Academic journal article Perception and Psychophysics

Viewer-External Frames of Reference in the Mental Transformation of 3-D Objects

Academic journal article Perception and Psychophysics

Viewer-External Frames of Reference in the Mental Transformation of 3-D Objects

Article excerpt

Most models of object recognition and mental rotation are based on the matching of an object's 2-D view with representations of the object stored in memory. They propose that a time-consuming normalization process compensates for any difference in viewpoint between the 2-D percept and the stored representation. Our experiment shows that such normalization is less time consuming when it has to compensate for disorientations around the vertical than around the horizontal axis of rotation. By decoupling the different possible reference frames, we demonstrate that this anisotropy of the normalization process is defined not with respect to the retinal frame of reference, but, rather, according to the gravitational or the visuocontextual frame of reference. Our results suggest that the visual system may call upon both the gravitational vertical and the visuocontext to serve as the frame of reference with respect to which 3-D objects are gauged in internal object transformations.

Object recognition is one of the most impressive abilities of the human organism. The visual system recognizes objects even though the retinal image varies following rotations of the object or following changes of the observer's viewing position. In fact, depending on its orientation, an object can correspond to an infinite number of different retinal projections. This ambiguity between the distal and the proximal stimulus is the elemental problem the visual system has to deal with (not only in object recognition).

Current Theories of Object Recognition

Contemporary theories of object recognition differ in how they consider the visual system solves this ambiguity. "Structural description models" assume that some specific features of the retinal projections of objects are still relatively independent of the object-observer relationship. Accordingly, the identification of these features is sufficient for the identification of the object (for details, see Biederman, 1987; Hummel & Biederman, 1992). These models predict that recognition performance should be invariant regarding spatial transformations. However, a large number of studies demonstrate that the identification of objects depends on their current orientation. Objects are recognized faster when presented from a canonical perspective ("three-quarters view"; Blanz, Tarr, & Bülthoff, 1999). Moreover, the more disoriented an object is with respect to the canonical perspective, the more time it takes to identify the object (Bülthoff, Edelman, & Tarr, 1995; Tarr & Bülthoff, 1998). For novel objects, new perspectives may become canonical, if subjects are presented repeatedly with these views. Tarr (1995) and Tarr and Pinker (1989) showed subjects novel objects from specific orientations. With increasing practice, subjects were able to recognize the objects equally quickly from all practiced perspectives. However, when the objects were suddenly presented from a new perspective, recognition performance depended on the distance from the nearest practiced view. Such effects of the object-observer relationship have been demonstrated in a variety of situations: for rotations in the picture plane (e.g., Jolicoeur, 1988) and rotations in the depth plane (e.g., Lawson & Humphreys, 1998; Lawson, Humphreys, & Jolicoeur, 2000); for novel objects (see also Bülthoff & Edelman, 1992; Edelman & Bülthoff, 1992), and for familiar objects (e.g., Hayward & Tarr, 1997; Lawson & Humphreys, 1998); on the subordinate level of categorization (e.g., Edelman & Bülthoff, 1992; Tarr, 1995), and for the entry level of recognition (Hayward & Williams, 2000; Lawson & Humphreys, 1998). All in all, there is, thus, compelling evidence that the recognition of objects systematically depends on the object's orientation: The more the actual perspective of the object departs from a canonical or familiar view, the worse the recognition performance (for some physiological evidence, see, e. …

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