Limits...
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 magnitude of the illusory brightness/darkness induction effect (index I) as a function of average background luminance and inducer contrast. Bars indicate standard error. (A) Homogeneous surround. Test stimuli with invariant CP axes. (B) Divided background. Test stimuli with invariant CP axes. (C) Divided background. Test stimuli with axes of variable CP. Bottom gray rectangle: the three types of inducers. Left to right: HC (high contrast), mean contrast (MC), low contrast (LC).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4202701&req=5

Figure 5: The magnitude of the illusory brightness/darkness induction effect (index I) as a function of average background luminance and inducer contrast. Bars indicate standard error. (A) Homogeneous surround. Test stimuli with invariant CP axes. (B) Divided background. Test stimuli with invariant CP axes. (C) Divided background. Test stimuli with axes of variable CP. Bottom gray rectangle: the three types of inducers. Left to right: HC (high contrast), mean contrast (MC), low contrast (LC).

Mentions: The inducer orientation always formed variable CP axes (Figure 4C). For each of the 18 test stimuli, a series of comparison stimuli were generated by gradually differentiating the luminance of the vertical bands between the inducer axes. From an initial configuration with between-column background of common magnitude (12.9 or 16.1 cd/m2), successive stimuli were obtained by increasing the luminance (L between Figure 4C arrows) of one HSL point (Hue, Saturation, Luminance in the standard color dialog) and decreasing luminance (D between Figure 5 arrows) of the neighboring region of same magnitude. The mean variation was ~0.2 cd/m2. For each step the luminance of the darker and lighter bands was measured using a Minolta LS-110 photometer and the magnitude difference, Lp-Dp (subscript p for photometric), calculated. The procedure was repeated 20 times to create a sequence of stimuli where luminance contrast between alternating bands gradually increased.


Brightness/darkness induction and the genesis of a contour.

Roncato S - Front Hum Neurosci (2014)

The magnitude of the illusory brightness/darkness induction effect (index I) as a function of average background luminance and inducer contrast. Bars indicate standard error. (A) Homogeneous surround. Test stimuli with invariant CP axes. (B) Divided background. Test stimuli with invariant CP axes. (C) Divided background. Test stimuli with axes of variable CP. Bottom gray rectangle: the three types of inducers. Left to right: HC (high contrast), mean contrast (MC), low contrast (LC).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: The magnitude of the illusory brightness/darkness induction effect (index I) as a function of average background luminance and inducer contrast. Bars indicate standard error. (A) Homogeneous surround. Test stimuli with invariant CP axes. (B) Divided background. Test stimuli with invariant CP axes. (C) Divided background. Test stimuli with axes of variable CP. Bottom gray rectangle: the three types of inducers. Left to right: HC (high contrast), mean contrast (MC), low contrast (LC).
Mentions: The inducer orientation always formed variable CP axes (Figure 4C). For each of the 18 test stimuli, a series of comparison stimuli were generated by gradually differentiating the luminance of the vertical bands between the inducer axes. From an initial configuration with between-column background of common magnitude (12.9 or 16.1 cd/m2), successive stimuli were obtained by increasing the luminance (L between Figure 4C arrows) of one HSL point (Hue, Saturation, Luminance in the standard color dialog) and decreasing luminance (D between Figure 5 arrows) of the neighboring region of same magnitude. The mean variation was ~0.2 cd/m2. For each step the luminance of the darker and lighter bands was measured using a Minolta LS-110 photometer and the magnitude difference, Lp-Dp (subscript p for photometric), calculated. The procedure was repeated 20 times to create a sequence of stimuli where luminance contrast between alternating bands gradually increased.

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