A new technique for generating disordered point-light animations for the study of biological motion perception

Abstract

Studies of biological motion perception often use stimuli depicting human actions portrayed via point-light (PL) displays. Typically, counterpart, or control, stimuli for PL biological motion are created by spatially scrambling motion trajectories of individual PL dots. Depending on the purpose of the study, however, this procedure may be inappropriate as a foil for genuine PL animations, because spatial scrambling not only disrupts coherent motion activity but also eliminates pair-wise motion relationships among dots and, unless corrected, alters the spatial spread of PL dot motions. We introduce a new technique for producing perturbed PL animations, called pair-wise shuffled motion, that preserves the elementary features of biological motion in spatial and motion energy domains and only disrupts the specific sense of global, coherent perception of biological motion. First we describe the procedure for creating pair-wise shuffled motion sequences. Next we compare unperturbed PL animations to pair-wise shuffled motion, to spatially scrambled motion, and to spatially constrained scrambled motion in terms of spatial distributions of the dots, spatiotemporal amplitude spectra derived from Fourier analysis of those sequences, and space-time motion energy associated with those perturbed animations. We then show that the results from those analyses generalize to a large family of PL animations, including the widely used PL walker. Finally we present results from a two-interval forced-choice biological-motion discrimination experiment comparing the robustness of scrambled and pair-wise shuffled motions as foil stimuli. Results from these comparisons suggest that pair-wise shuffled motion offers advantages as a foil stimulus compared to foils using the conventional scrambling technique. Pair-wise shuffled motion provides an additional, effective control display for evaluating PL biological motion perception in future psychophysical, computational, and imaging studies that focus on mechanisms of processing spatiotemporal information signifying biological motion within PL displays.

Facilitating Effects of Emotion on the Perception of Biological Motion: Evidence for a Happiness Superiority Effect

“…PSM preserves pairwise dot motions defining the local pendular movements associated with individual limbs. The advantages of PSM over the conventional scrambled motion include minimizing differences in overall motion between BM and its perturbed counterpart and selectively disrupting the global spatial relations among the pairwise motions (Kim, Jung, Lee, & Blake, 2015).…”

“…With these steps, the maximum number of dot arrays that could be produced from a single BM was 80, which allowed utilizing different PSM samples in an experiment without repetition. More details can be found in Figure 2 and in the corresponding description in Kim et al (2015).…”

Load-sensitive impairment of working memory for biological motion in schizophrenia

“…PSMs [ 64 ] were created by swapping six body parts (head-hip, shoulders, left and right arms, left and right legs) of a BM (each part consisted of two dots). Before shuffling the dot pairs, the mean locations of each dot throughout the temporal frames were calculated and then swapped with each other.…”

“…Before shuffling the dot pairs, the mean locations of each dot throughout the temporal frames were calculated and then swapped with each other. Detailed rules and restrictions for creating PSMs are described in our previous study [ 64 ]. PSMs are similar to the spatially SMs, in that they disorganize the global motion of BMs while keeping the local dot trajectories the same, but they have an additional strength, because they also maintain the unique local features of BMs, such as pendular movements.…”

PLAViMoP: How to standardize and simplify the use of point-light displays

“…Spatial transformations can also consist to average some PLDs with spatio-temporal morphing (e.g., Jastorff, Kourtzi, & Giese, 2006;Thoresen et al, 2012;Troje, 2002). Finally, it is possible to disturb the spatial coherence of the animation by scrambling the positions of the joints (Bscrambled motions^; e.g., Bidet-Ildei et al, 2014;Hiris, 2007;Simion et al, 2008), by using temporal or spatial bubbles (Thurman & Grossman, 2008), or by using pair-wise motions that preserve the local pendular movements associated with individual limbs (Kim, Jung, Lee, & Blake, 2015). Overall, these different studies have shown that the capacity of humans to perceive and recognize biological motion is closely related to the spatial properties of the movement, such as the canonical orientation and spatial coherence Hirai, Senju, Fukushima, & Hiraki, 2005) of the movement.…”