Perception and Environmental Ergonomics (chapt. 4) Flashcards
visual sensory system
eyes visual system sensory processing visual search reading lighting
stimulus light
our visual system is sensitive to a portion of electromagnetic spectrum. From a bit less than 400 nm to a bit more than 700 nm
visual stimulus
attributes the visual stimulus and related perceptual phenomena
Physical Perceptual
wavelength—color/hue
amplitude—–brightness
purity————saturation
color/hue
That is what we usually mean when we ask “what color is that”? The property of color that we are actually asking about is “hue”.
CIE Color Model
The theory (by french org L’Eclairage (CIE) is based on the fact that our eyes contain three differ type of color receptors called cones they respond differ to wavelengths of visible light.
The differential response of the three cones is measured in three very variables x,y, and z in the CIE color model. This gives a 3-d model which is then projected onto one plane to give a 2-d graphic.
amplitude brightness
Value- when we describe a color as light or dark we are discussing its value or brightness this property of color tells us how light or dark a color is based on how close it is to white.
chromaticity
think about a color’s purity when describing its chromaticity or CHROMA this property of color tells us ow pure a hug is.
saturation
how a color looks under certain lighting conditions. A room painted a solid color will appear different at night than in daylight.
lighting terminology
intensity brightness of a source candela
illumaniance-amount of light falling on a surface unite:LUX
luminance-amount of reflected or emitted light per unit or projected surface area.Lux lemens per square meter
lux meters (light meters)
instrument
reflectance
various surface absorb different amounts of the incident light. Reflectance:the percentage of reflected to incident light. with the luminance in cd/m2 and luminance in Lx the formula is as follows
Optic chiasma
nerves to creating an image
eye
retina: actual receptor organs are the visual cells embedded in the retina. Consisting cones for color vision in bright light. Rods are highly sensitive for vision in dim light. Conceive only shades of gray between black and white.
contains about 130 million rods and 7million cones
fovea:a few degrees on either side of the optical axis with thin covering allowing the light rays to pass directly to the visual cells. Consist entirely of cones outside the foveal area there are considerably fewer cones
visual field
the visual field is that part of ones surroundings that is taken in by the eyes when both eyes and head are held still.
a= zone of sharp vision angle of view of 7
b=middle field: vision unsharp angle of view from 1 degrees to 40 degrees
c=outer field:movements perceptible, angle of view from 41
accommodation
accommodation means the ability of the eye to bring into sharps focus objects at varying distances from infinity down to the nearest point of distinct, vision the near point. An object is seen clearly only when refraction through the cornea and lens produces a tiny but sharp image on the retina, the three components forming an optical system.
visual angle
the actual size of the object and the distance the object is from the eye
visual perception
object of the same size at different distances may have the same visual angles
speed and accuracy of accommodation
when the lighting is poor the far point moves nearer and the near point recedes, while both speed and precision of accommodation are reduced. The speed and the precision of accommodation decrease with age.
adaptation
effects of light and dark surfaces on the retina
eye movements
tremor-the continuously makes small movement which keeps the retinal image in slight motion. Without this continuous tremor the perceived image would fade away
mergence-eye movements are very precise and fast. An eye movement of 10 degrees maybe accomplished in about 40ms. For good vision the movements of convergence and divergence are of special importance
contrast sensitivity
how faded or washed out an image can be before it becomes indistinguishable from a uniform field. Is a function of the size of spatial frequency of the features is the image. Not a direct relationship as larger objects are not always easier to see that smaller objects.
Deafined as the reciprocal of the minimum contrast between a lighter and darker spatial area that can just be detected.
