Problem 6 - DONE Flashcards
depth + size perception
cue approach to depth perception
= explains how we get from the flat image on retina to three-dimensional perception of the scene
- learn connection between cue + depth through previous experience with environment
- -> association between particular cues and depth becomes automatic
- when depth cues are present: perceive three dimensions
different types of depth cues
- oculomotor cues
- monocular cues
- binocular cues
oculomotor cues
= cues based on ability to sense the position of eyes + tension in eye muscles
- convergence
- accommodation
convergence
= inward movement of eyes that occurs when we look at nearby objets
(german: schielen)
- -> feel inward movement of eyes that occurs when eyes converge to look at nearby objects
accommodation
= change in shape of the lens that occurs when we focus on objects at various distances
–> feel tightening of eye muscles that change shape of lens to focus on nearby object
monocular cues
= cues that work with one eye
- accommodation
- pictorial cues
- movement-based cues = sources of depth information created by movement
pictorial cues
= sources of depth information in a two-dimensional picture
- occlusion (any range)
- relative height (2-30+ metres)
- relative size (any range)
- perspective convergence
- familiar size
- atmospheric convergence (30+ metres)
- texture gradient
- shadows
occlusion
= one object is in front of another/one object hides another partially
- partially hidden object seen as being farther away
- -> not provide info about object’s distance
relative height
= object with its base closer to horizon is usually seen as being more distant
relative size
= when two objects are of equal size, the one farther away will take up less of our field of view than the one closer
–> depends on knowledge of physical sizes
perspective convergence
= when looking down parallel lines that appear to converge in distance
familiar size
= used when judging distance based on prior knowledge of size of objects
–> most effective: other depth information is absent
atmospheric convergence
= when distant objects appear less sharp, with a slight blue tint (than nearer objects)
texture gradient
= elements equally spaced in scene appear to be more closely packed as distance increases
- increased fineness of texture in distance: enhances perception of depth
shadows
= decreases in light intensity caused by blockage of light
–> provide info about location of objects
motion-produced cues
= emerge when we start moving
- motion parallax (0-20 metres)
- deletion and accretion (0-20 metres)
motion parallax
= when, as we move, nearby objects appear to glide rapidly past us, more distant objects appear to move more slowly
–> image of object closer to us move farther across retina (than objects farther away)
deletion and accretion
= as observer moves sideways, some things become covered (= deletion) and others become uncovered (= accretion)
binocular cues
= stereoscopic depth perception = cues that depend on both eyes
- stereoscopic vision = two-eyed depth perception
- -> involves mechanisms that take into account differences in the images formed on the left and right eyes
binocular disparity
= differences in images on the left and right retinas
- -> basis of stereopsis
- corresponding retinal points
absolute disparity
= degree to which objects deviate from falling on corresponding points
–> measuring angle of disparity
types of disparities:
- uncrossed disparity = behind horopter (far objects)
- crossed disparity = in front of horopter (near objects)
- -> cross your eyes to fixate on point that is closer than horopter (schielen)
angle of disparity
angle of disparity = amount of absolute disparity; angle between corresponding and non-corresponding retinal points (where it would be located, where it is actually located)
- located on corresponding point = 0
- located on non-corresponding points = non-zero degree
–> provides information object’s distance from horopter
(greater angles of disparity = greater distances from horopter)
relative disparity
= difference in absolute disparities of objects
- -> helps indicate where objects in a scene are located relative to one another
- remains the same as observer looks around scene
absolute vs. relative disparity
- absolute disparity: disparity of projections of one object
- relative disparity: difference between disparities of projections of two objects
correspondence problem
which points in the images on the left and the right retina belong to each other?
- compare images on left/right retina –> calculate amount of disparity
‘distance cues’
- uniqueness = features in the world will be represented once in each retinal image
- continuity = neighbouring points in the world lie at similar distances from the viewer (except at the edges)
physiology of binocular depth perception
pictorial cues:
- mostly what stream
- V2 neurones (occlusion)
stereopsis:
- binocular depth cells (disparity-selective cells) = neurone that respond best to binocular disparity
–> V1, 2, 5 neurones
neurones in higher visual system:
- primary receiving area: sensitive to absolute disparity
- temporal lobe/other areas: sensitive to relative disparity
disparity tuning curves
= indicate neural response that occurs when stimuli presented to the left and right eyes create different amounts of disparity
perceiving size
- relation between perceiving size and perceiving depth = size-distance scaling
- -> perception of size can be affected by perception of depth
size-distance scaling (formula)
overview lecture
S = K * (R * D)
=> object’s perceived size (S) depends on the size of retinal image (R) times the perceived distance (D) and times a constant (K)
{R = size of the image that you view on your retina}
=> D becomes larger = S becomes larger
–> explains why object perceived further away, seem larger (image with two giants/balls)
size constancy
= perception of object’s size is relatively constant even when we view object from different distances
–> size-distance scaling
visual illusions of size
müller-lyer illusion
= right vertical line appears longer than left vertical line (even if they are the same)
- misapplied size constancy scaling: mechanisms that help us perceiving in 3-D world sometimes create illusions when applied to objects drawn on 2-D surface
- -> fins on right line: appears like inside corner of room
- -> fins on left line: appears like corner viewed from outside
- -> size-distance scaling: (R) remains the same, (D) is larger, (S) is determined by perceived distance
- conflicting cues theory: perception of line length depends on (1) actual length of vertical lines + (2) overall length of figure
- -> overall length of right figure: larger –> vertical line appears larger
- -> rejection of idea: depth information is involved in determining illusions
visual illusions of size
ponzo illusion
= the animal on top appears longer, although animals are the same size on page + have same visual angle
- misapplied size constancy scaling: depth information provided by converging railroad tracks making the top animal appear farther away –> top animal appears bigger
- -> scaling mechanism corrects for this increased depth
visual illusions of size
ames room
= causes two people of equal size to appear very different in size
- reason: construction of room (shaped that left corner is almost twice as far from observer as right corner) –> woman on left: much smaller visual angle
- -> size-distance scaling: (D) remains same, (R) smaller for woman on left, therefore, (S) is smaller
- other factors: relative size: perception of size of two women is determined by how they fill distance between bottom and top of room}
visual illusions of size
moon illusion
= moon on horizon appears much larger than when it is higher in the sky
- constant visual angle: moon’s physical size + distance from Earth remain the same
- apparent distance theory: moon on horizon: appears more distant because it is viewed across filled space of terrain (contains depth information) + moon higher in sky: appears less distant because it is viewed through empty space, with little depth information
- -> size-distance scaling: (R) remains same, (D) is larger for moon on horizon, (S) is larger
- angular size contrast theory: moon appears smaller when surrounded by larger objects
- other factors: atmospheric convergence, colour, oculomotor factors
