Depth Perception

Question 1

What are the different types of cues to depth?

Answer 1

• Oculomotor cues: cues that depend on our ability to sense the position of our eyes and tension in our eye muscles
• Pictorial cues (monocular cues): cues that can be depicted in a still picture
• Motion-produced cues: cues that depend on the movement of the observer, or movement of objects in the environment
• Binocular disparity: a cue that depends on the fact that slightly different images of a scene are formed on each eye

Question 2

What are oculomotor cues and when are they useful?

Answer 2

• cues that depend on our ability to sense the position of our eyes and tension in our eye muscles
• Useful at short distances

Question 3

What do you experience when viewing something close to you?

Answer 3

• Convergence as your eye muscles cause your eyes to look inwards
• Accommodation as the lens bulges to focus on a near object
• They eye accommodates for close vision by tightening the ciliary muscles, allowing the pliable crystalline lens to become more rounded

Question 4

Give features of pictorial cues

Answer 4

• Do not require viewing with both eyes in order to work
• In fact often better to view monocularly
• TV, photos, paintings

Question 5

What is the overlap or interposition of occlusion pictorial cue?

Answer 5

 One objects obscures part of another, or overlaps with it (Gestalt law of completion)
 Used a lot in artwork

Question 6

What is the relative size pictorial cue?

Answer 6

 The retinal size of objects gets smaller as they get further away
 An object can look the same size at different distance but: retinal image size changes with distance
 Increase distance: decrease retinal image size
 Decrease distance: increase retinal image size
 The fact that an object can look the same size regardless of changing retinal image size is referred to as size constancy

Question 7

What is the relative height pictorial cue?

Answer 7

 As objects get further away they get nearer the horizon
 If the objects are below eye height the highest object is furthest away
 If the objects are above eye height then the lowest object is further away

Question 8

What is the atmospheric perspective pictorial cue?

Answer 8

 Distant objects appear less sharp because more air and particles to look through
 Distant objects tend to be more shifted into the blue light spectrum
 Used as a cue in paintings and computer games

Question 9

What is the familiar size pictorial cue?

Answer 9

If the object is familiar to you then the size of the retinal image is a very strong cue for depth

Question 10

What is the linear perspective pictorial cue?

Answer 10

 Lines that are parallel in the scene converge as they get further away
 Brains have to compensate for linear perspective

Question 11

What is the shading and shadow pictorial cue?

Answer 11

 Attached shadows: shadows within objects
 Detached shadows: shadows cast by object onto ground or other objects
 Brain assumes light source comes from above
 Shadows show how far something from the ground something is

Question 12

What is the texture gradient pictorial cue?

Answer 12

Texture becomes smaller/finer as distance increases

Question 13

What is Emmert’s law?

Answer 13

• Emmert’s law states that objects that generate retinal images of the same size will look different in physical size if they appear to be located at different distances
• Specifically the perceived size of an object increases as its perceived distance from the observer increases
• An object of constant size will project progressively smaller retinal images as its distance from the observer increases
• Similarly, if the retinal images of two different objects at different distances are the same, the physical size of the object that’s farther away must be larger than the one that is closer

Question 14

What is the motion parallax cue?

Answer 14

• movement produced cue
• As an observer moves relative to a 3D scene, nearby objects appear to move rapidly whereas far objects appear to move slowly
• Objects that are closer to you will move at a much greater angle of movement than objects further away from you
• Monocular cue to depth

Question 15

Who is the motion parallax cue used by?

Answer 15

• Used more by animals that don’t have much binocular overlap
• Head bob and orthogonal running (using motion to increase depth cues)

Question 16

What is the deletion and accretion movement produced cue?

Answer 16

• As one object moves in front of another, deletion occurs whereby the front object covers more of the back object
• As one object moves away from another, accretion occurs whereby the front object covers less of the back object

Question 17

What is binocular disparity?

Answer 17

• Also called binocular stereopsis
• Cue dependent on two eyes and the fact that our eyes see the world from slightly different positions determined by the distance between them
• Basis of stereoscope and 3D movies
• If there is too much disparity brain chooses one eyes vision to dominate perception – most the time it combines them (not overlays though)
• When two eyes receive slightly different images of the same scene, we experience an impression of depth because of corresponding retinal points

Question 18

What are corresponding retinal points?

Answer 18

• For every point on one retina, there is a corresponding point on the other
• These points would be identical if one retina was moved over to superimpose the other retina
• Regions on the two retinae would overlap if you slid one retina on top of the other
• When you fixate on an object it will stimulate corresponding points in the two eyes

Question 19

What are non-corresponding retinal points?

Answer 19

• Regions on the two retinae that would not overlap if you slid one retina on top of the other
• These points are separated on the retinae and create disparity

Question 20

What are fixation points and points at different depths?

Answer 20

• Fixation points: corresponding

- Point at different depth: non-corresponding

Question 21

What is the degree of disparity between the corresponding and non-corresponding points a measure of?

Answer 21

Depth

Question 22

What is Binocular disparity determined by and what can increase this?

Answer 22

• Determined by distance of the two eyes
• Hyper-stereo – can give increased depth from disparity
• (Hyperstereo telestereoscope – massively separates your eyes in space) – gives increased sense of binocular disparity – depth at greater distances

Question 23

What did Julesz demonstrate?

Answer 23

that the visual system can use disparity information directly to generate a percept of depth

Question 24

To create a vivid sense of stereoscopic depth what should you do?

Answer 24

• Present the same image to both eyes
• But, shift one slightly to the left or right
• The shifted area will appear to be displaced in depth
• The 3D image is called a stereogram (where you can see images amongst something else):
• Colour filters
• Orthostereography

Question 25

What are the different applications of binocular disparity?

Answer 25

• Shutter glasses – image on computer screen and goggles have black screen on them and screen becomes transparent when electrical signal passed through – monitor shows left eye image, right eye image very quickly – shutter glasses make one lens over each eye transparent
• Lenticular Displays/ Printing – left eye right eye left eye right eye images
• Parallax Barrier technology – 3DS, 3D TV – screen that interlaces left and right eye images, barrier in front, left eye images will only reach left eye ect.
• Virtual reality

Question 26

What different things are different depth cues useful over?

Answer 26

Different distances