Psych 1XX3 - Vision

Main Pathway

- after optic chiasm - optic nerve fibers split and travel along two pathways - axons synapse in LGN - sent to occipital lobe

Crude Lens

- allowed processing of visual input at different distances - better focusing, more transparent, better curvature

Optic Disc

- an exit hole for ganglion axons - contains no photoreceptors - our blind spot

Accommodation

- change in lens shape - lens ges fatter when object is close - lens get elongated when the object is far away

Ganglion Cells

- collect info from larger segment of the retina - its axons converge at the optic disc and make the optic nerve

Iris

- coloured part of the eye - controls size of pupil - band of muscles controlled by brain

Cones

- day vision, high light intensities - sensation of colour and detail - concentrated towards fovea

Prenatal Eye Development

- eyes formed during second month of pregnancy - react to light in sixth month - random firing of retinal cells occurs during prenatal period

Compound Eyes

- found in anthropoids, such as insects and crabs - made of ommatidia that point in all directions - manage to form single image by putting together signals - good at detecting movement, close up

Simple Eye

- found in molluscs, such as octopus and squid - has eyeball, lens and retina - type of eye when we think of eyes

Retinal Pigment Epithelium (RPE)

- layer at the back of they eye where photoreceptors get their nutrients from - photoreceptors would die without access to it

Curved "Cup" Eye

- light sensitive path formed into a slight depression - observed in clams - would allow direction of light be sensed - survival advantage over light-sensitive patch

The Retina

- neural tissue that lines the back of the eye - where the physical stimulus of light is first translated into neural impulses

Infant Visual Activity

- newborn can see at 20ft what adults can see at 600ft - 6 months can see at 20 ft what adult can see at 600ft - one year close to adult levels for visual acuity

Rods

- night vision, low light intensities - no colour information, poor detail - none in fovea - peripheral vision

Lateral Geniculate Nucleus

- part of thalamus - receives visual information - where retinal and ganglion cells synapse

Receptive Field of V1 Cell

- primary visual cortex - a combination of the receptive fields of many LGN cells - info from many sources being on one target

Extrastriate Cortex

- processed visual information sent here - separated into two streams: dorsal and ventral

Bipolar Cells

- receive information from photoreceptors - send their information to ganglion cells

Size of Eyes

- resolution and acuity: large eyes better at these - big eyes=need for better eyesight

Ventral Stream

- the "what" pathway - colour and form - sent to temporal lobe

Dorsal Stream

- the "where" pathway - depth and motion - sent to parietal lobe

Photoreceptors

- translates light stimulus into a neural signal - 3 layers: 1 layer photoreceptors at the back, 2 transparent retinal tissue layers

Immaturities in Eye

- weak lens muscles - pupil doesn't react properly to changes in light - at 3 months, focus ability has improved to adult level - much lower density of cells than adult - 4 years: retinal cells reach adult like levels - optic takes several years to mature - brain development not complete until around 11 years

Pupil

- what light passes through after the cornea - black dot in middle of the eye

Eye Placement

- where eyes are on head Eg. Rabbits (prey) have lateral view, to scan environment for predators. Humans (predators) has both eyes towards the front, key asset for successful hunting.

Cornea

- where light first passes through - transparent window at the front of they eye

The Lens

- where light passes through after pupil - flexible piece of tissue - a transparent structure - final focusing of light onto the retina

Vitreous Humour

- where light passes through after the lens - clear, jelly-like substance - compromises main chamber in eyeball

Primary Visual Cortex

- where visual signals are sent - in the occipital lobe - where receptive fields from the retina are arranged in a topographical map

Fraction of Brain Devoted to Processing Visual Information

1/3

Ratio of Rods to Cones

125 million rods but only 6 million cones

Amplitude

Brightness

Short Wavelength

High Frequency

Long Wavelength

Low Frequency

2 Kinds of Photoreceptors

Rods and Cones

Purity

Saturation or richness of colours Eg. light that is made up of a single wavelength is a pure light

Retina Receptive Field

a collection of rods and cones in the retina that when stimulated affects the firing of a particular ganglion cell

Light Sensitive Path

light could have started out as a simple light-sensitive patch like what jellyfish and worms have today

Optic Nerve

made of axons from ganglion cells

Cumulative Selection

small changes made to existing eye, and then new small changes were made to the modified eye, graduating increasing the sophistication of the eye

Optic Chiasm

the point at which the optic nerves from the inside half of each eye cross over to the opposite hemisphere

Light

travels as an electromagnetic wave, measured in nm

Benefits of Eye

vision makes it easier to find food, shelter, a mate and avoid predators and other dangers

Right Hemisphere

visual input from our left visual field ends up here

Left Hemisphere

visual input from our right visual field ends up here