Seeing Where the Stone Is Thrown by Observing a Point-Light Thrower: Perceiving the Effect of Action Is Enabled by Information, Not Motor Experience

Abstract

People are very adept at perceiving biological motion (e.g., Johansson, 1973). This ability has been an essential life skill to members of this social species. The human niche during the ice age was socially coordinated hunting for big game. Being able to judge the location targeted by the throw of a conspecific would be a valuable perceptual ability that we now study to investigate 2 competing theories of biological motion perception: Common Coding (CC; Prinz, 1997) and Kinematic Specification of Dynamics (KSD; Runeson & Frykholm, 1983). The 2 theories diverge in attributing perceptual ability to either motor or visual experience, respectively. To test predictions of the CC theory, we performed 3 experiments to manipulate observers' specific motor experience while they judged the targeted location of throwing by watching point-light displays. In Experiment 1, we tested whether the identity of the thrower in the display mattered. In Experiment 2, we tested whether the motor expertise of the observer mattered. In Experiment 3, we tested whether the gender/style of throwing demonstrated by the point-light thrower mattered. The combined results failed to support CC theory, suggesting that motor experience is not required for the perception of action. Because all participants judged the target location of throwing quite well, KSD theory suggests that the kinematic information available in the displays may have enabled the perception. We performed Experiment 4 to analyze the information. We found that the judgment pattern exhibited by the observers in both Experiments 1 and 2 was well predicted by the KSD theory. Thus, we concluded that the perception of biological motion is enabled by visual information and improved by visual experience.

ACKNOWLEDGMENTS

We thank graduate and undergraduate students (Ms. Rashmi Ravi and Mr. Todd Mirich) who have assisted with the data collection and video editing. We also thank Dr. Joe Lappin and Dr. Sverker Runeson for their intelligent and constructive comments on the early version of this article.

FUNDING

This research was supported by the Faculty Seed Grant from the University of Wyoming to Qin Zhu.

Notes

¹ Note that intentions are part of the dynamics in KSD as formulated by Runeson and Frykholm (1983).

² Zhu, Lu, and Wilson (2012) performed motion analysis of the throwing recorded in point-light displays and found a significant gender difference in release control. Whereas male experts released the ball faster with a flat angle, female expert throwers released the ball much less rapidly while exhibiting much larger angles. Thus, we use gender to define the style of throwing in the present study (i.e., male style of throwing vs. female style of throwing).

³ All throwers were quite accurate in throwing. Each produced only one or two invalid throws.

⁴ They represented two extremes of throwing style: the male-like throwing demonstrated throws made with the fastest speed and the minimum angle at release, and the female-like throwing demonstrated throws made with the lowest speed and the maximum angle at release (Zhu et al., 2012).