PSY 323: Perception
Müller-Lyer Illusion
Visit http://elvers.us/perception/ml/ and read the background information. Perform the study by
following the directions on that page. Answer the following questions.
1. Copy and paste the data table on the web page. To receive credit, what you paste must be in a
tabular format that reasonably approximates what is shown on the web page. If you are unable
to copy and paste the data table, create a table and enter the values by typing them:
2. Look at the bottom row of the data table. It shows the mean absolute error for each of the
variants of the illusion. Smaller values indicate that your judgments were more veridical – your
perception of the lengths of the shafts more closely matched the actual lengths of the shaft.
Create an explanation for why the illusion was weaker (less error) for a particular variant of the
illusion than for the classic illusion. In a few sentences, give your explanation. Be sure to state
the variant of the illusion that you are explaining:
3. After completing 25 trials, a link will appear at the bottom of the page. Click on the link and
read the five theoretical explanations that are commonly used to explain the Müller-Lyer
illusion. In a few sentences, compare or contrast your explanation to one of the theoretical
explanations given. Be sure to state which theoretical explanation you are comparing your
explanation to: