Lecture 2- Illusions Flashcards
What are the steps of information processing?
Converting outside world into internal events through encoding
What are the different levels of grey that humans can discriminate?
5000
What do illusions have a role in?
The study of sensory systems for illusion depth
What are the specific properties of an image?
Specific aspects such as spatial and visual, two dimensions, static
What are the basic properties of an image?
Brightness, colour and patterns
What is black and white?
The amount of light which interprets the visual system as measurement
What is colour?
A small number of linguistic categories
What did Berlin and May find?
Different number of colour names in different cultures
What is perpetual colour space?
How colours are arranged
How is the colour circle arranged?
According to similarity
What did 3M different colour measure?
Discrimination threshold
What is brightness contrast illusion?
The perceived brightness of an object being effected by the brightness of the surroundings
Why does the brightness contrast illusion occur?
Due to the way the visual system processes and compares the different light levels
What is an example of the brightness contrast illusion?
Simultaneous contrast effect
What is simultaneous contrast effect?
When a light object is placed against a dark background it appears brighter than when placed in a background of equal luminance
What does filters do in the visual stream for contrast?
Subtract stimulus intensity in the surround reigion to form lightness in the centre
What is contrast?
A perceptual measure not being absolute but the relative stimulus intensity in comparison to the surround
How is the outside world represented?
In retinotopic maps of neurones with the centre-surround receptive fields
What reduces redundancy?
Image compression
What is an example of a visual illusion?
Hermann grid
What happens in Hermann grids?
The grey spots are believed to be the result of opponency filtering
What is opponency filters?
Contrast enhancement when there is excitation-inhibition
What happens to spatial filters with opponcency receptive fields?
Enhance the contrast and reduce the redundancy
What happens inside black square for Hermann grids?
There is no stimulation of excitatory centre and inhibition that surrounds so overall excitation and a perception of darkness
What happens in white bars for Hermann grids?
Small parts of inhibitory surrounds are stimulated, excitation will dominates inhibition giving the perception of brightness
What happens at white intersections for Hermann grids?
Larger parts of inhibitory surrounds are stimulated so there is a small overall excitation so there is a reduction of brightness
What is real motion?
Perceived when an object is changing location in space and time
What is contrast illusion?
The enhancement of colour differences in space when presented next to each other
What is the Munker-White effect?
Assimilation of colour and a higher level colour interaction
What are after images?
The consequence of an illusion after long exposure to a stimulus followed by a sudden change
What is the third dimension reconstructed by?
Flat images that captures the eyes
What are the cues for third dimension?
Using two eyes, motion parallax, contrast, texture, size and perspective
What are pictorial cues?
A range of depth information being extracted from a static monocular image
What is binocular in depth cues?
Extending the visual field when there is a combination of information from 2 eyes allowing precise depth measurment through stereopsis
What is stereopsis?
A perception of depth produced in the brain from both eyes seeing visual stimuli
How does stereopsis work?
Retinal projection of the object on opposite sides of the fovea indication depth relative to the plane of fixation
What does stereopsis produce?
Depth impressions in projected/printed images
What are the cues for depth perception?
Geometric perspective, texture, occlusion and binocular disparity
What is size constancy effect?
The basis of the Ponzo illusion
What is the Ames room?
How the size of objects are perceived to be distorted because the misleading geometry generates an incorrect frame of reference
What are examples of colour illusions?
Colour effect and simultaneous colour contrast
What are not colour illusions?
Kanizsa triangle and red green colour blindness
What are the proximities in motion correspondence problems?
Vertical and horizontal proximity
What is the after effect of motion illusion?
The perceiced explanation of the stripe pattern is an illusion in itself
What are the key readings for illusions?
Jameson and Hurvich + White
What does Jameson and Hurvich say about brightness and colour vision
They are important aspects for visual perception and visual theory
What does Jameson and Hurvich say about adaptation?
It is an adjustment in sensitivity
What does Jameson and Hurvich say about sensitivities?
They change depending on inverse proportion to excitation when the visual system is exposed
What does Jameson and Hurvich say about the luminance of the test field?
When it increases the luminance of the surround should increase in the same proportions for a brightness match
What does White say about the effect of illusions?
It is stronger at high spatial frequencies
What does White say about the effect of pattern on perceived brightness?
It is lightness contrast and lightness assimilation
What does White say about the explanation of lightness contrast?
It is the lateral inhibition between retinal units
