Test of models of achromatic transparency

Consider an achromatic disk transparent on an achromatic background formed by two adjoining rectangles, with the common border of the rectangles dividing the disk in half. Current models of achromatic transparency contend that the perceived extent of transparency of the disk depends on the luminance contrast inside the disk and on the luminance contrast in the background outside the disk. Here, a model is proposed which contends that this perceived extent is determined only by the luminance contrasts inherent in the disk: inside the disk and between the disk and the background. Two experiments were designed to determine which luminance contrasts influence transparency. In the first experiment, subjects rated the perceived extent of transparency of the disk for different combinations of the luminances of the disk and of the background. The results strengthen the view that the perceived extent of transparency depends on the luminance contrasts inherent in the disk. In the second experiment, a test was made of the possibility that luminance contrasts between adjoining areas of the background outside the disk are nonessential for transparency. The results show that transparency occurred both when the areas of the background outside the transparent region adjoined one another and when they were separated, confirming that the perceived extent of transparency depended only on luminance contrasts between adjoining areas inherent in the disk.     

Phenomenal transparency in achromatic checkerboards.

The study explored the luminance relations that determine the occurrence of achromatic transparency in phenomenal surfaces on complex backgrounds. Let the luminances of the left and right parts of a transparent surface on a bipartite background and those of the left and right parts of the bipartite background be p and q and m and n, respectively. Metelli proposed that this surface looks transparent when the rule p < q if m < n (or p > q if m > n) is satisfied, and Masin and Fukuda that it looks transparent when the inclusion rule is satisfied, that is, when p epsilon (m, q) or q epsilon (p, n). These rules also apply to achromatic checkerboards formed by one checkerboard enclosed in another checkerboard. This study shows that only the inclusion rule correctly predicted the occurrence of transparency in these checkerboards.     

Determinants of perceived surface transparency in two-dimensional achromatic textured patterns

Achromatic transparency in 2-D surfaces composed of three adjacent areas, one created from the others, occurs when in the created area it is possible to see the two colours of the adjacent areas. Displays with two white and black intersecting bars were produced to verify the possibility of perceiving transparency in the intersection area when this was subdivided into a different number of white and black diamonds. By increasing the spatial frequency of the elements in the intersection area we investigated the impression of transparency, and found that (i) the impression of transparency increases up to a spatial frequency of 10 cycles deg(-1) and then levels off, (ii) there is a transition from a perception of transparency in which white and black are well discriminable to a perception in which a perceptually uniform grey is seen, (iii) the perception of transparency occurring when colours are discriminated seems consistent with Helson's area-luminance hypothesis [1964, in Adaptation Level Theory (New York: Harper & Row) pp 282-292], according to which the increase of spatial frequency determines the transition from the phenomenon of contrast to that of assimilation.     

Information integration study of Metelli's and Morinaga's theories of achromatic transparency

Information integration methodology was used to test Metelli's and Morinaga's theories of achromatic transparency. Stimuli were transparent achromatic disks on a background formed by two adjacent horizontal rectangles. The common border of these rectangles divided each disk in two halves. Let P and Q be the luminances of the left and right halves of a disk and let A and B be those of the left and right rectangles, respectively. Transparency is given by the ratio (P – Q)/(A – B) in Metelli's theory and is given by a weighted average of the ratios (P – Q)/(A – Q) and (P – Q)/(P – B) in Morinaga's theory. Participants rated the transparency of disks with A and B fixed and P and Q combined factorially. Morinaga's theory closely predicted the resulting pattern of curves and Metelli's theory predicted it incorrectly. Morinaga's theory could also account well for individual differences in the ratings of transparency. The results support the general idea that transparency depends on the integration of photometric luminance information rather than on the integration of perceived lightness information.     

Test of a convergence model for color transparency perception

Models of color transparency suggest that a region in which colors of surfaces converge in color space will appear transparent. The convergence is described by a transparency parameter alpha and a target of convergence. To test such models psychophysically, observers were presented a display with four colored areas. The colors of three of the areas were chosen in advance by the experimenter. The task of the observer was to choose the color of the fourth area to make a central region appear transparent. Settings for the fourth color were collected for a total of twenty-four color combinations chosen from three planes in color space. Observers' settings agreed well with the model, which predicts that choices for the fourth color lie along a line segment in color space that is parameterized by alpha. The results suggest further that color discriminability and color opponency also influence transparency judgment.     

