What is a visual expert?

ResearchBlogging.orgLast week, we presented research by Miranda Scolari's team about visual expertise and visual short-term memory. Their conclusion: "experts" don't have a larger visual memory capacity than non-experts, they just have the ability to process more details. Scolari's team was working under the assumption that all humans (or at least all the students in their experiment) are face-recognition experts.

It's true: we're amazingly good at recognizing faces we've seen before. Think how much easier it is to remember a face you've seen than it is to remember the name that goes with the face. But surely we can be visual experts in other types of objects besides faces, right? Otherwise Scolari's study would apply to faces and nothing else.

To find out, a team led by Kim Curby did a similar study, using car experts instead of face experts. They tested 36 volunteers on their knowledge of cars by showing them photos of cars from two different years; they had to say whether the cars were they same or different model. The highest scorers were the experts, and the lowest scorers were "novices."

Curby's memory-test was similar to the example I showed you last week:

Take a look at this quick video. You'll see a set of six small images, arranged in a circle, for 1 second. Then the screen will go blank for 1 second. Finally, one image will reappear in the place of one of the first six pictures. Your job: indicate whether the final image is the same or different as the image that originally appeared in that same spot.

Click here to view the movie (QuickTime required)

But there were a few differences. First, Curby's team asked viewers to repeat a pair of numbers like "7 2" while they watched the video. Second, half the time the viewers saw faces, and half the time they saw cars (both of which sometimes appeared upright, and sometimes upside-down). Finally, viewers saw the images for varying lengths of time: either 0.5 seconds, 2.5 seconds, or 4 seconds, instead of the 1-second viewing time in my example and the Scolari et al. study. Here are the results for faces:


The longer the faces were present, the larger the short-term memory capacity. But whether or not viewers were car experts, they were significantly better at remembering upright faces than upside-down faces. Now take a look at the results for cars:


This time, there's a big difference in the results for car experts versus novices. For novices, there was no difference in the number of cars in short term memory when they were inverted, but experts could retain significantly more upright cars than upside-down cars. This result is nearly identical to the result for faces -- so both car experts and face experts show the same pattern in short-term visual memory. For this kind of memory, this result suggests we can say that being a face expert is just like being a car expert.

But maybe car experts are just relying on their long-term memory to supplement short-term memory: They know what a Toyota Matrix and a Ford Explorer look like, so that's where their advantage comes from.

Since there is a limited total number of different cars, it's difficult to say whether this is true for car experts. But as "face experts," we might have an advantage for faces that we know well. So Curby's team developed a neat control experiment. They created 'faces' made from photos of celebrities. For forty well-known celebrities like Julia Roberts and Elijah Wood, they found three different photos of their faces. Just 1/3 of each photo was used: the eyes, nose, and mouth. Then they were reassembled in two different ways:


In the two pictures on the left, the three clips were combined to form one "familiar" face -- a complete photo of Elijah Wood and Julia Roberts. In the pictures on the right, parts of three different celebrities were combined to make "unfamiliar" faces. Then the same test was given as before, using these faces. Here are the results:


There was no significant difference in the results for familiar and unfamiliar faces, suggesting that for visual short-term memory, expertise isn't about prior knowledge, but ability to process visual images more efficiently.

Kim M. Curby, Kuba Glazek, Isabel Gauthier (2009). A visual short-term memory advantage for objects of expertise. Journal of Experimental Psychology: Human Perception and Performance, 35 (1), 94-107 DOI: 10.1037/0096-1523.35.1.94

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