The depth perception cue employed in the old-fashioned stereoscopes but not
in plain photographs is: (a) variation in color, (b) variation in sharpness, (c) binocular disparity, (d) previous knowledge. (Choose one.)
The depth perception cue employed in the old-fashioned stereoscopes but not in plain photographs is (c) binocular disparity.
The depth perception cue employed in the old-fashioned stereoscopes but not in plain photographs is (c) binocular disparity.
To understand why this is the correct answer, let's break down the options:
a) Variation in color: Variation in color is not a depth perception cue. It may provide information about objects or surfaces, but it doesn't specifically help us perceive depth.
b) Variation in sharpness: Variation in sharpness can provide some depth information, as objects that are closer tend to appear sharper than objects that are farther away. However, both old-fashioned stereoscopes and plain photographs can depict variation in sharpness, so it is not a cue that is unique to stereoscopes.
c) Binocular disparity: Binocular disparity refers to the slight difference in the images seen by each eye due to their slightly different perspectives. This disparity is used by our brain to perceive depth in three dimensions. In old-fashioned stereoscopes, two slightly different images are presented to each eye, creating a more pronounced binocular disparity and enhancing the perception of depth. Plain photographs, on the other hand, do not have this feature, thus lacking binocular disparity as a depth cue.
d) Previous knowledge: Previous knowledge can influence our perception of depth in certain situations, but it is not a depth perception cue that is specific to either stereoscopes or plain photographs.
Considering the explanations above, the correct answer is (c) binocular disparity.