Notes From Reading
CHAPTER 4: SENSATION AND PERCEPTION
1. Retina- the neural tissue lining the inside back surface of the eye. Absorbs
light, processes images, and sends visual info to the brain.
2. Optic Disk - a hole in the retina where the optic nerve fibers exit the eye.
3. Visual Receptors – Rods and Cones
a.Cones – specialized visual receptors in the retina that play a key role in
daylight vision and color vision.
i.Do not respond well to dim light
ii.Cones provide visual acuity (sharpness and detail)
iii.Concentrated in center of retina
iv. Fovea – tiny spot in center of the retina which only contains cones,
greatest visual acuity.
b. Rods – specialized visual receptors in the retina that play a key role in
night vision and peripheral vision.
i.More sensitive than cones to dim light
ii.Handle peripheral vision
iii.Density greatest outside the fovea, and gradually decreases
4. Dark and Light Adaptation
a.Dark Adaptation – the process in which the eyes become more sensitive
to light in low illumination.
b. Light Adaptation – the process where eyes become less sensitive to light
in high illumination.
5. Info Processing in the Retina
a.Light hitting cones and rods triggers neural signals that pass into the
intricate network of cells in the retina.
b. Signals move from receptors to bipolar cells to ganglion cells, sending
impulses to optic nerve (axons that connect the eye to brain).
c.Axons carry visual info encoded as a stream of neural impulses to the
d. The Receptive field of a visual cell – retinal area that when stimulated
effects the firing of that cell.
D.Visual and The Brain
1. Visual Pathways to the Brain
a.Axons from the eye form the optic nerve, travel to the optic chiasm
b. Optic Chiasm - The point at which the optic nerves from the inside half
of each eye cross over and then project to the opposite half of the brain.
Ensures that each half of the brain gets info from both eyes.
c.After reaching the optic chiasm, the optic nerve splits between 2
pathways – main and secondary.
i.Main – hypothalamus
ii.Secondary pathway function – coordination of visual info with other
d. Main visual pathway is divided in 2 more parts – magnocellular (where)
and parvocellular (what)