Pitfalls to Problem Solving: Learn It 4—Choice Blindness

Two Variables: Time and Similarity

Johansson and Hall’s 2005 study explored why people fail to notice when a chosen option is secretly switched. They focused on two variables that might affect detection:

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.

1. How much time participants had to choose

Participants were assigned to one of three timing conditions:

  • 2 seconds (very rushed)
  • 5 seconds (slightly rushed)
  • Unlimited time (free choice)

If you had more time to inspect the faces, would you be more likely to notice if you were handed the wrong one? That seems intuitive—but the study tested it directly.

2. How similar the two faces were

Each pair of faces was either:

  • Similar (very alike in features)
  • Dissimilar (more noticeably different)

You might predict that if the faces are very different, the swap would be obvious. But is that actually true?

Results

With three time conditions and two similarity conditions, the researchers created six total conditions.

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 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?

These findings deepen—but do not fully answer—the puzzle of choice blindness.

Key takeaways:

  • Similarity isn’t the main factor.

    Even when faces were very different, most people still failed to notice the switch.

  • Time helps, but not dramatically.

    Having unlimited time raised detection to about 25%, but did not eliminate choice blindness.

  • The process behind detection is unclear.

    Extra time might improve:

    • memory for the chosen face,
    • attention to specific features, or
    • the richness of the reasons participants mentally rehearsed.

In short:

Researchers still don’t know exactly which cognitive process drives improved detection.

Choice blindness is surprisingly robust. Even under favorable conditions—big differences between faces and unlimited time—many people confidently explain choices they never actually made.

  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. ↵