Visual perception Flashcards
Function of the iris
Pigmented membrane with a central opening (pupil). Regulates amount of light on retina by adjusting size
Function of the lens
refracts light and focuses it on the retina by altering its shape according to the distance of objects focused on
Function of the Cornea
Refracts light
Function of the Retina
the innermost layer of the eye, which is composed of several layers of specialised cells that convert light into neural signals.
Function of the Fovea
contains highest density of cones. Point of sharpest vision (100% visual acuity).
Function of the optic nerve
contains a bundle of ganglion axons that carry visual information to the lateral geniculate nucleus (LGN) of the thalamus.
Describe reception
detection of light energy by the sensory receptors of the retina
Process of reception
- light waves enter the eye
- The cornea refracts the light waves to focus them on the retina
- light travels through the pupil, and the iris regulates the amount of light that enters the eye via the pupil
- the kens further refracts the light waves to focus on the retina
- the photo receptors of the retina detect the light stimulus
Describe transduction
is the conversion of stimulus energy (light) into impulses of electrochemical energy by sensory receptors of the retina
What are the two types of specific features of light that photoreceptors respond to
Retinal rods, retinal cones
On center receptive fields
stimulated by light falling on the center of the receptive field and inhibited by light falling on the periphery
off center receptive field
stimulated by light falling on the periphery of the receptive filed and inhibited by light falling on the center
describe transmission (Step 4)
electrochemical impulses due to stimulus received via optic nerve
optic nerve exits retina at blind spot
optic nerve cross over as optic chiasm
Info then travels to primary visual cortex in occipital lobe (optic radiation)
describe organisation (Step 5)
All visual stimulus is organised
occipital lobe relies on application of visual perception principles (learnt rules our brain automatically uses to interpret visual info)
allow for perception of visual info
describe interpretation (Step 6)
Visual stimulus is given meaning
stimulus is assigned a meaning and is influenced by biological, psychological and social factors
Once organised they are sent along one of two different pathways
1. parietal lobe: where pathway, judging where object is
2. temporal lobe what pathway, comparing information to already stored info
Order of steps
reception
transduction
transmission
selection
organisation
interpretation
describe physiology influence on visual perception
damage or misinformation of the visual system causes changes in perception of visual stimulus
examples are:
- astigmatism: partial fuzziness due to more the one focal point
- pressure build up in aqueous humour: damage to blood vessels = vision loss
describe the ageing influence on visual perception
age causes many visual disturbances
examples:
- Presbyopia: lens becomes less elastic, less focus on close objects due to image converging after retina
- cataracts: progressive clouding of lens, due to protein build up (severe vision impairment)
- macular degeneration: most common cause of blindness, metabolic waste accumulates and attacks macular causing diminished central vision acuity
how does genetics effect visual perception
disorders caused by genetics
examples:
- retinitis pigmentosa: degenerative disease of the retina (night blindness/gradual vision loss), retina dies, inherited
- colour vision deficiency: inability to detect colour normally, results to changes to functioning of the cones (red blue green) in retina
What are the factors that contribute to perceptual sets
past experience, motivational state, emotional state, context
what are the perceptual constancies
size constancy, shape constancy, orientation constancy, brightness constancy
describe Gestalt principles
The tendency of our visual system to see things as a meaningful whole. Our brains can interpret the whole more easily than its parts.
what are the 5 gestalt principles
Figure-ground organisation
continuity
closure
similarity
proximity
what are binocular depth cues
retinal disparity: each retina giving slightly different images due to separation of eyes and angle of view. Brain merges two images. Bigger the disparity the closer the object
convergence: eyes converge when looking at close objects and diverge at further away objects, greater the angle of convergence the closer the object.
What are the monocular depth cues
accommodation: eyes change focus as an object moves closer, to focus an image the lens must change, the ciliary muscle measures amount of accommodation required
what are the pictorial depth cues
linear perspective - parallel lines appear to meet
interposition - overlapping an object makes it look further away
texture gradient - closer objects have better definitions then ones further away
relative size - when familiar with size of an object, the object that is bigger appears closer
height in the visual field - objects closer to the horizon are perceived to be further away
motion parallax - when moving objects closer seem to fly past whereas further away objects appear to move slower
