Neural Coding of Scene Volume: the Size of Space Represented across the PPA and LOC

Park, Konkle, & Oliva

Estimating the size of a space is intuitively central to our daily interactions, for example when deciding whether or not to take a crowded elevator. Here, we examined how neural areas respond to scenes that parametrically vary in the volume of depicted space. Observers were shown blocks of indoor scene categories and performed a one-back repetition task while undergoing whole brain imaging in a 3T fMRI scanner. The 18 scene categories varied in the size of depicted space on a 6 point log scale, from small and confined spaces such as closets and showers, to expansive areas such as concert halls and sports arenas. Using a regions-of-interest approach, we found that activity in the lateral occipital complex (LOC) systematically decreased as the size of space increased, showing a preference for smaller spaces (r=-.64, p<.01). On the other hand, activity in the parahippocampal place area (PPA) did not change as the size of space varied: this region responded equally strongly to all types of scenes regardless of the volume of the space (r=.14, p.1). We further examined the multivoxel pattern activity in the PPA using a linear support vector machine. Voxel patterns in the PPA classified the six different volumes of space well above chance (39% performance with leave-one-block-out cross-validation, chance level being 17%). Importantly, most classification errors were found across scenes that were close in size (within 1-2 scales), and not across scenes that were further in size (within 4-5 scales). Similar results were found in LOC (36% classification performance). These data suggest that scene volume information is coded in a distributed manner over a range of areas in the ventral visual pathway, consistent with the general idea that understanding the size of a space can influence a wide range of our interactions and daily navigation through the world.

Park, Konkle, T. & Oliva, A. (2010). Neural Coding of Scene Volume: the Size of Space Represented across the PPA and LOC. Journal of Vision. 10(7): 1248; doi:10.1167/10.7.1248.