Abstract
Visual form analysis is fundamental to shape perception and likely plays a central role in perception of more complex dynamic shapes, such as moving objects or biological motion. Two primary form-based cues serve to represent the overall shape of an object: the spatial position and the orientation of locations along the boundary of the object. However, it is unclear how the visual system integrates these two sources of information in dynamic form analysis, and in particular how the brain resolves ambiguities due to sensory uncertainty and/or cue conflict. In the current study, we created animations of sparsely-sampled dynamic objects (human walkers or rotating squares) comprised of oriented Gabor patches in which orientation could either coincide or conflict with information provided by position cues. When the cues were incongruent, we found a characteristic trade-off between position and orientation information whereby position cues increasingly dominated perception as the relative uncertainty of orientation increased and vice versa. Furthermore, we found no evidence for differences in the visual processing of biological and non-biological objects, casting doubt on the claim that biological motion may be specialized in the human brain, at least in specific terms of form analysis. To explain these behavioral results quantitatively, we adopt a probabilistic template-matching model that uses Bayesian inference within local modules to estimate object shape separately from either spatial position or orientation signals. The outputs of the two modules are integrated with weights that reflect individual estimates of subjective cue reliability, and integrated over time to produce a decision about the perceived dynamics of the input data. Results of this model provided a close fit to the behavioral data, suggesting a mechanism in the human visual system that approximates rational Bayesian inference to integrate position and orientation signals in dynamic form analysis.
Highlights
The ability to analyze the shape and character of moving objects in the environment is essential for adaptive behavior in a dynamic visual world
The current study documents several significant findings related to dynamic form analysis in the human visual system
Using the limited lifetime sampling technique to weaken the usefulness of local image motion information and to probe dynamic form processing, we created a novel stimulus in which Gabor elements provided orientation cues that were either congruent or incongruent with information provided by spatial position cues
Summary
The ability to analyze the shape and character of moving objects in the environment is essential for adaptive behavior in a dynamic visual world. Since the world is by no means stationary, human vision must deal with the fact that objects can undergo changes in shape, viewpoint, and position over time These changes add yet more complexity and ambiguity to the problem of dynamic form perception. One class of models is based on analysis of patterns of local image motion (Webb and Aggarwal, 1982; Giese and Poggio, 2003; Casile and Giese, 2005), while another class of models is based on sequential static form information over time, or dynamic form analysis (Lange and Lappe, 2006; Lange et al, 2006; Theusner et al, 2014) This dichotomy is rooted, in part, in the classical distinction between dorsal and ventral stream processing in the primate visual system (Ungerleider and Mishkin, 1982; Goodale and Milner, 1992). Recent evidence from behavioral (Atkinson et al, 2007; Thurman and Grossman, 2008; Thurman et al, 2010; Thurman and Lu, 2013a), neurophysiological (Vangeneugden et al, 2009, 2011; Singer and Sheinberg, 2010), and functional brain imaging studies (Jastorff and Orban, 2008, 2009; Jastorff et al, 2012; Thompson and Baccus, 2012) is converging on the view that several mechanisms may be employed simultaneously, based on analysis and integration of both motion
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