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Thursday, May 20, 2021

Behavioral and Neural Representations en route to Intuitive Action Understanding

L. Tarhan, J. De Freitas, & T. Konkle
doi: https://doi.org/10.1101/2021.04.08.438996


When we observe another person’s actions, we process many kinds of information – from how their body moves to the intention behind their movements. What kinds of information underlie our intuitive understanding about how similar actions are to each other? To address this question, we measured the intuitive similarities among a large set of everyday action videos using multi-arrangement experiments, then used a modeling approach to predict this intuitive similarity space along three hypothesized properties. We found that similarity in the actors’ inferred goals predicted the intuitive similarity judgments the best, followed by similarity in the actors’ movements, with little contribution from the videos’ visual appearance. In opportunistic fMRI analyses assessing brain-behavior correlations, we found evidence for an action processing hierarchy, in which these three kinds of action similarities are reflected in the structure of brain responses along a posterior-to-anterior gradient on the lateral surface of the visual cortex. Altogether, this work joins existing literature suggesting that humans are naturally tuned to process others’ intentions, and that the visuo-motor cortex computes the perceptual precursors of the higher-level representations over which intuitive action perception operates.

From the Discussion

Intuitive Action Representations in the Mind

Our primary finding was that judgments about the similarity of actors’ goals was the best predictor of intuitive action similarity judgments. In addition, these goals accounted for the most unique variance in the intuitive similarity data. We interpret this to mean that humans naturally and intuitively process other actors’ internal motivations and thoughts, even in the absence of an explicitly social task. This conclusion adds to a rich literature showing that humans automatically represent others in terms of their mental states, even from a very young age (Gergely and Csibra, 2003; Jara-Ettinger et al., 2016; Liu et al., 2017; Reid et al., 2007; Thornton et al., 2019a,b). In addition, we found that similarity in the actors’ movements also predicted intuitive judgments moderately well and accounted for a smaller amount of unique variance in the data. This finding goes beyond our current understanding of the factors driving natural action processing, to suggest that kinematic information also contributes to intuitive action perception. In contrast, similarity in the videos’ visual appearance did not account for any unique variance in the data, suggesting that lower-level visual properties such as color, form, and motion direction do not have much influence on natural action perception.

A natural extension of these findings is to investigate the specific features that we use to calculate actors’ goals and movements. For example, how important are speed, trajectory, and movement quality (e.g., shaky or smooth) for our assessment of the similarity among actions’ movements? And, do we consider physical variables – such as facial expression – when inferring actors’ goals? Digging into these specific feature dimensions will bring further clarity to the cognitive processes driving intuitive action perception.