You may have noticed that Cognitive Daily hasn’t exactly been living up to its name recently. During the summer vacation season, we travel quite a bit, so it’s difficult to maintain our usual pace of posting. But along the way we’ve collected some great photos, and we’ll try to share a few of them with you when it’s relevant. For example, take a look at this picture I took in Maine about a week ago:

It’s a lovely section of the Maine coast, readily identifiable by anyone as “shoreline.” Earlier in the summer we vacationed with our nieces on the North Carolina coast, just a few hours’ drive from where we live:

Once again, this is clearly a shoreline, but it’s quite different from the Maine coast. Many studies have offered evidence that recognizing a general image category like “shoreline” uses a different mental process than recognizing a specific image — the Maine coast photo versus the North Carolina coast photo. The most convincing evidence comes from a 1999 study by C.J. Marsolek. Marsolek showed people pictures of many different items and asked them to name them. Then the same people saw pictures in either the left or right visual field. Some of these pictures were identical to the first set, but others were in the same category (like “piano” or “dog”) but a different exemplar (a grand versus upright piano; a pekingese versus an Irish setter). Objects in the left visual field (which corresponds the right hemisphere of the brain) were recognized better when they were exactly the same as previously-viewed photos rather than different examples of the same category. So the right hemisphere seems to be better at processing specific examples, while the left hemisphere is better at processing general categories.

So is this difference in processing general versus specific examples found only in the visual system, or does it extend to all our senses?

Julio González and Conor T. McLennan adapted Marsolek’s procedure and played a variety of sounds on headphones to 24 undergraduates. First the students listened to 24 different 1- to 6-second sound clips (bagpipe, jackhammer, monkey, and so on) and had to identify each one. Then they heard 24 shortened clips — just the first 0.75 seconds of each clip. Eight were clips they had heard before, eight were different exemplars of the same sounds, and eight were completely new sounds. Half the time the sound was played back through the left ear, and half the time it came through the right ear. Once again, they were asked to identify the sounds. Here are the results:

The graph shows the accuracy on the second test, with the shortened clips. When the sounds were played through the left ear, the students were significantly more accurate at recognizing the identical sounds they had heard before compared to different exemplars of the sound category. But there was no significant difference in accuracy when the sounds were played through the right ear, as long as they had heard one exemplar from that sound category before.

When the task was made more difficult, the results were even more dramatic. This graph shows the results for a new group of students who had to identify the shortened clips while a masking sound was being played in their other ear:

Gonzalez and McLennan say that both of these experiments demonstrate that the brain identifies sounds using two different processes, just like the visual system. One system is used for identifying the general category of a sound, and one system is used for identifying particular, specific sounds. The general system is housed in the left hemisphere (which processes sounds coming through the right ear), and the specific system is housed in the right hemisphere.

González J, & McLennan CT (2009). Hemispheric differences in the recognition of environmental sounds. Psychological science : a journal of the American Psychological Society / APS, 20 (7), 887-94 PMID: 19515117