Tolerance for local and global differences in the integration of shape information E Dickinson, S Cribb, H Riddell, D Badcock |
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School of Psychology, University of Western Australia, Australia
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| Objects are often identified visually by the shape of their profiles, and global encoding of shape is implied by evidence that, for boundaries distorted from circular by sinusoidal modulation of radius, information is integrated across cycles. The relationship between evidence for integration within regular shapes and encoding of complex profiles has, however, been neglected. In this psychophysical study, rather than attempting to reconcile competing models of shape analysis, we chose to manipulate the function describing the boundary modulation to explore the envelope of integration. In a previous study we identified that detection threshold scales with modulation frequency and, hence, maximum orientation difference from circular. Exploiting this property we first rectified the modulating function and showed that integration was preserved, but also that patterns with rectified and un-rectified modulation could not be discriminated at threshold demonstrating that continuity of curvature is not critical to integration or object recognition. Second we concatenated cycles of different frequency by matching their orientations at zero crossings of the sine function to create irregular patterns. Again integration was preserved. Mirror images of an irregular pattern could not, however, be discriminated at threshold suggesting that the two patterns are not represented by different spatial templates. |
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