Visual And Visual Perception Flashcards
What is the cornea
This is the transparent layer at the front of the eye with the purpose of refracting light.
What is the lens?
It changes the focal length of the eye, focusing the light that passes through it to project a clear image onto the retina.
What is the retina?
A light-sensitive layer of tissue that translates images into electrical neural impulses which are then sent to the brain to process
What is the fovea?
It is an area on the retina where visual acuity is at its highest and the cone cells are located
What is the optic nerve disc?
This is where the optic nerve enters the eye. The eye is unable to produce an image at this point of the eye and as such it forms a permanent blind spot. The brain will generally fill this void with what it “expects” to see.
What are rod and cone cells in the eye?
Rod and Cone cells are photoreceptor cells located in the retina with the sole purpose of allowing us to see.
What’s the difference between cones and rods? (CONES) (5)
- Used for direct vision in good lighting
- Good acuity and fine detail
- Colour sensitive
- Single connection to nerve fibre (1:1)
- Approx 6-7 million cells per eye
What’s the difference between cones and rods? (RODS) (5)
- light sensitive, good for poor lighting
- good at detecting movement (peripheral vision)
- insensitive to colour
- bundled nerve connection to nerve fibre (17:1)
- approx 120 mill cells per eye
Explain the process of dark adaptation
Eye adapts to low light in a number of stages
First, pupil opens to allow more light into retina. (Less than a second)
Second, when cones aren’t stimulated by sufficient light will begin to shut down and stop sending info to the brain, (7 minutes)
Last, as cones shut down, rods take over. (Takes rods 30 minutes)
State the normal time for full night vision adaptation
30 minutes
Identify precautionary actions to protect night vision adaptation
- Adjust instrument and cockpit lighting to the lowest level possible
- avoid inhaling CO from smoking or exhaust fumes
- get enough vitamin A
- avoid exposure to bright lights
Describe the limitations of the eye in terms of the ability to discern objects at night and day
During the day, objects can be identified relatively easier at distance with good visual acuity in colour. This is a result of the cones being activated.
Sometimes, however, even with good lighting, e.g. glare, reflection of surfaces/objects, excessive illumination, this does not equate to the same identification range; instead, may cause uncomfortable squinting, watery eyes and temporary blindness.
Describe limitations in the eye of terms of poor lighting
in poor lighting conditions and/or at night, dim or unlit objects cannot be identified at the same range, with the visual acuity being poor.
In addition, the colour perception is very poor in these conditions.
Describe the factors for selecting suitable sun glasses (5)
- Incorporate 100% UV protection
- Avoid tints
- Avoid Polaroid
- Avoid photochromatic
- Avoid thick frames
Describe the resting state focus and its effect on object detention. (3)
Times of low visual stimulus, the eye will take up its relaxed resting state focal length of approx 3 m. Known as empty field myopia.
Eyes fail to detect any object past this distance
Pilot stares but sees nothing until it enters the visual field which could potentially be too late
Explain effective visual search techniques
Scanning a 20 degree sector every 2 seconds
Describe the visual cues (14)
- Elevation
- Runway size
- Runway shape
- Runway slope
- Runway surface
- Terrain and surrounding areas
- Time of day
- Aiming point
- Ground speed
- Approach profile
- Centreline tracking
- Windsock
- Peripheral vision
- Horizon
Explain autokinesis and its prevention
At night a single light source can appear to move around even if its stationary.
Maintain frequency eye movements, focus on a stationary landmark, monitor instruments to resolve conflict.
Explain stroboscopic illumination illusion/flicker vertigo
And how to avoid and cope it
When a bright light source is flashed into the eye at a rate of 10 - 30 flashes per second.
Occurs when the sun is shining through the propellor blades and can occurs within seconds and cause vertigo, convulsions and unconsciousness.
Turn away from the light source or block the light, Don’t close eyes.
Describe the break-off phenomenon and how to avoid and cope
Sometimes experienced by pilots flying solo at high altitudes.
Described as a feeling of physical separation from the earth, a feeling of remoteness, loneliness, insecurity and anxiety or exhilaration.
Increase workload and keep busy, or descend.
Explain the black hole phenomenon and how to avoid.
At night, flying in an area where there are few lights on the ground to aid depth and height perception, or over water.
A nigh approach with no lights before the runway and city lights or rising terrain in the background can produce an illusion on being high on final approach resulting in a dangerous undershoot
Avoid long straight in approaches
Describe conditions which can lead to the creation of a false horizon.
Flying over a sloping cloud
Night flying over featureless terrain with ground lights that are indistinguishable from a dark sky with stars
Night flying over terrain with a clearly defined pattern of lights and a dark starless sky
Cause pilot to fly aircraft at banked altitude
Explain relative motion
An aircraft on exact opposite headings tracking towards one and other will not appear to be moving towards each other until the very last second when it may be too late.
Effect of fog, haze, dust on visual perception.
Affect the brains ability to determine relative distance from visual cues due to the atmospheric conditions which interfere with light transmission.
Refer at light rays differently than clear air, causing eyes to perceive that objects are out of focus
What are the optimal characteristics of the windshield
Cleaned before every flight to ensure the best visibility is given.
Windscreen should be flat so that vision isn’t distorted.
Explain the effect of sloping terrain on visual perception.
Sloping up to the approach can cause illusion of being high leading to undershoot.
Sloping down is opposite.
Explain the effect of steep/shallow approach angles
If an approach is required to be made steeper than normal will cause pilot to appear high on approach
If an approach is required to be made shallower than normal will cause the pilot to appear low on approach.
Explain the effect of length, width and texture of the runway on visual perception.
Narrow will look long and skinny, wide will look closer to the ground.
Long will give illusion of being high resulting in undershooting, short will give illusion of being low, resulting in overshooting.
Explain the effect of the intensity of the approach lights. (3)
Very bright lights or lights viewed through extremely clear air, appear closer.
Leading to an approach above the glide slope and early flare.
Low vis tempts you to make approach lights the aim point when they first come into view causing undershooting.
34.18.12 Methods of cockpit/flight deck lighting and the problems associated with each
Light levels in the cockpit need to be bright enough to retain central vision but not so bright that they damage night vision
•Rods are NOT stimulated by light at the red end of the spectrum, this can be useful for crew to illuminate instruments but still receive high acuity from the cones required for reading
Effect of rain on windshield
When flying through heavy rain, any built up water on the windscreen refracts the light rays causing an illusion.
- This can cause the aircraft to appear higher than it is causing the pilot to become low on approach.
- Heavy rain can defuse the lights or increase the lights causing the runway to appear further or closer than it actually is.
