In a first experiment, 48 psychology students viewed degraded facial images of lecturers from their department. The students were split into four groups - one viewed static images only, whereas the other groups saw the faces either moving rigidly (nodding or shaking their head), talking (without sound), or forming a facial expression. Lander and Chuang found that students who observed the faces talking or expressing were better at recognising the faces. Rigid facial movements, by contrast, didn't seem to provide any advantage.
This led them to hypothesise that we may each have a unique way of moving our face - which is revealed when we speak or form an expression. To test this further, they harvested 2.5 second clips of dozens of famous faces from film and TV. Thirty people then rated these clips for how distinctive they thought each face's movement was.
Another 48 students then tried to identify the faces in degraded versions of these clips, as well as trying to identify static images of some of the faces. Lander and Chuang found the students were better able to recognise moving images of the famous faces, compared with static images, but that this advantage was significantly greater when the movement had been deemed distinctive by the earlier raters.
"We speculate that as the face moves in a more 'characteristic' or distinctive manner, so the usefulness of the motion cue is increased", the authors said.
Lander, K. & Chuang, L. (2005). Why are moving faces easier to recognise? Visual Cognition, 12, 429-442.
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