Eye and Retina

Where does light pass through?

Cornea and lens

Cornea

About 80% of focusing power - fixed

Lens

About 20% of focusing power

Can change shape to adjust for distance of objects

Ciliary muscles

Accommodation

Accomodation

Brings objects located at different distances into focus by changing the shape of the lens

Image on retina

flipped

Photoreceptors

Specialized receptors that detect light

Important retinal cells

Photoreceptors

Bipolar cells

Ganglion cells (2 types)

Horizontal cells

Two types of ganglion cells

M cells, P cells = pretty - colors are pretty (cones)

Transduction

occurs in visual pigments

Two parts to visual pigments

Opsin and retinal

Spectral sensitivity

Sensitivity of visual receptors to different parts of visual spectrum

Absorptions spectrum

Graph of amount of light absorbed by a visual pigment vs wavelength of light

Rods: one peak

Cones: three peaks, one for each type of cone pigment

• Short wavelength - blue

• Medium wavelength - green

• Long wavelength - red

Convergence

Synapsing of many cells onto one cell

Many more photoreceptors than ganglion cells

Rods converge more than cones —> cones have more fine detail info (acuity), rods have better sensitivity

What is perception shaped by

Neural convergence

Area of retina matters

Less convergence in fovea than peripheral retina

Receptive field

The area on the receptor surface that when stimulated affects the firing of that neuron

Ganglion cell receptive field

Large and overlapping

Lateral inhibition

Inhibition that is transmitted laterally

Via horizontal cells and amacrine cells

Contributes to edge enhancement

Preferential looking technique

Used to measure visual perception in infants

2 stimuli are presented

Infant’s looking behavior is monitored for the time infant spends viewing each stimulus

Spontaneous looking preferences - prefer to look at objects wiht contours over homogenous one

Visual acuity over time

Poor early in life (at 1 month) and rapidly increases from 6-9 months

Full acuity reached after 1 year old

Visual transduction process

light hits retinal —> retinal changes shape (isomerization) —> leads to activation of cell