PSY280: Lecture 4 Notes
1. Calculate relative levels of activation of ON/OFF bipolar cells and centre-
surround RGCs based on their relative inputs.
2. Describe how the spatial organization of the visual field is represented in
the cortex (along with its distortions)
a. Activity on the retina causes activity in the cortex.
b. Vernier acuity and grating judgments both use just noticeable
differences to estimate visual acuity in participants.
3. Describe evidence that shows cortical magnification contributes to visual
a. It depends on how far the object it is from the eye.
i. If a mouse is placed close and an elephant is placed far,
they can occupy the same space on retina.
b. To get an estimate of cortical magnification, researchers presented
spots of light of varying visual angles and measured the size of the
c. The higher a participant’s visual acuity, the greater their magnitude
of cortical magnification.
4. Summarize the characteristics of the columnar organization in the striate
cortex, including ocular dominance and hypercolumns.
a. Neurons that are perpendicular to the surface of the cortex have
receptive fields at approximately the same location on the retina.
i. Same preference in space
ii. Same preference of orientation of light
b. When researchers cut across the orientation columns, they found
orientation preference changed systematically.
c. Ocular dominance is meandering, and orientation columns can
have multiple configurations.
d. There are more hypercolumns representing in fovea than in
1 5. Summarize the characteristics of the magnocellular and parvocellular
a. Pathways from LGN to V1 stay segregated.
i. This compartmentalization of brain allows specialization
Visual function Magnocellular Parvocellular
Retinotopic emphasis Peripheral Central
Receptive field size Large Small
Contrast sensitivity High Low
Color sensitivity Low High
Spatial resolution Low High
Temporal resolution High Low
- detects changes
Motion sensitivity High Low
Neural transmission Rapid Sluggish
- ~fast draft - ~ portrait painting
6. Define and identify the extrastriate cortex.
a. The extrastriate cortex borders V1 and is also important for visual
i. Broadmann’s Area 18 and 19
2 7. Describe where information form the magnocellular and parvocellular
pathways ends up beyond V1.
a. Using electrophysiology, behavior and lesion studies, researchers
determined these pathways extend beyond the striate cortex into
the association areas.
b. Association area is where connect the perception with meanings
c. Magnocellular V1 area MT (medial-temporal)
i. MT: moving object
d. Parvocellular V1 V4
i. V4: stationary object form, color, shape
ii. V4: literally below the MT
8. Recognize the difference between dorsal and ventral
9. Describe the separable functions of the dorsal and ventral pathways in the
a. Dorsal: area MT parietal lobe (“where” pathway)
i. The dorsal pathway is responsible for determining where in
space an object is.
b. Ventral: area V4 temporal lobe (“what” pathway)
i. The ventral pathway is responsible for determining the
identity of an object.
3 c. The two pathways are highly interactive. Bidirectional crosstalk
10. Describe the reasoning behind ablation research.
a. Ablation: if you don’t know what something does, remove it and see
how the system now functions.
b. The monkey with parietal lobe removed fails to remove the food
well cover that is closest to the cylinder because there are no
associations in space with the objects.
c. The monkey with the temporal lobe removed fails to recall which
item was previously presented because it can no longer
discriminate the 2 objects.
11. Explain the landmark discrimination and object discrimination tasks, and
how performance relates to lesions in the parietal or temporal lobes.
a. Landmark discrimination: the goal