3,872 research outputs found
The role of physical contrast in Agostini & Galmonte's reversed lightness-induction Necker cube
No full textAgostini and Galmonte (2002 Psychological Science 13 88 - 92) reported a configuration showing that when grouping factors are optimised, a grey target totally surrounded by black appears darker than an equal grey target totally surrounded by white. The theoretical assumption is that, when higher-level factors act simultaneously with lower-level factors, the former prevails over the latter. Specifically, it is assumed that the lightness induction produced by the global organisation principle of perceptual belongingness prevails over retinal lateral inhibition. The aim of the present study was to test the hypothesis that lightness induction produced by perceptual grouping does depend on the physical contrast between induced and inducing elements. To test this hypothesis, we systematically manipulated, in a number of psychophysics experiments, the relative physical contrast among the regions forming the original Agostini and Galmonte configuration. Observers were asked to match the lightness of both the inducing and induced element on a Munsell scale. We found that lightness induction produced by perceptual organisation principles depends on relative physical contrast between the induced and the inducing elements. Results are interpreted in accordance with previous studies on the relationship between lightness induction and physical contrast
A coloured version of Agostini & Galmonte's Necker cube display
No full textIn what is known as a reversed contrast display it has been found (Agostini & Galmonte, 1997, 2002) that a grey region surrounded by a black area can appear darker than an identical grey region surrounded by white, and the induction cannot be explained by assimilation. Both high- and low-level factors are simultaneously present in this configuration, but the former prevail in determining the effect. The present work was aimed to verify whether global grouping factors induction holds also for coloured displays. In this new version of Agostini & Galmonte's display we used red/yellow inducing backgrounds/corners, while induced regions (dashed lines) were orange. We tested also two control conditions, where we did not expect any effect: 1. inducer corners of the same orange as targets; 2. inducer corners replaced by disks having the same area and colour. Observers' task was to judge the colour of the induced regions on a red/yellow scale. Results are comparable to those obtained for lightness: The targets perceived colour is determined by global factors; in fact, orange was judged as reddish in the yellow corners/red background display and yellowish in the opposite one. Both controls provided no statistically significant difference. To conclude, it seems plausible that global induction overcomes local induction also for coloured displays
Does physical contrast affect global induction in Agostini & Galmonte's reversed lightness-induction Necker cube?
No full textIn 2002 Agostini & Galmonte offered a reversed-contrast display where a gray target entirely surrounded by a black area appears darker than an identical gray target entirely surrounded by white. This effect can not be attributed to assimilation phenomena; moreover, it occurs because of higher-level grouping factors: when both higher-level factors and lower-level factors affect a configuration simultaneously, the former prevail. Hence, the authors showed that the lightness induction determined by perceptual belongingness prevails against retinal lateral inhibition. The purpose of this work was to investigate whether the lightness induction produced by global grouping factors does change as a function of the physical contrast between induced and inducing elements. We systematically manipulated the relative physical contrast among the regions forming the original Agostini & Galmonte display. Observers had to judge the lightness of both the inducing and induced element on a Munsell Scale. From the results we can conclude that: 1. the global induction overcomes local induction for all the tested physical contrasts, 2. it is stronger for decrements, 3. the amount of the global induction does not depend on the size of physical contrast, 4. the global induction seems to be modulated by the physical contrast of increments only
Propagazione a distanza degli effetti di induzione acromatica
No full textIl modo di apparire dei colori è largamente influenzato dalla distribuzione spaziale delle superfici. Nonostante siano state proposte spiegazioni centrate su meccanismi di interazione locale tra intensità diverse di regioni adiacenti, ci sono numerosi esempi che non possono essere interpretati in questo modo (Wertheimer, 1923; Benray, 1924; White, 1979).
Altri autori (Agostini, 1999; Agostini e Proffitt, 1993; Galmonte e Agostini, 1998) hanno dimostrato che anche in assenza di adiacenza spaziale il colore di una superficie viene modificato dalle specifiche relazioni di appartenenza.
Lo scopo della presente ricerca è di approfondire l'indagine sul rapporto tra appartenenza percettiva e contrasto simultaneo di bianchezza misurando l'entità del contrasto in funzione di manipolazioni sistematiche delle relazioni di appartenenza tra zone indotte e zone inducenti. Sono stati manipolati sistematicamente i seguenti parametri: 1. il numero di elementi indotti (dischi grigi di riflettanza media) e quello degli inducenti (dischi ad alta o bassa riflettanza) e 2. la posizione spaziale relativa (posizioni interne o esterne). Gli osservatori dovevano aggiustare il valore della luminanza degli elementi indotti organizzati con gli elementi inducenti di bassa/alta riflettanza in maniera da annullare l'effetto. L'esperimento ha messo in luce il fatto che anche quando il numero di elementi indotti è considerevolmente maggiore rispetto a quello degli inducenti, l'appartenenza percettiva produce una propagazione spaziale dell'effetto di contrasto su tutti gli elementi unificati, indipendentemente dalla posizione spaziale relativa. Questa scoperta ha importanti implicazioni per le teorie sulla percezione dei colori acromatici e suggerisce che la forza dell'appartenenza percettiva possa essere misurata indirettamente rilevando l'entità dell'effetto di contrasto
Perceptual belongingness and spatial propagation of lightness contrast
No full textAgostini and Proffitt (1993) showed that perceptual belongingness can cause simultaneous lightness contrast (SLC) to be seen in configurations where the inducing elements are not adjacent to the target. In some observations, in Agostini and Proffitt-type configurations, we showed that belongingness determines SLC also when the numbers of inducing elements is drastically reduced, and that the induction effect spatially propagates on all the unified elements
Reversing the reversed contrast
No full textGalmonte and Agostini (1998 Investigative Ophthalmology & Visual Science, 39(4), S158),
Agostini and Galmonte (2002 Psychological Science, 13, 89–93), Bressan (2001 Perception, 30, 1031–
1046), and Gilchrist and Annan (2002 Perception, 31, 141–150) reported three different lightness
contrast configurations in which grouping factors make a gray target totally surrounded by black
appear darker than an equal gray target surrounded by white, reversing the classical contrast effect.
