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Publication Detail
Object Knowledge Shapes Properties of Early Feature-Detectors by Top-Down Modulation.
Classic models of visual perception assume that early stages of information-processing are carried out by arrays of specialized and static feature-detectors that operate independently of high-level representations of a stimulus. Current developments in computational vision research have challenged this notion, hypothesizing that feedback connections from higher- to lower-level stages of processing shape the properties of feature detectors to optimize their performance. Evidence to support this hypothesis is difficult to obtain since any experimental design trying to test it has to ensure that sensory stimulation of early detectors remains identical while high-level representations of the stimulus are manipulated. Here, we used two-tone images of objects in a psychophysical procedure to achieve this and demonstrate a significant influence of high-level object knowledge on response properties of early edge-detectors. Two-tone images feature stimulus regions that are physically homogenous but are experienced as an object contour (somewhat similar to illusory contours in Kanizsa figures) once the observer is provided with relevant image information. We embedded edge-elements in these areas that were consistent or inconsistent with the high-level contour representation and measured absolute contrast detection-thresholds for these elements before and after providing relevant object knowledge. Results indicate that prior knowledge facilitates absolute contrast-threshold for edge elements that are consistent with the high-level representation of a stimulus but has no effects on contour-inconsistent edge-elements. The experimental design of the study ensured that this pattern of results is unlikely to be due to uncertainty reduction about target orientation, a notion supported by a simulation based on a neurophysiologically-plausible population-code. Together, these findings provide clear evidence that early feature-detectors do not operate independently of visual cognition. Rather response properties of early information-processing units are shaped by top-down modulation from high-level image representations. Meeting abstract presented at VSS 2015.
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