Task 6: Three dimensions Flashcards
Types of cues to perceive depth
Oculomotor cues
Monocular cues
Binocular cues
Oculomotor cues
- position of the eyes and tension in eye muscle
- created by convergence and accommodation
Most effective oculomotor cue
convergence - inward movement of the eyes that occurs when we look at nearby objects
Monocular cues
- cues that work with one eye
- include accommodation, pictorial cues and motion-related cues
Pictorial cues
Occlusion (V2 neurons) = one objects is hidden (partially) by the other
Relative size = two objects are the equal size but the one further away will take up less of our visual field
Familiar size = knowledge of size
Texture gradient = parallel lines appear more closely packed as distance increases
Relative height = closer to horizon means more distant
Perspective convergence = parallel lines converge in distance
Atmospheric perspective = further away => less sharp and bluish
Shadows
Motion-produces or movement-related cues
work once we start moving
- motion parallax
- deletion
- accretion
Motion parallax
image of objects closer to us move farther across the retina => nearby objects appear to glide rapidly past us / distant objects move more slowly
Deletion and accretion
- observer moves sideways
=> thing becomes covered = deletion
thing becomes uncovered = accretion
Binocular cues
- cues that relies information from both eyes and leads to binocular disparity
Stereoscopic vision
impression of depth that results from information provided by binocular disparity
Binocular disparity
differences between two retinal images of the same scene
Binocular disparity relies on
Corresponding and non-corresponding retinal points
Corresponding retinal points
- points on the retina that overlap if eyes are superimposed on each other = zero disparity => horopter
Horopter
- surface of zero disparity
- point of focus
Non-corresponding retinal points
- surface of non-zero disparity
- objects that are not on the horopter
- absolute disparity
- relative disparity
Absolute disparity
- primary receiving area
- one object
- degree to which the object deviates from falling on corresponding points/horopter (measuring angle)
- crossed or uncrossed disparity
Greater angle of absolute disparity
indicates greater distance of the object from the horopter
Crossed disparity
- object in front of the horopter
- right eye => object appears to be displaced to the right
- left eye => object appears to be displaced to the left
Uncrossed disparity
- object behind the horopter
- right eye => object displaced to the left
- left eye => obj. displaced to the right
Relative disparity
- temporal lobe
- difference between the absolute disparities of projections of two objects
- indicate where objects in a scene relative to one another
Visual processing of stereopsis in the brain
messages from V2 (contours) must be fed back to V1 (disparity) to modulate processing of smaller features
Correspondence problem
- how to match images on the left and right retinas
Constrains to “solve” the correspondence problem
- uniqueness = feature is represented exactly once one each retinal image
- continuity = neighbouring points lie at similar distances from the viewer
Experiments like selective rearing (cats alternating vision between two eyes) and Microstimulation (monkeys) demonstrated that
eliminating disparity-selective neurons elimintaes stereopsis => responsible for depth perception
Perception of size can be affected by
our perception of depth
Holway and Boring experiment
we can misperceive size when accurate depth information is not present
Visual angle
- extending lines lens to the object
- depends on the size of the stimulus and distance from the observer
- object is closer => visual angle and retinal image become larger
- small objects near and larger objects far can have the same visual angle
Size distance scaling formula
S = K (R x D)
S = perceived size of the object R = size of retinal image D = perceived distance
If X goes further away from us, the size of retinal image R becomes smaller, therefore
perception of X’s distance D becomes larger
=> a balance is created between R and D, so S (size of X) remains the same
Emmert’s law
- the farther away an afterimage appears, the larger it will seem
- if R remains the same and D increases => S seems larger
Muller-Lyer illusion
- equal vertical lines seem to have different lengths
- R remains the same and D is larger => S is determined by D
Ponzo illusion
- animal on the top of the page appears longer
- converging railroad tracks
- D is larger => S is larger
Ames room
- people of equal size appear different in size since they are in different corners of the room
- perceived distance D is the same but R is smaller for person X => therefore the size S of X is smaller
Moon illusion
- moon on horizon appears much larger
- R is the same, D is large when the moon is on the horizon => S is larger
