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Caterina Magri, Talia Konkle, Alfonso Caramazza; Visual object responses of the ventral stream reflect both size and motor-relevance . Journal of Vision 2016;16(12):505. doi: https://doi.org/10.1167/16.12.505.
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Visual non-animate object representations in the occipito-temporal region can be distinguished by their real-world size, with stronger responses to smaller objects in lateral areas, and stronger responses to larger objects in medial areas. However, small objects tend to be manipulated more while larger objects tend to stand as support for other objects. Thus, the observed separation of these neural responses may reflect information about the motor-relevance of these objects, rather than their size. To examine this hypothesis, we directly compared the dimensions of real-world size and motor-relevance. A stimulus set was created with small motor-relevant, small non-motor-relevant, large motor-relevant and large non-motor-relevant objects, with 18 different objects per condition. We collected fMRI data from 21 subjects who observed these objects. First we explored targeted scene- and object-regions to observe whether they show a modulation by motor-relevance instead of, or in addition to, size. Activity in these regions was indeed modulated by the motor-relevance of the objects, and also independently by real-world size. Next, we examined responses across the whole brain. The big/small regions identified in previous studies were replicated, but these same regions were also independently sensitive to motor-relevance. Interestingly, we found that regions with a big-size preference have a non-motor-relevance preference, and regions with a small-size preference have a motor-relevance preference. Thus, while size and motor-relevance dimensions were pitted against each other in this experiment, the neural responses to the two dimensions were aligned, suggesting an "ecological organization." In the world, small-sized objects tend to be higher in motor-relevance, while large objects are usually lower in motor-relevance, and the large-scale neural responses of occipito-temporal cortex reflect this ecological covariation.
Meeting abstract presented at VSS 2016
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