The WHERE/HOW (Dorsal Stream/Magnocellular) Pathway

Question 1

Motion

Answer 1

Many cells in pathway leading to MT & MST are direction-sensitive (respond to stimulus moving in certain direction)

• Probably depends on Uni-Directional Lateral Inhibition
• In STS (Superior Temporal Sulcus in lateral Temporal lobes) active during observing Biological Motion
• Includes observed motion of walking, head movements, facial expressions, etc

Question 2

Uni-Directional Lateral Inhibition

Answer 2

• These cells’ RFs consist primarily of Rods, which are sensitive to movement because of their convergence and clustering
• i.e. Image sweeping across multiple Rods clustered in peripheral Retina is more likely to trigger Ganglion response than if sweeps across individual, non-convergent Cones that are dispersed through periphery

Question 3

In MST (Medial Superior Temporal Cortex)

Answer 3

some cells respond best to (“Optic Flow”)

• .i.e Whole environment streaming toward/from observer as when observer moves forward/backward

Question 4

in STS (Superior Temporal Sulcus)

Answer 4

• in lateral Temporal Lobes
• active during observing Biological Motion
• Includes observed motion of walking, head movements, facial expressions, etc

Question 5

Depth

Answer 5

• via Binocular Disparity - (or “Retinal Disparity”)
• When both eyes focus on one environmental pt (i.e. both Foveas aligned w/“Focal Point”) the farther any other pt is from that pt,
  the greater the disparity (in degrees of visual angle) between where that non-focal pt will fall on the 2 Retinas

Question 6

Point not far from focal point

Answer 6

will fall on nearly corresponding positions on 2 Retinas (= just a few degrees of disparity)
while a point very far from focal point will fall on very diff locations (= many degrees of disparity) on the 2 Retinas

Question 7

such disparities are used by visual system to help judge…

Answer 7

…relative distance in depth of such points

Question 8

V2 Disparity Detectors

Answer 8

• differentially respond to different ranges of disparity (0o, 15 o, 30 o
  etc) in a given RF

Question 9

MT, Disparity Detectors

Answer 9

respond to different ranges of disparity, regardless of RF (i.e. anywhere on retina)