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Brightness/darkness induction and the genesis of a contour.

Roncato S - Front Hum Neurosci (2014)

Bottom Line: Particular configurations have been introduced that allow us to observe the induction effects of one contour taken in isolation.This effect weakens or s when the contour of the invariant CP separates surfaces filled with different gray shades.These conflicting results stimulate a deeper exploration of the induction phenomena and their role in the computation of brightness contrast.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento Psicologia Generale, Università Padova Padova, Italy.

ABSTRACT
Visual contours often result from the integration or interpolation of fragmented edges. The strength of the completion increases when the edges share the same contrast polarity (CP). Here we demonstrate that the appearance in the perceptual field of this integrated unit, or contour of invariant CP, is concomitant with a vivid brightness alteration of the surfaces at its opposite sides. To observe this effect requires some stratagems because the formation in the visual field of a contour of invariant CP normally engenders the formation of a second contour and then the rise of two streams of induction signals that interfere in different ways. Particular configurations have been introduced that allow us to observe the induction effects of one contour taken in isolation. I documented these effects by phenomenological observations and psychophysical measurement of the brightness alteration in relation to luminance contrast. When the edges of the same CP complete to form a contour, the background of homogeneous luminance appears to dim at one side and to brighten at the opposite side (in accord with the CP). The strength of the phenomenon is proportional to the local luminance contrast. This effect weakens or s when the contour of the invariant CP separates surfaces filled with different gray shades. These conflicting results stimulate a deeper exploration of the induction phenomena and their role in the computation of brightness contrast. An alternative perspective is offered to account for some brightness illusions and their relation to the phenomenal transparency. The main assumption asserts that, when in the same region induction signals of opposite CP overlap, the filling-in is blocked unless the image is stratified into different layers, one for each signal of the same polarity. Phenomenological observations document this "solution" by the visual system.

No MeSH data available.


Related in: MedlinePlus

The genesis of contour of invariant contrast polarity in Figure 2. (A) A portion of Figure 2 vertically reoriented. (B) The two binding phenomena in the corner regions of Figure 2C. The dotted lines indicate the conjunction pathways. (C) The dotted line indicates one of the two axes (axis 1 hereafter) of invariant CP resulting from the chaining of the local binding effects in the corner regions. (D) A dotted line follows the outer perimeter of the rectangles to indicate the second Axis of invariant CP (axis 2 henceforth) resulting from the chaining of the local binding effects: the horizontally directed ones in (B). (E) The rectangles in (A) are occluded, at their extremes, by irregular shapes of opposite contrast polarity. The reversal of the contrast sign inhibits the chaining process so that only the axis 1 survives. (F) The overall result of binding effects after the manipulation illustrated in (D): the vertical axis 1 and horizontal binding effects that do not integrate to complete an illusory contour.
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Figure 3: The genesis of contour of invariant contrast polarity in Figure 2. (A) A portion of Figure 2 vertically reoriented. (B) The two binding phenomena in the corner regions of Figure 2C. The dotted lines indicate the conjunction pathways. (C) The dotted line indicates one of the two axes (axis 1 hereafter) of invariant CP resulting from the chaining of the local binding effects in the corner regions. (D) A dotted line follows the outer perimeter of the rectangles to indicate the second Axis of invariant CP (axis 2 henceforth) resulting from the chaining of the local binding effects: the horizontally directed ones in (B). (E) The rectangles in (A) are occluded, at their extremes, by irregular shapes of opposite contrast polarity. The reversal of the contrast sign inhibits the chaining process so that only the axis 1 survives. (F) The overall result of binding effects after the manipulation illustrated in (D): the vertical axis 1 and horizontal binding effects that do not integrate to complete an illusory contour.

Mentions: In Figure 3A a portion of Figure 2 is depicted vertically reoriented. In Figure 3B an enlargement of a corner region illustrates the contrast polarities at the edges and the two directions of the binding effects. A series of local bindings, as such, sum to give rise to two overall effects symbolized by dotted lines in Figures 3C,D, respectively. Note that the former follows a vertical pathway to bind the square sides vertically aligned (axis 1). The latter follows a waving pathway to circumvent the outer square perimeters (axis 2). There result, then, is the overall chaining effects that interpolate the local binding phenomena.


