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148 Cards in this Set
- Front
- Back
What are geometrical illusions |
*One class of visual illusions *Simple line figures that produce large errors in perception |
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What kind of illusions do geometrical illusions produce |
*Extent (length) *Alignment *Size *Angle *Shape |
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Most of the geometrical illusions are named how |
Are named after the person(s) who discovered them |
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What are among the most popular visual phenomena |
Geometrical illusions |
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What is this geometrical illusion called? |
Ponzo illusion |
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What do we see with this illusion? |
Looks like upper line is longer but they are actually same length |
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What is this geometrical illusion called? |
Muller-Lyer Illusion |
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What are you supposed to see with this illusion? |
Upper line looks longer But they are actually the same length |
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This illusion is an illusion of _______ |
Extent |
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This illusion is an illusion of ______ |
Extent |
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What is this geometrical illusion called? |
Morinaga Illusion |
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This illusion is an illusion of _____ |
Alignment |
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What are we supposed to see with this illusion |
Arrows cross each other but in fact are lined up |
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What is this geometrical illusion called? |
Poggendorff illusion |
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This illusion is an illusion of _____ |
Alignment |
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What are you supposed to see with this illusion |
Looks like if you extended each end they would not cross but they do |
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What is this geometrical illusion called? |
Ebbinghaus Illusion |
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This illusion is an illusion of _______ |
Size |
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What are you supposed to see with this illusion? |
The center circle of the left one looks somewhat larger but they are both the same size |
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What is this geometrical illusion called? |
Jastrow Illusion |
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This illusion is an illusion of ______ |
Size |
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What do you see with this illusion? |
Bottom curve tends to look larger than the upper one but they are the same size |
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What is this geometrical illusion called? |
Zollner Illusion |
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This illusion is an illusion of ______ |
Angle |
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What do you see with this illusion? |
Tend to not see the lines are paralllel but they are |
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What is this geometrical illusion called? |
Twisted Cord Illusion |
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This illusion is an illusion of ______ |
Angle |
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What do we see with this illusion? |
Vertical parts of letter don't look like they're in parallel but they are |
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What is this geometrical illusion called? |
Horizontal-vertical & bisection illusion |
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This illusion is an illusion of _______ |
Shape |
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What are you supposed to see with this illusion |
Vertical line looks longer but they are actually the same length |
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What is this geometrical illusion called? |
Shepard's Illusion |
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This illusion is an illusion of ______ |
Shape |
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What are we supposed to see with this illusion? |
Looks like different shapes but actually the same shape |
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Are geometrical illusions easy to investigate? |
Yes, there are many studies published |
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Does every geometrical illusion have a lot or little variations |
Many variations |
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Is there a lot of consensus or disagreement about the causes of many of the geometrical illusions |
Still disagreement Different illusions may have different explanations |
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What does the eye-movement theory for geometrical illusions say? |
These say illusions are caused by eye movement errors Another version relates illusiosn to errors in "efferent readiness" |
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What is something that debunks the eye movement theory for geometrical illusions |
Illusions occur when presentation is too short for eye movements (if show in a flash, no eye movements occur but illusion still occurs) |
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What debunks the "efferent readiness" of eye movement theory |
But there is evidence that perception is not based on efferent readiness |
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What is the eye movement explanation of the Muller-Lyer illusion |
(circle indicates where eye is drawn) Because of the arrow head that is where the eye is drawn and perceive length of eye with where fixate However, it is not true, if show in a flash, no eye movements occur but the illusion still occurs |
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What does the low-level theories for geometrical illusions say |
*Illusions arise from low-level sensory processes such as lateral inhibition |
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Do low level theories work for all geometrical illusions? |
Such processes may contribute to SOME illusions, but this theory can be rejected for some illusions, such as the Poggendorff (Variants of the illusion provide evidence that it is not caused by acute angle expansion) |
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What is the hypothesized acute angle expansion? |
(Solid = real acute angle) (Dashed = what looks like) Lateral inhibition, line produce some form of inhibitory field that tends to push them apart |
