the relation between physical stimulus properties (light) and perceptual experience, (brightness)
physical stimulus energy -> receptors transduce energy which are sent to neurons. and go to the brain
"Elements of Psychophysics" was written by _________?
Gustav Fechner who defined classical ways to measure thresholds in three ways. (method of limits, adjustment and constant stimuli)
minimum intensity of a stimulation required to produce a detectable sensory experience
minimum change in intensity required to produce a detectable change in sensory experience
method of constant stimuli
you take a fixed set of stimulus intensities (tones) selected in advance that are each extreme - clearly above and below threshold. present the stimulus intensities in RANDOM ORDER and present each intensity several times, each time asking the subject for a "yes"/"no" judgment.
What is psychophysical scaling used for?
To describe the relationship or mapping between physical stimulus intensity and the magnitude of perceptual experience
JND/S = k
the relationship between physical magnitude and subjective magnitude
Who conducted the Prism Experiment in 1704?
Sir Isaac Newton. White light source -> narrow slit -> prism -> divides light sources in to ROYGB
What are the physical parameters of light?
wavelength, intensity and spectral composition
What are the psychological correlates?
Hue, brightness, and saturation
What are additive mixtures?
All wavelengths in each component are present in the mixture
What is color constancy?
the tendency for the perceived color of an object to remain the same under different conditions of illumination
Young-Helmholtz. Theory proposing that our perception of color is determined by the ratio of activity in three receptor mechanisms with different spectral sensitivities
Opponent-process theory (Hering)
perception of color is determined by two opponent mechanisms 1. blue-yellow mechanism and 2. red-green mechanism. The responses to the two colors in each mechanism oppose each other, one being excitatory and the other inhibitory.
Color-matching experiments are behavior evidence for which theory of color vision?
color matching experiments - observes adjust amounts of three wavelengths in a comparison field to match a test field of one wavelength. --> Trichromatic Theory of Color Vision
Physiological evidence for Trichromatic Theory:
- research measured absorption spectra of visual pigments in receptors and found pigments that responded maximally to (short, medium and long wavelengths)
What are metamers?
two patches of light with different spectral compositions that appear to be identical in color.
What is some support for the opponent process theory?
1. No yellowish blues or reddish greens are perceived 2. Simultaneous color contrast (green vs. red, blue vs. yellow) 3. Afterimages (red->green, blue-> yellow)
Combine Trichromatic and Opponent-Process Theories!
Trichro. explains the responses of the cones in the retina.
Opponent-process explains neural response for cells connecte to the cones further in the brain
Our experience of color...
Light enters and (trichromatic) receptors perform color matching while opponent cells (opponent process) perform afterimages, simultaneous contrast before being sent to the brain
What are the various functions of color vision?
Signaling function (to help us identify and classify things)
Facilitates perceptual organization, the process by which elements become grouped perceptually into larger objects.
Greatly facilitates the ability to tell one object from another and especially to pick out objects within scenes.
What physical characteristic is most closely associated with color perception? How is this demonstrated by differences in reflection of different objects?
The colors of objects are largely determined by the wavelengths of light that reflected from the objects into our eyes.
When some wavelengths are reflected more than others they are called hues.
Selective reflection is the property of reflecting some wavelengths more than others.
Additive color mixture vs. subtractive color mixture: How can the results of these two types of color mixing be related to the wavelengths that are reflected into an observer's eyes?
Additive color mixture- mixing lights that involves adding up the waves length of each light in the mixture (blue has short wavelengths + yellow has medium and long wavelengths = short, medium and long wavelengths = white in the center.)
Subtractive color mixture - paint mixing. When mixed, both paints still absorb the same wavelengths they absorbed when alone, so the only wavelengths reflected are those that are reflected by both paints in common,
Describe trichromatic theory and experiments on which it was based. How does this theory explain the results of color-matching experiments?
color vision depends on activity of three different receptor mechanisms. (Young and von Helmholtz)
By adjusting the proportions of THREE wavelengths, it was possible for observers to match any wavelength presented.
---people with normal color vision couldn't match all the wavelengths in the spectrum with only two wavelengths.
What are metameters and how can our perception of them be explained by code for color?
two physically different stimuli that are perceptually identical.
look alike because both result in the same pattern of response in the three cone receptors.