Muller-Lyer Illusion
What methods did we employ in this experiment?
On each trial, two vertical lines were shown. One line had the outward-drawn wings to make the Muller-Lyer stimulus, and was always the same size. The other (comparison) line had no wings and its length varied from trial to trial. Your task was to choose which vertical line was longer on a given trial.
The independent variable in this experiment was the length of the comparison line. The dependent variable was the proportion of trials in which you reported that the Muller-Lyer line was longer than the comparison line.
What do we predict participants will do? Why?
The graph, below, plots the proportion of trials in which the Muller-Lyer line was reported as longer than the comparison line. The Muller-Lyer line was always 100 pixels long. The x-axis gives the pixel length of the comparison line. The Muller-Lyer illusion is that the line with wings appears to be longer than a line without wings. Typical data shows that proportions are close to zero on the left and increase toward one on the far right. If there was no illusion, the line would be at approximately 0.5 for a comparison line with a length of 100 pixels. Evidence of the illusory effect would be when the 0.5 proportion is for a pixel length greater than 100 pixels.
How robust is this effect? Are there limits to this effect?
The Muller-Lyer illusion is one of the most studied illusions in cognitive psychology. It has been replicated thousands of times. The strength of the illusion can be varied by changing the properties of the line, the wings, and context in which the stimuli are placed.
Experiment results
Data summary for experiment Muller-Lyer Illusion. 2013-09-06 16:40:17 Eastern Daylight Time
The graph below plots the proportion of trials you chose the vertical line without wings as bigger than the line with wings. The line with wings was always 100 pixels long. The x-axis gives the pixel length of the line without wings. The Muller-Lyer illusion is that the line with wings appears to be longer than a line without wings. Typical data shows that proportions are close to zero on the left and increase toward one on the far right. If there was no illusion, the line would be at approximately 0.5 for a line without wings length of 100 pixels. Evidence of the illusory effect would be when the 0.5 proportion is for a pixel length greater than 100 pixels.
If the effect exists, it may be stronger for the group or global averages than for your individual data.
