Sensation and Perception Ch.2

Light physics

Light is the physical stimulus that we are able to see (they are waves)

Wavelength

Determines hue

Altitude

Determines brightness

Scattered

Irregular fashion

Transmitted

One place to another

Refracted

Can bend passing through something

Absorbed

Won’t be transmitted at all due to absorption

Cornea

Covers the front of the eye

Iris

Colored muscle that adjusts the pupil size

Pupil

Circular opening when light will open

Lens

Oval structure that focuses the light

Retina

Membrane with photoreceptors that transduce light waves into neural signals

Fovea

Area of the retina with the highest visual acuity

Aqueous humor

The grey matter in front of the eye

Vitreous

All the liquid behind the lens

Accomodation

When our muscles adjust the lens to change shape to accept light

Close object

Thicker lens

Far object

Thinner lens

Far object

Thinner lens

Astigmatism

Images are reflected all over the place

Neural Circuity

• light comes in reflects and then makes its way to the retina all the way at the back

• at the back, it goes to photoreceptors

Cones

Color and fine detail

Rods

Detect dim light

Fovea

Area of retina with the highest visual acuity (most cones)

Photoreceptors then go to bipolar cells

• One pole that attaches to photoreceptors

• One to the ganglion cell

Receptive field

The region on the retina in which visual stimuli influences a neuron’s firing rate

Ganglion cells have a

Concentric receptive field

Ganglion cells are the most sensitive to

Contrast

Ganglion cells have a preference for

Light in the “center” and “surround”

In the center there is

No firing

Center Light

Firing

Many photoreceptors make up

Each receptive field

Lateral inhibition

Signals that reach the retinal ganglion cells are based on differences between nearby photoreceptors

Light process step 1

Passes transparent cornea

Light process step 2

Enters through pupil (controlled by iris)

Light process step 3

Bent by lens to focus on the back of the retina

Light process step 4

Light is sensed by photoreceptors in the retina

Light process step 5

Photoreceptors pass info from within their receptive fields through additional retinal cell layers

• bipolar cells- synapse with rods and cones

• ganglion cells- synapse with bipolar cells

Light process step 6

Ganglion cells transmit the signal through the optic nerve

Light process step 7

The optic nerve carries the signal to the brain