PSYC 121 Midterm 1

Cornea 

1. Does most of the focusing (80%)

2. Rigid and cannot adjust its focusing power for objects at different distances → lens come into play

Lens

1. Can accommodate for CORNEA by contracting (getting thicker) or dilating (getting flatter) to do the remaining focusing work

2. Looking at a far-away object, the lens is flat

3. closer → if it doesn’t contract → blur 

4. After the lens contracts/thickens, the object is focused correctly

Cones

1. 3 types (sensitive to different wavelengths)

2. Most useful for color vision in bright light

3. High resolution

4. Most dense in fovea

Rods 

1. Only one type (sensitive to light vs. dark)

2. No color information, useful in dim light

3. Low resolution

4. Most dense in periphery

Fovea which contains only

cones

In most of retina, there are many more ____ than ____

rods; cones

Blind spot 

1. The region on the retina where ganglion cells exit the eye via the optic nerve, sending signals to the brain

2. No receptors at all in this area

Superior colliculus

The remaining 10% of ganglion cells go to here which is a region involved in controlling eye movements.

Binocular disparity

The difference between the images on the left and right eyes

Functions of the LGN

1. Organizes the information from retina

2. Receives feedback (top-down) signals from cortex (e.g. attention modulation)

3. Regulate the signal from retina, sending fewer impulses to cortex

LGN organizes the info from the retina according to:

• Which eye it came from

• Which type of receptor it came from (rods or cones)

• Receives feedback (top-down) signals from cortex (e.g. attention modulation)

• Regulate the signal from retina, sending fewer impulses to cortex

Lateral Geniculate Nucleus (LGN)

Organized into 6 layers, each layer receiving information from one eye

• Layers 2, 3, 5 ipsilateral (same side)

• Layers 1, 4, 6 contralateral (opposite side)

LGN → V1 Process

Sends most of its axons to the primary visual cortex (V1), and then the signal gets relayed to V2, V3, and so on.

Visual Processing

Light → pupil → cornea + lens → retina →  rods and cones receptors → signals emerge from the back of the eye in the optic nerve → LGN → V1 cells break down different orientations of light using simple cells, complex cells, and hyper-complex cells

Simple cells

Excitatory and inhibitory areas arranged side by side, respond best to bars of a particular orientation

Complex cells

Respond best to movement of a correctly oriented bar across receptive field, direction tuned

Hyper-complex cells

respond best corners or angles, or particular length bars moving in particular direction.

What is the LGN pathway? Draw a diagram of it.

• 90% of optic nerve fibers go

Left and right visual field → LGN (thalamus) → V1 (primary visual cortex)

• Signals from each half of each retina meet at the optic chiasm.

• Half stay in the ipsilateral LGN, and half go to the contralateral LGN 

Cortical magnification

A phenomenon whereby the central visual field, particularly the fovea, is represented by a disproportionately large area of the primary visual cortex (V1) relative to the peripheral visual field.

• Higher density of photoreceptors and greater processing demands of foveal vision, resulting in finer spatial resolution and more detailed visual processing for stimuli presented near the center of gaze.