103 Lab 6 Physiology of Vision OPTICAL ILLUSIONS Observe the illusion on Figure 6-18.
39. How does the size of the far cylinder appear in relation to the close cylinder? Figure 6-18
Illusion Card
Solution
Optical illusion
39) In the illusion card shown in the figure, three cylinders are exactly of the same size and are
also exactly at the same distance from your eyes. But, the right-most cylinder appear to be largest
and left-most cylinder appear to be smallest among the three.
40) Perception of size of an object is the basic component of perception of the object. It depends
on several factors. The visual angle subtended by the object on the retina is one of the factor.
The right-most cylinder appear to be largest and left-most cylinder appear to be smallest in the
illusion card because the lines in the background trick your visual system into judging that the
cylinders are at different distances. The retinal images corresponding to the three cylinders are
exactly of the same size. If one of the cylinders is judged by our distance perception system as
being the farthest away, that cylinder is perceived to be the largest. Here, the cylinder at the
right-most subtends larger visual angle and hence, it appears larger.
41) Visual illusions occur due to properties of the visual areas of the brain. This is because it is
the brain that receives and process the information. The information gathered by the eye is
processed by the brain, creating a perception that in reality does not match the true image.
42) Visual ability to perceive the world in three dimension and ability to gauge how far away an
object is termed as depth perception.
Some of the factors affecting depth perception include:
1. Stereo vision. It provides the brain with most signals with respect to distance to objects.
2. Focus of the eyes
3. Stimulus size
4. Viewing distance
5. Duration of exposure
6. Separation magnitude
39. How does the size of the far cylinder appear in relation to the close cylinder? Figure 6-18
Illusion Card
Solution
Optical illusion
39) In the illusion card shown in the figure, three cylinders are exactly of the same size and are
also exactly at the same distance from your eyes. But, the right-most cylinder appear to be largest
and left-most cylinder appear to be smallest among the three.
40) Perception of size of an object is the basic component of perception of the object. It depends
on several factors. The visual angle subtended by the object on the retina is one of the factor.
The right-most cylinder appear to be largest and left-most cylinder appear to be smallest in the
illusion card because the lines in the background trick your visual system into judging that the
cylinders are at different distances. The retinal images corresponding to the three cylinders are
exactly of the same size. If one of the cylinders is judged by our distance perception system as
being the farthest away, that cylinder is perceived to be the largest. Here, the cylinder at the
right-most subtends larger visual angle and hence, it appears larger.
41) Visual illusions occur due to properties of the visual areas of the brain. This is because it is
the brain that receives and process the information. The information gathered by the eye is
processed by the brain, creating a perception that in reality does not match the true image.
42) Visual ability to perceive the world in three dimension and ability to gauge how far away an
object is termed as depth perception.
Some of the factors affecting depth perception include:
1. Stereo vision. It provides the brain with most signals with respect to distance to objects.
2. Focus of the eyes
3. Stimulus size
4. Viewing distance
5. Duration of exposure
6. Separation magnitude
