Introduction to Visual Illusions

 

 

 

OPTICS

-- the study of the behavior of light; it is a branch of physics

PROJECTIVE GEOMETRY

-- One LAW of PROJECTIVE GEOMETRY: the size of the objects in a projected image vary inversely with the distance portrayed in the scene.


If we are trying to represent 3 men of the same height, the picture on the right VIOLATES the laws of projective geometry.

So this is an illusion, of sorts. The pictures of the men are in fact exactly the same size, but the one on the end APPEARS taller.

Illusions, then, are especially important in the study of vision, because they provide dramatic clues concerning the underlying assumptions that are built into our visual systems.

The Müller-Lyer Illusion

The Linear-Perspective Hypothesis

A linear perspective drawing is produced when an artist draws on a flat (two-dimensional) surface and uses line drawings to create objects that appear to have three-dimensions.

The artist takes advantage of projective geometry.

Our visual system expects objects that are further away to appear smaller.




 

 

Hypothesis Testing

The linear perspective hypothesis makes sense, but is it a good explanation of the illusion?

Experimental tests of this kind can provide some evidence in support of a hypothesis (like the linear pespective hypothesis), but an hypothesis can never be "proven" because other explanations always remain possible.

 

 

Methods Used to Study Vision

INTROSPECTION

-- Paying careful attention to the subjective character of your own experiences.

EXPERIMENTAL PSYCHOLOGY -- performing experiments on living subjects (esp. human)
-- present human subjects with stimuli, observe their behavior

NEUROSCIENCE RESEARCH

-- experiments on the brain (electrodes,MRI, etc)

COMPUTER MODELING

-- creating computer programs that model the workings of the human mind

 

Proceed to NEXT LESSON.