Bringing the Real World into Brain Scanning

By Neuroskeptic | February 29, 2012 7:35 am

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.

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:

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…

ResearchBlogging.orgSnow, 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

CATEGORIZED UNDER: fMRI, methods, papers
  • Anonymous

    Very impressive and creative work to obtain these observations. Well done J Snow et al.

  • Anonymous

    Awesome idea and an important finding! Creative indeed…I'm coming to Western for all my real-world scanning needs.

  • DS

    Presently I am very skeptical of these results. Head motion is an extremely important confound in fMRI – one which can entirely account for many signal changes seen in fMRI studies. The means by which motion was assessed in this study were not sufficient to discriminate motion that may be correlated to viewing 2D images versus 3D objects. Since the measurements were not sufficient then no attempt could be made to to analyze such a correlation.

  • Unknown

    Shockingly (considering the conclusions of the authors) the study failed to show a significant interaction between repetition condition and object type (2-D vs 3-D).

    As we know from our trusty “Erroneous analyses of interactions in neuroscience: a problem of significance.” you must show, not just that one of the two conditions is significantly different from zero, but that the two conditions are significantly different from each other. In the original paper the authors provide these statistics:

    “Finally, a paired-samples t-test contrasting the AIs for 2D versus 3D stimuli in each ROI revealed a trend toward significance between the AIs for 2D versus 3D stimuli in LO (t(12) = 2.04, p = 0.06), but no significant differences between AIs in pFS (t(12) = 0.05, p = 0.29).”

    Even ignoring the multiple tests, neither of these values makes it below p=0.05. If these crucial stats were in the abstract rather than hidden in a gargantuan results section, I doubt this study would have ever been published.

    The conclusions aren't necessarily false, but there's definitely not enough evidence here to convince us they're true.

  • Matt

    I had a similar reaction to Unknown, as I said on twitter, and although I was told I was wrong, I pretty much stand by it – at least for the ROI analysis. In a way, those two tests Unknown highlights are tests of the interaction between repetition condition and stimulus in each individual area, since the AIs quantify the difference between repeated object and different object trials. But then they have no statistically significant interactions in either area, and they still do not test the interaction between the size of the effect across the two areas – all they have are separate t-tests for each area. In any case, I can't see why a reviewer wouldn't have told them to just put the whole lot in an ANOVA instead of doing all these separate, uncontrolled t-tests.

    Okay, so they do test the interaction properly in the whole brain analysis, but the results of that also seem a bit weak.

    Ultimately I'm left unconvinced by their rather grand claims: all they have in the ROI analysis is, at best, a trend in one area (LO). That trend is against their own predictions, and given the lack of control for multiple comparisons, that's not very convincing.

    I think the method and principle is great, really do; I appreciate how difficult it must have been to get the set up right in fMRI. For that they deserve plaudits.

  • sports handicapping services

    a very particular method or system and hopefully with good results



No brain. No gain.

About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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