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Reinterpreting behavioral receptive fields: lightness induction alters visually completed shape.

Keane BP, Lu H, Papathomas TV, Silverstein SM, Kellman PJ - PLoS ONE (2013)

Bottom Line: This pattern arose when pixels immediately adjacent to the discriminated boundaries were excluded from the analysis (Experiment 2) and also when the noise was restricted to the key regions so that the noise never overlapped with the physically visible edges (Experiment 3).Moreover, behavioral receptive fields derived in CI studies do not correspond to contours per se but to filled-in surface regions contained by those contours.The relevance of lightness to two-dimensional shape completion supplies a new constraint for models of object perception.

View Article: PubMed Central - PubMed

Affiliation: Center for Cognitive Science, Rutgers University, New Brunswick, Piscataway, New Jersey, USA. Brian.Keane@gmail.com

ABSTRACT

Background: A classification image (CI) technique has shown that static luminance noise near visually completed contours affects the discrimination of fat and thin Kanizsa shapes. These influential noise regions were proposed to reveal "behavioral receptive fields" of completed contours-the same regions to which early cortical cells respond in neurophysiological studies of contour completion. Here, we hypothesized that 1) influential noise regions correspond to the surfaces that distinguish fat and thin shapes (hereafter, key regions); and 2) key region noise biases a "fat" response to the extent that its contrast polarity (lighter or darker than background) matches the shape's filled-in surface color.

Results: To test our hypothesis, we had observers discriminate fat and thin noise-embedded rectangles that were defined by either illusory or luminance-defined contours (Experiment 1). Surrounding elements ("inducers") caused the shapes to appear either lighter or darker than the background-a process sometimes referred to as lightness induction. For both illusory and luminance-defined rectangles, key region noise biased a fat response to the extent that its contrast polarity (light or dark) matched the induced surface color. When lightness induction was minimized, luminance noise had no consistent influence on shape discrimination. This pattern arose when pixels immediately adjacent to the discriminated boundaries were excluded from the analysis (Experiment 2) and also when the noise was restricted to the key regions so that the noise never overlapped with the physically visible edges (Experiment 3). The lightness effects did not occur in the absence of enclosing boundaries (Experiment 4).

Conclusions: Under noisy conditions, lightness induction alters visually completed shape. Moreover, behavioral receptive fields derived in CI studies do not correspond to contours per se but to filled-in surface regions contained by those contours. The relevance of lightness to two-dimensional shape completion supplies a new constraint for models of object perception.

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Related in: MedlinePlus

Key region and results for Experiment 2.(A) The shape differences in this experiment were twice as large as the first experiment, but the ROIs spanned the same narrow area. (B) Mean ROI values are shown for each condition. Errors provide +/− SEM.
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pone-0062505-g006: Key region and results for Experiment 2.(A) The shape differences in this experiment were twice as large as the first experiment, but the ROIs spanned the same narrow area. (B) Mean ROI values are shown for each condition. Errors provide +/− SEM.

Mentions: To show more convincingly that filled-in surface regions alter shape perception, a second experiment was conducted wherein the shape differences were increased so that the key regions were twice as large as before (see Figure 6). The same narrow ROI filter was applied as in the first experiment, so that the analyzed pixels were no longer immediately adjacent to the discriminated contours. Visually meaningful CIs did not emerge because there was one-sixth as much data as in the previous experiment. However, the more sensitive ROI method once again showed a strong effect of inducer polarity, F(2, 48) = 7.02, p = .002. More specifically, light or dark key region noise pixels tended to be assimilated into the shape when the induced surface color was light or dark, respectively. This effect did not depend on whether the shape was real or interpolated, F(2, 48) = 0.51, p>.6. These results did not differ appreciably with those found in Experiment 1, F(2,146) = 1.04, p = .36, indicating that the magnitude of noise influence does not drop off sharply with distance from the discriminated contour.


