Mental Rotation

Introduction

How do we work with mental images? Consider F1.1 Rotation task. When you did that task, it probably felt like you were taking one object and rotating it in your mind, much as you would if it were a real object in space. How can we test that intuition? Roger Shepard and Jacqueline Metzler realized that they could measure the time it takes to make the decision called for in this task. If mental rotation really is like physical rotation, it should take longer to make large rotations than small ones. (By the way, this is the same Roger Shepard who devised the ambiguous tones used in B1. Pitch Perception.)

Experiment

You can now do an experiment based on Shepard and Metzler (1971). Your reaction times will be measured, so it is important to answer quickly (use the arrow keys on the keyboard as instructed). However, your results will not be meaningful if you make many errors, so do not respond until you are sure of your answer. It may take a few seconds to do some of these, so don’t feel that you must respond instantly. You will have 10 practice trials before collecting data and can do more practice if you wish. Do F1.2 Object rotation (60 trials, ~15 minutes).

Discussion

Shepard and Metzler (1971) found a linear relation between reaction time and the amount of rotation required to make the two images congruent. They found a rate of 60°/s with very clean consistent data. Your data were probably not quite so clean and linear. There are several likely explanations. First, each of Shepard and Metzler’s subjects did 800 trials. Second, they were highly trained in the task, so they reacted very efficiently and made few if any errors. If you made many false-same errors, your rotation rate may have faster than 60°/s but with a lot of variation (compare rotation rates and errors in F1.4 Rotation results, for example).

Further Exploration

• Subjects in Shepard and Metzler’s original study practiced beforehand and did over 800 trials in the experiment itself, with rotations separated by 20° intervals. Your experiment was much shorter, with 45° intervals and 10 trials per rotation. Half of those trials, where the shapes were equal, were used in the analysis. You can improve your data set by increasing the number of trials per rotation:
  F1.2 Object rotation (120 trials, ~25 minutes)
  F1.2 Object rotation (240 trials, ~40 minutes)
  F1.2 Object rotation (480 trials, ~60 minutes)
• These experiments used representation of 3-dimensional objects. Would you expect the task to be easier with flat shapes rotated only in the plane of the screen? You can test that with rotated letters:
  F1.3 Letter rotation (50 trials, ~15 minutes)
  F1.3 Letter rotation (100 trials, ~25 minutes)
• Many studies find that males are, on average, faster or more accurate than females at mental rotation tasks (e.g. Tapley & Bryden, 1977; Voyer et al., 1995; Lauer et al., 2019). Test this by combining data from your class.
• If your class is large enough, compare right- and left-handed people, those who do or do not play video games, or any other groups you can think of.

Questions

1. Why is it important, in a study like this, that subjects be highly trained before generating data? Is there a risk that training might cause unrealistic results?
2. Your results were given in the form y = ax + b. What do a (slope) and b (intercept) represent in terms of reaction time and rotation speed?
3. When calculating the rotation rate, only data from trials where the two objects were the same could be used. Why?
4. Why would your rotation rate increase if you made more errors?

References

• Lauer JE, Zhang E, Lourenco SF (2019). The development of gender differences in spatial reasoning: A meta-analytic review. Psychological Bulletin 145:537-565. []
• Shepard RN, Metzler J (1971). Mental rotation of three-dimensional objects. Science 171:701-703. []
• Tapley SM, Bryden MP (1977). An investigation of sex differences in spatial ability: Mental rotation of three-dimensional objects. Can J Psychol 31:122-130. []
• Voyer D, Voyer S, Bryden MP (1995). Magnitude of sex differences in spatial abilities: A meta-analysis and consideration of critical variables. Psychological Bulletin 117:250-270. []