Shape from shading in starlings (Sturnus vulgaris).

Abstract

Birds behave as if they quickly and accurately perceive an object-filled visual world. Beyond the extensive research with pigeons, however, there is a large and important gap in our knowledge about the mechanisms of object perception and recognition in other avian visual systems. The pattern of shading reflected from object surfaces is one important optical feature providing fundamental information about shape. To better understand how surface and object shading is processed by a passerine species, five starlings were tested with differentially illuminated convex and concave curved surfaces in three experiments using a simultaneous visual discrimination procedure. Starlings rapidly learned this shape-from-shading discrimination independent of varied lighting direction, surface color, and camera perspective. Variations in the pattern of lighting through experimental manipulations of camera perspective, surface height, contrast, material specularity, and surface shape were consistent with the hypothesis that the starlings perceived these illuminated surfaces as having three-dimensional shape, similar to results previously collected with pigeons. These similarities across different orders of birds indicate that the relative shading for objects in a visual scene is a highly salient feature for shape processing in birds and is likely a highly conserved visual process that is widely distributed within this class of animal.

Experimental Divergences in the Visual Cognition of Birds and Mammals

“…Conversely, extending our knowledge of pigeon visual cognition beyond the touchscreen, either by using real objects in laboratory contexts or using the broader, open-field tests similar to those conducted with tits above, may also contribute critical information regarding comparative visual processes, as well as providing valuable ecological validity (cf. Qadri, Romero, & Cook, 2014; Rowland, Cuthill, Harvey, Speed, & Ruxton, 2008). In addition to better controlling the experimental methods applied to each species, selecting species according to the visual cognition necessary for their ecological niche or natural history would further strengthen evaluations of unique and general avian visual mechanisms.…”

The perception of Glass patterns by starlings (Sturnus vulgaris)

“…Four had served in a shape-from-shading experiment (Qadri et al, in press). They were individually housed in a single room on a 12:12 LD cycle (7:00 AM–7:00 PM).…”

“…As details for this apparatus have been reported elsewhere (Qadri et al, in press), only the critical details are outlined here. Each starling was continuously tested in its own “live-in” housing/testing chamber consisting of a home cage and a testing area without any divider.…”

“…One study has suggested that starlings and pigeons may differ in their lateralization of different visual functions (Templeton & Gonzalez, 2004) Lastly, a multivariate analysis of the brain compositions of various birds has suggested that since diverging between 70 to 120 million years ago (Brown, Rest, Garcia-Moreno, Sorenson, & Mindell, 2008; Chojnowski, Kimball, & Braun, 2008), passeriformes and columbiformes have evolved dissimilar cerebrotypes, with different relative proportions of cerebellum, brainstem, and telencephalic regions, including areas known to process vision (Iwaniuk & Hurd, 2005). Surprisingly little is known about how starlings cognitively process more complex visual information, especially in comparison to other birds (Bennett, Cuthill, Partridge, & Lunau, 1997; Cook, Qadri, Kieres, & Commons-Miller, 2012; Qadri, Romero, & Cook, in press; Swaddle, Che, & Clelland, 2004; Templeton & Gonzalez, 2004). Here we started by examining how starlings process Glass patterns.…”

The Role of Life-History and Ecology in the Evolution of Color Patterns in Australian Chrysomeline Beetles

“…The distribution of color intensities on a convex shape, like a beetle, would vary in a natural landscape because of multiple illumination sources, such as light scattering from forest gaps or surrounding objects (Khang et al, 2006). Studies of humans, pigeons and starlings show that the perceived shape and depth of an object is affected by the amount of illumination on it (Ramachandran, 1988;Cook et al, 2012;Qadri et al, 2014). As the shape and depth of an organism may be correlated with its nutritional return as a prey item, the shape and depth may also reflect an animal's value to a predator (Stephens and Krebs, 1986;Rychlik, 1999).…”