What is biological motion?

Do you know what “biological motion” is? I am considered an expert on biological motion perception but I am not entirely sure myself where to use the term and where not to use it. No question, biological motion is a super interesting thing. But also a very diverse one. People have used the term for a whole bag of goodies, often without even realizing that the same label may not always refer to the same thing. Its meaning seems to have evolved over time, too. In a chapter that just came out in a wonderful new book, I attempt to provide an overview about the broader phenomenology that falls under the term “biological motion”. A link to an early version of my chapter is here. But you may rather want to get hold of a copy of the book itself. It is entitled “Social Perception” and edited by M. D. Rutherford and V. A. Kuhlmeier. The book provides a comprehensive overview not just about the perception of biological motion (whatever that is), but also about other aspects of social visual perception. A very interesting read that contains contributions from a considerable number of acclaimed experts in the field.
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Annual meeting of the Vision Science Society

It is VSS time again! This year I came here with two graduate students and two posters. Seamas Weech and Sophie Kenny both present studies relating to some recent discussions of the "facing-the-viewer bias" that we observe in biological motion perception: Even though standard point-light displays and related depictions of the human body in action do not contain any cues to the order of the elements in depth, observers seem to prefer one of the two theoretically possible percepts: The walker seems to be facing the observer rather than facing away. While this observation has been demonstrated multiple times, it is not clear why it occurs. The poster by Weech and Troje offers an explanation. Troje, Kenny and Weech explore whether linear perspective can really disambiguate depth in these displays. I am posting both posters here for you to explore.

Weech, S., Troje, N. F. (2013) Does a convexity prior explain the facing-the-viewer bias in the perception of biological motion?

Troje, N. F., Kenny, S. Weech, S. (2013) Can we perceive linear perspective in biological motion point-light dispays?

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What pigeons think about “direction”

If someone would present you with the display of a person stepping backwards on a treadmill and you were asked “Which way is the person going“ you might ask for more specific instructions: “The person is facing in one direction, she is moving as if walking into the other direction, but overall she remains stationary. So what do you mean with 'direction'?" How would a pigeon respond?

Human are able to retrieve information from biological motion through at least two different channels: The global articulated structure as revealed by the non-rigid, yet highly constrained deformation of the dot pattern, and the characteristics of local motion trajectories of individual dots. In the example above, the articulated structure indicates the facing direction, and the local motion indicates the intended walking direction of the backwards walking walker.

In a new study that has just come out in the journal Vision Research, we tested eight pigeons on a task in which they had to discriminate stationary left-facing from right-facing biological motion point-light figure. We then challenged them with a number of test trials introduced into the sequence of the normal training trials.

Tested on backwards moving walkers, the majority of the birds indicated that they used local motion cues to solve the training task, while the remaining birds obviously used global, configural cues. Testing the pigeons on different versions of scrambled biological motion confirmed that each individual bird had made a clear decision for one of the two potentially available strategies. While we confirm a previously described local precedence in processing visual patterns, the fact that some birds used global features suggests that even the birds who relied on local cues probably dispose of the perceptual abilities to use global structure, but “chose” to not use them.

Rate of correct responses from 8 individual pigeons. In the case of backwards walkers, "correct" means that their response indicated facing direction rather than walking direction.

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Holiday walker

Creative coder Nicolas Barradeau just sent me the link to this Christmas calender. The walker might look familiar to you. Click on the image to start the animation.

I often get requests from people interested in the BMLwalker who use it for all sorts of interesting purposes. One of the most impressive installations is the one on the outside of the Otto-Bock Science Museum in Berlin, were a light installation of the BMLwalker covers two of the four walls of a four story building. I have never tried it, but I assume you can see at night time from the observation dome of the Reichstag.
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Sophie Kenny

Time flies by, and with the change of seasons came new lab members. Among them is Sophie Kenny, who joined the Biomotion Laboratory in September. Having previously completed her Master's degree at Memorial University of Newfoundland on the enactment effect (see, e.g., Engelkamp, 1998) with Dr. Ian Neath, she is now expanding the scope of her research on memory for abstract human movement sequences. As a Ph.D. student in our Brain, Behaviour and Cognitive Science graduate program Sophie will attempt to extend general principles of memory that were well defined in verbal memory by her former supervisors to nonverbal memory. Among her objectives is to demonstrate that memory operates according to the same rules over a broader range of information types than was previously thought to be true. She is funded through NSERC, and after having received a Julie-Payette Research Scholarship for her Master's, she has received a CGS-D3 for her Ph.D. With the expertise and the technology currently available at the Biomotion Lab she will be able to create highly controlled point-light motion stimuli and build algorithms which can accurately represent the match between the presentation of a stimulus and the performance of a participant. Doing so, she will be able to accurately reflect the quality of movement memory representation in a quantitative manner. She is looking forward to spending the next few years here with us, in Kingston.
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