Psychology Ch 4.2 THE EYE

Physical properties of light and related perceptions

Physical properties of light and related perceptions

Wavelength - hue (colour) Amplitude - Brightness Purity - Saturation

Cornea

Focuses light so we can see clearly

Pupil

Lets light in

Iris

Controls amount of light that comes in, it controls the pupils to contract or expand

Lens

Allows eyes to focus on stimuli on various distances

Retina

Where the sensory receptors are located, visual stimuli comes in and transforms into neuro impulses

Fovea

Responsible for sharp central vision

Optic disk (blind spot)

Exit point for the ganglion access cells

Optic nerve

Bundle of neurons

Nearsightedness

Lens of eye makes visual image bend before the fovea, can't see clearly thats far away

Farsightedness

Can't focus on close things, visual image lands after fovea

Astigmatism

Bending of light between cornea and lens

Bipolar cells

a type of neuron that has two extensions (one axon and one dendrite). Many bipolar cells are specialized sensory neurons for the transmission of sense. As such, they are part of the sensory pathways for smell, sight, taste, hearing, touch, balance and proprioception.

Amacrine cell

the first neurons in the visual system to fire action potentials, and also the first to generate transient responses.

Ganglion cell

the projection neurons of the vertebrate retina, conveying information from other retinal neurons to the rest of the brain

Rods

Sensitive to light and dark Low delta More on the periphery of retina

Cones

Process colour High detail More in fovea

Ganglion cells

Sensitive to blue wavelengths Circadian rhythms

Normal changes in vision while aging

Need more light, difficulty seeing colours, presbyopia

Presbyopia

• Loss of elasticity in lens and muscles that control it

• Age related “farsightedness”

macular degeneration

Due to thinning of macula 10% of people get this aged 66 - 74 30% of people get this aged 75 - 85

Cataracts

Clouding of eye (makes image blurry) Treatment couching (lens is dislodged) 51% of world blindness Intraocular lens

Glaucoma

Pressure on optic nerve (fluid pressure) Progressive damage Second leading cause of blindness

Dorsal stream

The where/how pathway Occipital -> parietal Important for spatial understanding, gilding actions

Ventral stream

The what pathway Occipital -> temporal Important for object recognition, visual agnosia (perceive objects, understand what they are), face recognition (prosopagnosia) Perceptual constancy

Perceptual constancy

Familiar objects keep their shape, size and colour regardless of the sensory input changes Ex) changes in angle, distancing and lightning

Binocular cues (need both eyes)

Our eyes can see slightly different views Retinal disparity Convergence Depth perception

Monocular Cues

Linear perspectives (traintracks) Texture gradients (more detail the closer you get) Interposition Relative size Height in plane Light and shadow (the way light hits an object) Motion parallax (things coming to us that are close seem like they’re coming faster than things from afar)