PSY 456: Week 7 Notes
PSY 456: Week 7 Notes PSY 456
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This 6 page Class Notes was uploaded by Brianna on Saturday March 26, 2016. The Class Notes belongs to PSY 456 at Colorado State University taught by Amberg in Spring 2016. Since its upload, it has received 14 views. For similar materials see Sensation & Perception in Psychlogy at Colorado State University.
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Date Created: 03/26/16
Ch 9: Color Vision Function of Color ● classify and identify objects ● organize elements into objects ● foraging What colors do we see? ● 250 Colors ● Primary ○ red, yellow, blue ● Secondary ○ created by combining 2 primaries ● Intermediate or Tertiary ○ created by combining primary with secondary ● Achromatic Colors: contain no hue ○ white, gray, black ● Why is there variety? ○ colors are changed by ■ Intensity: changed perceived brightness ■ Saturation: adding white to a color results in less saturated color Color and Wavelength ● Color perception is related to wavelength of light ○ 400450 nm violet ○ 450490 nm blue ○ 500575 nm green ○ 575590 nm yellow ○ 590620 nm orange ○ 620700 nm red ● Wavelengths ○ short blue ○ medium green ○ long & medium yellow ○ long red ○ long, medium & short white ● Selective Transmission ○ transparent objects selectively allow wavelengths to pass through ● Simultaneous Color Contrast ○ background of object can affect color perception ● Colors of Objects ○ color of objects is determined by the wavelengths that are reflected ○ Reflective Curves: percentage of light reflected for specific wavelengths to perceive color ■ Selective Reflection: certain colors are selected to be reflected back ● Additive Color Mixture ○ mixing lights of different wavelengths ○ all wavelength available to observer ○ superimposing blue and yellow lights leads to white ● Subtractive Color Mixture ○ mixing paints with different pigments ○ additional pigments reflect fewer wavelengths ○ mixing blue and yellow leads to green ■ blue and yellow have green wavelength, red and blue wv cancels out Trichromatic Theory of Color Vision ● three different receptor mechanisms responsible for color vision ● Behavioral Evidence (Young & Helmholtz) ○ ColorMatching Experiments ■ observers adjusted amounts of 3 wavelengths in a comparison field to match a test field of one wavelength ■ Results ● “normal” color vision: three wavelengths ● color deficient: two wavelengths ● Physiological Evidence ○ measured absorption spectra of visual pigments in receptors ○ found receptors that responded maximally to ■ short wavelengths (419 nm) ■ medium wavelengths (531 nm) ■ long wavelengths (558 nm) ● Summary ○ color perception is based on response of three different cone types ■ responses vary depending on wavelengths available ● Are three receptors necessary for color vision? ○ one receptor type (monochromat) cannot lead to accurate color vision ■ absorption of a photon causes the same effect no matter the wavelength ■ any 2 wavelengths can cause the same response by changing the intensity ○ two receptor types (dichromats) solve this problem ○ three receptor types (trichromats) allow for perception of more colors Color Deficiencies ● Trichromatic Color Vision: 3 wavelengths ● Anomalous Trichromat: 3 wavelengths in different proportions than normal trichromat ● Dichromatic Color Vision: 2 wavelengths ○ Three Types ■ Protanopia (redgreen) ● affects 1% of maes and .02% of females ● individuals see short wavelengths as blue ● neutral point occurs at 492 nm ● above neutral point, see yellow ● missing the long wavelength pigment (red) ■ Deuteranopia (redgreen) ● affects 1% of males and .01% of females ● see short wavelengths as blue ● neural point occurs at 498 nm ● above neutral point, see yellow ● missing medium wavelength pigment (green) ■ Tritanopia (blueyellow) ● affects .002% of males and .001 of females ● see short wavelengths as blue ● neutral point occurs at 570 nm ● above neutral point, see red ● missing short wavelength pigment (blue) ● Unilateral Dichromat: trichromatic vision in one eye and dichromatic in the other ● Monochromatic Color Vision: 1 wavelength (truly color blind) ○ 4 types ○ very rare hereditary condition ○ only rods, no functioning cones ○ only perceive white, gray, and black tones ○ poor visual acuity ○ very sensitive to bright light ● Test with Ishihara Test OpponentProcess Theory of Color Vision ● Proposed by Hering ○ color vision is caused by opposing responses ■ blue and yellow ■ green and red ○ result of chemical reaction in the retina ● Behavioral Evidence ○ color afterimages and simultaneous color contrast show the opposing paring ○ types of color blindness are red/green and blue/yellow ● Physiological Evidence ○ researchers performing singlecell recordings found opponent neurons ○ Opponent Neurons ■ in retina and LGN ■ excitatory response to one end of the spectrum ■ inhibitory response to other end Trichromatic and Opponent Process Theories combined ● each describes physiological mechanisms ○ trichromatic theory explains responses of cones in retina ○ opponent process theory explains neural response for cells further in the brain Color in the Cortex ● there is no single module for color perception ○ cortical cells in V1 and V4 respond to some wavelengths or have opponent response cells usually also respond to forms and orientations ○ cortical cells that respond to color may also respond to white ● Types of Opponent Neurons in the Cortex ○ SingleOpponent Neurons ■ looking at larger scope, responds strongly to specific wavelength and inhibits others ○ DoubleOpponent Neurons ■ looking at boundaries, responds to more than one specific wavelength Color Constancy ● perception of colors as relatively constant in spite of changing light sources ○ sunlight has approximately equal amounts of energy at all visible wavelengths ○ tungsten lighting has more energy in the long wavelengths ○ objects reflect different wavelengths from these two sources ● Chromatic Adaptation: prolonged exposure to chromatic color leads to receptors ○ adapting when the stimulus color selectively bleaches a specific cone pigment ○ decreasing in sensitivity to the color ○ adaptation occurs to light sources leading to color constancy ● Uchikawa ○ shown sheets of colored paper in three conditions ■ Baseline: paper and observer in white light ■ Observer not Adapted: paper illuminated by red light; observer in white ■ Observer Adapted: paper and observer in red light ○ Results: ■ baseline: paper is green ■ not adapted: paper is slightly red ■ adapted: paper is yellowish ● Effect of Surroundings ○ color constancy works best when an object is surrounded by many colors ● Memory and Color ○ past knowledge of an object’s color can have an image on color perception ● Hansen ○ saw photographs of fruits with characteristic colors against a gray background ■ they adjusted the color of the fruit and a spot of light ■ when the spot was adjusted to physically match the background, the spot appeared gray ■ but when the color of the fruits was changed to the color of background, they were still perceived as being colored ● Achromatic Colors ○ perceived as remaining relatively constant ○ Perception of Lightness ■ is not related to the amount of light reflected by an object ■ is related to the percentage of light reflected by an object ○ The Ratio Principle: areas that reflect different amounts of light look the same if the ratios of their intensities are the same ■ this works when objects are evenly illuminated ○ Lightness Perception under Uneven Illumination ■ source of information about illumination ● information in shadows: system must determine that edge of a shadow is an illumination edge ○ system takes into account object meaningfulness ○ penumbra of shadows signals an illumination edge Color is a Construction of the Nervous System ● physical energy in the environment does not have perceptual qualities ○ light waves are not colored ● different nervous systems experience different perceptions ● honeybees perceive color outside of human perception Infant Color Vision ● difficult to know what an infant sees ○ chromatic color ○ brightness ● Bronstein et al ○ habituation ○ young infants have color vision ■ can perceive color and changes in brightness