120 Statistics Vision II
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High Resolution Vision
For a full visual examination of objects, we must move our eyes so that all parts of the object's image fall for a time on the fovea. We do this by moving our eyes from place to place over the object in a jerky fashion.
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Eye Movements
Fixation : A period of time when the eye is focused on a single point. Saccade : An eye motion from one fixation point to another. Normal vision alternates between saccades and fixations, with each lasting just 100ths of a second.
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Eye Movement Studies
An image is presented to a subject. The subject may (or may not) be given a specific task to carry out. A record is made of where the subjects eyes are directed as they study the image.
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Studies by I. L. Yarbus
Experimental work carried out in Russia during the 1940s and 1950s. A suction "cap" was fitted directly onto a subject's eyeball. A small mirror on the cap reflected a light beam on to photo-sensitive paper.
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How We Look At Faces
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An Unexpected Visitor by I. E. Repin.
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Examine the picture
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Decide how wealthy the family is
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Estimate the ages of the people in the room
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Decide what the family were doing before the visitor arrived
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Remember the position of the objects and people in the room
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Estimate how long the visitor has been away
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Trace the figure right-to-left, then trace the sloping line and follow its direction beyond the horizontal line.
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Seeing in Three Dimensions
projected Images through the pupil on to the retina are two dimensional. When we look at the world, we perceive it as three dimensional. How do we achieve this sense of depth?
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The Eye as a Pinhole Camera
Because light passes through a narrow hole (the pupil) before begin projected on the retina, the eye acts as a pinhole camera. Left/Right and Up/Down are inverted.
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Perspective
h
h'
d'
d
h h = d d
h =
d h d
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Perspective Example
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Projections
Orthographic
Perspective
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Perspective as a Depth Cue
Perspective gives us information about depth for objects at near to medium distances. When there is any hint of perspective, our visual systems try hard to extract depth information from the scene. We can be fooled by the appearance of perspective.
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The Ames Room
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The Ames Room Explanation
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Stereoscopic Vision
Each of our eyes occupies a different position in space. When we look at an object, each eye sees a slightly different image....