Seeing through the haze: Recognizing biomotion in degraded conditions of low luminance and blur

Abstract

Nearly 40 years ago, Gunnar Johansson discovered that a person-in-action is perceived vividly and rapidly from the motion of light-points attached to the major joints. He called the effect biological motion. Numerous later studies have shown the phenomenon is powerful and fundamental. We now report an investigation of the effects of blur and reduced luminance on perception of biological motion. One previous study (Grossman & Blake, 1999) reported that biological motion is not perceived in scotopic luminance, but this conclusion is questionable because their stimuli were degraded further by reverse contrast and a background of dynamic noise. We used positive contrast video recordings of multiple light-point actions, presented in normal and inverted orientations, at four luminances (−2.14 to 1.46 log cd/m2) and with two levels of myopic blur selected to match the acuity obtained in low luminance. Results from 21 young adults showed perception of biomotion was largely unimpaired, with >90% correct identification under all conditions. RT's were significantly longer (M=344ms) in the lowest (scotopic) luminance condition. These findings suggest that perception of biological motion is independent of acuity, and probably mediated by magnocellular pathways.