Basic Research 
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People spend enormous amounts of money to watch other people move. For example, in the United States in 2007 alone, Major League Baseball and the National Football League had combined revenues of over 12 billion dollars. Obviously, sports fans could save lots of money, not to mention hours and hours of time, by simply reading the scores and statistics after each game. Instead, they pay to watch games unfold on TV or in stadiums. Why? Because human beings are fascinated by the way other people move. Watching an outstanding athlete perform can be mesmerizing. Sitting in an outdoor café and watching people walk by is somehow deeply pleasurable. The lyrics of numerous songs attest to the fact that there is something in the way she (or he) moves.
When we watch other people, what information is detected by our visual systems and how is that information processed? In other words, how does our visual system interpret the actions and postures of other people? Modern research addressing these questions started in the 1970s when Gunnar Johansson constructed movies of point-light defined people in action. Johansson attached small lights to an actor’s major joints and head and then filmed that actor’s actions so that only the lights were visible (insert a static (or dynamic if it’s possible) point-light figure somewhere nearby). When naïve observers view these point-light displays, they accurately detect the presence of human movement in as little as a fifth of a second. In our lab, we’ve used point-light displays of human motion to understand how the visual system uses movement cues to detect the presence of another person (e.g., Thornton et al., 1998) as well as a moving person’s identity (Loula et al, 2005), actions and intentions (Sebanz & Shiffrar, 2009). Using point-light displays, and many other experimental stimuli and techniques, our lab has discovered that the human visual system typically processes the movements of people and objects in fundamentally different ways. For example, observers can integrate motion information over larger spatial (e.g., Shiffrar et al., 1997) and temporal (e.g., Shiffrar & Freyd, 1990, 1993) extents when that motion comes from people rather than objects. People are also able to extrapolate human movement farther and more accurately than object movement (Kourtzi & Shiffrar, 1999).
Obviously, people (e.g., George and Sally) are very different from objects (pencils and cars). So we’ve also compared visual sensitivity to human motion and animal motion. Our results suggest that people use some similar perceptual mechanisms to analyze the movements of people and animals, but that the perception of human movement nonetheless differs from the perception of animal movement (e.g., Pinto & Shiffrar, 2009; Chouchourelou et al, in press).
In collaboration with collaborators who are experts in brain imaging, we’ve also examined the brain mechanisms involved in the perception of human actions. With Naznin Virji-Babul, we’ve found that overlapping brain processes are activated during the first 200 msec after the perception of moving people and moving objects. However, after this point, the perception of human motion triggers divergent neural processes (Virji-Babul et al., 2007). With Jean Decety and Jennifer Stevens, we’ve found that the motor systems of stationary people are activated during the perception of actions that people can perform but not during the perception of actions that people cannot perform (Stevens et al., 2000). Finally, with Kevin Pelphrey, we’ve recently found that different patterns of neural activity result when people observe human motion and non-human animal motion (Kaiser et al., in press).
After establishing that the perception of human motion differs from the perception of other categories of motion, our lab set out to answer the question of “Why.” Our lab has also identified three reasons why people typically analyze human movement and object movement differently. First, because we are inherently social animals, human movement is very common and we pay more attention to it than to any other type of motion. Thus, our visual systems have more experience with human motion than with another other type of motion. We have demonstrated that visual experience helps shape our perception of other people’s bodily actions (e.g., Jacobs, Pinto & Shiffrar, 2004). Second, the category of human movement is the only motion category that people can perceive and perform. You can move like another person, but you can’t move in the same ways as crashing waves or wind blown trees. We and other research groups have found that the human visual system doesn’t work in isolation, but instead is constrained by and benefits from input from the observer’s motor system. Thus, the ways in which you can move change the ways in which you perceive other people’s actions (to learn more about this, see the “Motor Abilities and Disabilities” page). For example, because observers used their own motor systems to visually perceive the movements of other people, one would expect to find that each person is most sensitive to their own actions. We’ve found that to be the cause (Loula et al., 2005, Prasad & Shiffrar, 2009). Finally, when people produce postures, gestures, and actions, their bodies naturally convey their feelings, identities, intentions, and goals (aka: body language, for review see Shiffrar, 2008). We and other labs have shown that, typically, the human visual system is tuned for the detection of this socially relevant information in a way that differentiates human movement from other movement (Chouchourelou et al., 2006; Shiffrar et al., 2011).
Shiffrar, M. & Freyd, J. (1990). Apparent motion of the human body. Psychological Science, 1, 257-264. download pdf
Shiffrar, M. & Freyd, J. (1993). Timing and apparent motion path choice with human body photographs. Psychological Science, 4, 379-384. download pdf
Shiffrar, M., Lichtey, L., & Heptulla Chatterjee, S. (1997). The perception of biological motion across apertures. Perception & Psychophysics, 59, 51-59. download pdf
Thornton, I., Pinto, J. & Shiffrar, M. (1998). The visual perception of human locomotion. Cognitive Neuropsychology, 15, 535-552. download pdf
Kourtzi, Z. & Shiffrar, M. (1999). Dynamic representations of human body movement. Perception, 28, 49 - 62. download pdf
Jacobs, A., Pinto, J., & Shiffrar, M. (2004). Experience, context, and the visual perception of human movement, Journal of Experimental Psychology: Human Perception & Performance, 30, 822-835. download pdf
Loula, F., Prasad, S., Harber, K., & Shiffrar, M. (2005). Recognizing people from their movement. Journal of Experimental Psychology: Human Perception & Performance, 31, 210-220. download pdf
Chouchourelou, A., Matsuka, T., Harber, K., & Shiffrar, M. (2006). The visual analysis of emotional actions. Social Neuroscience, 1, 63-74. download pdf
Virji-Babul, N., Cheung, T., Weeks, D., Kerns, K., & Shiffrar, M. (2007). Neural activity involved in the perception of human and meaningful object motion, NeuroReport, 18, 1125-1128. download pdf
Shiffrar, M. (2008). The visual perception of dynamic body language. In I. Wachsmuth, M. Lenzen, & G. Knoblich (Eds). Embodied Communication in Humans and Machines, Oxford University Press, pp. 95-110 download pdf
Pinto, J., & Shiffrar, M. (2009). The visual perception of human and animal motion in point-light displays, Social Neuroscience, 4(4), 332-346. download pdf
Prasad, S. & Shiffrar, M. (2009). Viewpoint and the recognition of people from their movements. Journal of Experimental Psychology: Human Perception & Performance, 35, 39-49. download pdf
Kaiser, M. D., Shiffrar, M., & Pelphrey, K. A. (2011). Socially tuned: Brain responses differentiating human and animal motion. Social Neuroscience, in press. download pdf
Shiffrar, M. (2011). People Watching: Visual, motor, and social processes in the perception of human movement. Wiley Interdisciplinary Reviews: Cognitive Science, 2, 68-78. download pdf
Chouchourelou, A., Jacobs, A., & Shiffrar, M. (2012). What Does “Biological Motion” really mean? Differentiating visual percepts of human, animal, and non-biological motions. In K. Johnson & M. Shiffrar (Eds). Visual perception of the human body in motion. Oxford University Press, in press. download pdf