reverse terms Flashcards
rods more sentive then cones (endency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.) Reds get darker
Purkinje Shift
Three lightness perception phenomena explained by (or edge enhancement)
- The Hermann Grid: Seeing spots at an intersection
- Mach Bands: Seeing borders more sharply
- Simultaneous Contrast: Seeing areas of different brightness due to adjacent areas
lateral inhibition
Damage to retinal blood vessels causes leakage, neovascularisation and potentially, retinal detachment
Diabetic Retinopathy
Disease of old age
Central part of visual field deteriorates
Results in loss of central vision
Macular Degeneration
Hereditary retinal degeneration
Starts in retinal periphery
Initial symptom night-blindness and loss of
peripheral vision, then tunnel vision, then
total blindness
Retinitis Pigmentosa
Eye disease usually associated with increase in intraocular pressure
Untreated can lead to blindness
Several different forms
Glaucoma
A disorder of the extraocular muscles in which the two eyes are not aligned with one another, resulting in a double image, which impairs binocular depth perception.
strabismus
A condition in which both eyes develop normally but the neural signals from one eye aren’t processed properly, so that fine vision doesn’t develop in that eye.
amblyopia
- Cylindrical error
- Cornea is lemon-, rather than orange-shaped
- Point image brought into focus in two places
e. g. horizontal and vertical lines may not both be in focus
Astigmatism
nearsighted, eye is too long, too much optical pwr, focus point is in front of retnia
myopia
farsighted, eye too short, low optical pwr,
hyperopia
Shadows on the retina thrown by debris within the vitreous humor; perceived as small, semitransparent spots or threads that appear to be floating before the person’s eyes and tend to move with the eyes.
Floaters
cloudy lens
Corneal Opacities
Opacity of the lens prevents clear vision
Typically occurs later in life, but seen in infants
Corrected by removing lens and using either spectacle correction or intraocular lens implants
Cataract
represent a compromise between the method of limits and the method of constant stimuli
Efficient
Avoid observer bias
Avoid errors of anticipation and habituation
The “Staircase” Methods
Experimenter has control of stimulus
Several stimulus values chosen to “bracket” assumed threshold (5-9)
Stimuli presented many times in random order
“Psychometric function” derived from proportion of ‘yes’ responses
Can be used to measure both detection and discrimination
-Advantages:
Essentially eliminates observer bias
Reduces adaptation
Gives very reliable results
Eliminates errors of anticipation and habituation
-Disadvantages:
Very inefficient and time consuming
Needs preliminary estimate of threshold to decide on stimulus values
Method of Constants
Experimenter has control of stimulus Adjust intensity in discrete steps until observer reports that stimulus is just detectable Typically make adjustments from above (descending series) and below (ascending series) Can be used to measure both detection and discrimination -Advantages: Reduces observer bias Reduces adaptation Simple to calculate threshold -Disadvantages: Inefficient Errors of anticipation (“jump the gun”) Errors of habituation (“maintain response”)
Method of Limits
Vary location of stimulus among various times or locations
Participant is asked to “locate” the stimulus
Is used in combination with other methods
-Advantages:
Lower thresholds
Avoids observer bias
-Disadvantages:
More stimulus presentations because every trial involves two intervals or locations
Forced Choice Methods
Typically, observer has control of stimulus
Adjust intensity of stimulus until target is just detectable
Typically make adjustments from above and below
Can be used to measure both detection and discrimination
-Advantages:
Fast
Avoids boredom
-Disadvantages:
Subject bias
Possibility of adaptation
Method of Adjustment
ability to see is poor at first then it studies out and at 5 minutes starts getting progressively better as rods take over
Dark adaption
- rod dominated
- sensitive in dim light
- poor visual acuity
- no colour sensation
Scotopic Vision
- cone dominated
- insensitive in dim light
- good visual acuity
- good colour vision
Photopic Vision
- Difficulty with reaching and grasping objects
- have trouble acting on things, only visually guided, close eyes and is fine
Optic Ataxia
V4 colour damage
Achromatopsia
inability to perceive motion
Akinetopsia
more neurons focused on one task vs. another. number of neurons for center is higher than those of peripheral, in terms of cortex, Low covergence needs lots of neurons
cortical magnification
population coding: one cell is ambiguous but if you look at multiple cells, different response patterns of activity can uniquely define 90degrees across multiple cells.
Distributed coding
A neuron in the visual cortex that responds to the presence of a line segment with a particular orientation that ends at a particular point within the cell’s receptive field.
hypercomplex cells
