Dorsal and ventral streams- 2001
I. Overview of dorsal and ventral pathways.
 A. Ventral - form and color
 B. dorsal - movement.
 C. this division is only an approximation
II. There are two types of retinal ganglion cells with different receptive fields-Magno and parvo
 A. properties of parvo-small cells
  1. small receptive fields
  2. many are sensitive to color.
  3. respond tonically to stationary stimuli
 B. properties of magno cells-large cells
  1. larger receptive fields.
  2. Not sensitive to specific colors
  3. phasic
  4.    motion sensitive
III. LGN: Parvo cells go to upper 4 layers, magno go to lower 2 layers.  In LGN parvo and magno pathways are anatomically separate.  They were mixed in the retina and will be mixed again in cortex.
 A. review layering in geniculate.
IV. magno and parvo systems in V1.
 A. magno and parvo LGN cells connect to different layers in V1.
 B.  Form and color cells are represented in patches in layer 3 but are intermixed in patchy fashion.
  1.receptive fields small, high resolution.
 C.Magno goes from V1 to dorsal pathways
  1.large receptive fields, phasic, directionally selective.
 D. Cells in V1 project to V2.  All three systems project to V2, but again the synapses and cells belonging to the 3 systems are kept in somewhat separate alternating regions.
 E. Note that there is cross talk between magno and parvo systems even at level of V1 and this increases as we go higher.
V. Magno pathway to MT (V5)
 A. Area MT receives inputs from V2 magno system.
  1. columnar organization of directionally sensitive cells.  Each part of visual field has a column for each direction of movement.
 B. receptive field properties of MT cells:MT contains a retinotopic map with information about speed and direction of movement.
  1. receptive fields are 8-10 times larger in linear dimensions than are receptive fields in V1.
  2. Many cells do not have complex stim requirements.  Some are driven by simple spots of light but some are orientation selective.
  3. sensitive to movement: directionally selective and have a wide range of velocity sensitivities
  4. sensitive to global motion of pattern: vector sum of component motion. In contrast, V1 cells are sensitive to component motion. (Plaid demonstration)
  5. many disparity selective cells.  Similar to those in V1.
 C. Stimulation experiments
  1. Try to show that stimulating a column of cells that respond to a particular direction of movement increases the monkey's ability to see movement in that direction.
  2. Task
   a. Show monkey a moving dot display where a certain percentage of the dots move in a fixed direction.  Rest of the dots move randomly.  Vary percentage of dots moving in the fixed direction.
   b. monkey indicates that he saw a direction of motion by saccading toward a target dot in that direction.
   c. Monkey is more likely to report that he sees movement in the fixed direction if more dots are moving in that direction.
  3. Now stimulate a column of cells that prefer movement in direction that the dots move.  This will increase proportion of time that monkey reports seeing movement in this direction. (Newsome et al J. Neurosci. 12:2331.
VI. V4 (OMIT)
 A. receptive fields: cells respond to orientation length, width and color.
  1. large rf but cells respond to very small objects,objs the same size as entire V1 receptive fields.  This may increase the ability to generalize shape over many retinal positions.
  2. suppressive surrounds. The cell responds if you put different stimuli in center and surround, but not if you put same stimulus in center and surround. Perhaps used in figure ground separation.
VII. inferotemporal cortex
 A. receptive fields
  1. no map of visual field.
  2. receptive fields almost always include fovea
  3. large fields (typical 25 x 25 deg)including ipsilateral field.  60% extend into ipsi field.
  4. many cells respond to simple stim such as bars. Many sensitive to color.
  5. about half units have complex requirements, e.g. shapes. about 10% require very complex stimuli, e.g. face, hand.
   a. some specific for profile or frontal, others respond to all faces
   b. don't respond to a specific face
   c. But it is not clear that these are "face recognition cells".  Tanaka has shown that many may respond to much simpler stimuli.
VIII. PET studies: Region of the cortex that is active depends on property of stimulus that subject is asked to attend to.
 A. attention to location  activates inferior parietal cortex; roughtly equiv to MT and MST
 B. attention to shape activates temporal cortex, may correspond to TE and TEO.
IX. Clinical lesion data supports physiology data.
 A. strokes can cause loss of color, form or motion, or face recognition selectively.
 B. patient with MT lesion could not indicate direction of movement of dots unless coherence was high.
  1. note that patient did well on other visual tasks, e.g. acuity.