Cognitive Daily

It is well known that humans and other animals can recognize biological motion when shown only a point-light display. Other research has shown that social cues are deeply embedded in our perceptual system. We can also perceive emotions and intentions in simple geometric displays.

So what is going on in our brains while we watch such displays? A team of researchers led by Johannes Schultz found some answers (Johannes Shultz, Hiroshi Imamizu, Mitsuo Kawato, and Chris Frith, “Activation of the Human Superior Temporal Gyrus during Observation of Goal Attribution by Intentional Objects,” Journal of Cognitive Neuroscience, 2004). The team, based in the Wellcome Department of Imaging Neuroscience in London and the ATR Computational Neuroscience Laboratories in Kyoto, took MRI images of volunteer’s brains while they watched a simple animated display.

The display showed a red dot moving in an arc, which was then “followed” by a blue dot in one of two possible paths. Either the blue dot simply followed the same arc as the red dot, or it “predicted” where the red dot was going and took a straight-line path to intercept it. Observers were asked to either indicate whether the blue dot “caught” the red dot, or to describe the “strategy” the blue dot used to pursue the red dot. Here’s a map of one portion of the brain that is activated during the task:

i-fc2d7ae06929706a1aadc4b35637341e-dots.jpg

The amount of activity in the active area, called the superior temporal gyrus (STG), is plotted on the small graph in the corner. The blue bars correspond to the “strategy” task, when observers were asked to describe the dot’s strategy. The red bars are for the “outcome” task, when participants needed only to indicate whether the blue dot successfully “caught” the red dot. The P and F columns indicate whether the blue dot “predicted” the path of the red dot or simply followed it along its curved path. As you can see, the STG is more active when observers try to explain the dot’s strategy, and also more active when the blue dot seems to “predict” where the red dot is going.

The STG is known to be responsible for both perception of biological motion and of intention. This result suggests that humans are quite ready to assign “intention” to any object, and that they use the same area of the brain to do this, whether the object is an inanimate dot or an academy-award-winning actor.

Comments

  1. #1 Ted Wright
    April 6, 2005

    I am having trouble understanding your summary of the results in this article. (I’m lazy, I have not yet dug up and read the article.) Presumably, the barchart already represents some comparison (subtraction) between conditions, otherwise how could activation go negative. So it seems like another (better?) way of summarizing the results in this chart posits two effects: (a) rSTG is more active when the blue dot predicts the movement of the red dot and (b) rSTG is more active under “explain” instructions than for the “outcome” task instructions.

    How this all says anything about attributions of intention is beyond me. One might believe that this is all simply explained by processing difficulty.

  2. #2 Dave Munger
    April 6, 2005

    Ted, you shouldn’t have to dig up the original article–that’s what we’re here for!

    I don’t claim to know a lot about how the analysis of MRIs is done, but my understanding is that it usually involves some sort of “masking”–subtracting one state from another so as to allow comparison between participants. Otherwise, the data would be lost among the individual differences of overall brain activity. So yes, I think that’s why we’re seeing negative numbers. However, these values are all in the context of higher activity in the STG than in the rest of the brain.

    “Processing difficulty” is an interesting objection. One thing I don’t make clear in the post is that many areas of the brain show more activity during the experiment, but only the STG shows a difference between the “predict” and “follow” tasks, suggesting that something more is going on besides a “more difficult” task.

    In addition, there were several control conditions, where the dots moved in opposite directions but along the same type of path, and again the STG did not show different levels of activity during these.

    The participants did report that the blue dot “appeared to know where the target object was going,” in the “predict” trials, which does suggest some sort of intentionality. Still, your objection is a valid one.

    I do think the other experiment I discussed concerning this region (actually the STS, which is nearby) makes a clearer case for the idea that this area is concerned with processing intentionality.

    Finally, thanks for your revision of my writing. This is tough stuff, and anything that can make it a bit clearer is welcome.

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