measuring visual acuity Flashcards
what is the visual angle
it is subtended at the eye by the height of the image, seen from distance
what does 1 degree equal to
1 degree= 60 arc mins
what happens when viewing distance becomes closer to the image in terms of the visual angle and the amount of photoreceptors that detect it
as the image becomes closer, the visual angle increases, so that two cones can cover two receptive fields, increasing spatial resolution and visual acuity
define spatial frequency
number of cycles per degree (fine detail)
define contrast
difference between minimum and maximum luminance
What sets the upper limit on spatial
frequency?
cone spacing (the more closely packed they are, the better the fine-detail discrimination, ie resolution is higher)
what is the contrast threshold
minimum contrast required to detect
target
is contrast sesnitivity
reciprocal of contrast threshold
Do high spatial frequencies require high or low contrast?
high contrast
what are orientation-sensitive neurons?
they respond to a preferred orientation and those similar to it so it not just responding to one particular orientation
describe and explain the tilt after-effect
when you stare at a tilted image, such as stripes slanted to the left for a extended peiord of time, neurones in the visual cortex will respond to this specific orientation of the striped bar pattern and becoem adapted to this stimulus. when you look away from the image and then view a straight or differrntly tilted stipe pattern, the adapted neurone will respond less strongly while otehr non-adapted neurones will continue to fire as normal. this differential neuroanl activity causes the tilt after effect, making the bar oritentation look as if its tilted in the opposite direction from original image.
what is an idealized orientation tuning curve composed of
-high contrast of the visual image inorder for best discrimination of fine details
preferred orientation for a more effective rapid response by orientation-tuned neurones.