- special frequency;high and low
- contrast
- illumination
visual disabilities color blindness
red-green color blindness is common about 4-5%of the population. 8-10%of the male population is red-green colorblind
color vision
cone cells are called red, green, blue based on the photo pigments are sensitive to different wavelengths of light
long wavelengths-red
middle “ “-green
short- “ “ blue
colorblindness
when someone is colorblind, these is something wrong with one of their groups of photo pigments, usually the red (L) or green (M) which is why they are called red-green colorblind.
processing model
bottom-up
top-down
top-down perception
knowledge, expectations or thoughts influence perception
constructivism-we structure the world
perception is not determined simply by stimulus patterns; rather it is a dynamic searching for the best interpretation of available data
bottom up pereption
physical characteristic of stimulus realism
relative size
the more distant an object say a person is the smaller the image of that object will be on your retina, the back of the eye where we really been to see
interposition
impression of depth
textural gradient
the fineness of detail or texture that can be seen decreases systematically with increasing distance from the observer.
relative motion
parallax is an apparent displacement of difference in the apparent position of an object viewed along two different lunes of sight
Luminous flux
energy per unit that is radiated from a source over visible wavelengths.
Lumen (lm)
standard unit of luminous flux
Luminous intensity
a light source emits its luminous flux with a different intensity depending on the direction it is shined. The luminous intensity is a measure of the energy emitted by a light source in a particular direction
candela (cd)
standard unit of luminous intensity
illuminance
the total amount of visible light illuminating a point on a surface from all directions above the surface
lux (lx)
standard unit of illuminance (lumens per square meter)
distance objects
without accommodation, the image of an object close to the eye would fall behind the retina, resulting in a blurred impression. To avoid this the ciliary muscle increases the curvature of the lens so that the image is focused on the retina. When we look at objects.
the near point and far point
the shortest distance at which an object can be brought into sharp focus. The longest distance at which an object can be brought into sharp focus.
Muller lyer Ilusion and ponzo illusion
looking at one thing and another thing that may seem bigger or smaller but are equivalent sizes. Gonzo is for shortening one point perspective goes into space.
Type of colorblindness
1) Trichromatic (normal color vision) have their color vision based on 3 different types of photo pigment, one from each of the L,M, and S group.
2) Dichromats- severely colorblind are missing one whole group of phot pigment. Most mammals (including cats and dogs) have dichromatic color vision.
3) Monochromats- very rare) cannot distinguish between any colors.
4) Anomalous trichromats- mildly or moderately colorblind have color vision based on 3 different photo pigments, but from only 2 the photo pigment groups.
depth perception
host of depth cue bottom up cues only effective for judging distance slat, and speed for objects that a are within a few meters form viewer.
liner perspective, relative size, interposition,light and shading, textural gradients, relative notion (motion parallax) top down influence
linear perspective
parallel lines that recede into the distance appear to get closer together or converge
number of eye movements
the number of eye movements required when reading a book maybe as many as 10000coordinated eye movements per hour.
visual reading field
the fovea and the adjacent on the retina pick up visual information from a rather small proton of the total print surface. The so called visual reading field.
signal detection methods and theory
in a signal detection task, some event is classified as a signal and the subject’s task is to detect whether the signal is present.
On the occurrence of the trip; event, the subject sets the information presented and decides whether this informations sufficient to warrant a signal present response. Sample of information is assumed to provide a value along continuum of evidence states regarding like likelihood of the signal being present.
The noise trials form a probability distribution of states, as do the signal trials. The decision that must be made on a trial can be characterized as whether the event is from the signal or noise distribution.
The subject is presumed to adopt a criterion value of evidence above which he or she responds signal present and below which he or she responds signal absent.
discrimination
ability to discriminate between one of the two signals rather than to detect the existence of a signal.
weber’s law
weber’s law states the ratio of the increment threshold to the background intensity is a constant. So when you are in a noisy environment you must shout to beheard while a whisper works in a quiet room.And when you measure increment thresholds on various intensity backgrounds, the threshold increase in proportion to the background. The relationship between the physical magnitudes of stimuli and the perceived intensity of the stimuli.
Artificial sources: Florescent tubes
produced by passing electricity through a gas (argon or neon) or through mercury vapor.