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How was hypothesized angle expansion used to explain the poggendorff illusion? |
Misalignment produced by hypothesized angle expansion. There's an acute angle on both sides and this acute line is expanded so it looks less acute |
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What can we reject about the hypothesized angle expansion explanation for the poggendorff illusion? |
There are two parts of the illusion 1) Acute angle (Right) 2) Obtuse angle (left) The obtuse angle looks like the most unaligned when compared to the acute angle |
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What is the scene processing theory for geometrical illusions related to |
Processing of 3D scenes |
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What does the scene processing theory for geometrical illusions say |
We have 2 ways (or modes) of attending to pictures of 3D scenes We can attend to information about the depicted 3D scene or we can attend to informatin about the flat surface of the picture |
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Explain this picture in terms of the scene-processing theory |
Picture of a 3D scene can say two things about it: 1) Can see as flat on the surface and make judgements about lines on the paper 2) Look as a 3D scene If look at it as a 3D scene pay attention to perspective and scale in 3D scene 1) Persion in back is further away but takes up the same physical size as the person in front 2) Could also look at it as a 2D picture and see that the upper image is smaller than the lower image If attend to the image as a flat surface. The guy in the back is seen as smaller than the guy in the front however, we misperceive the size and think it is larger than it actually is. Context that helps to perceive in a 3D is still used even when try to attend to the scene as a flat surface (2D surface) Produces error in perception |
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Is there cross talk between the two modes (seeing scene as 3D vs 2D) |
Yes Some 3D scene context influences our perception of the picture surface this prodcues illusion |
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Talk about this picture in terms of scene processing theory |
It is a real 3D scene and the linear perceptive provides a scale Perceive the relative size of the 2 black objects in relation to the context Even as a 2D image the top line still looks slightly bigger even though they are the same size |
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To an extent which geometrical illusion does this match with? |
Ponzo illusion Context of converging lines influence the perception of horizontal lines |
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Explain this illusion in terms of scene processing theory |
In a 3D scene the front line would be 1/3 the size of the back scene. But as a flat surface, measure these two lines they are the same length but back line still looks substantially longer |
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What geometrical illusion does this correspond to? |
Muller-Lyer Illusion |
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Explain this illusion |
Poggendorff 3D variant of it (embedded within it) Obliqueness is now seen as recession into depth |
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Explain the reasoning of Shepard's illusion |
*Projective shape is compressed by slant in depth *Shape constancy uncompresses the perceived shape When rotate it 90 degrees it changes from being expanded up and down to expanded side to side |
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Does scene based explanations describe all of the geometrical illusions or just some of them |
Some (but not all) of them |
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Why are the conclusions of geometrical illusions controversial |
*There is some evidence they can't explain *Several other theories have some support *Many illusions may have multiple causes |
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What is illuminance |
The amount of light incident on a surface |
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What is reflectance |
(Albedo) The percentage of incident light reflected by a surface |
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What is luminance |
The amount of visible light that comes to the eye from a surface |
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_____ and _____ affect luminance |
Illuminance Reflectance |
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What is brightness |
The perceived luminance of a surface |
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What is lightness |
The perceived reflectance of a surface (its constant property) |
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What is lightness constancy |
The tendency for perceived reflectance to remain constant in spite of variations in surface luminance |
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Does familiarity have a strong or weak effect on lightness constancy |
Weak effect |
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Does perceived illuminance have a weak or strong effect on lightness constancy |
Has little if any effect |
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Lightness of an area is mainly determined by what |
Its relation to the surrounding areas |
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What happens to ratios of luminance when illuminance changes |
Ratios of luminance remain constant as illuminance changes --> this provides a basis for lightness constancy |
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Explain this picture in terms of lightness constancy |
Ratio of light of object relative to ratio of frame work it is in. Ratio of both is the same |
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How does low-level constancy mechanisms work |
Low level: "sensory", early stages of visual processing, usually farily local IE lateral inhibition - occurs with center/surround receptive fields |
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What does lateral inhibition do to the absolute level of luminance |
Reduces effects of absolute level of lumiannce Enhances local relations such as ratios and so contributes to lightness constancy |
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What is simultaneous contrast |
The same mechanisms that produce constancy can also produce illusions IE background context is varied Simultaneous contrast is the result Lateral inhibition contributes to this illusion |
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Are low level mechanisms sufficient to account for all the phenomena of lightness constancy and lightness illusions? |
No |
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What are mid-level mechanisms |
