Vision Flashcards
Cornea
Consists of transparent cells that slightly refract the light passing through
Not adjustable
Pupil
Opening in the center of the iris that allows light to enter the eye (aperture formed by the iris)
Iris
Coloured portion of the eye
Lens
Oval shape can be narrowed or widened by the ciliary muscle that surrounds the lens
Adjustable
Function is to focus the light optimally on the retina
Vitreous Humour
Clear fluid which fills the chamber of the eye and gives the eye its firmness
Retina
Rear surface of the eye, linked to visual receptors (photoreceptors)
Light from left side of world strikes right half of retina
Light from above strikes bottom half of retina
Like a computer: information that light is on upper left, but doesn’t have to be stored in upper left of computer
Optic Disc
Blind spot
Blood vessels and axons from retinal cells exit the eye
No photoreceptors on this disc
Reasons For Increase In Myopia
Genetics (maybe)
Book/screen time (maybe)
Bright light influences biochemical processes involved in the development of the eye
If children are not exposed to enough light, their eyes become misshapen, leading to myopia
Fovea
Tiny area specialized for acute, detailed vision
Central portion of retina
Blood vessels and ganglion cell axons are almost absent near fovea, so it has nearly unimpeded vision
Tight packing of receptors aids perception of detail
Better acuity (sensitivity to detail)
Good colour vision
Each receptor connects to single bipolar cell which connects to single ganglion cell with axon to brain
Midget Ganglion Cell
Ganglion cells in fovea
Small and responds to just a single cone
Provide 70% of input to brain
Vision is dominated by what is seen in and near the fovea
Rods
Respond to faint light
Not useful in daylight because bright light bleaches them
Abundant in periphery of retina
Situated in pigment epithelium
Cones
Essential for colour vision
More useful in bright light
Abundant in and near the fovea
Situated in pigment epithelium
Photopigments
Chemicals that release energy when struck by light
Opponent Process Theory
Perceive colour in terms of opposites
Explains kickbacks of visual perception
Brain has a mechanism that perceives colour on a continuum (pairs) from red to green, another from yellow to blue, and another from white to black
If you stare at one colour in one location for long enough, you fatigue that response and switch to the opposite (e.g. stare at green for too long, look to white you see red)
Colour Contrast
Regions emitting the same wavelength of light are perceived as having different colours
Colour Constancy
Regions emitting different wavelengths of light are perceived as having the same colour
Retinex Theory
Explains colour constancy
Perceive the brightness of an object by comparing it to other objects
Brain compares the colour of one object with the colour of another to subtract the result
Cortext compares information from various parts of the retina to determine the brightness and colour for each area
White and gold vs black and blue dress
Take away surrounding information and they become the same colour in either picture
Colour Vision Deficiency
Colour blindness
Results because people with certain genes fail to develop one type of cone or develop an abnormal type of cone
Red-green colour deficiency (most common, more in men)
Lateral Inhibition
Reduction of activity in one neuron by activity in neighbouring neurons
Retina’s way of sharpening contrasts to emphasize the borders of objects
Receptive Field
Area in visual space that excites or inhibits it (area of space a cell responds to)
Feature Detectors
Neurons whose responses indicate the presence of a particular feature
Retinal Disparity
Discrepancy between what the left and right eyes see
Required for stereoscopic depth perception
Experience fine tunes binocular vision and abnormal experience disrupts it
Strabismus
Condition when eyes don’t point in same direction (attend to one eye and not the other)
Treatment generally is to put patch over good eye to work on bad eye
Works best when begun early but most refuse to wear it for as long as needed
Second treatment to use 3D video games that require attending to both eyes
Neither procedure has effect on stereoscopic depth perception
Astigmatism
Blurring vision for lines in one direction
Caused by asymmetric curvature of the eyes
