Challenges in Understanding Visual Shape Perception and Representation: Bridging Subsymbolic and Symbolic Coding
Perceiving and representing the shapes of contours and objects are among the most crucial tasks for biological and artificial vision systems. Much is known about early cortical encoding of visual information, and at a more abstract level, experimental data and computational models have revealed great deal about contour, object, and shape perception. Between the early “subsymbolic” encodings and higher level “symbolic” descriptions (e.g., of contours or shapes), however, lies a considerable gap. In this chapter, we highlight the issue of attaining symbolic codes from subsymbolic ones in considering two crucial problems of shape. We describe (1) the dependence of shape perception and representation on segmentation and grouping processes. We show that in ordinary perception, shape descriptions are given to objects rather than visible regions, and we review progress in understanding interpolation processes that construct unified objects across gaps in the input. We relate these efforts to neurally plausible models of interpolation, but note that current versions still lack ways of achieving symbolic codes. We then consider (2) properties that (some) shape representations must have and why these require computations beyond the local information obtained in early visual encoding. As an example of how to bridge the gap between the subsymbolic and symbolic, we describe psychophysical and modeling work in which contour shape is approximated in terms of constant curvature segments. Our “arclet” model takes local, oriented units as inputs and produces outputs that are symbolic contour tokens with constant curvature parts. The approach provides a plausible account of aspects of contour shape perception, and more generally, it illustrates the kinds of properties needed for models that connect early visual filtering to ecologically useful outputs in the perception and representation of shape.
We thank Brian Keane, Evan Palmer, and Hongjing Lu for helpful discussions and Rachel Older for general assistance. Portions of the research reported here were supported by National Eye Institute Grant EY13518 to PJK.
- 3.Albert MK, Hoffman DD (2000) The generic-viewpoint assumption and illusory contours. Perception 29(3):303–312 Google Scholar
- 15.Ghose T, Erlikhman G, Kellman PJ (2011) Spatiotemporal object formation: contour vs surface interpolation. Perception 40 ECVP Abstract Supplement, p 59 Google Scholar
- 16.Gibson JJ (1979) The ecological approach to visual perception. Houghton Mifflin, Boston Google Scholar
- 24.Keane BP, Lu H, Papathomas TV, Silverstein SM, Kellman PJ Reinterpreting behavioral receptive fields: lightness induction alters visually completed shape, accepted pending minor revision. PLoS ONE Google Scholar
- 26.Kellman PJ (2003) Segmentation and grouping in object perception: a 4-dimensional approach. In: Behrmann M, Kimchi R (eds) Perceptual organization in vision: behavioral and neural perspectives: the 31st Carnegie symposium on cognition. Erlbaum, Hillsdale Google Scholar
- 27.Kellman PJ, Garrigan P (2007) Segmentation, grouping, and shape: some Hochbergian questions. In: Peterson MA, Gillam B, Sedgwick HA (eds) In the mind’s eye: Julian Hochberg on the perception of pictures, film, and the world. Oxford University Press, New York Google Scholar
- 31.Kellman PJ, Guttman SE, Wickens TD (2001) Geometric and neural models of object completion. In: Shipley TF, Kellman PJ (eds) From fragments to objects: segmentation and grouping in vision. Elsevier, Oxford Google Scholar
- 34.Koffka K (1935) Principles of Gestalt psychology. Harcourt Brace, New York Google Scholar
- 36.Marr D (1982) Vision. Freeman, New York Google Scholar
- 38.Pasupathy A, Conner CE (1999) Responses of contour features in macaque area V4. J Neurophysiol 82:2490–2502 Google Scholar
- 39.Pasupathy A, Conner CE (2001) Shape representation in area V4: position-specific tuning for boundary conformation. J Neurophysiol 86:2505–2519 Google Scholar
- 43.Rock I (1973) Orientation and form. Academic Press, San Diego Google Scholar
- 51.Ullmann S (1979) The shape of subjective contours and a model for their generation. Biol Cybern Google Scholar