In this paper we demonstrate that the three configurations known as ‘reversed contrast’ are based on
different mechanisms. Sixteen participants judged the lightness of the gray targets of the original and
modified versions of the three configurations. Our results highlight that the Agostini and Galmonte
effect is reversed when the global grouping factors are removed, while in a number of variations of
Bressan’s and Gilchrist and Annan’s displays the direction of the effect does not change, even in
absence of global grouping factors. Our results indicate that the factors determining the Agostini and
Galmonte effect are different from those acting on the other two configurations, in which the lightness
change is also due to factors other than belongingness
The role of spatial articulation in Agostini & Galmonte reversed lightness induction Necker cube.
No full textgostini and Galmonte (2002 Psychological Science 13 88 - 92) offered a display in which a gray surrounded by black is perceived as darker than an identical gray surrounded by white because of global induction effects elicited by grouping factors, showing that, at least under certain conditions, higher-level factors prevail on lower-level factors, ie the lightness induction produced by the global organization principle of perceptual belongingness prevails on retinal lateral inhibition. The present study was aimed to test whether the lightness induction produced by perceptual grouping does depend on the configuration spatial articulation. In order to test this hypothesis we systematically manipulated the spatial articulation, starting from the original Agostini and Galmonte configuration and then gradually decreasing its complexity. Observers had to perform a global judgment, matching the lightness of the induced elements on a Munsell scale. We found that the lightness induction produced by belongingness is modulated by the spatial articulation level. Results are interpreted in the light of previous studies on the relationship between lightness induction and spatial articulation
When perceptual belongingness over-rules lateral inhibition
No full textIt is well known that a gray surface surrounded by a light background appears darker than an identical gray surface surrounded by a dark background. This phenomenon is called simultaneous contrast and it is mostly explained by low-level mechanisms. Other examples of simultaneous contrast have been offered where higher level processes must be taken into account (Benary, 1924; White, 1979; Agostini & Proffitt, 993). Recently, Agostini & Galmonte (submitted for publication) reported a novel display of simultaneous contrast where, for the first time, perceptual belongingness and local contrast directly compete one against the other. They found that the effect is largely due to perceptual belongingness. In the present work we manipulated local and global factors to measure their relative strength on the size of simultaneous contrast. Observers were asked to perform a matching task on a gray scale placed on the same background of the tested displays. We found that when global factors are weak contrast is induced by the background intensity while when they are strengthened contrast is entirely determined by belongingness relationships. When low- and high-level mechanisms are directly competing, the latter overrule the previous. In order to account for these results, contrast models would have to factor in also higher level processes computing perceptual belongingness relationships
Influence of the context on simultaneous lightness contrast
No full textAgostini & Bruno (Perception & Psychophysics in press) showed that the size of simultaneous lightness contrast effect measured under homogenous illumination doubles under Gelb lighting; that is, an illumination border is made to coincide with the outer border of the display, and the rest of the visual field is left in near darkness. According to the authors this effect is due to the spatial distribution of illumination. Gilchrist et al (to be published) propose a more detailed explanation. According to this theory, the doubling of the contrast effect results from a compromise between predictions made in relation to two competing frameworks, local and global. To test this hypothesis, we manipulated the relative weight of the two frameworks. The experimental display consisted of a middle gray surface on a black background and of a Munsell scale (16 steps from black to white) on a white background. The two backgrounds were suspended in mid-air but they where not adjacent. In the experiment, we gradually changed the luminance ratio between the experimental display and the rest of the visual field. Observers chose the closest match on the Munsell scale for each of the selected luminance ratios. In support of Gilchrist et al's explanation, the larger increase of contrast measured by Agostini and Bruno is reached only within a narrow range of luminance ratios
Perceptual belongingness and spatial propagation of lightness contrast on the unified elements
No full textIn the domain of lightness perception, Galmonte & Agostini (1998) have demonstrated that perceptual belongingness over-rules retinal lateral inhibition: When the two explanations directly compete one against the other to account for simultaneous lightness contrast phenomenon, the former one wins. The aim of this work was to further investigate the relationships between perceptual belongingness and lightness contrast by measuring the strength of perceptual belongingness in determining simultaneous lightness contrast when 1. the number of inducing and induced elements and 2. their relative spatial inclusion is systematically manipulated in Agostini & Proffitt-type configurations (1993). Observers had to perform a nulling task. They adjusted the luminance of the middle reflectance elements spatially arranged (according to specific laws of perceptual organization) with the low reflectance inducing elements to cancel the induction effect out. It has been found that even when the number of induced elements is considerably larger than that of inducing elements, perceptual belongingness causes simultaneous lightness contrast to spatially propagate on all the unified elements, independently from the inclusion factor. This finding has important implications for lightness perception theories. Furthermore, it suggests that perceptual belongingness can be indirectly measured by testing the size of simultaneous contrast
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