Pitfalls to Problem Solving: Learn It 4—Choice Blindness

Two Variables: Time and Similarity

In the 2005 study, Johansson and Hall looked at two interesting variables that might influence the detection of the mismatch. First, how rushed were the participants to make their decision? They gave some people only 2 seconds to choose the more attractive person. Others were given 5 seconds, and another group was given as long as people wanted (free choice). Should more time make someone more likely or less likely to notice that they have been given the picture they did not choose?

The second variable was how similar the two faces were to one another. In some cases, the two faces were similar to each other in general features, while in other cases the two faces were more distinctly different. If the two faces are quite different, how should that affect your ability to notice?

Two sets of images. One shows incredibly similar faces of caucasian women, while the next pair shows dissimilar female faces.
Figure 1. Johansson and Hall wanted to know if people were more likely to notice a similar or dissimilar image when shown a picture they did not choose.

Results

If we put the two manipulated variables (time and similarity) together, that gives us six conditions:

Six conditions with variance in two categories: Similarity of two faces, and time to choose. The six conditions are as follows: 2 seconds to choose similar faces, 2 seconds to choose dissimilar faces, 5 seconds to choose similar faces, 5 seconds to choose dissimilar faces, unlimited time to choose similar faces, unlimited time to choose dissimilar faces.
Figure 2. The six conditions of the experiment show that people were shown either similar or dissimilar faces, or given various amounts of time.
In the figure below, adjust the bars to fit your predictions about how often people would notice the picture switch. Higher bars mean people more often noticed that the cards had been switched. Lower bars mean that people made one choice and didn’t notice when they were given the wrong picture. This isn’t easy because you need to take into account the two variables: (1) the amount of time looking at the pictures before your choice and (2) the similarity of the faces in the pictures.

What Do These Results Tell Us?

With just these results, we are still a long way from understanding choice blindness. The experiment you just read takes us a couple of steps in the right direction. First, the similarity of the faces is (surprisingly) not a particularly influential factor. This does not mean that the case is closed and similarity is unimportant, but it does suggest that confusion due to similarity may not be the whole story.

The amount of time participants had to choose did have a big influence on detection of a switch in faces. When the participants were rushed (2 second condition), the chance of detecting a change was very slight. Given 5 seconds, detection improved, but not by a great amount. Unlimited time to choose made a substantial difference, but detection was still only around 25%. These results suggest that time to choose may be an important factor, but it is not the whole story. Furthermore, we are still not sure what it was about the extra time that led to improved detection. Did more time allow the participants to remember the faces better? Or perhaps their memory for faces was not improved, but they had more time to think of reasons they preferred one person over the other (her earrings, the way her hair flowed, a look in her eyes). These preferred features could signal to them that something was missing when the wrong picture was presented.

  1. The results are more complex than the figure suggests. The data shown above are limited to first detections of the switch in pictures. After people notice that there has been a switch, they tend to be a bit suspicious and they are more vigilant about noticing changes. If all trials are taken into account, the data are still similar to these, but not quite as pretty. See the original paper for all the details. ↵