Learning Objectives
- To understand how previous experience can influence perception.
- To understand what factors, contribute to mental shortcuts in making predictions for action.
- To practice how to experimentally isolate variables that contribute to perceptual effects.
Materials
- Whiteboards
- Dry Erase Markers and Erasers
- Tomato cans – A big and a small, per table.
- Kitchen scale.
- Cloth bags with drawstrings – two per table.
Overview
In this lab, students will experiment with the size-weight illusion and then compare the magnitude of the effect to when procedures are introduced to attenuate this effect. Finally, we will discuss the nature of illusions, and how previous life experience or other types of mental shortcuts can often lead to conflicts between material reality and perception.
Time Allocation:
| Activity | Time Allocation |
|---|---|
| Introduction | 5 Minutes |
| Activity 1: Group Discussion | 10 Minutes |
| Activity 2: The Tomato Can Experiment | 10 Minutes |
| Activity 3: Removing the size-wight illusion | 15 Minutes |
| Debrief and Wrap-Up | 5 Minutes |
| Submission Time | 5 Minutes |
Introduction (10 min)
After a short overview of the topic for the lab, students will be presented with this short prompt:
“You have a flimsy red Solo cup in front of you. You are somehow able to pick it up and drink without squishing the cup and spilling your drink down your front. How do you do this?
How does your brain know how to lift it smoothly without spilling on your first try?
What sources of information is your brain using to accomplish this deceptively delicate task?”
Activity 1: Group Discussion (10 min)
Based on the prompt, students will discuss their answers to the question and make a list of all possible factors they can think of. This will then be taken up as a whole class for the following discussion topics:
- What were the points your group noted down?
- What senses did you list in your notes?
- Are there other sources of information you noted beyond sensory information?
Activity 2: The Tomato Can Experiment (10 min)
Students will take turns lifting the two tomato cans on their table at the same time and rating their perception of their weight according to the scale presented on the slides. They will then tally up the ratings for all group members and compute a group average.
Afterwards, the results obtained will be discussed as a class.
Activity 3: Isolating the Size-Weight Illusion (15 min)
Students will repeat the previous experiment, now with the difference of the tomato cans being placed inside the provided cloth bags. Students should close their eyes and have someone else in the group place the bags on their hands by the drawstrings, so that they have no idea, either by vision or touch, about which can is in which bag.
Afterwards, a class discussion will return to similar points as the previous one, with the addition of a final step of weighing the cans on the provided digital scale.
Students should conclude that both cans weigh the same, at which point the discussion should revolve around how the procedures in the second experiment may change the perception of their weight, and what are the factors that contribute to this illusion.
Debrief and Wrap-Up (5 min):
After confirming that the phenomenon observed is a type of illusion, the whole class should discuss what are the contributing factors for producing this effect.
A main point to approach here, is that our brains make use of previous knowledge or pre-existing expectations to create mental shortcuts in more efficient perception, even if that may result in certain moments of conflict.
Final Submission Question (5 min):
Can you think of other situations where our brains make use of these “shortcuts” in perception? Give an example and discuss what are the advantages of the mental shortcut in that situation.