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Visual System III – Dorsal Pathway

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.),

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Visual System III – Dorsal Pathway

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  1. Visual System III – Dorsal Pathway

  2. 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

  3. ​- Lesions in the human parietal cortex can cause • ​- Attentionalhemineglect: neglect of contralateral space, also manifested in memory • ​- Constructional apraxia: inability to reproduce complex objects.

  4. 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.

  5. 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.

  6. ​- 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.

  7. 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)

  8. ​- Lateral: has role in smooth eye pursuit • ​- Ventral intraparietal (VIP): integration of visual and tactile space, tuned to congruous motion/tactile stimulus.

  9. ​- The sequence LIP MIP AIP is responsible for grabbing objects of interest • ​- Lateral intraparietal (LIP): eye saccades • ​- Medial intraparietal (MIP): arm reaching movements.

  10. ​- Anterior intraparietal (AIP): hand grasping • ​- Area 7a: considered highest level of ventral pathway, convergence and integration of several types of visual information.

  11. 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.)

  12. ​- How coordinates systems are dealt with • ​- Sequential transformation from one system to another as one progresses along the visual pathway.

  13. so any given level uses only one coordinating system: 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.

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