| How are depth and size related? | How big an object appears can affect how far away it appears, and how far away an object appears can affect how big it appears. |
| How do we perceive depth? | By using a number of different cues, which can be divided into three groups:
Oculomotor cues - cues based on our ability to sense the position and state of our eyes.
Monocular cues - cues based on the visual information available within one eye.
Binocular cues - cues that depend on visual information within both eyes. |
| What are the main oculomotor cues? | Binocular convergence - when your eyes rotate inwards to focus on an object and the degree to which determines its depth.
Accomodation - when your eye changes optical power to maintain a clear image of an object as distance varies. |
| What are the main monocular cues? | Accomodation.
Pictorial cues.
Movement-based cues. |
| What are the 7 main pictorial cues? | Occlusion.
Relative height.
Familiar and relative size.
Perspective convergence.
Atmospheric perspective.
Texture gradient.
Shadows. |
| How are shadows a pictorial cue? | Cue for relative depth.
Cue for depth perception (humans assume light is coming from above). |
| What are the main movement-based cues? | Motion parallax - objects closer to you move closer.
Deletion and accretion - Deletion is the gradual occlusion of a moving object as it passes behind another object. Accretion is the gradual reappearance of a moving object as it emerges from behind another object. |
| Which cues indicate relative depth at 0-2 meters? | Occlusion. |
| Which cues indicate absolute depth at >20 meters? | Size of retinal image.
Texture gradients. |
| What is binocular disparity? | The difference in image location of an object seen by the left and right eyes, resulting from the eyes' horizontal separation (parallax). |
| What is the effect of point of fixation on relative disparity? | Point of fixation does not alter relative disparity. |
| What is the effect of point of fixation on absolute disparity? | Point of fixation does affect absolute disparity.
All objects that lie on the horopter fall on corresponding parts of the retina's horopter.
Whichever object is fixated on has zero absolute disparity, meaning left and right images of this object fall onto corresponding parts of the retina. |
| What is the correspondence problem? | Problem of determining which parts of one image correspond to which parts of another image.
e.g. if there are multiple identical objects in the scene, it can be hard to figure out which images in the left retinal image should be associated with which images in the right retinal image. |
| How can the correspondence problem be fixed? | If the object in the visual scene are made distinct from each other by colour (each one a different colour) the associations become unambiguous. |
| How is the perceived size of an object determined? | Its angular size.
Its perceived depth. |
| What is angular size? | The visual angle an object subtends.
The closer an object is to a person, the larger its angular size. |
| What is size constancy? | The phenomenon where an object's apparent size does not depend on its physical distance.
To achieve size constancy an observer needs to consider both the size of the retinal image and the distance of the object. |
| What is the equation for size constancy? | S = K * (R * D)
where: S - apparent size of an object.
K - constant.
R - size of the retinal image.
D - perceived distance to the object. |
| What are size illusions? | When people mistake the distance of an object so it appears smaller/larger than it really is.
If it appears closer - appears smaller.
If it appears further - it appears larger. |
| What did Holway and Boring (1941) investigate? | How observers accurately estimate the size of objects.
In particular, how depth cues influence size judgements. |
| What were the different conditions in Holway and Boring's experiments and what were the results? | Goal of observer: match size of comparison circle to test circle.
Condition 1 - observers could determine the depth of the test patch using binocular disparity, motion parallax and shadows.
Condition 2 - observers viewed the test circle with one eye to remove binocular disparity cues.
Condition 3 - observers viewed the test circle through a peephole to remove motion parallax cues.
Condition 4 - in addition to viewing the circle through a peephole, drapes were used to remove the shadows. |
