The Pip and Pop Effect: Sound helps us find visual changes

Take a look at the following picture:


Your job is to look for the one line that's either perfectly horizontal or perfectly vertical. It took me about 25 seconds to find it. Can you do better?

How about now?


A little easier, right?

ResearchBlogging.orgBut the task can be made difficult again by randomly changing the colors of all the other lines in the picture, a few at a time. Now you don't know which flash to look at and the task is just as hard as it was before.

But a team led by Erik Van der Burg found an interesting way to make the task easy again: just add a clicking sound that plays only when the horizontal or vertical line is displayed. They call this the "Pip and Pop Effect." The question which then arises is, why does the sound help?

The researchers showed displays like this to six paid volunteers, who were instructed to focus on the central dot and try to identify as quickly as possible whether the key line in the picture was horizontal or vertical. Half the time a tone was played in sync with the horizontal/vertical line changing colors. This graph shows the results:


As you can see, viewers were dramatically -- and significantly -- faster when the sound was played. The sound seemed to help them correctly identify the line. But can only sound help? Perhaps some visual signal would also help viewers locate the change.

The researchers recruited six new volunteers to watch a different set of displays. This time, the central dot flashed when the horizontal/vertical line changed colors. Did this help viewers spot it? Here are the results:


There was no significant difference between when the central dot changed along with the horizontal/vertical line and when it did not change at all. So while an audio cue helps viewers find the dot, a visual cue does not.

But how is the sound helping? Does it just motivate people to search a little harder, or are its effects automatic? In a new study, 16 new students participated in one of two experiments. The lines changed and were accompanied by clicking sounds, as before, but for one group of observers the click was relevant 80 percent of the time: it actually coincided with the horizontal/vertical line changing, while the other 20 percent of the time the clicks were irrelevant. For the other group of observers, relevance was reversed: the click was only relevant 20 percent of the time, while the other 80 percent of the time the clicks were irrelevant. Here are the results:


Even when the clicks were relevant just 20 percent of the time, the students were still significantly faster at recognizing the horizontal/vertical line during relevant clicks.

The researchers say this suggests that the connection between the audio cue and visual search is automatic. Even though the sound has nothing to do with the location of the change, just hearing a sound while the relevant object changes helps viewers to spot it more quickly.

Van der Burg, E., Olivers, C., Bronkhorst, A., & Theeuwes, J. (2008). Pip and pop: Nonspatial auditory signals improve spatial visual search. Journal of Experimental Psychology: Human Perception and Performance, 34 (5), 1053-1065 DOI: 10.1037/0096-1523.34.5.1053

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Obvious interpretation: a disembodied click primes the attention system (which is multimodal) at those particular times, making that particular blinking point stand out further. A visual blink - with a definite spatial position - also primes the system but distracts from the correct point. The clear follow-up experiment would be to play a click sound at a particular point in space separate from the correct line and see if the effect diminishes.

I found the line in the first display in a couple of seconds, but you did not say we were supposed to fixate the central dot. If I had done that, I very much doubt that I could have found the (unblinking) horizontal line at all.

Interesting -- I design e-Learning interfaces, and attention focus and managing cognitive load are constant issues. Using sound as a focusing device could be very helpful.