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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 three figures have the same homogeneous gray background. (A) Columns of jagged squares alternating in shade at the opposite side of a vertical dividing line. The building schema is the same as the Adelson's “argyle illusion.” Note the illusory alternation of dark and light gray regions. Opaque regions similar to piles of road signs alternate in dark and light gray shades. Vertical bands alternate as shadow or illuminated zones. (B) Columns of irregular shapes split into dark/light surfaces are used to generate vertical invariant CP axes. The basic drawing is identical to (A), irregular shapes have been superimposed on the squares so that the CP reverses along their outer contour. The vertical axes are indicated by the bidirectional arrows. The perception of alternating dark and bright bands on the background is illusory, since they have the same luminance. Note that the background appears to dim when embedded between +/− −/+ axes and to brighten when embedded between and −/+ +/− axes. Labels D and L indicate the regions between +/− −/+ and −/+ +/− axes, respectively, and are regions that appeared as dimmed or lightened, respectively, in the test condition “divided background” (see text). (C) The same as (A) but with inducers on the left of the column mirror-imaged. Whatever pathway is followed, the CP inverts periodically. The arrows below point to the axes of variable CP (±). Labels D and L indicate the corresponding regions that were progressively darkened or lightened when the figure served as comparison stimulus.
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Figure 4: The three figures have the same homogeneous gray background. (A) Columns of jagged squares alternating in shade at the opposite side of a vertical dividing line. The building schema is the same as the Adelson's “argyle illusion.” Note the illusory alternation of dark and light gray regions. Opaque regions similar to piles of road signs alternate in dark and light gray shades. Vertical bands alternate as shadow or illuminated zones. (B) Columns of irregular shapes split into dark/light surfaces are used to generate vertical invariant CP axes. The basic drawing is identical to (A), irregular shapes have been superimposed on the squares so that the CP reverses along their outer contour. The vertical axes are indicated by the bidirectional arrows. The perception of alternating dark and bright bands on the background is illusory, since they have the same luminance. Note that the background appears to dim when embedded between +/− −/+ axes and to brighten when embedded between and −/+ +/− axes. Labels D and L indicate the regions between +/− −/+ and −/+ +/− axes, respectively, and are regions that appeared as dimmed or lightened, respectively, in the test condition “divided background” (see text). (C) The same as (A) but with inducers on the left of the column mirror-imaged. Whatever pathway is followed, the CP inverts periodically. The arrows below point to the axes of variable CP (±). Labels D and L indicate the corresponding regions that were progressively darkened or lightened when the figure served as comparison stimulus.

Mentions: In Figure 4 different configurations of inducers have been created so that to allow the comparison of the effects generated by or two interlaced contours of invariant CP. Inducers with a jagged contours were drawn in order to put a further obstacle to the rise of the phenomenal transparency. The three configurations have been depicted against the same mid-gray homogeneous background, therefore whenever light and dark region are perceived a brightness illusion is generated.


Brightness/darkness induction and the genesis of a contour.

Roncato S - Front Hum Neurosci (2014)

The three figures have the same homogeneous gray background. (A) Columns of jagged squares alternating in shade at the opposite side of a vertical dividing line. The building schema is the same as the Adelson's “argyle illusion.” Note the illusory alternation of dark and light gray regions. Opaque regions similar to piles of road signs alternate in dark and light gray shades. Vertical bands alternate as shadow or illuminated zones. (B) Columns of irregular shapes split into dark/light surfaces are used to generate vertical invariant CP axes. The basic drawing is identical to (A), irregular shapes have been superimposed on the squares so that the CP reverses along their outer contour. The vertical axes are indicated by the bidirectional arrows. The perception of alternating dark and bright bands on the background is illusory, since they have the same luminance. Note that the background appears to dim when embedded between +/− −/+ axes and to brighten when embedded between and −/+ +/− axes. Labels D and L indicate the regions between +/− −/+ and −/+ +/− axes, respectively, and are regions that appeared as dimmed or lightened, respectively, in the test condition “divided background” (see text). (C) The same as (A) but with inducers on the left of the column mirror-imaged. Whatever pathway is followed, the CP inverts periodically. The arrows below point to the axes of variable CP (±). Labels D and L indicate the corresponding regions that were progressively darkened or lightened when the figure served as comparison stimulus.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 4: The three figures have the same homogeneous gray background. (A) Columns of jagged squares alternating in shade at the opposite side of a vertical dividing line. The building schema is the same as the Adelson's “argyle illusion.” Note the illusory alternation of dark and light gray regions. Opaque regions similar to piles of road signs alternate in dark and light gray shades. Vertical bands alternate as shadow or illuminated zones. (B) Columns of irregular shapes split into dark/light surfaces are used to generate vertical invariant CP axes. The basic drawing is identical to (A), irregular shapes have been superimposed on the squares so that the CP reverses along their outer contour. The vertical axes are indicated by the bidirectional arrows. The perception of alternating dark and bright bands on the background is illusory, since they have the same luminance. Note that the background appears to dim when embedded between +/− −/+ axes and to brighten when embedded between and −/+ +/− axes. Labels D and L indicate the regions between +/− −/+ and −/+ +/− axes, respectively, and are regions that appeared as dimmed or lightened, respectively, in the test condition “divided background” (see text). (C) The same as (A) but with inducers on the left of the column mirror-imaged. Whatever pathway is followed, the CP inverts periodically. The arrows below point to the axes of variable CP (±). Labels D and L indicate the corresponding regions that were progressively darkened or lightened when the figure served as comparison stimulus.
Mentions: In Figure 4 different configurations of inducers have been created so that to allow the comparison of the effects generated by or two interlaced contours of invariant CP. Inducers with a jagged contours were drawn in order to put a further obstacle to the rise of the phenomenal transparency. The three configurations have been depicted against the same mid-gray homogeneous background, therefore whenever light and dark region are perceived a brightness illusion is generated.

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