Vision Flashcards
What is vision?
Transformation from light waves (electromagnetic energy) to recognition
What is considered to be the primary sensory system?
Vision.
What are the stimulus properites included in vision?
Stimulus properties include wavelength (color) and amplitude (brightness).
What is the energy at the source?
Luminous intensity.
What is the name for the energy reaching the object?
Illuminance.
What is the name for the energy reflected off the object to allow for vision?
Luminance.
What does the cornea do?
Protects the eye.
What does the lens do?
It focuses images.
What does the retina do?
Nerve cells that receive the image in the eye.
What does the optic nerve do?
The optic nerve transmits visual information from the retina in the eye to the brain
What are the main parts of the eye?
- Cornea
- Pupil
- Lens
- Retina
- Optic Nerve
What does the pupil do?
The pupil is used for controlling the amount of light entering the eye through the change in the size of the pupil.
What is near sighted (myopia)
The inability of the lens to flatten.
How does age effect vision?
The lense becomes less flexible and has issues focusing. The lense also becomes discolored and the cornea can cloud (cataracts). With aging, less light through cornea, thus decreased effective illumination – less contrast sensitivity
What is scotpic vision?
Viewing below the light threshold
What two types of receptors are found within the retina?
Rods and Cones.
Which is more sensitive rods or cones?
Rods are more senstive an require less light than cones.
Which is provides more image detail, rods or cones?
Cones provide more detail as they are more dense, which you use to see details. Rods are less dense and have less detail.
Where are rods and cones located?
Rods are located on the periphery and cones are located in the center (fovea)
Which helps more in low light visibility, rods or cones?
Rods help more in low light conditions.
When viewing below the light threshold (scotpic vision), which is used cones or rods?
Only rods are used below the light threshold, so their is less detail.
Are cones senstivie to glare?
Yes. They become hypersensitive when they receive little stimulation. Thus, they are sensitive to glare.
Can rods determine color?
Rods don’t determine color, as they cannot discriminate wavelength.
When do rods lose sensitivity?
Rapidly lose sensitivity when exposed to light (up to 30 min to regain)
What is contrast sensitivity?
Contrast Sensitivity: the reciprocal of the minimum contrast between a lighter and darker spatial area that can just be detected: ability to see the difference between lighter and darker areas
With movement, is there a decrease in contrast sensitivity?
Yes.
What is contrast?
Contrast is the difference between the luminance of light and the dark areas to the sum of the luminance values: L = luminance of light area, D = luminance of dark area.
What is the contrast formula?
Constrast = (luminance of light area - luminance of dark area) / (luminance + lumninance of dark areas)
C= (L - D) / (L + D)
What is contrast sensitivity?
The higher the contrast sensitivity (CS) that an observer possesses, the smaller the min amount of contrast that can be detected Cm.
What is sensitive to what amount of cycles/degrees?
Human eye most sensitive to 3 cycles/degree (spatial frequency).
What is the contrast sensitivity formula?
Constrast Sensitivity (CS) = 1/Cm
What is a visual field?
What is a visual field: The area that can be seen when the head and the eyes are motionless.
What is the visual field for one-eyed vision when the eye is motionless?
Extends from 70 on the nasal side to 104 on the temporal side.
What is the visual field for each eye when the eyes are allowed to rotate?
VF for each eye when the eyes are allowed to rotate, but not the head is about 166.
What is the visual angle?
What is visual angle: The angle formed at the eye by the viewed object.
What is the measurement of the visual angle?
Usually this is given in degrees of arc [1 (degree) = 60 (minutes of arc); 1’ = 60” (seconds of arc)] . Visual Angle (minutes of arc) = (57.3)(60)L/D
Where L = the size of the object measured perpendicular to the line of sight, and D = the distance from the front of the eye to the object.
This formula is for an angle of less than 10 degrees and assumes that the line of regard bisects L
Under good viewing conditions, what is the visual angle?
Under good viewing conditions the visual angle should subtend at least 15 minutes of arc.
Under degraded viewing condistions, what is the visual angle?
Under degraded viewing conditions (e.g. low light levels) the angle should subtend at least 21 minutes of arc.
What is the minimum perceptible visual angle?
Minimum perceptible visual angle is approximately 1 second of an arc (e.g., a thin wire against a bright sky)
What is the visual field for color?
Color is perceived for about 60 degrees on either side of a fixed point when the eyes are motionless
Are all receptors in the retina equally sensitive to color?
Not all receptors in the retina are equally sensitive to color.
What is color sensitivity with the eye motionless?
What are three common issues with vision design?
1) Visual acuity
2) Visual defects
3) Color deceptiveness
What are the visual defects?
How is visual acuity measured?
It is measured with the Snell eye chart.
What are the two types of color deceptiveness?
1) Color weakness
2) Color blindness
What is color weakness?
Color Weakness: people are capable of seeing all colors, but tend to confuse some of them, ESPECIALLY under dim Light
What is color blindness?
Color Blindness: People who are color blind tend to confuse red, green and gray. In some cases no color perception (3 in 100,000).
What is focal vision?
Focal: fine detail and pattern recognition.
What is ambient vision?
Ambient: peripheral vision for orientation and ego motion.
Focal (aprox. 2 degrees of vision, i.e. fovea) and ambient vision appear to define separate resources in the sense that:
- Support efficient time-sharing
- Characterized by qualitatively different brain structures
- Associated with qualitatively different types of information processing