Assimilation of achromatic color cannot explain the brightness effects in the achromatic neon effect

If the mouths of the pacmen of a Kanizsa square are colored, for example red, then an illusory red transparent square is seen. In many visual theories such 'neon color spreading' is explained by assimilation of chromatic and achromatic color. In this paper the achromatic case was investigated. In a two-alternative forced-choice task thirty observers judged the brightness of achromatic neon figures. The results suggest that assimilation of achromatic color inside and/or outside of the illusory figures cannot explain the brightness effects seen in achromatic neon color spreading. Although these displays may produce assimilation, it appears that contrast (perhaps acting nonlocally) is a stronger influence on their perceived brightness.     

A new effect of luminance gradient on achromatic simultaneous contrast

A new effect in the domain of achromatic simultaneous contrast has been observed. A middle gray region placed at the center of an area filled by a linear achromatic gradient from black (outer part) to white (inner part) is perceived as being much darker than an identical middle gray region surrounded by a reversed gradient. By using a matching task in two experiments, it has been shown that this phenomenon is much stronger than the classical achromatic simultaneous contrast effect. The new effect is interpreted in terms of thealbedo hypothesis.     

The role of contrast in the perception of achromatic transparency: comment on Singh and Anderson (2002) and Anderson (2003)

M. Singh and B. L. Anderson proposed a perceptual theory of achromatic transparency in which the perceived transmittance of a perceived transparent filter is determined by the ratio of the Michelson contrast seen in the region of transparency to that of the background seen directly. Subsequently, B. L. Anderson, M. Singh, and J. Meng proposed that Michelson contrast should be replaced by perceived contrast in this theory. However, their experimental stimuli were nongeneric (i.e., special cases), and their observers had little choice in their matching strategy. Here, the author shows that both of their ratio-of-contrasts theories are incorrect and that problems with their theoretical analyses and experimental designs led them to conclude that mean luminance does not affect perceived transmittance when contrast is held constant. The author also shows that B. L. Anderson's (2003) transmittance anchoring principle is not valid when a transparent surface is perceived to penetrate rather than overlay another surface. Finally, the author shows that M. Singh's (2004) theoretical proof that the ratio-of-Michelson-contrasts theory accurately predicts lightness matching through transparency is incorrect.     

A comparative quantitative analysis of Greek orthographic transparency

Orthographic transparency refers to the systematicity in the mapping between orthographic letter sequences and phonological phoneme sequences in both directions, for reading and spelling. Measures of transparency previously used in the analysis of orthographies of other languages include regularity, consistency, and entropy. However, previous reports have typically been hampered by severe restrictions, such as using only monosyllables or only word-initial phonemes. Greek is sufficiently transparent to allow complete sequential alignment between graphemes and phonemes, therefore permitting full analyses at both letter and grapheme levels, using every word in its entirety. Here, we report multiple alternative measures of transparency, using both type and token counts, and compare these with estimates for other languages. We discuss the problems stemming from restricted analysis sets and the implications for psycholinguistic experimentation and computational modeling of reading and spelling.     

Newborns' discrimination of chromatic from achromatic stimuli

Two experiments assessed newborns' ability to discriminate chromatic from achromatic stimuli. In Experiment 1, newborns differentiated gray from green, from yellow, and from red: For each of these hues they preferred chromatic-and-gray checkerboards over gray squares matched in mean luminance, even though the luminance of the gray checks was varied systematically over a wide range so as to minimize nonchromatic cues. However, newborns showed no evidence of differentiating gray from blue: At some luminances they showed no preference for a blue-and-gray checkerboard over a gray square. In Experiment 2, newborns differentiated red from gray but appeared not to differentiate blue from gray: Following habituation to a series of gray squares of varying luminance, they looked longer at a red square than at a gray square of novel luminance but showed no such pattern of recovery to a blue square. The results imply that newborns have some, albeit limited, ability to discriminate chromatic from achromatic stimuli and hence, that they are at least dichromats.     

Perceived angle of incidence and achromatic surface color

Theory and evidence proposing illumination, and therefore necessarily angle of incidence of light, as a perceptual cue for lightness judgments are described. In two experiments, angle of incidence was varied by having 46 Ss view an upright trapezoid that monocularly appeared flat and binocularly, upright. In the first experiment, numbers of cues to the direction of a fixed source above the trapezoid were varied and combined. In a second experiment, the background for an illumination gradient was varied. Angle of incidence and cues to the location of the source did predict the trends in lightness judgments but not the magnitude of the effects. An alternative explanation to cue theory is proposed.