Sherief Hammad's research while affiliated with University of Toronto and other places

Publications (8)

Chapter
Visual illusions cut across academic divides and popular interests: on the one hand, illusions provide entertainment as curious tricks of the eye; on the other hand, scientific research related to illusory phenomena has given generations of scientists and artists deep insights into the brain and principles of mind and consciousness. Numerous thinke...
Article
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In the picture-surface illusion, 2D features on the picture’s surface are seen biased towards their 3D referent e.g. an angle of 200 depicting a 900 corner of a cube is seen as 300. We tested linear and parallel perspective drawings of cubes with cube drawings subtending 50 to 500. The picture-surface illusion occurs for both parallel and linear pe...
Article
In a case-history, Ben, a university-graduate blind adult, is shown to draw a cube as if it were folded out, but with slim rectangles for the sides around a central square. This form is drawn by sighted 8-year-olds. It might involve foreshortening and parallel projection, despite the presence of more sides than would be present in parallel projecti...
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Lydia Maniatis (2009) adroitly argues our theories of a perspective illusion to do with angles are rigged in favour of our conclusions. Nice point. She develops useful alternative accounts of our illusion. However, her rigging argument involves the Bishop Berkeley induction problem. In response, we point out 2D features can specify 3D shapes. Count...
Article
Shapes on picture surfaces are not seen accurately (Arnheim, 1954). In particular, if they depict 3-D forms, angles between lines on a picture surface are misperceived. To test four theories of the misperception, subjects estimated acute and obtuse internal angles of quadrilaterals. Each quadrilateral was shown alone or as part of a drawing of a cu...
Article
Shapes on the surface of a perspective picture may be misperceived. Subjects picked a match for an ellipse depicting the circular top of a cylinder. The top was depicted as tilted forward from 5 degrees to 85 degrees, generating a series of ellipses on the picture surface. The matches were biased towards a circle over a wide range of midrange tilts...
Article
Full-text available
Shapes on the surface of a perspective picture may be misperceived. Subjects picked a match for an ellipse depicting the circular top of a cylinder. The top was depicted as tilted forward from 58 to 858, generating a series of ellipses on the picture surface. The matches were biased towards a circle over a wide range of midrange tilts, which sugges...
Article
Arnheim wrote extensively about perspective and percepts that were "in between" correct perception of objects and projected shapes. We apply Arnheim's views to a Renaissance piazza of square tiles. We show the kind of formalization to which the analysis leads and give a formula applicable to a perspective picture as an example. We argue that Arnhei...

Citations

... A runner is often shown with arms bent, and the Ford Mustang running-pony badge has a foreleg bent at the knee in an acute angle, and a rear leg meets the horizontal body at 45°. Likewise, a wedge shape, such as an isosceles triangle, in an oblique position, may suggest motion-in-depth with the point of the triangle taken to be receding afar, and the convergence of long sides of the triangle suggesting diminution due to perspective (Hammad and Kennedy, 2017;Mastandrea and Kennedy, 2016;. The triangle is readily taken as pointing (Attneave, 1971) and suggests a direction of motion. ...
... Because our participants could not use a ruler 4 to measure the pots they produced, they had to rely on perceptual judgment about when the pots were the right size. It is possible that the shortening we observed in the reduced feedback conditions created or contributed to a height distortion illusion similar to the vertical-horizontal illusion (e.g., Wolfe, Maloney, & Tam, 2005) or the picture-surface illusion (Kennedy & Hammad, 2014). ...
... Furthermore, given the correct symbolic input, Esref's practice shows it is possible for a Philosophical Theory of Color Tested Through Fine Art Practice person born blind to understand, describe and create art works using what are traditionally thought to be other visual concepts too. This includes what are thought to be wholly visually concepts, such as lack of light as shadow and distance making objects appear smaller (Kennedy, Juricevic, Hammad & Rajani, 2007;Kennedy & Juricevic, 2006). Thus, it can be argued that what the philosophical theory of color considered to be elements of perception linked solely to vision or an element of impairment can be understood through Esref's non-visual experience. ...
... That is, perception of the 2-D form on the picture surface was biased towards the depicted form tilted in 3-D (Hammad & Kennedy, 2011;Hammad, Kennedy, Juricevic, & Rajani, 2008b). Presumably, an illusory bias resulted from crosstalk between two kinds of information presented simultaneously, one being information for 2-D flat features on the bidimensional surface (the ellipse per se) and the other being information for features in a 3-D space behind the picture surface (Kennedy & Hammad, 2010;Koenderink & van Doorn, 2003;Sedgwick & Nicholls, 1993;Treisman, 1983). The crosstalk idea is that if two sources of information for size are present, emerging from one physical form that represents another, vision adopts a compromise, seeing one form biased towards the other. ...
... The study of angular illusions is related to shape constancy, as a proportion of angle illusions are thought to have their foundations in shape constancy mechanisms (Hammad et al., 2008). In a systematic study of angular illusions, which either did or did not rely on the processing of 3D depth cues (i.e. were reliant or not reliant on shape constancy mechanisms), Ostrofsky et al. (2015) found that there was a correlation between perceptual reproduction of angles embedded in triangles (no 3D cues) and quadrilaterals (3D cues) and errors made when drawing the same angles. ...
... The process of visual perception can be described as inferring properties of the distal stimulus from the available proximal information [8]. For example, perceived reflectance (lightness) is a distal property that is deduced from light on the retina (brightness) [9], or a distal circle is inferred from a proximal ellipse [10]. This is akin to 'recovering intrinsic scene characteristics' (which are distal) from images (which are proximal) in computer vision [11] . ...