psych 230 - unit 8 the visual system; the eye

light

Form of electromagnetic energy

wavelength

distance between peaks

intensity

height of wave

frequency

frequency of waves per unit of time

scattered/diffracted

bouncing around the enviornment

absorbed

anything black is an object that absorbs all the light energy that it recieves, and it does not reflect any

reflected

• The color of objects results from the light that bounces back towards you, and what’s not absorbed will be reflected, which is what gives you some of the sensation of the color of the object

transmitted

Light information can be transmitted when it passes from one medium to another medium.

refracted

• When it goes from one medium to another, it tends to be refracted

• Structures with fixed refractive power: cornea, anterior chamber, posterior chamber

properties of light

scattered/diffracted

absorbed

reflected

transmitted

refracted

human field of view

Visible light is 400-700 nanometers

anatomy of the eye (different structures)

• Sclera: protective membrane

• Gives us the white color in our eyes

• Cornea: clear surface; focuses light towards the retina

• Anterior chamber

• Iris: muscle; colored part of the eye

• Pupil: opening in the iris

• Not a structure, just a hole inside the iris

pupillary reflex

Automatic process where the pupil expands in dim light and contracts in bright light.

accomodation

Rapid process of adjusting the lens so that both near and far objects can be seen.

near point

The closest distance at which an eye can focus

retina

Paper thin layer of cells where transduction takes place

what is the fovea and where is it on the retina?

When we look at objects, the image is projected onto this. It is located in the back of the eye, right in front of the retina

optic disc

Region at the back of the eye where the optic nerve meets the retina. It is the blind spot of the eye because it contains only nerve fibers, no rods or cones, and is thus insensitive to light.

photoreceptors

cones and rods, located at the very end of the eyeball

horizontal cells

Receive information from photoreceptors and other horizontal cells, cross talk across photoreceptors

midget cells

the primary type of retinal ganglion cell in the primate retina (constituting about 80% of the total), responsible for high-acuity, red-green color vision, and spatial detail.

diffuse cells

• Input from ~ 50 photoreceptors

• Pooling of information: loss of fine details, but increased light sensitivity

• Periphery

amacrine cells

• Receive information from bipolar cells and other amacrine cells; cross-talk functions

ganglion cell: P

• involved in processing fine visual acuity, shape, and color

• 1 cone → 1 bipolar cell → P ganglion cell

ganglion cell; M

• involved in processing motion and spatial relations

• Input from ~ 50 photoreceptors → Diffuse bipolar cell → M ganglion cell

transduction of light

photopigment; opsin; classes of receptors

photopigment

• a molecule that absorbs light and releases an electric potential

opsin

the protein part of the photopigment that captures the photon of light and begins the process of transduction

classes of receptors

The human eye has two primary classes of photoreceptor cells in the retina—rods and cones—which convert light into neural signals

duplex theory of vision

• the doctrine that there are functionally two distinct ways in which our eyes work, the photopic (associated with cones) and the scotopic (associated with rods).

• photopic vision; scotopic vision

photopic vision

Cones and daytime vision

scotopic vision

Rods and nighttime vision

convergence and acuity

Consequences of pooling across multiple photoreceptors, improves light sensitivity.

dark and light adaptation

• the process in which the eyes become more sensitive to light in low illumination

• Light bleaches the rods, rhodospin needs time to replenish. light-the visual system's sensitivity to low light levels decreases so that it can operate in higher light levels.

receptive field

the specific region of the retina—and corresponding area of the visual field—where light stimuli alter the firing rate of a particular neuron (such as a ganglion cell)

on-center ganglion cell

• When you put a light in the center of the ganglion cell, there will be a response

• If you put it in the surrounding area, there will not be a response

off center ganglion cell

• When you put a light in the center, there will be no response

• If you put it in the surrounding area, there will be a response

lateral inhibition

excited photoreceptors inhibit neighboring neurons, primarily via horizontal cells, to enhance contrast and sharpen image edges

diseases of the eye

myopia, hyperopia, astigmatism, cataract, macular degenration, retinitis pigmentosa

myopia

aka nearsightedness. Lens refracts too much so that light focuses in front of the retina and faraway objects appear blurry.

hyperopia

Aka farsightedness, lens does not have enough refractive power so light focuses behind the retina and near objects appear blurry

astigmatism

A condition that develops from an irregular shape of the cornea or the lens, which makes it impossible for the lens to accommodate a fully focused image.

cataract

Result from the clouding of the lens. Solution is surgery, so can be corrected. Occurs mostly as people age, but can occur in children as well

macular degeneration

Affects central vision, blurring our perception of whatever it is we are trying to look at. Either inherited or caused by looking directly into the sun.

retintis pigmentosa

Affects peripheral vision, creating a "tunnel" vision effect in which we see what we are looking at with normal acuity, but can't see what surrounds our focus.

vision prostheses

Affects peripheral vision, creating a "tunnel" vision effect in which we see what we are looking at with normal acuity, but can't see what surrounds our focus.

presbyopia

Light focuses behind the retina, difficulty focusing on close objects

bipolar cells

Receive information from photoreceptors and sends signals to retinal ganglion cells. 2 types: Midget (1 cone processes the information and sends it down to 1 bipolar cell. High visual acuity maintained) and Diffuse (input from ~50 photoreceptors where the info is pooled so loss of fine details but increased light sensitivity).