time and reason for the brain to determine that a picture of a lake in the
desert is just a mirage and does not actually exist even though the eye will
continue to transmit pictures of the lake.
(b) Accommodation: It is necessary for both eyes to converge on
an object to see it clearly. Therefore, the transition from focusing on a
close object to a far object or from a far object to a near object takes
(c) Color: Color can both help and hinder visual perception.
The contrast between some colors (black and white) can clarify the
perception. However, the contrast between other colors may hinder visual
perception (camouflage) or confuse visual perception (clashing of colors).
(2) Depth perception: Depth perception requires the use of numerous
visual cues. The interpretation of these cues requires the use of central
vision and good illumination. The binocular cues required for depth
perception are accommodation and stereopsis. Monocular cues are also
required for depth perception.
(a) Accommodation. Depth perception is determined at a
subconscious level by the comparison of differences between the image size
of an object projected on the retina and the known size of the object.
(b) Stereopsis. Each eye transmits a different picture to the
brain. The difference in the angle of the two pictures is combined in the
brain to form a 3-dimensional picture of what is being seen.
(c) Monocular cues. Monocular cues are those cues that can be
perceived by the use of one eye. These cues were presented in Lesson 2
(interposition of objects, geometric perspective, motion parallax, retinal
Erroneous visual perceptions are experienced in most modes of flight,
being most pronounced in autorotations.
a. Wider Than Normal Runway. When a pilot experiences this illusion
his perception will be that he is lower than normal due to his relatively
smaller visual reference angle to the sides of the runway at equivalent
heights above the ground. He tends to pull pitch too soon which may result
in a hard landing.
b. Narrower Than Normal Runway. Here, Just the opposite occurs. The
pilot may perceive that he is higher than normal due to his relatively
larger visual reference angle to the sides of the runway. This may cause
him to pull pitch too late causing a faster than normal landing speed.