Distinct Neural Mechanisms for Body Form and Body Motion Discriminations

Abstract

Actions can be understood based on form cues (e.g., static body posture) as well as motion cues (e.g., gait patterns). A fundamental debate centers on the question of whether the functional and neural mechanisms processing these two types of cues are dissociable. Here, using fMRI, psychophysics, and transcranial magnetic stimulation (TMS), all within the same human participants, we show that mechanisms underlying body form and body motion processing are functionally and neurally distinct. Multivoxel fMRI activity patterns in the extrastriate body area (EBA), but not in the posterior superior temporal sulcus (pSTS), carried cue invariant information about the body form of an acting human. Conversely, multivoxel patterns in pSTS, but not in EBA, carried information about the body motion of the same actor. In a psychophysical experiment, we selectively impaired body form and body motion discriminations by manipulating different visual cues: misaligning the ellipses that made up a dynamic walker stimulus selectively disrupted body form discriminations, while varying the presentation duration of the walker selectively affected body motion discriminations. Finally, a TMS experiment revealed causal evidence for a double-dissociation between neural mechanisms underlying body form and body motion discriminations: TMS over EBA selectively disrupted body form discrimination, whereas TMS over pSTS selectively disrupted body motion discrimination. Together, these findings reveal complementing but dissociable functions of EBA and pSTS during action perception. They provide constraints for theoretical and computational models of action perception by showing that action perception involves at least two parallel pathways that separately contribute to the understanding of others' behavior.

Revisiting the importance of common body motion in human action perception

“…Critically, the strength of this influence was significantly modulated by the sparseness, or reliability, of intrinsic body form cues determined by the number of spatial elements sampled along the human figure. Of note, increasing the number of points beyond 8 would cause some limbs to be sampled with more than one element, which would likely facilitate the extraction of limb orientation information in addition to positional signals. Previous research has shown limb orientation to be a very potent visual cue for body form analysis (Lu, 2010;Thurman & Lu, 2013;Thurman & Lu, 2014a;Vangeneugden, Peelen, Tadin, & Battelli, 2014), and this also may have Fig. 2 Mean group results (n = 16) of the walking vs. running action discrimination task where the probability of a runner response is plotted as a function of morph weight.…”

Dissecting the visual perception of body shape with the Garner selective attention paradigm

“…A broad distinction that has been proposed to hold for the visual representation of bodies (and faces; Duchaine and Yovel, 2015) is one between static and dynamic cues (Giese & Poggio, 2003;Vangeneugden, Peelen, Tadin, & Battelli, 2014). This is based partly on neural evidence for distinct brain regions that respond preferentially to either silhouettes.…”

“…Downing, Peelen, Wiggett, & Tew, 2006;Giese & Poggio, 2003;Vangeneugden et al, 2014). An important following question, then, is what is the structure of the static body representation?…”

The Application of kNN and SVM in the Decoding of fMRI Data

“…In our fMRI study, the discrimination of multi-voxel pattern in EBA and pSTS made clear their roles in human motion representation. In a recent study, the author and colleagues used walking direction to represent motion information to show that the activity pattern of pSTS carried motion information, whereas this was not the case for EBA [7]. The inconsistency could be caused by different measurement indexes.…”