1,721,177 research outputs found
Psychology and art: Towards an empirical aesthetics..: Towards also accessible
No full textC’è una cospicua letteratura in psicologia della percezione che si
è occupata del mondo dei non vedenti, tra cui troviamo i lavori di
Kennedy (1993), Hammad, Kennedy, Juricevic e Rajani (2008), Argenton
(2012), Heller (1989, 1992) e, prima ancora, di Rubin (1921)
e di Arnheim (1974). In questi ultimi anni sono stati fatti molti passi
avanti dalla ricerca scientifica nei confronti del mondo delle persone
con disabilità visiva, e la ricerca lavora costantemente per fornire alle
persone con questo deficit sensoriale modalità e strumenti sempre più
efficaci per interagire con il mondo
Contrast and assimilation: the belongingness paradox.
No full textContrast and assimilation phenomena have a central role in the theories on the appearance of surface color. It is well known that principles of perceptual organization affect color perception. Paradoxically, the belongingness principle has been used to explain constrast as well as assimilation. In this paper, we try to solve this paradox by arguing that assimilation occurs earlier during the formation of perceptual groups, whereas contrast occurs after the formation of perceptual groups
Luminance gradients and lightness constancy.
No full textThe ability of the visual system to perceive surface color correctly despite changes in the level of illumination is referred to as lightness constancy. It has been shown that strong cues of changes in the level of illumination are provided by smooth luminance changes. A smooth luminance gradient has been placed at the border dividing the lower from the higher luminances side of a classical-lightness-constancy-type display, presented on a CRT-monitor (Bruno, 1994). Observers performed a matching task in a within-subject design: 3 luminance ratios (30:1-10:1-2:1) x 4 conditions, i.e., gradient throughout the whole display dividing border (“congruent” condition), gradient throughout the inner background dividing border only (first “incongruent” condition), gradient throughout the outer background dividing border only (second “incongruent” condition), and no gradient (control condition). Compared to the control condition, congruent condition holds better lightness constancy, while the two incongruent conditions show only little failures of constancy, independently from the specific tested ratio. For the congruent condition there is the maximum increase in lightness constancy, but, since the loss of constancy in the incongruent conditions is modest, it seems that the visual system considers smooth luminance gradients as important sources of information on illumination changes even if edge cues are partially incongruent
The phantom contrast effect
No full textAgostini and Galmonte (1997 Investigative Ophthalmology & Visual Science 38 S895; 2002 Psychonomic Bulletin & Review 9 264 - 269) showed that a linear luminance gradient can largely modify the lightness of a target region. In the present work, a version of the gradient configuration is offered where the luminance range has been drastically reduced. In this condition, the gradient is almost unnoticeable. Comparing the lightness of a gray target placed at the centre of this gradient with that of an identical target surrounded by a surface having a homogenous luminance value equal to the highest luminance of the gradient, they appear quite different even though their backgrounds appear the same. This perceptual paradox is remarkable because it suggests that smooth changes in luminance, even when difficult to detect, can affect lightness perception. This paradox could be due to the local contrast between the target and its closest surrounding luminance. But, by narrowing the spatial distribution of an identical reduced-range luminance gradient, the direction of the effect is reversed. It is not possible to account for this result by considering only the local contrast between the last luminance of the gradient and that of the target. This suggests that the visual system computes surface colours taking into account the global spatial distribution of luminance gradients
Perceptual organization overcomes the effect of local surround in determining simultaneous lightness contrast
No full textLightness induction can occur on the basis of the immediate surround of a region (local interactions) and also on the basis of global factors of perceptual organization. The experiments reported in this article used novel displays that made it possible to differentiate the contributions of these two kinds offactors. The experiments demonstrated, for the first time, that when higher-level factors act contemporaneously with lower-level factors, the contrast effect induced by the global-organization principle of perceptual belongingness overcomes the effect due to retinal lateral inhibition
Spatial articulation affects lightness.
