M2 Lecture 9: Feb 12 Flashcards
Perception involves what
figuring out which interpretation of the reality is the most likely
what is The pandemonium model of perception
demons represent neurons, and each level is like a brain area.
Committees must integrate conflicting opinions and reach a consensus.
what are The Four steps of sensation and perception
physical stimulus–> 1. transduction –> 2. transmission –> 3. perception
what is modulation
Cognitive factors, like expectations, attention, etc. will influence how sensations are perceived.
e. g. Top-down vs bottom-up processing
e. g. Bayesian prediction process
what are the Committee rules in the pandemonium model
- Put together what goes together (ex.: Gestalt grouping rules)
- Avoid accidents (ex.: accidental viewpoint)
- Honour physics (ex.: occlusion)
4, Reach consensus (ex.: ambiguous figures) - Separate what should be separated (ex.: figure vs ground)
what i
what is Accidental viewpoint
A viewing position that produces some regularity in the visual image that is not present in the world.
(like the 3d paintings on roads that look like such from a certain angle but completely warped from other angles)
what is Occlusion
solid objects block light
what is Figure-ground assignment
The process of determining that some regions of an image belong to a foreground object (figure) and other regions are part of the background (ground).
what are the 5 main Gestalt figure-ground assignment principles
surroundedness size symmetry parallelism Extremal edges
what is Surroundedness:
The surrounding region is likely to be ground.
what is Size:
The smaller region is likely to be figure.
what is Symmetry:
A symmetrical region tends to be seen as figure.
what is Parallelism:
Regions with parallel contours tend to be seen as figure.
what is Extremal edges:
If edges of an object are shaded such that they seem to recede in the distance, they tend to be seen as figure.
what is Structuralism
Dots make lines -> lines make corners -> corners make shapes -> shapes are connected one to another and make objects.
what is the formula for perception
structuralism + committee rules = object perceived
what is the Face inversion effect
We are better at recognizing faces that are upright.
Logically, it seems that object recognition should follow figure-ground assignement, but then it shouldn’t matter if the face is up or down….
Object recognition also helps with what
figure-ground assignement.
is perception just a feed forward process
It cannot all be a feed-forward process, there has to be reciprocal communication between object recognition and figure-ground assignement.
what is the Global superiority effect
The properties of the whole object take precedence over the properties of parts of the object
(aka you see the ‘H’ that the small ‘s’s’ make instead of just the small ‘s’s’
HOW DO WE RECOGNIZE OBJECTS ?
2 attempted ways to tackle it:
Naïve template theory
Structural description
what is Naïve template theory:
The proposal that the visual system recognizes objects by matching the neural representation of the image with a stored representation of the same “shape” in the brain
do Naïve template theory work
Naive template theories don’t work
what is Structural description
maybe what we recognize is a particular organisation of simpler features?
does the Structural description work
Biederman (1987) proposed that any object could be made of a finite set of simpler geons (“geometric ions”).
so yes!
are Geons and relationships between geons (ex. «geon A is on top of geon B») are viewpoint invariant
yes
what is viewpoint invariant.
Minor changes in shape won’t alter the structural description.
(you can recognize a coffee mug as such even If upside-down)
even if the structural description is mostly viewpoint invariant, are there still issues
yes– people still take a much longer time identifying an object the more it has been rotated
what are the Three steps to color perception
- Detection: Wavelengths of light must be detected in the first place.
- Discrimination: We must be able to tell the difference between one wavelength (or mixture of wavelengths) and another.
- Appearance: We want to assign perceived colors to lights and surfaces in the world and have those perceived colors be stable over time, regardless of different lighting conditions.
what are the Three types of cone photoreceptors
S-cones
M-cones
L-cones .
what do S-cones detect
short wavelengths.
what do M-cones detect
medium wavelengths.
what do L-cones detect
long wavelengths
why are S M and L cones not referred to as blue/green/red
More accurate to refer to them as “short,” “medium,” and “long” rather than “blue,” “green,” and “red,” since they each respond to a variety of wavelengths
The L-cone’s peak sensitivity is 565 nm, which corresponds to yellow, not red!
how common and sensitive are s cones
relatively rare, and they are less sensitive than M- and L-cones.
what are the 2 types of COLOR DETECTION
Photopic
Scotopic
what is Photopic:
Light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors to their maximum responses.
