FA LOs Flashcards
What information if provided by adaptation and after effects?
organisms respond best to changing stimulus impingments
is a stimulus is presented for sufficiently long time, it will cause a decrease in sensitvity to that stimulus (in short term)
by increasing the ddifference between test and adapting stimuli you can measure the generalizability of the effects of the adapting stimulus
How are spatial frequencies processes by the visual system
Spatial frequency of gratings describes in terms of visual angle (size of the retinal image in degrees)
Gratings change regularly over space and can be defined precisely using fourier analysis
Fourier analysis decomposes spatial pattern in terms of sine waves
Blakemore/Sutton used moving gratings, shows we don’t see things in absolute but see in relative - they found that adapting to a wide grating made test stimuli seem narrow and vice verse, adapting to high-contrast grating decreases sensitivity (grating of same spatial frequency but lower contrast may be seen as uniform grey field) - adapting to a vertical grating effects gratings with low angular disparity but not a horizontal grating
Grating stimuli: waveform, physical contrast, spatial frequency, orientation
Modulation Transfer Function: ability of a system to preserve spatial frequency info after it has been encoded - in humans this is the contrast sensitivity function (CSF)
Contrast ratio = (Lmax - Lmin) / (Lmax + Lmin) - based on physical measures of light, apparent contrast affected by spatial frequency (wide bars appear darker than narrow bars)
CSF may be comprised of a series of spatial frequency channels - each simple cell responds best to narrow range of spatial frequencies - adaptation effects may be due to neural fatigue
What can the spatial frequency approach tell us about feature detectors
A given centre-surround receptive field of a certain size can detect only a grating stimulus that has a specific matching size
Visual system uses spatial filters of sine waves to decompose a visual scene - this is seen when you move a stimulus across a centre-surround receptive field and the function looks like a DOG
Feature detectors are slightly ambiguous - see through the tilt aftereffect which is a cortical mechanism
What does perceptual development inform about the contributions of nature vs nuture
Vision does not develop passively, develops through interactive exploration of the visual worlds - found in study that selectively reared kittens in a tube of vertical stripes. One cat could walk freely the second was on a gondola that moved only when first kitten walked. Both kittens had same visual experience but self-guided kitten developed normal vision and gondola kitten did not have normal vision
There is a critical period for visual development - found in experiment where kittens eyes were sewn shut either at birth or later in life, those with at birth had irreversible blindness to shapes/forms, later in life still had normal vision
