Effects of surface reflectance on local second order shape estimation in dynamic scenes

Abstract

In dynamic scenes, relative motion between the object, the observer, and/or the environment projects as dynamic visual information onto the retina (optic flow) that facilitates 3D shape perception. When the object is diffusely reflective, e.g. a matte painted surface, this optic flow is directly linked to object shape, a property found at the foundations of most traditional shape-from-motion (SfM) schemes. When the object is specular, the corresponding specular flow is related to shape curvature, a regime change that challenges the visual system to determine concurrently both the shape and the distortions of the (sometimes unknown) environment reflected from its surface. While human observers are able to judge the global 3D shape of most specular objects, shape-from-specular-flow (SFSF) is not veridical. In fact, recent studies have also shown systematic biases in the perceived motion of such objects. Here we focus on the perception of local shape from specular flow and compare it to that of matte-textured rotating objects. Observers judged local surface shape by adjusting a rotation and scale invariant shape index probe. Compared to shape judgments of static objects we find that object motion decreases intra-observer variability in local shape estimation. Moreover, object motion introduces systematic changes in perceived shape between matte-textured and specular conditions. Taken together, this study provides a new insight toward the contribution of motion and surface material to local shape perception.

Computational model for human 3D shape perception from a single specular image

“…In this study, the sign and magnitude of the surface second derivatives are separately described. Similar representation can be seen in some psychophysical experiments [35,36], in which subjects classified 3D shapes based on curvature signs. Furthermore, the neural representation of surface curvatures was studied in electrophysiological experiments.…”

“…A similar phenomenon can be seen in human shape perception. When subjects classified local shapes based on the curvature signs, saddles were often misclassified as ridges or ruts (convex or concave cylinders) [35,36], suggesting that humans often neglect the small surface curvature of saddle shapes. Since the small surface curvature is less visible in the image, its estimation is intrinsically difficult.…”

Influence of optical material properties on the perception of liquids

“…Although it is commonly argued that shape dominates other cues in object recognition (Biederman, 1987;Landau, Smith, & Jones, 1988), liquids are highly mutable, so it is plausible that color and other optical characteristics might be more diagnostic than shape. At the same time, if shape and motion can be computed accurately across a wide range of different optical conditions (Todd, Norman, Koenderink, & Kappers, 1997;Todd, 2004;Nefs, Koenderink, & Kappers, 2006;Khang, Koenderink, & Kappers, 2007;Vangorp, Laurijssen, & Dutré, 2007;Doerschner, Yilmaz, Kucukoglu, & Fleming, 2013;Dövencioglu, Wijntjes, Ben-Shahar, & Doerschner, 2015), then viscosity could be estimated in a way that is unaffected by the surface material appearance, enabling ''viscosity constancy.'' Thus, there are grounds for believing that optical and mechanical properties may contribute to different extents depending on the specific judgments that observers are asked to make: whether it is estimating viscosity; rating other properties of liquids; or identifying (e.g., naming) specific materials, like paint, toothpaste or molasses.…”

Specular motion and 3D shape estimation

“…Surface reflection affects local shape estimation Dövencioglu, Wijntjes, Ben-Shahar, and Doerschner (2015) showed that surface reflectance affects the perceived local curvature sign of a computer-rendered moving object. Specifically, they found the shape estimations of complex matte objects to be closer to the ''ground truth'' (3D model of the object) compared with specular ones.…”

“…Unfortunately, the perceptual evidence to that effect is inconclusive. For example, studies by Doerschner et al (2013), Dövencioglu et al (2015), and Vota et al (2015) suggest that estimated curvature, slant, tilt, and object rotation axis are quite different for moving specular objects compared with their matte-textured counterparts (Mazzarella, Cholewiak, Phillips, & Fleming, 2014). But even if motion is taken out of the equation (Blake & Bulthoff, 1990Mazzarella et al, 2014), findings about the contribution of specular reflections to estimated 3D shape are conflicting.…”