Visual illusions Flashcards
(11 cards)
What are illusions comprised of
Brightness: perception of light intensity
Colour: interpretation of wavelengths
Patterns: arrangements forming meaningful shapes
Spatial position: position within an image
Why do visual illusions occur
Our brain relies on:
Heuristics: mental shortcuts to make quick decisions
Context: surrounding information influences perception
Assumptions: based on past experiences and expectations.
What are the 2 key processes
Bottom-up processing: sensory-driven perception
Top-down processing: knowledge and expectation driven expectation
Luminance vs brightness
Luminance is just the subjective brightness
Whereas brightness itself depends on absolute intensity and relative contrast to its’ surroundings
Why do brightness illusions occur?
Each retinal cell has a receptive field.
The centre of the field is excited by light and the surround is inhibited by light.
Lateral inhibition: retinal cells supress the responses of neighbouring cells, enhancing detection and contrasts of edges.
The balance between excitation and inhibition determines the signal sent to the brain which are used to determine relative brightness.
Herrmann grid
The centre gets lots of light-excitation
The surround covers more white lines- strong inhibition
There grey spots appear due to lateral inhibition.
Retinal cells compare light in their centre and surroundings to enhance contrasts. At intersections the surrounding white lines cause more inhibition- intersections look grey.
When focused on the intersection, smaller recepetive fields are used and the grey spots disappear.
2 types of colour illusions
Chromatic adaption: brain compensates for colour biases in lighting conditions
Simultaneous contrast: colours appear different based on surrounding hues
How does stereopsis work?
The combination of slightly differing images from both eyes to create a 3d perception of depth.
The brain uses disparity to figure out how far objects
(retinal disparity near 0= fix at horizon)
(Small retinal disparity = distant object)
(large retinal disparity = close object)
What is motion
The change in space (where objects are located) and time (when objects appear/ disappear)
When objects move around, the brain must solve the motion correspondence problem; which was are the objects moving around?
Why do ambiguous figure illusions occur
1) Ambiguity and perception
Visual input is inherently ambiguous.
Brain actively constructs perception using bottom-up/top-down processing
2) Dynamic alteration:
Ambiguous figures lack sufficient sensory cues- brain switched between plausible interpretations
