UMass Amherst Research Questions Improved Memorability of License Plates with Symbols

AMHERST, Mass. – Results of a new study by memory experts at the University of Massachusetts Amherst suggest that adding symbols such as stars or circles to license plates does not make them easier for adults to remember than the traditional plate with only letters and numbers.

Cognitive psychologist and memory expert Caren Rotello says, “We found that whether the license plate contained a symbol or not didn’t matter when people tried to remember details. There was no overall benefit to license plates with symbols in our study. Like others, we intuitively had thought symbols might be better recalled, but that wasn’t the case, at least with adults.” She and colleagues plan a future study to test children’s recall of license plates with and without symbols.

A change in license plate design was put forward last year in Massachusetts Senate bill S-2299, but the legislative session ended with no action taken on the proposal. Rotello became interested when a reporter asked her whether changing the state’s license plate to include symbols would make it easier for witnesses at crime scenes to recall details of license plates and vehicles for police.

“I had to say that I didn’t know,” Rotello says. “But that doesn’t mean that I wasn’t interested or that it couldn’t be tested.” She enlisted another UMass Amherst cognitive psychologist, Andrew Cohen, as well as doctoral candidate Lisa Fiorenzo, and set out to investigate.

With data now analyzed from their large study of 619 adults and replicated in two additional investigations with over 300 adults each, Rotello says, “We think it’s important to get this information out now, when there appears to be renewed interest in making these changes. There’s a huge amount of money at stake and it has such clear policy implications. There may be other more effective designs, or other changes we can make to license plates to improve people’s ability to recall them, but adding symbols isn’t the answer.”

Rotello and colleagues tested a large number of participants, which offers high precision for obtaining a reliable result.  Each person was asked to make just one judgment. Study participants between ages 18 and 70 were recruited on Amazon’s Mechanical Turk service and asked to look at one photograph of a license plate mounted on the rear of a car for one, two or three seconds.

License plates in the experiment either had four characters (numbers and letters) and a symbol, five characters with no symbol (to control for length), or six characters (the current plate design). The researchers introduced one more variable, as well, asking about half of participants to view the license plate in reverse, as if in a rear-view mirror. Because the star, heart, square, triangle and circle symbols used in this experiment and proposed in the law are symmetrical, the idea was that they might be easier to remember than characters when seen in a mirror image.

After participants viewed the license plate, they watched a 15- or 30-second video as if sitting in a car riding along a road with the radio on. Subjects then were asked to type three digits on a keyboard and to report the license plate number and color of the car they had viewed.

Results showed clearly that study participants did not remember license plates with symbols better than those with letters and numbers, Rotello says. Also, seeing things in reverse reduced memory for the plate overall, but recall of the symbols and characters was equally impaired. The researchers also looked to see if there were gender or age effects, “but none popped out,” she adds, noting that these subgroups may not have been large enough to detect an effect.

Rotello notes, “We were a little surprised that there’s really nothing there. There’s just no benefit at all to this particular design.”