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From "Biological motion"

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Experiments[edit | edit source]

Experiments on biological motion commonly include point-light displays. These are small lights that outline the shape of a moving body, human or non-human, that let participants perceive motion. Experiments using point-light displays provide information, including how the mind interprets motion, which areas of the brain are responsible, and the extent to which we can identify specific people from an array of moving lights. Emotion can also be conveyed through computer generated point-light displays.

Humans perception of biological motion matures with age, usually capping at around five years of age. In an experiment by Pavlova et al., 2001, three-year olds, four-year olds, five-year olds, and adults were asked to identify animals (walking human, running dog, flying bird, and walking dog) displayed with moving point-light displays. The adults and five-year olds were able to accurately identify the moving animal, while four-year olds and three-year olds struggled (although 4-year olds were significantly better than 3-year olds). This implies that our perception of motion gets better as we age and reach the cap at five years. While animals tend to recognize their own species over others (for example, cats recognize their own point-light displays over scrambled ones), the three-year olds had the most success identifying a walking dog and least with a walking human. A possible explanation of this might be because of the children's small physical stature and their resulting visual perspectives: dogs are on the same horizontal plane as small kids, while human walkers are a lot taller and harder to perceive. In the next part of the experiment, different participants were asked to identify the same point-light display animals but with static images instead of moving dots. Five-year olds and adults gave results of chance performance, while the younger participants were omitted due to the harder nature of the task. Therefore, this experiment suggests that at five-years old, we are adept at identifying animals with point-light displays and that motion is critical to how we perceive it.

Humans use similar cognitive functions in identifying a real verb and replicable motions. An experiment by Christel Bidet-Ildei and Lucette Toussaint gave participants a lexical and a action decision task to measure how long it took for them to identify whether the words were real, or the action doable. Participants took much longer to identify pseudo words and actions. Interestingly, the correlation between verbs and actions was found to be rather strong (r= 0.56), while the correlation between nouns and actions was much lower (r= 0.31). This suggests that humans use similar cognitive functions to identify motion, whether it is presented through written language or point-light display. The author suggests that these findings are in favor of the embodied theory, which states that the processing of actions and words use similar motor functions.

Humans recognize point-light displays of themselves more so than those of their peers. An experiment performed by Cutting and Kozlowski involved six participants who were previously acquainted. Small lights were secured to the participant's elbows, knees, wrists, and ankles. Cutting and Kozlowski took videos of each participant as they walked and then showed the videos a few months later to the participants, to see if they could identify which of these moving lights belonged to each friend. The experiment found that individuals are better at identifying themselves than others.