Monday, 2 October 2006

Expanding representations

By Dave and Greta Munger of Cognitive Daily.

Greta and I always have a tough time deciding on a "best" or "favorite" study. For both of us, generally, it's typically more of a yes / no distinction: either we like a study enough to write about it on Cognitive Daily, or we don't. We're both surprised when one of our posts gets noticed by a high-traffic blog or web site, and suddenly thousands of readers stop by to read it. Other studies that we like just as much rate hardly a blip in our site statistics.

That said, the work of Helene Intraub has been extremely important both in how it influences my writing in Cognitive Daily and other venues, and how it affects Greta's research and teaching. Intraub and Michael Richardson were the first researchers to identify the phenomenon of boundary extension. In boundary extension, when you see a scene such as a photograph or even a three-dimensional representation with a clear border, then your memory of that scene tends to extend beyond the original boundary: you remember the scene as larger than it actually was, sometimes even just a few seconds after seeing it. As we discussed in our March 2005 post, Intraub explains the phenomenon in this way:
Boundary extension may be due to the active creation of a mental representation of a scene. Since our mind constructs a "scene" based on scant available information (the area visible by the fovea as the eye looks at different parts of the scene), it makes sense that it might also construct a representation of parts beyond the boundary of what is actually viewable. If we "fill in the blanks" between places we've actively looked at, why not extend our representation beyond the boundaries of what we've seen as well?
Intraub's 2004 Cognition paper (ref. below) is the one we'd like to nominate as our favourite of the past three years. In a remarkable set of experiments, Intraub extends the phenomenon of boundary extension to a new modality: touch. Here's the description we wrote of the study last year:
She showed participants six different "scenes" composed of real, physical objects (groups of ordinary things like toys, books, and toiletries), each demarcated by a "boundary" of black cloth. She then had an assistant remove the boundaries and asked the participants to mark where the boundaries had been. As expected, they placed the borders well beyond where they had been in the original scenes.

Next, she blindfolded another set of participants and showed them the same scenes, with an easily detectable three-inch-tall wooden "boundary" replacing the original cloth border. When they returned later to the same scenes with the border removed (and still blindfolded), they were asked to place wooden blocks where the borders had been.

Finally, she repeated the "blindfolded" condition with a volunteer who had been deaf and blind from early childhood. Intraub calls this participant (named only by her initials, KC) a "haptic expert" because she has spent her entire life negotiating the world by the sense of touch. At the age of 25, KC was a successful college student who could easily identify the objects in the experiment by touch (the only difficulty was reminding her to use the entire 30 seconds allotted for each scene, so as to match the blindfolded group).

As you might guess now, the results for KC were the same as those from the blindfolded group: She extends boundaries in the same way sighted people do. There was one difference between the blindfolded and the vision group: the vision group showed more boundary extension than the blindfolded group, suggesting that the modalities of sight and touch are not precisely analogous.

Nonetheless, the study does raise some provocative questions about the relation between the senses and the perceptual systems that we use to understand them. Do we represent tactile regions and visual areas using the same neurological systems? Do blind people "see" the world the same way others do? Or are visual representations analogous, but separate from tactile ones? It's the type of study that makes you want to roll up your sleeves and try to understand even more. That's what the best science is all about.

The study also inspired Greta to see if other phenomena are related to boundary extension. The result was a paper coauthored with Ryan Owens and John Conway in Visual Cognition, "Are boundary extension and representational momentum related?" The experiment supported the notion that boundary extension and representational momentum are actually separate cognitive processes, even though they are both distortions of memory for a scene.
__________________________________

Intraub, H. (2004). Anticipatory spatial representation of 3D regions explored by sighted observers and a deaf-and-blind observer. Cognition, 94, 19-37.

Munger, M.P., Owens, T.R. & Conway, J. (2005). Are boundary extension and representational momentum related? Visual Cognition, 12, 1041-1056.

Dave Munger is a writer whose works include Researching Online and The Pocket Reader. Greta Munger is Associate Professor of psychology at Davidson College.

No comments:

Post a Comment