W10 - Visual Illusions ✅ Flashcards
What does optical illusions tell us?
- illusions occur when what we see does not correspond to what is physically present in the world.
- suggest that the eye is not a passive camera
- perception is an active process that takes place in the brain.
What are the classification of visual illusion?
- Distortions (e.g. Muller-Lyer, Ponzo, Poggendorff, Herring, Wundt, Titchner)
- Ambiguous figures (e.g. Necker cube, Rubin vase)
- Paradoxical figures (e.g. Penrose impossible
objects) - Fictions (e.g. Kanizsa triangle)
What is the explanation for Muller-Lyer distortion?
Muller-Lyer distortions: 2 equal lines, but the one with outward facing arrows appear longer.
Basis of misapplied size constancy.
- outward fins = inside corner of a room.
- inward fins = outside corner of a room.
=> inside corner tends to be further to us so due to size constancy, brain thinks it’s larger
Limitations:
1. Illusion still found in 3D displays
2. Illusion does not applied cross-culturally
What is the explanation for Ponzo distortion illusion?
Ponzo: illusion of size, two lines converge towards vanishing point gives impression that line nearer vanishing point is further away -> appear larger
Limitation:
- Illusion diminish when the picture is upside down
What is the explanation for Poggendorff distortion illusion?
Poggendorff: a straight line that passes behind a rectangle but the line doesn’t look like it is ‘lined up’ properly
-> we tend to overestimate the smaller angle as appear larger
What is the explanation for Herring, Wundt and Titchner distortion illusions?
- Herring: the straight lines in the illusion appear to bow out in the centre.
- Wundt: instead of the centre converging like Herring, the two opposite ends of the background lines are converging -> middle becomes thinner
- Titchner: same ball appears smaller if group with bigger balls surrounding than with smaller balls
Explanations
- Herring: interpret the background radiating lines in terms of depth, central spot seems further away than the edges -> heavy black lines must also be further away in the centre but since same thickness => wider
- Wundt: vice versa as Herring
- Titchner: brain overemphasizes size differences in grouping and separating objects
What is the explanation for ambiguous illusions (e.g. Necker cube & Rubin vase)?
Necker cube: the cube seems to flip so the dot in one corner is sometimes inside and outside the cube
Rubin vase: the image can flip between showing the vase or the outline of two people facing each other.
Explanation:
- When the drawing does not give enough information for your visual system to know exactly the stimulus.
- Multiple interpretations happening simultaneously causes the image to flip
What is the explanation for paradoxical figures illusions?
Paradoxical figures: Impossible shapes (2D shape with depth cues) show how our brains automatically try to make us see in 3D.
Explanation: compensation for retinal image where everything appears flat, yet everything you see has depth.
What is the explanation for Kanizsa Triangle fiction illusions?
Kanizsa Triangle: three circles each with an angle cut out on white background gives the illusion of a white triangle in front of them.
-> subjective contour
Explanation:
- Usually, a near object looks brighter than a more distant one of the same colour.
- Your brain interpret the illusory triangles as being closer than the circles. (the cut out angle acts as depth cue).
What is Ames Room and the explanation for it?
- First constructed by Adelbert Ames in 1946, based on original idea by Helmholtz
- Two illusions:
1. Room appears cubic when viewed monocularly from a special point, its true shape is trapezoidal
2. Objects and people appear to grow or shrink as they travel from one corner of the room to the other
Explanation:
- Viewing from a single peephole prevent binocular depth cue
- Assumption of a normal rectangular room
- Our perception is that both people are at the
same distance away -> larger person appears taller
What is the moon illusion and its explanation?
When moon is on the horizon it appears much larger than when it is directly overhead.
Kaufman & Rock proposed: apparent distance theory:
- We see the sky as a flattened dome. It appears closer over our heads than near the horizon.
- The horizon moon looks larger because it appears further away.
What is the Ouchi illusion and its explanation?
Ouchi illusion: disk-ring pattern with horizontally oriented checks in the centre seems to move relative to the vertically oriented checks in the background.
Explanation: based peripheral drift
- Eyes’ small random movements even when fixated
- Brain compensated for at the fovea, but
not at the periphery.
=> cause perception of movement (special situation only)