No full textIn a recent paper, Agostini and Bruno (1996) showed that the size of simultaneous lightness contrast increases under Gelb lighting. To extend Agostini and Bruno's work, we applied their methodology to a set of more spatially articulated displays. In four experiments, we investigated the role of spatial articulation on the size of the simultaneous lightness contrast effect. In the first experiment, we found a decrease of the simultaneous lightness contrast effect as the spatial articulation increased. In the second experiment (the control experiment), performed under homogeneous illumination, we found that the effect of spatial articulation is not detectable, even though the data seem to show the same trend as that in the previous experiment. In the third experiment, we found that spatial articulation affects not only the middle reflectance region, but also the lowest one. As the spatial articulation increases, the effect on the lightnesses of both regions decreases. In the last experiment, performed with a reduced range of reflectances, we found a lightening effect for all the reflectances and, again, an effect of spatial articulation. The results of these experiments are interpreted according to the model proposed by Gilchrist et al. (in press)
Luminance gradients, perceived illumination, and lightness perception.
No full textRecently, Agostini & Galmonte (1997) showed a new effect of luminance gradient on lightness perception. This short note reports a number of original qualitative observations risen from the basic display. These variations suggest the interpretaion of the effect in terms of apparent illumination to be a plausible one
Contrast or Assimilation? Two ambiguous cases
No full textAgostini and Galmonte (submitted), Bressan (in press), and Economou, Annan, and Gilchrist [1998 Investigative Ophthalmology & Visual Science 39(4) S857] reported three different configurations showing that when grouping factors are optimised, a gray target totally surrounded by black can appear darker than an equal gray target surrounded by white. The common theoretical assumption is that, when higher-level factors act contemporaneously with lower-level factors, the contrast effect induced by the global organisation principle of perceptual belongingness prevails on retinal lateral inhibition. However, spatial frequencies of Bressan and Economou et al displays suggest an alternative interpretation. In a number of variations of their configurations, we observed that the direction of the effect does not change even in absence of global grouping factors. Our observations suggest that their results can be explained according to a mechanism of spatial summation eliciting lightness assimilation (adaptation-level theory) rather than to the principle of perceptual belongingness. This hypothesis is further supported by the observation that their illusion increases with viewing distance
Why is the Benary effect so small?
No full textBenary [1924 Psychologische Forschung 5 131 - 142; translated into English in A Source Book of Gestalt Psychology Ed. W D Ellis (1939, London: Routledge & Kegan Paul)] was the first to systematically show that simultaneous lightness contrast (SLC) can be observed also when the local conditions at the target edges are identical. In his famous configuration, two identical gray triangles were placed one between two arms of a black cross and the other on the top of a big black triangle. The overall background was white. Therefore, they were locally bordering with the same amount of black and white area. Nevertheless, the gray triangle between the arms of the cross was perceived darker than the other triangle. Benary explained the effect according to the belongingness principle. It must be noted, however, that the effect is smaller than that observed in the classical SLC display. Recently, Agostini and Galmonte (1999 Perception & Psychophysics 61 1345 - 1355) showed that contrast induced by belongingness is not an all-or-nothing process. To investigate whether the lightness of the two targets is influenced by the colour of the non-belonging bordering regions, in the present work we measured the Benary effect separately. A Munsell scale was placed on a white background. The two halves of the Benary configuration were measured separately under Gelb lighting. Observers were asked to choose from the scale the patch matching the target in lightness. Since the scale was on a white background, the target belonging to the white background should be matched with its veridical value, while the target belonging to the black area should be matched with a lighter value. Surprisingly, both targets were matched with a lighter value, even though the amount of the induction was larger for the target included in the black area. Our experiments show that the colour of the non-belonging bordering regions in the Benary configuration has a detectable effect on the lightness of the target patch
Colour appearance is affected not only by perceptual but also by linguistic context
No full textTerminology is a crucial problem in science, since quite often the terms used to denote theoretical concepts are directly taken from the vocabulary of common words, which usually have multiple meanings. To solve this problem, scientists must operationalize the theoretical concepts they use but, in psychology, sometimes, this can be a difficult task, since the meaning of the terms used to give the instructions to observers can interfere with the spontaneous meaning that observers give to those terms. Starting from some empirical observations, we show that colour appearance is affected not only by the perceptual but also by the linguistic context
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