When you look at a scene: a building, a park, a mountain, your visual system processes the information differently from when you look at a single object: a face, a pen, or a coffee mug. For example, this first image is from our trip to Prague this past summer:
When you look at this picture, your eye might move first to the bridge, then to the lampposts on the bridge, to the castle in the background, to the overhanging limbs. The next picture is much simpler:
It's a coffee mug, plain and simple. There's not much left to do with it. There are three regions of the brain that respond more strongly to scenes than to objects: the parahippocampal place area (PPA), the retrosplenial cortex (RSC), and the transverse occipital sulcus (TOS).
But do these areas respond differently to different types of scenes? That's what a new study by a team led by Russell Epstein (and including Steve Higgins of Omni Brain) sought to uncover.
They showed student volunteers from University of Pennsylvania and Temple University pictures of buildings from each school's campus. The photos were shown in pairs. Sometimes the photos depicted two different perspectives of the same building, and sometimes the two buildings were different. The volunteers had to decide if the buildings were the same or different while their brains were scanned using fMRI. As you might expect, the responses were faster and more accurate when students were looking at familiar buildings -- those from their own campus -- than when they looked at unfamiliar buildings from the other campus.
Also as expected, the PPA, RSC, and TOS were strongly activated while the scenes were being viewed. Whether the scenes were familiar or unfamiliar, the PPA and TOS were activated at the same level. But what the chart at left shows is the areas of the brain that were more activated when familiar scenes were being rated compared to unfamiliar scenes. As you can see, only the RSC was more active during viewing of familiar scenes. The RSC appears to be a key area of the brain for evaluating unfamiliar scenes.
But what makes a scene familiar? If you've seen the same scene within the past few minutes, does that qualify? Or does the scene have to be a part of your long-term memory?
In a second experiment similar to the first, the team showed a much smaller set of images, repeating the identical scenes in three separate run-throughs. Even when viewers saw the same scenes of unfamiliar buildings again, there was no difference in activity. The effect the team had found in the first experiment appeared to occur solely when scenes were part of the participants' long-term memory.
But the second experiment offered one additional twist. At the end of the session, viewers were asked to perform a new task. They were shown the campus photos, along with photos of famous landmarks like Big Ben and the Taj Mahal. For each photo, they indicated whether it depicted a famous or non-famous building. This time, when they viewed buildings from the unfamiliar campus they had seen in the first part of the experiment, their activation pattern was different, not only in the RSC, but also in the PPA. Now the brain was responding as if these buildings were familiar, when it hadn't only moments earlier. Why would this happen?
Epstein's team could come up with a couple plausible explanations, but no firm answers. The most reasonable-sounding one to me is that viewers were using different strategies to complete the first task and the second task, and familiarity with the building wasn't as important to the strategy they chose when completing the task. Steve, you'd better get back to work figuring out exactly why the RSC doesn't always respond the same way to familiar scenes. I expect a report in the morning.
Epstein, R.A., Higgins, J.S., Jablonski, K., & Feller, A.M. (2007). Visual scene processing in familiar and unfamiliar environments. Journal of Neurophysiology, 97, 3670-3683.
Hah... it IS surprising sometimes (as evidenced on my blog) that I actually do legit research!
If anyone is interested in obtaining a copy of the paper it's available, as well as some of my others, on my reprint archive: http://viscog.vp.uiuc.edu/reprints/index.php?site_id=23
Thanks for bringing this paper to peoples attention Dave and Greta!
Epstein, R.A., Parker, W.E., & Feiler, A.M. (2007). Where am I now? Distinct roles for parahippocampal and retrosplenial cortices in place recognition. Journal of Neuroscience, 27: 6141-6149.
Answers some of the questions as to why the RSC doesn't always respond the same way.
Your post reminded me of a syndrome called Capgras' delusion, which I read about. People suffering from this syndrome come to regard their close acquaintances as strangers. Maybe the section of the brain which identifies familiar things is damaged in such patients?
(I am just a novice very interested in this subject. I am afraid I may be sounding very silly to experts like you :-) )
I'm a little confused:
As you can see, only the RSC was more active during viewing of familiar scenes. The RSC appears to be a key area of the brain for evaluating unfamiliar scenes.
How do you get from the first sentence to the second? Maybe the RSC is key for evaluating *familiar* scenes...?!
(Also, when during the 10 years since I left the field of neuroscience, did the term "retrosplenial" come into existance?? heh.)