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Mind

Bringing the Real World into Brain Scanning

NeuroskepticBy NeuroskepticFebruary 29, 2012 6:35 PM

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Canadian Neuroscientists Jacqueline Snow et al propose a new method of making brain scanning studies a bit more realistic.

Typically, in an fMRI or other neuroimaging study, any visual stimuli shown to the volunteer are just pictures on a screen. Sometimes videos will be used, but in almost all cases they're just 2D images. Is that adaquate? People have hoped so.

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Snow et al's data suggest that it might not be.

They created a contraption for presenting subjects with real objects during a scan. See above. Now, to the uninitiated this might not seem like a big deal, but those with MRI experience will appreciate how impressive this is.

Everything from the angle of the volunteer's head to the LED lighting is an achivement, given the nature of MRI. The stimuli were controlled by one of the researchers, who had to sit next to the scanner, in total darkness, and operate the turntable with the help of some glow-in-the-dark stickers.

Having built this device, they then used it to compare the brain's responses to real objects vs photos of those same objects. The experiment was designed to test fMRI adaptation - the phenemenon whereby if you present the same stimuli repeatedly, the neural responses are reduced.

fMRI adaptation has been found to happen in many studies using 2D pictures, but Snow et al show that the effect was much smaller, maybe entirely absent, when people were repeatedly shown real objects: this graph shows the BOLD neural response in the lateral occipital complex. Seeing the same pictures over and over led to a weaker response, as expected; but seeing the same 3D objects didn't:

This is a good study and an important result, which suggests that the much-studied fMRI adaptation might not be a universal phenemonon. And the potential implications are big, as the authors write:

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Finally, our preliminary fMRI results raise the provocative suggestion that the presence of real-world objects (i.e., as indicated initially via stereoscopic cues) invokes qualitatively different computations to those elicited by 2D images. Researchers in the field of behavioral psychophysics have expressed long-standing concern about the extent to which pictures of objects capture the properties of their real-world counterparts (i.e., their ecological validity), with reservations as to their appropriateness as stimuli with which to examine the nature of human object perception...

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Snow, J., Pettypiece, C., McAdam, T., McLean, A., Stroman, P., Goodale, M., and Culham, J. (2011). Bringing the real world into the fMRI scanner: Repetition effects for pictures versus real objects Scientific Reports, 1 DOI: 10.1038/srep00130

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