Sergio Cesare Masin

Early alternative derivations of Fechner’s law

Historians of psychology, notably Boring, fostered Fechners idea that Webers law is the indispensable basis for the derivation of the logarithmic psychophysical law. However, it is shown here that Bernoulli in 1738 and Thurstone in 1931 derived the logarithmic law using principles other than Webers law and that Fechner and Thurstone based their derivations on the principles originally employed by Bernoulli. It is concluded that awareness of researchers about Bernoullis and Thurstones derivations could expand the directions of research on the form of the psychophysical law. (c) 2009 Wiley Periodicals, Inc.

A functional-measurement study of apparent rarefaction

The apparent density of a group of elements (lines, dots, etc.) is affected by the area of the group itself: the smaller the area, the lower the density of the elements (apparent rarefaction). An explanation of apparent rarefaction, in terms of an averaging model, has been offered by Spinelli and Vicario (submitted for publication). If working in isolation, portions of the retina far from the center would contribute an apparent density different in magnitude from that contributed by the center. Thus, the overall apparent density would be a weighted average of the contributions due to the different portions of the retina. The averaging model has been tested here by functional-measurement methods. The results confirm the model.

Attentional scanning and space errors

Using the method of paired comparisons, pairs of simultaneous horizontal or vertical lines, with one line above and one below or one on the left and one on the right of a fixation point, respectively, were presented tachistoscopically for length comparison. Space errors were found to have a pattern similar to that of time errors. The tendency to guess the comparative response from the absolute magnitude of stimuli is proposed as a basis for time and space errors. Manipulation of attentional scanning, which implies a more frequent usage of this guessing strategy for one of the two lines in a pair, was shown to affect space errors.

The Luminance Conditions of Transparency

In two experiments the luminance conditions for the occurrence of phenomenal transparency in achromatic flat patterns was studied. Let a, p, q and b be, respectively, the luminances of the parts A, P, Q, and B of a pattern comprising a transparent square on a two-part background, where P and Q are the parts of the square on backgrounds A and B, respectively. The results showed that |p – a|, |q – b|, and |p – q| were quantitative conditions of transparency. Metelli has proposed two ordinal conditions of transparency, |a – b| > |p – q| and p > q if a > b (or p < q if a < b). Alternatively, Masin and Fukuda have proposed the single ordinal condition p ∈ (a, q) [or q ∈ (p, b)]. The results showed that this second condition best predicted the occurrence of transparency.

An experimental comparison of three- versus four-surface phenomenal transparency

The three-surface transparency occurs when an object seen through a transparency does not jut out under the transparent surface. The four-surface transparency occurs when the object juts out. Observers rated the density of the transparent surface in both kinds of transparency. The results seem to show that the topological diversity between the two kinds of transparency has no functional significance. The stimulus conditions ruling the generation of judgments were detected and expressed in terms of an algebraic model.The three-surface transparency occurs when an object seen through a transparency does not jut out under the transparent surface. The four-surface transparency occurs when the object juts out. Observers rated the density of the transparent surface in both kinds of transparency. The results seem to show that the topological diversity between the two kinds of transparency has no functional significance. The stimulus conditions ruling the generation of judgments were detected and expressed in terms of an algebraic model.

Test of balanced transparency.

It is implicitly or explicitly assumed in current transparency models that all the parts of a completely transparent surface have the same perceived degree of transparency. In general, the two experiments reported here have shown that this assumption is false. Consequently, any general transparency equation based on this assumption is unjustified. Separate transparency equations for the different parts of a transparent surface are instead justified. This indicates the need for a model of the overall judgment of transparency of these parts. In the second experiment the hypothesis that the judged degree of transparency of a whole transparent surface is a weighted average of the judged degrees of transparency of the different parts of this surface was tested. The results contradict this hypothesis and support the idea that the judgment of transparency of a whole surface and that of its parts depend on different stimulus conditions.

Different biases in the methods of constant and single stimuli

The method of constant stimuli is unreliable, because it causes an unpredictable constant error. An explanation of the constant error in terms of adaptation-level theory implies that the point of subjective equality changes with time. When the method of constant stimuli was used, the constant error was present from the first response and did not change substantially with time, thus indicating that an explanation in terms of an adaptation level is implausible. A modified version of the method of single stimuli was also used, in which observers had to estimate the magnitude of the length of both lines in a pair. The use of a direct method produced a reversal of the direction, and a substantial reduction in magnitude, of the constant error.

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.

The valuation of the apparent density of a filter on a bicolored background

When the transmittance of a filter on a bicolored background is varied, the lightness differences that vary are those between the filter and the background and that between the parts inside the filter. It is hypothesized that these are the differences of importance for the valuation of the apparent density of the transparent layer. The results of two experiments seem to show that the rated apparent density does not depend only on the lightness difference inside the filter, or only on the two lightness differences between the filter and the background. All three lightness differences would enter the valuation mechanism. An averaging model is proposed.

Luminance determinants of perceived surface stratification in two-dimensional achromatic transparent patterns

Two overlapping transparent surfaces forming a two-dimensional pattern stand out in front of each other alternately. Let y denote the luminance of the region where these surfaces overlap and b the luminance of the background. In achromatic patterns, the probability that the lighter transparent surface appears to be in front of the other surface is known to increase with y and with b. The present results show that grouping by achromatic colour similarity cannot explain the effect of b. An alternative conjecture is that the luminance factors that control perceived surface segregation can explain the effects of y and b. Such an explanation predicts a new effect: the probability that one transparent surface appears to be in front increases with the absolute difference in luminance between the surface and the background. The present results confirm this prediction.