unit 2 Flashcards
Psychophysics of color vision
Wavelengths of the light rays
We see reflected light and are absorbed by surfaces they hit
(more light a surface absorbs, the darker it appears)
Color depends on the mix of wavelengths that reach the eye
Photopic
daylight light levels. Based on 3 cones; (short, middle, long wavelength) which appear blue, green and red
scotopic
dimmer light; high spatial acuity. Uses only rods to see (objects are visible but in black and white)
3 types of photoreceptors
s cones (short wave)
m cones (medium wave)
l cones (long wave)
s cones
sensitive to blue
m cones
sensitive to green
l cones
sensitive to red
principle of univariance
there is only 1 type of rod, receptor responses may be similar for different wavelengths
How does the trichromatic theory allow us to see different colors?
Ability to discriminate one light from another
Color of any light is defined by our visual system by the relationship between 3 numbers
So when light strikes the retina it stim cone cells to different degrees depending on wavelength
additive
occurs when colored light is combined (when primary colors are combined and create white light) taking 1 wavelength or set of wavelengths and adding it to another
subtractive
when pigments/dyes are combined and surface selectively absorbs some wavelengths and reflect others
What is a “color space”
a three-dimensional space that describes all colors
some examples of different ways of organizing color
RGB, HSB, color circles
RGB
defined by long, medium, and short wavelength lights (red, green blue)
HSB
defined by hue(color), saturation(strength) and brightness (distance from black)
color circles
places colors that seem similar near each other and diff colors opposite
Opponent color theory and the opponent color pairs
Red-green, blue-yellow, black-white
Concept of an “illegal color pairing”
Cellular explanation of how we perceive colors. Color perception depends on 3 opponent color paints
How the opponent color theory explains “color afterimages”
Different color pairings are processed by different cells. Staring at a certain image makes certain cones fatigued so the opponent pairings appear creating an afterimage
individual differences
Individual variations in terms of perception of the world around them. Influenced by culture, genetics, ex, preferences and lang
how age may change color perception
Aging lens absorb more short wavelength light decreasing blue spectrum making warmer colors seem more vibrant
Lens yellow as you age
tetrachromacy
extra cone that permits extended color vision (4 cone cells)
dichromacy
only 2 functioning cones that reduces color vision (color blindness)
monochromacy
only 1 functioning cone (black, white grey; good visual acuity)
achromatopsia
no functioning cones, only rods (poor acuity, light sensitivity, no color vision)
protanope
No L Cones (red defective)
Deuteranope
No M cones (green defective)
Tritanope
No S cones (blue defective)
Ways of testing for color blindness
ishihara and arrangement
Ishihara
tests with number color
arrangement
arrange color based on shade
synethesia
Stim of noe sensory/cog pathway leads to automatic invol exper in a second pathway
color contrast and opponent colors
When neighboring colors are opponents, perception of 1 color is affected by color that surrounds it
color assimilation
Colors near each other take on qualities of their neighbors
color constancy and lighting
Tendency of a surface to appear the same color under a wide range of lighting conditions
Ambiguous lighting affects accurate color perception
monocular
how we process depth using 1 eye
binocular
how we process depth with 2 eyes
occulsion
cue to relative depth order. One object partially blocks view of another
familiar size
based on knowledge of typical sized objects
relative height
objects touching the ground, those higher in the visual field appear to be farther away
texture gradient
items of the same size form smaller. Closed space images the farther away they get
aerial perspective
more light is scattered when we look through more atmosphere
linear perspective
parallel lines appear to converge with distance
triangulation cues
ways to know where objects are
motion parallax
caused by the change in the position of an object that is caused by your motion (when in a moving car)
how can we use accommodation to determine depth
Physical cue of lens changing in focus for nearer objects
Nearby objects: lens thicks to focus; farther- lens thins
binocular disparity
slight differences in images perceived by each eye - visual process that 3D movies take advantage of
horopter
reference point for aligning images to perceive objects in 3D
Calculation based on horopter
(location of objects whose images lie on corresponding points; area of no disparity
stereopsis and basic cellular process involved
Input from two eyes must converge onto the same cell.
Some neurons have receptive fields for corresponding retinal images (those on the horopter).
Others respond to a particular binocular disparity
top down
guided by cog factors like goals, expect, prior knowledge
bottom up
captured by salient sensory stim - a “pop out” search is an example of this
overt
directing attention through physical movements (eyes, head turns)
covert
attending without movement
how does the posner paradigm work
Cues provide spatial info that parts can use to orient attention. Participants press a button and reaction time is used to measure attentional cost
how does the RSVP paradigm work?
used to investigate the timing of attention, the limitations of visual processing and the effects of cog processes on attention
Whether target was present or absent
Visual field defects
partial or complete loss of vision in one or both eyes withinthe visual field. Caused by damage to pathways from retina to V1.
what is spatial neglect and what brain areas are damaged in spatial neglect?
inability to attend or respond to stim in the contralesional visual field. Caused by damage to the right parietal lobe - left visual field is neglected by people with spatial neglect
selective pathway
permits recognition of one or a very few objects at a time. This pathway represents the spotlight of attention and the selective attention bottleneck
nonselective pathway
info about the distribution of features across a scene as well as the gist of the scene. This pathway does not pass through the bottleneck of attention
change blindness
failure to notice a change between 2 scenes
inattentional blindness
failure to notice or report a stim that would be easily reportable if it were attended
