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This article presents an experimental study on the naturally biased association between shape and color. For each basic geometric shape studied, participants were asked to indicate the color perceived as most closely related to it, choosing from the Natural Color System Hue Circle. Results show that the choices of color for each shape were not random, that is, participants systematically established an association between shapes and colors when explicitly asked to choose the color that, in their view, without any presupposition, they saw as the most naturally related to a series of given shapes. The strongest relations were found between the triangle and yellows, and the circle and square with reds. By contrast, the parallelogram was connected particularly infrequently with yellows and the pyramid with reds. Correspondence analysis suggested that two main aspects determine these relationships, namely the "warmth" and degree of "natural lightness" of hues.

In the present study, we investigated whether luminance and the side of response execution are associated, showing a SNARC-like effect (faster responses with the left hand for dark stimuli, and vice versa for light stimuli). A total of 30 participants were tested in two experiments. In Experiment 1, the association between space and the luminance of chromatic stimuli was directly tested (brightness discrimination). In Experiment 2, the same spatial association was tested indirectly (hue discrimination). The results showed that participants responded faster with their left hand to hues with lower luminance, and with their right hand to hues with higher luminance, in either the direct or the indirect task. The consistency of this association in both tasks demonstrates the automaticity of the SNARC-like effect for luminance.

Beck, Prazdny, and Ivry's (1984) interpretation of Metelli's theory of phenomenal transparency is reexamined here. There are no constraints, because the theory considers only balanced transparency and nothing is asserted against the existence of forms of unbalanced transparency. Experiment 4 of the present study proves that conditions of intensity are primary for complete balanced transparency and cannot be overcome if figural conditions strongly suggest transparency.The equation ex = (p-q)/(a-b) does not require further restrictions because the cases cited by Beck et al. concern nonbalanced transparency. Experiment 1 proves that figural conditions cannot be considered primary and thus be the cause of the perception of transparency. The present paper reports that, contrary to the results Beck et al. obtained in their Experiment 4, a series of experiments in which experienced subjects were used and in which estimation oftransparency was compared with predictions calculated with the ex formula gave satisfactory results. Beck et al.'s thesis, according to which ex *ex' hinders transparency whereas t*t' allows it, is confirmed. Experienced subjects and simple instructions appear to yield clearer results.However, one must keep in mind-a thing Beck et al. failed to do-that the deduction of Equations 3 and 4 is valid only in the case of the episcotister, where the as and the ts are the same in Equations I and 2. 4 where a, b, p, and q are the reflectances of the respective regions (Figure la), t is the virtual reflectance of the transparent layer T, and a and (I-a) are the proportions into which the p and q colors split in giving rise to the color of that part of region A (or B) seen through transparency, and to the transparent layer T. 3 From the system of two equations with two unknowns, the values of a and t can be obtained; that is, speed before a bicolored ground, the perceptual result is a gray transparent disk, through which the colors of the background are visible (Figure 1). Figure la indicates the symbols of the four resulting regions; that is, A and B are parts of the bicolored ground that are directly visible, and P and Q are regions where a transparent disk, T, and parts of the underlying background are perceived. But if part of one of the regions where scission is perceived is isolated with a pierced screen, scission disappears and a single fusion color, p, in the P region, or q, in the Q region, is perceived through the hole."The situation can be described by the following two equations.(1) (2) p = aa+(1-a)t q = ab+(l-a)t, Beck, Pradzny, and Ivry's (1984) paper, "The perception of transparency with achromatic colors, " starts with an exposition of the theory of transparency proposed by the senior author of this paper, which however lacks an essential part.The theory, based on Heider's (1933) theory and, restated by Koffka (1935), is that transparency is a phenomenal scission, in which a stimulation-which, if isolated, gives rise to a single color-gives rise, with scission, to the perception of two co...

In the Müller-Lyer illusion, human subjects usually see a line with two inducers at its ends facing outwards as longer than an identical line with inducers at its ends facing inwards. We investigate the tendency for fish to perceive, in suitable conditions, line length according to the Müller-Lyer illusion. Redtail splitfins (Xenotoca eiseni, family Goodeidae) were trained to discriminate between two lines of different length. After reaching the learning criterion, the fish performed test trials, in which they faced two lines (black or red) of identical length, differing only in the context in terms of arrangement of the inducers, which were positioned at the ends of the line, either inward, outward, or perpendicular. Fish chose the stimulus that appear to humans as either longer or shorter, in accordance with the prediction of the Müller-Lyer illusion, consistently with the condition of the training. These results show that redtail splitfins tend to be subject to this particular illusion. The results of the study are discussed with reference to similar studies concerning the same illusion as recently observed in fish. Contrasting results are presented. The significance of the results in light of their possible evolutionary implications is also discussed.