Perception III Flashcards
What is the meaning of sensitivity d’ in signal detection theory?
(Recap)
sensitivity d’
-> measures the ease of telling two signals apart
High d’
= signal and noise are easy to discriminate
Low d’
= signal and noise are difficult to discriminate
How is the Receiver operationg characteristic curve of the signal detection theory structured?
(Recap)
y-axis
= visualization of hits
(as a function of false alarms)
x-axis
= visaulization of false alarms
shifting the criterion
= moving along hte curve
-> higher hit rate
-> more false alarms also
sensitivity (d’)
-> signal and noise easy to discriminate
- high hit rate, little false alarm
-> signal and noise difficult to discriminate
- more false alarms
Why do we need Color Perception?
(CP: basic principles)
-> a lot of Tasks can be carried out without color
perception
-> colors on an object make in important difference for some objects
-> Can help detect and recognize objects
-> Can influence other cognitive processes
- change of taste
How do we see color?
(CP: basic principles)
Perception of Color
-> light of different wavelengths
(reflected into the eye)
visible light
-> Electromagnetic radiation perceived by the human eye
(only a small range of light perceivable - 400 - 700 nm)
=> color a psychophysical property
(result of an interaction of a physical stimulus with a particular nervous system)
Where is color perceived?
(CP: basic principles)
3 cone types carrying opsins sensitive to light at different wavelengths
-> S-cones (short wavelength, blue)
-> M-cones (medium wavelength, green)
-> L-cones (long wavelength, red)
one type of rods
Why are the different cone types needed?
(CP: basic principles)
Principle of univariance
-> A single receptor produces ambiguous outputs (equal firing rates) for different colors
only rods
-> world looks grey/blue in twilight
solving univariance
-> Trichromacy
(rgb coding throug 3 cones)
What is the opponent color theory by Hering 1878?
(CP: basic principles)
Color represented by 3 channels of opposing colors
-> red vs green
-> blue vs yellow
-> white vs black
Opponent colors can be combined
Evidence
-> opponent colors in afterimage
-> opponent colors coded in ganglion/LGN cells
What are afterimages?
(CP: basic principles)
Afterimage
-> image seeen after a stimulus has been removed from the retina
Negative afterimage
-> Afterimage with polarity opposite to original stimulus
(can be used to create “positive afterimages”)
- light <-> dark
- red <-> green
- blue <-> yellow
-> existence of negative afterimages thought to support opponent color theory (falsified)
What are Complementary color Afterimages by Pridmore 2013?
(CP: basic principles)
Complementary colors
-> add to shade of grey
(red - cyan, green -magenta, yellow - purple)
=> afterimages better decribed using complementary instead of opponent colors
How do color constancy and color contrast influence color perception?
(CP: color illusion)
context even influences color perception
Checkershadow illusion (Adelson 1995)
-> two fields of same brightness perceived as different
colors
-> brain “corrects “ for different lightening conditions,
subtracting the assumed illumination
(“blue” veins not actually blue but grey)
Does everyone see color the same way?
(inter-individual differences in CP)
Yes
-> general agreement on “basic color” names
-> cultural differences in the number of basic colors
=> color perception is mostly independent of culture /
language
No
-> slight variations due to age (lens turns yellow)
-> color vision defeciency (8% men, 0.5% women)
What type of color vision deficiencies are there?
(inter-individual differences in CP)
Anomalies of one or more cone types
-> Monochromacy: No or only one type of cones
ex. Protanope
-> L-cones missing (red-weakness)
ex. Deuteranope
-> M-cone missing (green-weakness)
ex. Tritanope
-> S-cone missing (blue-weakness)
-> Dichromacy
(Absence of one cone type)
-> Anomalous trichomacy
(Two cone types respond to similar wavelength)
(gene defect affecting opsins)
ex. Protanomaly
-> sensitivity of L-cones is shifted towards shorter
wavelengths (green)
