Distortions of perceptions – visual illusions.

A visual illusion is a consistent perceptual error in interpreting real external stimulus. This is different to hallucinations where people perceive objects/events that have no external reality.

When we experience a visual illusion, the stimulus provides us with cues that mislead our perception. As a result, a mismatch between our perception and the reality of the actual stimulus occurs. Although perception of common stimuli is often described as unique, this is not the case with a visual illusion. With visual illusions, all individuals tend to be misled by the stimulus in the same way. In a visual illusion, motion, length, position, curvature and direction of the stimulus is consistently misjudged.

Define visual illusion.

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The Müller-Lyer Illusion

The activity requires the use of an apparatus that allows students to estimate the length of one line against the length of the other. What makes this tricky is that one line has “arrow-heads” while the other has V-shapes emitting from its ends. These differing line ends, for reasons that have been debated for decades, seem to trick the perceiver into perceiving one line is longer than it actually is and/or the other as shorter. This is what the lines look like:

Which line looks longer to you?

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One explanation of this illusion is that it is based on our experience with the angular lines created by the inside and outside corners of

buildings. These angular lines suggest either a further away line or a closer one; if we interpret a line of the same length on the back of our retina as being further away, we shall naturally perceive it as longer. Think about this while looking at the pictures below.

The lines in the first photo are similar to the line with the arrowheads. Since we perceive this building corner as pointing towards us, we interpret the vertical line as shorter than that of such a corner that is receding into the distance.

On the other hand, if the corner we are viewing is pointing away from us, as in the second photo, the lines created by the angles of the corner are like the V-shaped line. We interpret this line as being further away and therefore longer, according to this theory of why the illusion occurs.

http://psychologyrats.edublogs.org/about/visual-perception/the-muller-lyer-illusion/

In your own words, explain why this illusion occurs.

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Ames Room Illusion

https://www.youtube.com/watch?v=gJhyu6nlGt8

What happens in this illusion?

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How is this illusion explained?

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