Decoding point‐light displays and fully visible hand grasping actions within the action observation network

Abstract

Action observation typically recruits visual areas and dorsal and ventral sectors of the parietal and premotor cortex. This network has been collectively termed as extended action observation network (eAON). Within this network, the elaboration of kinematic aspects of biological motion is crucial. Previous studies investigated these aspects by presenting subjects with point‐light displays (PLDs) videos of whole‐body movements, showing the recruitment of some of the eAON areas. However, studies focused on cortical activation during observation of PLDs grasping actions are lacking. In the present functional magnetic resonance imaging (fMRI) study, we assessed the activation of eAON in healthy participants during the observation of both PLDs and fully visible hand grasping actions, excluding confounding effects due to low‐level visual features, motion, and context. Results showed that the observation of PLDs grasping stimuli elicited a bilateral activation of the eAON. Region of interest analyses performed on visual and sensorimotor areas showed no significant differences in signal intensity between PLDs and fully visible experimental conditions, indicating that both conditions evoked a similar motor resonance mechanism. Multivoxel pattern analysis (MVPA) revealed significant decoding of PLDs and fully visible grasping observation conditions in occipital, parietal, and premotor areas belonging to eAON. Data show that kinematic features conveyed by PLDs stimuli are sufficient to elicit a complete action representation, suggesting that these features can be disentangled within the eAON from the features usually characterizing fully visible actions. PLDs stimuli could be useful in assessing which areas are recruited, when only kinematic cues are available, for action recognition, imitation, and motor learning.

Differential contributions of body form, motion, and temporal information to subjective action understanding in naturalistic stimuli

“…Whereas studies using point-light displays suggested that motion information was sufficient for action recognition (Dittrich, 1993 ; Ziccarelli et al, 2022 ), we show that form information can also be sufficient for action recognition and adding motion and temporal information can, in some instances, further enhance accuracy. This aligns well with the proposal by Gärdenfors and Warglien ( 2012 ), who suggested that actions could be represented in an “action space” of forces acting upon a conceptual space.…”

The rewards and the risks of using naturalistic images. How form, motion, and temporal information differentially contribute to subjective action understanding.

“…Whereas studies using point-light displays suggested that motion information was sufficient for action recognition (Dittrich, 1993;Ziccarelli et al, 2022), we show that form information can also be sufficient for action recognition and adding motion and temporal information can further enhance accuracy. This aligns well with the proposal by Gärdenfors and Warglien (2012), who suggested that actions could be represented in an 'action space' of forces acting upon a conceptual space.…”

Biological Motion in Robots and Users’ Action Understanding

“…Humans are adept at understanding action when observing biological motion, and in particular, motion that follows human psychophysical constraints (Troje, 2013). In the point-light display paradigm (Johansson, 1973), in which small lights are attached to the joints of an actor in dark clothing, observers watching the moving lights for a few seconds can effortlessly identify the actor's mood (Alaerts et al, 2011) and recognise full-body or hand actions (Ziccarelli et al, 2022).…”