This is part of the summary of Course 2.4 Perception at Erasmus University Rotterdam. I put a lot of effort into making these summaries and included pictures and graphs to make things as understandable as possible. I managed to get quite a high grade on the course exam at the end (8.8). Note though...
Problem 6: The third dimension
Literature: Blake
Depth perception:
= (1) distance between object and observer (= egocentric distance/absolute distance). Guides activities.
= (2) distance between 2 different objects/parts of object (= relative distance)
- 2 types of depth perception have different sources
- Judgement of absolute distance much worse than judgement of relative depth
- Retinal images: 2D, change continuously → source of depth information
- 2 eyes (= 2 sources) → binocular vision
- Cues (= source information)
- Depth perception without effort/thought
- Coordination of sources → accurate judgements of distance
- Different distances have different sources (Cutting, 1997)
o Personal space: arms reach; objects that can be manipulated by person
o Action space: within 30m of the body; can quickly move/throw etc.
o Vista space: within eyesight, beyond action space; planning, navigation
→ depend on situation (e.g. in driving car the action space is bigger)
- Types of cues:
1. Occulomotor cues = usually kinesthetic; cue due to muscular contraction; unambiguous information
2. Visual ques = monocular ones and binocular ones; require additional information
Occulomotor cues to depth
- Eyes converge a specific amount depending on distance to focused object
o Close object → more accommodation + convergence
o Far objects → less accommodation convergence
- Way of measuring:
o Monitoring degree of muscle contraction → compute 2 values
Angle of convergence = direction of eyeballs
Amount of accommodation of lens
→ related to distance to object, therefore useful index of absolute distance
Accommodation and converges work in yoked manner (= vereint/gekoppelt)
o Measuring strength of signal (from brain to muscle)
- Accommodation: range is limited (few meters ahead)
o Only restricted amount possible
→ solely based on accommodation, distance judgement is inaccurate
- Convergence: also limited range, but more extended than accommodation
o Convergence angle = 0° when looking straight ahead (±6m)
o Within range of 6m → reliable depth cue
Binocular Visual Depth Information – Stereopsis
- Lateral separation of eyes → slightly different vantage point
- Almost same image twice, but small disparities (differences) → ability to
discriminate small differences
- Stereopsis = perception of relative depth using binocular vision
Retinal disparity: Stimulus for Stereopsis
= difference between left eye and right eye view of an object; specifies in
relative depth
- When object is located behind or in front of another object
- Magnitude (distance of objects on the retina) depends on distance
between objects (large distance if one object is much closer to observer)
- Types:
o Far away object → disparity is uncrossed
o Close object → disparity is crossed (close object need convergence to be seen → crossed disparity)
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