Chapter 6: Depth Perception Flashcards
Cue Approach to Depth Perception
Compare images on retina
Stereoblind
Couldn’t experience vivid sense of depth that occurs when brain combine different retinal images of two eyes into single image
Many-to-one
Many different 3-D scenes can produce one and the same retinal image
Different Objects, Same Retinal Image
Can produce same retinal image if arranged appropriately
Depth Cues
Oculomotor Cues-gives info from muscles of eyes
Monocular Cues- static/ pictorial vs dynamic
Binocular Cues- compares one eye vs the other
Oculomotor Depth Cues
These cues arise from the workings of two different sets of oculomotor muscles
- Accommodation - Convergence
Causes that are based on feedback from oculomotor muscles controlling the shape of lens and positions of eyes
Accommodation
How shape of lens adjusts to focus on image sharply
Convergence
Depth cue only over fairly short distance in front of eyes
Angles:
- 10 cm- 33 degrees
- 1 m- 3.5 degrees
- 4 m- less than 1 degree
Monocular Depth Cues
Cues that are based on retinal image and that provide info about depth even with only one eye open
- Static monocular cues (pictorial cues)
- involve motionless 2-D depictions of 3-D scenes
- include position, size, and lighting in retina
Position-based cues
- Partial Occlusion
- Relative Height
Partial Occlusion
Position-based depth cue- in scenes where one object partially hides another object, occlusion indicates that former is closer than ladder
- partial occlusion is an extremely common and reliable depth cue
- Intersection between two objects are called T-junctions
- Interposition- making predictions about unknown in space
Relative Height
- Allows inference of depth from position of objects relative to the horizon or eye level
- Provides info about the objects’ relative distance from the observer
- Affects depth perception even in absence of visible floor or ceiling
Size in the retinal image
What size-based cues tell us
- Size-distance relation
- Visual angle
- Size perspective
Size- distance relation
The further away on object is from retina, the smaller its retinal image
Visual Angle
Angle subtended (occupied) by an object in field of view
Size perspective
Depth info in scenes in which size-distance relation is apparent
Sized-based cues
Familiar size
Relative size
Texture gradient
Linear perspective
Familiar Size
Knowing retinal image size of familiar object at familiar distance lets us use its retinal image size to gauge its distance
- requires top-down processing
Relative Size
Under assumption that two or more are about same size, size of retinal image can be used to judge their relative distance
- same size in real life, but different on retinal images
Texture Gradient
If surface variations/ repeated elements of surface are fairly regular in size and spacing, the retinal image size of these equal-size features decrease as their distance increases
Linear Perspective
Parallel lines appear to converge as they recede in depth
Lighting-based cues
- Atmospheric perspective
- Shading
- Shadows
Atmospheric Perspective
The farther away an object is, the more air the light must pass through to reach us and the more light can be scattered, with result that distant objects appear less distinct than nearby object
Shading
Light falls on curved surfaces to create shading differences
*our natural assumption is that light comes from above
Shadows
Depth can also be signaled by the shadows cast by objects
Dynamic Cues
Movement in the retinal image
- still from one eye
- Motion-based cues:
- Motion parallax
- Optic flow
- Deletion and accretion