Reinterpreting behavioral receptive fields: lightness induction alters visually completed shape.

Keane BP, Lu H, Papathomas TV, Silverstein SM, Kellman PJ - PLoS ONE (2013)

Key region and results for Experiment 2.(A) The shape differences in this experiment were twice as large as the first experiment, but the ROIs spanned the same narrow area. (B) Mean ROI values are shown for each condition. Errors provide +/− SEM.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672097&req=5

pone-0062505-g006: Key region and results for Experiment 2.(A) The shape differences in this experiment were twice as large as the first experiment, but the ROIs spanned the same narrow area. (B) Mean ROI values are shown for each condition. Errors provide +/− SEM.
Mentions: To show more convincingly that filled-in surface regions alter shape perception, a second experiment was conducted wherein the shape differences were increased so that the key regions were twice as large as before (see Figure 6). The same narrow ROI filter was applied as in the first experiment, so that the analyzed pixels were no longer immediately adjacent to the discriminated contours. Visually meaningful CIs did not emerge because there was one-sixth as much data as in the previous experiment. However, the more sensitive ROI method once again showed a strong effect of inducer polarity, F(2, 48) = 7.02, p = .002. More specifically, light or dark key region noise pixels tended to be assimilated into the shape when the induced surface color was light or dark, respectively. This effect did not depend on whether the shape was real or interpolated, F(2, 48) = 0.51, p>.6. These results did not differ appreciably with those found in Experiment 1, F(2,146) = 1.04, p = .36, indicating that the magnitude of noise influence does not drop off sharply with distance from the discriminated contour.

Bottom Line: This pattern arose when pixels immediately adjacent to the discriminated boundaries were excluded from the analysis (Experiment 2) and also when the noise was restricted to the key regions so that the noise never overlapped with the physically visible edges (Experiment 3).Moreover, behavioral receptive fields derived in CI studies do not correspond to contours per se but to filled-in surface regions contained by those contours.The relevance of lightness to two-dimensional shape completion supplies a new constraint for models of object perception.

View Article: PubMed Central - PubMed

Affiliation: Center for Cognitive Science, Rutgers University, New Brunswick, Piscataway, New Jersey, USA. Brian.Keane@gmail.com

ABSTRACT

Background: A classification image (CI) technique has shown that static luminance noise near visually completed contours affects the discrimination of fat and thin Kanizsa shapes. These influential noise regions were proposed to reveal "behavioral receptive fields" of completed contours-the same regions to which early cortical cells respond in neurophysiological studies of contour completion. Here, we hypothesized that 1) influential noise regions correspond to the surfaces that distinguish fat and thin shapes (hereafter, key regions); and 2) key region noise biases a "fat" response to the extent that its contrast polarity (lighter or darker than background) matches the shape's filled-in surface color.

Results: To test our hypothesis, we had observers discriminate fat and thin noise-embedded rectangles that were defined by either illusory or luminance-defined contours (Experiment 1). Surrounding elements ("inducers") caused the shapes to appear either lighter or darker than the background-a process sometimes referred to as lightness induction. For both illusory and luminance-defined rectangles, key region noise biased a fat response to the extent that its contrast polarity (light or dark) matched the induced surface color. When lightness induction was minimized, luminance noise had no consistent influence on shape discrimination. This pattern arose when pixels immediately adjacent to the discriminated boundaries were excluded from the analysis (Experiment 2) and also when the noise was restricted to the key regions so that the noise never overlapped with the physically visible edges (Experiment 3). The lightness effects did not occur in the absence of enclosing boundaries (Experiment 4).

Conclusions: Under noisy conditions, lightness induction alters visually completed shape. Moreover, behavioral receptive fields derived in CI studies do not correspond to contours per se but to filled-in surface regions contained by those contours. The relevance of lightness to two-dimensional shape completion supplies a new constraint for models of object perception.

Show MeSH
Related in: MedlinePlus