Translation and articulation in biological motion perception

Abstract

Recent models of biological motion processing focus on the articulational aspect of human walking investigated by point-light figures walking in place. However, in real human walking, the change in the position of the limbs relative to each other (referred to as articulation) results in a change of body location in space over time (referred to as translation). In order to examine the role of this translational component on the perception of biological motion we designed three psychophysical experiments of facing (leftward/rightward) and articulation discrimination (forward/backward and leftward/rightward) of a point-light walker viewed from the side, varying translation direction (relative to articulation direction), the amount of local image motion, and trial duration. In a further set of a forward/backward and a leftward/rightward articulation task, we additionally tested the influence of translational speed, including catch trials without articulation. We found a perceptual bias in translation direction in all three discrimination tasks. In the case of facing discrimination the bias was limited to short stimulus presentation. Our results suggest an interaction of articulation analysis with the processing of translational motion leading to best articulation discrimination when translational direction and speed match articulation. Moreover, we conclude that the global motion of the center-of-mass of the dot pattern is more relevant to processing of translation than the local motion of the dots. Our findings highlight that translation is a relevant cue that should be integrated in models of human motion detection.

Contribution of global and local biological motion information to speed perception and discrimination

“…The point-light actions of walking, throwing, and kicking were presented in sagittal views, and the jumping jacks and elbow-to-knee were presented in frontal views, where larger point-light motions can be seen. The mean position of the pointlight dots in each frame was used as the spatial center of each image frame because the present study focused on the articulational aspect (positional changes in the body parts relative to each other) rather than the translational aspect (changes in the body location in space over time) of human movements (Masselink & Lappe, 2015). Scrambled biological motions were created by randomizing the starting positions of each point while keeping its motion path within the area covered by the Figure 1.…”

Causal Action: A Fundamental Constraint on Perception and Inference About Body Movements

“…Recent research has revealed that humans are sensitive to the temporal binding between limb movements and body displacements, given that we commonly observe the two types of motion occurring in near synchrony. Disrupting the temporal congruency between the two sources of motion information curtails the perception of animacy (Thurman & Lu, 2013), the detection of social interaction between two agents (Thurman & Lu, 2014), and the discrimination of locomotion style (Masselink & Lappe, 2015;. However, it is unclear whether people show tolerance to some situations in which limb movements and body displacements are temporally misaligned but in a causally consistent way (e.g., limb movements may be shifted ahead in time but still precede body displacements in locomotion).…”

Combining biological motion perception with optic flow analysis for self-motion in crowds

“…It is characterized by an articulation and a translation component. Articulation refers to the relative change of the joint positions to each other ( Blake & Shiffrar, 2007 ; Johansson, 1973 ; Masselink & Lappe, 2015 ). Translation refers to the linear progressive motion of the body through space ( Blake & Shiffrar, 2007 ; Masselink & Lappe, 2015 ; Riddell & Lappe, 2018 ).…”