PsyC54 Lecture Jan. 18: Part I Color and Motion in Shape-from-shadow Pictures Humera Iqbal, John Kennedy & Juan Bai

Hering’s Umbra and Penumbra Loose shadow perception when penumbra is covered. Loose shadow perception when penumbra is covered. Penumbra Umbra WHY?

Shape-from-shadow perception Number-of-Contours Account Contours of a line play a role in shape-from- shadow perception and too many contours prevent shape from shadow perception

Shape-from-shadow perception Belongingness Hypothesis Dark-to-light shadow border has to belong to both the shadowed and the illuminated areas to allow perception of a continuous face bearing shadow

Border-Polarity Hypothesis For shape-from-shadow perception the luminosity of the shadowed region and the shadow border must be lower than the luminosity of the illuminated region Shape-from-shadow perception

All Possible Visual Borders Static or Motion Luminance or Spectral Monocular or Binocular Manipulate each possibility 2 x 2 x 2 = 8

All Possible Visual Borders Spectral Difference (colored) Luminance Difference (B/W) Colored stereo movies Colored stereo illustrations B/W stereo movie B/W stereo illustrations Colored motion Colored painting B/W motion B/W drawings MotionStaticMotionStatic Binocular Monocular

Number of Contours John Kennedy (1993) Too many contours, prevents shape-from- shadow perception In the black-line image the line has two contours: from grey-to- black and from black- to-white

Belongingness Hypothesis… Monocular and Binocular depth perception Looking through a stereoscope, Ss. May see the small dotted line only belonging to shadowed region or illuminated region

Border-Polarity Hypothesis Luminosity of shadow region and shadow border must be lower than the luminosity of non-shadowed region. (i.e. positive border polarity)

All Possible Visual Borders original table from Kennedy et al. (2003)

Experiment 1 In a static image, changed the luminosity of the shadowed region while maintaining the luminosity of the red shadow border

Experiment 1 Created nine images with border polarity changing gradually from positive to negative and region polarity kept positive except for the last image Red BorderBlack Shadow Hue = 239 Hue = 0 Hue = 239 Hue = 0 Saturation = 240 Saturation = 0 Saturation = 240 Saturation = 0 Participants asked to rate each image on a scale from 1-to-10, where 10 was “easy to recognize the old person” 1 was “difficult to recognize”

Experiment 1 Border polarity changed from positive to negative

Experiment 1 Results The face was more evident in frame 1, but started to become difficult by frame 5, and was totally gone by frame 9…gradation effect Conclusion Shape-from-shadow perception becomes difficult as luminosity of the shadowed region becomes higher than the luminosity of the shadow border

Experiment 2 Using “Polka Dots” instead of solid region Using “Polka Dots” instead of solid region Changed luminosity of the shadow border and shadow region by changing number of dots in a square area Changed luminosity of the shadow border and shadow region by changing number of dots in a square area Created motion of the shadow border by changing positions of the polka dots Created motion of the shadow border by changing positions of the polka dots

Experiment 2 1 st Test Black-dot border Black-dot shadow Negative border polarity 2 nd Test Black-dot border Black-dot shadow Positive border polarity

Experiment 2 3 rd Test Red-dot border Black-dot shadow Negative border polarity 4 th Test Red-dot border Black-dot shadow Positive border polarity

Predictions difficult easy