Depth Perception Flashcards
What are the properties of depth ‘cues’?
Monocular (one eye) vs Binocular (two eyes)
Pictorial (available in a photograph) vs non-pictorial (not available in a photograph)
Visual (comes purely from the retinal image) vs oculomotor (info comes from the eye muscle signals)
Ordinal (which object is closer) vs metric (by how much is that object closer)
What are the advantages of two eyes?
Lateral placement (sides of head): all round coverage of the world to detect predators, minimal overlapping reduces depth perception
Frontal placement: visual field overlaps considerably, allows for enhanced depth perception
What are the pros and cons of frontal eyes
Cons: reduces the visual field
Pros: For objects in the binocular field, allows
- binocular summation (two “chances” to see the object and lower detection/discrimination thresholds)
- depth perception (two separate viewpoints allowing us to extract depth information)
What is vergence?
The angular position of each eye - which can be used to calculate the depth of the fixated object.
- long distances: vergence angle will be small
- short distances: vergence angle will be large
Binocular (two eyes)
Non-pictorial (flat image - all at the same distance)
Oculomotor (eye muscles)
Metric (how far)
What is stereopsis and binocular disparity?
Stereopsis = binocular visual cues to depth
- each eye has a unique view point (have different images)
Binocular disparity: the location of the images in each eye are not equal, allowing us to gain depth
Binocular
Non-pictorial
Visual (retinal image)
Metric (how far)
Discuss corresponding points and the horopter in binocular disparity:
If both eyes are fixating on a cross a couple metres away, the cross falls on the fovea in each eye - the half images of the cross fall on corresponding points of each retina.
If a different stimulus is at the same place as the cross, but to the left –> the half images fall just to the right of the cross on each retina (still corresponding points).
If a third stimulus falls behind the cross to the right - the half images fall just to the left of the cross on the left retina, but a long way to the left on the right retina –> NON CORRESPONDING POINTS - therefore the object has a binocular disparity.
The horopter is a line of possible locations where an object’s half images fall on corresponding points (i.e. where objects have no disparity)
Closer than the horopter have ‘crossed’ disparity
Further from the horopter have ‘uncrossed’ disparity.
What is fusion and diplopia?
Fusion: When disparity is quite small, you are able to blend the images together and fuse them. Panum’s fusional area is the zone around the horopter where single vision occurs (here we have a combined location of the two objects, good metric depth).
Diplopia: Outside this area, diplopia occurs (you see two unfused images) meaning poor metric depth.
differentiate fixation, fusion and focus
fixation = directing your gaze towards something so the image is on your fovea
fusion = not seeing a double image
focus = focussing light rays to a certain point
How do you simulate stereoscopic 3D from 2 flat images?
Need 2 images taken approximately 6.5 cm apart and display one to each eye.
What are autostereograms?
Autosterograms make use of free fusion
AKA Single Image Random Dot Stereograms
One image with pattern that repeats horizontally, and you adjust vergence to align neighbouring regions.
Familiar size
Familiar objects that have a stereotypical size can appear further away when their retinal image is smaller
simple relationship (half the distance = double the retinal image size)
Monocular (one eye)
Pictorial (can provide in an image)
Visual (don’t need to use eye muscles)
Metric (on a scale)
Perspective
Uses the same information as familiar size clue
Uses linear perspective and detail perspective
- assumes lines are parallel
- assumes texture elements are of similar size
Monocular
pictorial
visual
metric
Motion parallax
As the observer moves, stationary objects at different depths move at different velocities on the retina.
Closer things move more quickly, distant things move more slowly.
Monocular (comes from retina)
Visual (retinal image)
Non-pictorial (requires motion)
Metric (how far away)
Height in the visual field
- assumption that things generally tend to rest on the ground plane
- things higher up in the visual field tend to be distant
Monocular
Pictorial
Visual
Metric
Aerial (atmospheric) perspective
More distant objects tend to be lower contrast, lighter, more blue
Monocular
Pictorial
Visual
Metric
