT receptive fields are larger than in lower levels
- MT columns are organized in smooth gradients of direction preference and stereoscopic depth
- Microstimulation of MT cells can bias perception of motion direction and depth
IV. MST, VIP, LIP, MIP, AIP, 7a: higher level processing
- Medial superior temporal (MST)
- Dorsal: tuned to direction and foci of optic flow (due to self-motion)
- Lateral: has role in smooth eye pursuit
- Ventral intraparietal (VIP): integration of visual and tactile space, tuned to congruous
motion/tactile stimulus
- The sequence LIP MIP AIP is responsible for grabbing objects of interest
- Lateral intraparietal (LIP): eye saccades
- Medial intraparietal (MIP): arm reaching movements
- Anterior intraparietal (AIP): hand grasping
- Area 7a: considered highest level of ventral pathway, convergence and integration of several
types of visual info
V. Note on visuospatial coordinate systems
- Visual system must deal with information coded in various coordinate systems (e.g. retinotopic,
head-centered, body-centered, etc.)
- How coordinates systems are dealt with
- Sequential transformation from one system to another as one progresses along the visual
pathway, so any given level uses only one coord sys: evidence for this in lower levels
- Integration of info in multiple coordinate systems, resulting in a mix of spatial sensitivity: most
cells in higher areas do this
Summary of major ideas
- See Objectives on p. 1