Research asserting that the visual system instantiates a global closure heuristic in contour integration has been challenged by an argument that behaviorally-detected closure enhancement could be accounted for by low-level local mechanisms driven by collinearity or "good continuation" interacting with proximity. The present study investigated this issue in three experiments. Exp. 1 compared the visibility of closed and open contours using circles and S-contours from low to moderately high angles of path curvature in a temporal alternative-forced choice task. Circles were more detectable than S-contours, an effect that increased with curvature. The closure enhancement observed can, however, be explained by the fact that circles contain more 'contiguity' than S-contours. Additional tests added discontinuities to otherwise closed paths to control for the effects of good continuation and closure independently. Exp. 2 compared the visibility of incomplete circles (C-contours) and S-contours derived from the full circles and S-contours in Exp. 1. Exp. 3a compared the visibility of arc pairs arranged in an enclosed position similar to "()" and a non-enclosed position similar to ")(". Results consistently showed enhanced visibility of contour configurations enclosing a region even after controlling for differences in contiguity and changes of curvature direction. A control test (Exp. 3b) demonstrated that the gap in the contours of Exp. 3a was too large to be bridged by local-level collinearity/proximity alone. The combination of good continuation and proximity alone does not explain the closure effects observed across these tests, as demonstrated through the application of a Bayesian model of collinearity and proximity (Geisler et al., 2001) to the stimuli in Exps. 3a and 3b. These results argue for the presence of a global closure-driven contour enhancing mechanism in human vision.

Previous research has indicated that the ability to integrate individual elements in the presence of noise is immature in 3-month-old infants. The present study extended the developmental timeline by investigating 6-month-olds' ability to integrate individual elements into whole contours through an assessment of their capability to discriminate circle and square contours constructed from oriented Gabor patches via a newly designed cueing paradigm for infants. If infants discriminate the centrally-presented contour cues, then their eye movements would correctly anticipate subsequent target presentation at a rate greater than chance. The results indicated that infants integrated the contours and discriminated the different shapes, but, consistent with past research, this ability is still fairly immature at this age, tolerating limited amount of noise.

The purpose of the current article is to highlight the importance of operant techniques in developmental research. Although many researchers employ operant techniques within their individual fields of study, the pervasive nature of these techniques is not often acknowledged in the general literature. The present article describes the history of the use of operant techniques in developmental contexts and summarizes current basic research using this approach across a variety of disciplines. In addition, the recent use of operant techniques to explore cognitive development and the unique advantages it brings to this field over more traditional approaches are highlighted. Finally, the application of these techniques to clinical contexts is presented to demonstrate the usefulness of operant procedures with clinical populations.

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