*Perceptual *Are at a higher level of processing, are more sophisticated *Tend to operate over a wider spatial range but are still somewhat local (not the global scene) |
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What does mid-level constancy mechanisms contribute to |
Lightness constancy |
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What is the anchoring problem |
Problem: where to locate the range of luminance values on the scale of perceived gray shades |
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Perceived lightness is based on what |
Relative luminance |
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Can relative lumiannce produce lightness values without an anchoring rule? |
No |
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What are mid-level anchoring rules |
*The visual system uses several rules to determine anchoring *One rule is that the highest lumiancne area is seen as white *The lightness of other areas is determined by their ratio in relation to the anchor *This can lead to illusions with a limited lumiannce range IE gray to black |
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Does the size of the area have an effect with mid-level anchoring rules |
Yes (IE small areas of high lumiancne may be seen as different luminate rather than white) |
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What does grouping establish |
Local frameworks |
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Changing the framework can change what |
Perceived lightness |
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What are examples of grouping effects? |
*Koffka's rings *White's illusion |
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What is this |
Koffka's rings |
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What does Koffka's rings show? |
Simultaneous contrast If eliminate separation and bring them together will group into 1 disc and so will be the same |
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What does this show? |
The one on the left is mostly surrounded by white but looks lighter. Opposite for one on right. Opposite effect of what expect with simultaneous contrast. Think of it as grouping with the ones on the side |
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Do more global frameworks also affect lightness perception/ |
Yes |
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What happens in terms of simultaneous contrast for this? |
Both squares are also affected by the more global white surround |
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What affects the weighing of local and global frameworks |
Various factors |
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More "articulation" does what to local weight? |
Increases (IE more "articulation" of the local surrounds increases their relative weights and so that increases the perceived lightness difference between the squares) |
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What is happening with this in terms of "weighing" |
Can look at this white area --> "global surround" is white. Also have an effect will roduce more equal gray because has weighing of local and global surround. compelx "weighing" going on |
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What happens when you add lots of these little squares |
Gives local surround a greater weight so color differenciation of the two grays are more obvious |
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What is occlusion? |
One thing in front of another if careful would say partial oclcusion (back not completely hidden) |
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Is familiarity necessary for occlusion |
No Still see A in front of B even though not familiar shape |
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What do the dashed lines represent? |
Where contour meet = contour junction (The action is there) |
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If you change what happens at the contour junction what does that do |
Changes it so the other shape looks like it's in front |
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What are "T" junctions |
Particular configuration at junction to show perception of partial occlusion T junction is associated with occlusion |
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What is perceptual completion |
Perception attempts to find the simplest or most probably organization |
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What would you expect to see if the gray square in A is taken away between B, C and D? |
"B" Only part of the circle is visible, but you perceive it as a partially occluded whole circle, this is called "perceptual completion" Tend to see that occlusion because of T junction |
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What does it mean when things are perceptually relatable? |
Sometimes two partial occlusions appear to join behind the occluder to form one object. They are perceptually relatable |
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What does it mean when things are not perceptually relatable |
Two partial occlusions do not appear to link up behind the occluder (they are seen as two separate objects). They are NOT perceptually relatable |
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Are these relatable edges or unrelatable edges? |
Relatable |
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ARe these relatable edges or unrelatable edges? |
Unrelatable |
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What are illusory contours |
A contour is seen when no physical contour is present in the image. This is another kind of perceptual completion A contour is seen where the overall figural organization indicates that one should be |
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Where does the contour belong in illusory contours? |
Belongs to the surface that is seen in front (occluding) |
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For illusory contours, the contour inducers appears to be completed where |
Behind the occluding surface |
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What is this? |
Curved illusory contours |
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What is this showing? |
Illusory curvature from straight inducers Getting the curved subjective controus because of the angles between the straight inducers |
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Is the regular or irregular contour stronger? |
Irregular |
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What are the two kinds of perceptual completion |
*Modal completion *Amodal completion |
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What is modal completion |
Illusion looks like really there, sensory perception |
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What is amodal completion |
