lecture 6 Flashcards
how is the image we receive from the real world different to our perception?
image we receive is 2D but our perception is 3D
generally people are quite accurate at judging an ambient distance up to…?
20 feet
Visual cliff experiment
36 babies
plexiform platform with illusory cliff on one side
no babies coaxed to their mothers when it meant movement from the shallow end across the deep end
all babies coaxed to mothers when they could stay on shallow end
conclusion of the visual cliff experiment
depth perception is partially innate, but develops further when a baby starts crawling etc
cues to depth
oculomotor cues
pictorial cues (monocular cues)
motion produced cues
binocular disparity
basis of oculomotor cues
cues that depend on our ability to sense the position of our eyes and the tension in our eye muscles
what happens as an object moves closer to our eyes?
our eyes move inwards and the tension in them increases
convergence
eye muscle cause you to look inwards (closer teh object the smaller the convergence
accommodation
as the lens bulges to focus on a near object
tightening of the ciliary muscles, allowing the pliable crystalline lens to become more rounded
what distances produce effective oculomotor cues
only closer that 5-10 feet
what are shape of the lens and position of the eye correlated with?
the distance of the object you are observing
what are pictorial cues?
cues that can be depicted in a still picture (TV, photos, paintings) and do not require viewing with both eyes in order to work
8 pictorial cues
1) overlap, interposition or occlusion
2) relative size
3) relative height
4) atmospheric perspective
5) familiar size
6) linear perspective
7) shading and shadows
8) texture gradient
overlap, interposition or occlusion
one object obscures part of another, or overlaps with it
relative size:
the retinal image of an object gets smaller as they get further away
what can change, even if an object looks the same size at different distances?
the retinal image size
what happens to the retinal image when the object is at an increased distance?
retinal image size decreases
what happens to the retinal image when the object is at a decreased distance?
the retinal image size decreases
size constancy
the ability for an image to look the same size despite changing retinal image size
Emmert’s law
1) objects that generate retinal images of the same size will look different in physical size if they appear to be located at different distances
2) the perceived size of an object increases as its perceived distance from the observer increases
3) an object of constant size will project progressively smaller retinal imaged as its distance from the observer increases
4) if retinal images of two different objects at different distances are the same, the physical size of yeh object that is further away must be larger than the one that is closer
relative height
as an object gets further away, the nearer they get to the horizon
if the objects are below eye height, the highest object is furthest away
if the objects are above eye height, the lowest object is the furthest away
atmospheric perspective
distant objects appear less sharp because there is more air and particles to look through
distant objects appear more blue as blue light is scattered by the atmosphere
familiar size
for a larger object in real life to be perceived as the same size as a smaller object in real life, it must always be further away
linear perspective
lines that are parallel in a scene converge as they get further away
(remember the retina is curved)
shading and shadow
attached shadows
the shading that results from the depth within an object is a cue to depth
detached shadows
why is the meaning of shadows ambiguous?
a depression and an elevation in a surface will be shaded on one side, telling the difference relies on knowing the direction of the light source
where do we assume all light sources come from?
above
attached shadows
shadows within an object
texture gradient
texture becomes smaller/ finer as distance increases
motion produced cues
cues that depend on movement of the observer, or movement of objects in the environment
types of motion-produced cues
motion parallax
deletion and accretion
motion parallax
an observer moves relative to 3D space, nearby objects appear to move rapidly while far away objects appear to move slowly
motion parallax informs you of
1) relative direction
2) amount of motion
who uses motion parallax?
animals that dont have much binocular overlap
head bob and orthogonal running
deletion
as one object moves in front of another, deletion occurs
-front object covers more of the back object
accretion
as one object moves away from another, accretion occurs
front object covers less of the back object
binocular disparity
a cue that depends on the fact that slightly different images of a scene are formed on each eye
what causes our binocular disparity? what is it dependent on?
because our eyes are in slightly different positions, determined by the distance between them
how does binocular disparity cue for depth diminish?
with distance
another name for binocular disparity
binocular stereopsis
what is the basic of stereoscope 3D movies?
binocular disparity
corresponding retinal points
for every point on one retina there is a corresponding point if the other
- these two points would be identical if one retina was moved to superimpose the other retina
- when you fixate on an object it will stimulate corresponding points on the eyes
non corresponding retinal points
regions on the retinae that would not overlap if you slid one retinae on top of the other
separated on the retinae and cause disparity
what does the amount of disparity tell us
how far an object is from our focus
what is stereo blindness?
people that appear to lack mechanisms for processing disparities
how many people show stereo blind performance?
2-5% of people
what is the usual cause of stereo-blindness?
strabismus in early childhood prevents the normal development of binocular disparity detecting cells in the visual cortex
what is strabismus?
misalignment of the eyes, failure to converge on a common target
hyperstereo
can give increased depth form disparity
stereogram to create 3D image
present same stimulus in both eyes but shift one slightly to the left or right
the shifted one will appear to be displaces in depth ad create a 3D image