Sunlight and bright indoor lighting are both photopic lighting conditions.
what is Scotopic:
Light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors.
Moonlight and extremely dim indoor lighting are both scotopic lighting conditions.
why is DISCRIMINATION between colours dificult
A single photoreceptor shows different responses to lights of different wavelengths but the same intensity
eg. Lights of 450 and 625 nm each elicit the same response from this particular photoreceptor.
If you decrease the intensity of the light, lights of 490 and 600 nm will also elicit the same response.
what is The principle of univariance
An infinite set of different
wavelength x intensity combinations can elicit exactly the same response from a single type of photoreceptor.
Therefore, one type of photoreceptor cannot make color discriminations based on wavelength.
for every wavelength, there is a particular combination of activity across the three type of cones that remains_____ across different intensities
constant
imagine that you don’t have one type of cones (say M-cones), what happens
every frequency above S-cone limit is only encoded by L-cones and can therefore produce the same response for different wavelength/intensity combination.
-> However, colors to the left will be preserved.
how common is colour blindness
About 8% of male population and 0.5% of female population has some form of color vision deficiency: “color blindness.”
what is Color-anomalous
A term for what is usually called “color blindness.” Most “color-blind” individuals can still make discriminations based on wavelength. Those discriminations are just different from the norm
what are the types of colourblindness
Deuteranope:.
Protanope:
Tritanope:
Cone monochromat:
what is Deuteranope
Due to absence of M-cones
what is Protanope
Due to absence of L-cones.
what is Tritanope
Due to absence of S-cones.
what is Cone monochromat
Has only one cone type; truly color-blind.
what is Trichromacy
The theory that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptor types now known to be the three cones.
Thomas Young (1773–1829) and Hermann von Helmholtz (1821–1894) independently discovered the trichromatic nature of color perception using a color-matching technique developed by James Maxwell (1831–1879).
Three colors were required to match any other color.Two were sometimes insufficient.
do we see “pure” wavelengths
Generally, we don’t see “pure” wavelengths, but rather mixtures of wavelengths.
When mixing two “pure” wavelengths (say green and red), what happens
the combination of M- and L- cone activity is identical to the combination resulting from a “pure” wavelength in the yellow frequency. We can’t distinguish the two – they will all look yellow
what are Metamers
Different mixtures of wavelengths that look identical; more generally, any pair of stimuli that are perceived as identical in spite of physical differences.
what is Additive color mixing
: A mixture of lights
If light A and light B are both reflected from a surface to the eye, in the perception of color, the effects of those two lights add together.
in additive colour mixing, Blue and yellow make what
white
what is Subtractive color mixing
A mixture of pigments
If pigment A and B mix, some of the light shining on the surface will be subtracted by A and some by B. Only the remainder contributes to the perception of color
in subtractive color mixing, blue and yellow make what
green
In theory: Since there is no overlap between red and blue paint, when you combine the two all wavelengths are filtered out….the mixture is what
black
red paint is really what
white paint + drops of «pure» red
blue paint is really what
white paint + drops of «pure» blue
- Red pain is white paint + drops of «pure» red
- Blue pain is white paint + drops of «pure» blue
- > note: «pure» red or blue is very dark - When you combine the two, everything is darker overall, but there are still two peaks in red and in blue.
- thus, the reflected light is what
both blue and red
what are nonspectral hues
hues that can arise only from mixtures of wavelengths, i.e. there is no «purple» in the spectrum, it has to come from a particular combination of activity across S, M and L cones.