Without sensory modality, behind the inducers |
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How many objects and why do we see it that way? |
2 Visual system tends to split into two objects (rings) when split up do both forms of perceptual completion The part seen as in front is modal Part seen as back is amodal |
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What are these objects called? |
Self splitting objects |
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What are self splitting objects? |
Ambiguous Can either see horizontal or vertical in front. One seeing in front has (modal contour) one seen in back have amodal Can get that to switch because the depth order is ambiguous |
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Transparency depends on what |
The relations between regions |
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Can 1 shape by itself look transparent |
No (Only when bring several regions together can create transparency) |
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If we separate this into componenets will transparency still be seen? |
No |
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What is an "X" junction? |
@ith transparency |
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What are rules for transparency |
Two necessary conditions for perceived transparency with regions of different luminance 1) contrast is reduced by transparent surface 2) Contrast polarity is maintained by the transparent surface |
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What is this showing |
Transparent Illusory Contours (Looks like the vertical edges are continuous) |
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What is this showing? |
Neon Color Spreading |
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What is ambiugous completion? |
Transparent square in front of four black circles (modal) 4 circular windows hidden behind which is opaque gray square (amodal) Can do both so is ambiguous |
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Can you have transparency in a line drawing? |
Yes |
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Can image contours be produced by various kinds of edges in the environment? |
Yes (This is another kind of optic array ambiguity that is resolved by environmental constraints) |
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What is edge labeling |
Process that decides what kind of edge produced each contour |
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Explain what we can see with this picture |
Four kinds of edges. This scene contains four different kinds of luminance edges: *Orientation edges (O) due to abrupt changes in surface orientation *Depth edges (D) due to gaps between surfaces at different distances *Reflectance edges (R) due to different surface pigments or materials *illumination edges (I) due to shadows |
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How do we use symbols to label the image? |
"+" = convex edge "-" = concave edge " -> " = occluding edge (object on right; left is empty space) |
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Should an edge have the same or different label all along its length |
Same |
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Are all combinations of edge labels able to be met at a contour junction? |
No |
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What are "inconsistent" edge labelings |
That don't obey the rules They don't normally occur in the real environment |
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Is this consistent labeling or inconsistent labeling? |
Consistent labeling |
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What is edge labeling of a reversible object like? |
IE Necker Cube |
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Is this an inconsistent or consistent impossible object? |
Inconsistent (Arrows change dependign on the side of the scene) |
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Is this an inconsistent or consistent impossible object? |
Consistent (Has a consistent label but is impossible figure because violating generic viewpoint constraints) |
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Are you more or less likely to notice if an object is an impossible image if the two sides are further apart |
Less likely |
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Is it more or less likely to notice an object is an impossible image if the two sides are closer together |
More obvious |
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How are most perceptual processing? |
Fairly local So more global contour relations are less saliant |
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The same luminance changes across contours can be produced in different or the same ways |
Different |
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The same luminance changes across contours can be produced in different or same ways |
Different |
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Luminance changes can be produced by differences in what |
Reflectance (IE different areas are painted differently) or Differences in "shading" (IE different areas are illuminated differently) |
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Are the edges of the reflectance image and the illuminance image the same or different |
Locally they are identical |
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Explain the impossible stairs illusion |
Inconsistent labelling On left side, we see differences between top/middle/bottom stripe due to differences in reflectances On right side, see difference due to surface more horizontal so get more light and the vertical gets less light so is now difference in illumination |
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When this illumination was first created it was believed to be due to what |
perceived direction of illumination (Top has more light and bottom is seen as in shade. If 2 patches send out same amount of light, the top is receiving more more light so has lower reflectance (because get more light and send out less light) additionally the lower one is reflecting a higher percent) |
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What is a better explanation for this? |
mid-level grouping |
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What does this picture show? |
The weak illusion in this variant is hard to explain by perceived direction of illumination or by grouping. This componenet may be due to low-level lateral inhibition |
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What is a penumbra |
When an object casts a shadow on another surface this produces a luminance change. A shadow border usually has a "penumbra" which helps distinguish shadow borders from reflectance borders. This can be used to create powerful lightness illusions |