Brightness/darkness induction and the genesis of a contour.

Roncato S - Front Hum Neurosci (2014)

The genesis of contour of invariant contrast polarity in Figure 2. (A) A portion of Figure 2 vertically reoriented. (B) The two binding phenomena in the corner regions of Figure 2C. The dotted lines indicate the conjunction pathways. (C) The dotted line indicates one of the two axes (axis 1 hereafter) of invariant CP resulting from the chaining of the local binding effects in the corner regions. (D) A dotted line follows the outer perimeter of the rectangles to indicate the second Axis of invariant CP (axis 2 henceforth) resulting from the chaining of the local binding effects: the horizontally directed ones in (B). (E) The rectangles in (A) are occluded, at their extremes, by irregular shapes of opposite contrast polarity. The reversal of the contrast sign inhibits the chaining process so that only the axis 1 survives. (F) The overall result of binding effects after the manipulation illustrated in (D): the vertical axis 1 and horizontal binding effects that do not integrate to complete an illusory contour.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4202701&req=5

Figure 3: The genesis of contour of invariant contrast polarity in Figure 2. (A) A portion of Figure 2 vertically reoriented. (B) The two binding phenomena in the corner regions of Figure 2C. The dotted lines indicate the conjunction pathways. (C) The dotted line indicates one of the two axes (axis 1 hereafter) of invariant CP resulting from the chaining of the local binding effects in the corner regions. (D) A dotted line follows the outer perimeter of the rectangles to indicate the second Axis of invariant CP (axis 2 henceforth) resulting from the chaining of the local binding effects: the horizontally directed ones in (B). (E) The rectangles in (A) are occluded, at their extremes, by irregular shapes of opposite contrast polarity. The reversal of the contrast sign inhibits the chaining process so that only the axis 1 survives. (F) The overall result of binding effects after the manipulation illustrated in (D): the vertical axis 1 and horizontal binding effects that do not integrate to complete an illusory contour.
Mentions: In Figure 3A a portion of Figure 2 is depicted vertically reoriented. In Figure 3B an enlargement of a corner region illustrates the contrast polarities at the edges and the two directions of the binding effects. A series of local bindings, as such, sum to give rise to two overall effects symbolized by dotted lines in Figures 3C,D, respectively. Note that the former follows a vertical pathway to bind the square sides vertically aligned (axis 1). The latter follows a waving pathway to circumvent the outer square perimeters (axis 2). There result, then, is the overall chaining effects that interpolate the local binding phenomena.

Bottom Line: Particular configurations have been introduced that allow us to observe the induction effects of one contour taken in isolation.This effect weakens or s when the contour of the invariant CP separates surfaces filled with different gray shades.These conflicting results stimulate a deeper exploration of the induction phenomena and their role in the computation of brightness contrast.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento Psicologia Generale, Università Padova Padova, Italy.

ABSTRACT
Visual contours often result from the integration or interpolation of fragmented edges. The strength of the completion increases when the edges share the same contrast polarity (CP). Here we demonstrate that the appearance in the perceptual field of this integrated unit, or contour of invariant CP, is concomitant with a vivid brightness alteration of the surfaces at its opposite sides. To observe this effect requires some stratagems because the formation in the visual field of a contour of invariant CP normally engenders the formation of a second contour and then the rise of two streams of induction signals that interfere in different ways. Particular configurations have been introduced that allow us to observe the induction effects of one contour taken in isolation. I documented these effects by phenomenological observations and psychophysical measurement of the brightness alteration in relation to luminance contrast. When the edges of the same CP complete to form a contour, the background of homogeneous luminance appears to dim at one side and to brighten at the opposite side (in accord with the CP). The strength of the phenomenon is proportional to the local luminance contrast. This effect weakens or s when the contour of the invariant CP separates surfaces filled with different gray shades. These conflicting results stimulate a deeper exploration of the induction phenomena and their role in the computation of brightness contrast. An alternative perspective is offered to account for some brightness illusions and their relation to the phenomenal transparency. The main assumption asserts that, when in the same region induction signals of opposite CP overlap, the filling-in is blocked unless the image is stratified into different layers, one for each signal of the same polarity. Phenomenological observations document this "solution" by the visual system.

No MeSH data available.


Related in: MedlinePlus