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Biomedical subjects

S C Masin

Publications and source records attributed to S C Masin.

At least 19 recordsLinked to original sources
PubMed2000

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.

Adult↗
PubMed2000

Petter's effect in patterns formed by outlined surfaces.

In patterns formed by two equally colored or by two transparent overlapping surfaces of different size that alternately appear in front of one another, the larger surface has a greater probability of appearing in front of the smaller surface. This effect is known as Petter's effect. The present study found that Petter's effect also occurred in patterns formed by colorless outlined surfaces. In these patterns Petter's effect was smaller than in chromatically homogeneous patterns. The results agree with the possibility that Petter's effect occurred in patterns formed by outlined surfaces because relative size was a cue to visually perceived distance.

Anisotropy↗
PubMed2000

Test of the validity of the judged sensory ratio of 1:2.

Garner found that observers judged the sensory ratio of 1:2 invalidly; however, it is possible that in Garner's experiment judgments were influenced by the different sets of variable stimuli used for the test. This paper reports an experiment designed to test the validity of the judged sensory ratio of 1:2 without using different sets of variable stimuli. Bipolar continua of brightness and darkness were used. Participants first adjusted a brightness so that it was the double of a standard brightness located between the middle and the black end of the brightness continuum and subsequently adjusted a brightness so that it was the double of this double (the quadruple of the original standard brightness), or adjusted a darkness so that it was the double of a standard darkness located between the middle and the white end of the darkness continuum and subsequently adjusted a darkness so that it was the double of this double (the quadruple of the original standard darkness). Participants reported quadruples of each standard even if such quadruples could not exist on the bipolar continuum. This confirms that participants judged the sensory ratio of 1:2 invalidly.

Darkness↗
PubMed1999

Test of Petter's rule for perceived surface stratification.

Petter's rule applies to two-dimensional patterns formed by two overlapping surfaces that alternatively appear in front of one another. It states that the surface with the shorter contours in the region where the surfaces look superimposed has a greater probability of appearing in front of the other surface. An experiment is reported the results of which show that Petter's rule is valid for chromatically homogeneous and for uniformly dense dotted patterns, and invalid for different kinds of chromatically inhomogeneous patterns. Petter's rule has been found to be valid when the overlapping surfaces have contours with gaps. It is proposed that Petter's rule derives from the dynamics of filling-in of contour gaps.

Depth Perception↗
PubMed1999

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.

Depth Perception↗
PubMed1999

Attention and estimated line length.

Whether attention affects the estimated length of a line has been debated for a long time. Some authors have found estimated length to increase with attention; others have found that it decreased. The present study further investigated this problem with two experiments. The first confirmed that estimated length decreased with attention; however, this result had low reliability. The second experiment indicated that estimated length significantly decreased with attention for some participants and significantly increased for others. This finding accounts for the low reliability of the first experiment and for the conflicting results of previous studies. Implications of opposite effects of attention for models of sensory intensity are discussed. An interpretation of these effects in terms of response preferences is proposed.

Attention↗
PubMed1999

Differences in lightness in achromatic transparency.

It is presently unresolved whether lightnesses or differences in lightness are appropriate independent variables for models of perceived achromatic transparency. This experiment shows that differences in lightness rather than lightnesses affected the rated transparency and that local changes in differences in lightness altered the rated transparency locally. These results indicate that models of the perceived degree of transparency should be separately formulated for the different parts of a transparent surface and for the whole transparent surface. Two new models of the combined effects of lightness differences on the perceived transparency are proposed.

Form Perception↗
PubMed1999

Color scission and phenomenal transparency.

When an observer with a holistic viewing attitude perceives transparency in an achromatic two-dimensional pattern, some areas of the pattern form a single transparent phenomenal surface. In each of these areas the observer simultaneously perceives the gray color of the transparent surface and the gray color of the background that is visible through the transparent surface. With an analytic viewing attitude the observer perceives a single gray color in each area of the pattern. When the viewing attitude changes from analytic to holistic, the term color scission means the phenomenal replacement of the single analytically perceived gray color of an area of the pattern with the two gray colors that are perceived in the same area when such area forms a transparent surface. The concept of color scission has been used by Moore Heider and Metelli to explain phenomenal transparency. An analysis of experimental results reported in the literature shows that color scission does not occur in transparent patterns formed by only three areas and that it involves incorrect predictions of the occurrence of transparency in patterns formed by four or more areas. It is concluded that in general the concept of color scission is inadequate to explain phenomenal transparency.

Color Perception↗
PubMed1998

The luminance conditions of Fuchs's transparency in two-dimensional patterns.

Fuchs's transparency occurs when the contour of a transparent surface encloses the contour of another surface located on an underlying homogeneous background. The luminance conditions of Fuchs's transparency have not yet been determined. Six experiments were designed to study this problem with achromatic two-dimensional patterns. An ellipse enclosing a coplanar square was briefly presented. It simulated the cast of an elliptical spotlight or shadow on the square. The duration of the ellipse, the luminance of the square before the ellipse appeared, and the luminance of two squares outside the ellipse did not substantially affect the probability of perceiving the ellipse as transparent. However, this probability varied largely with the single values of the stimulus luminance differences and with the order relations of the stimulus luminances. It is concluded that this local and global luminance information conditioned the occurrence of Fuchs's transparency in two-dimensional patterns.

Contrast Sensitivity↗
PubMed1998

The time it takes to stratify two phenomenal surfaces.

The time the perceptual system takes to generate two overlapping phenomenal surfaces is estimated to be about 60 ms by a recognition task and 200-250 ms by a primed matching task. Here, a reaction-time task was used to test these estimates. It is plausible that when two overlapping phenomenal surfaces appear abruptly in the visual field the perceptual system sends a signal to the response system when the localisation of the parts of these surfaces begins. The perceptual system should send a subsequent signal when the phenomenal overlapping of the surfaces is achieved. The reaction times to these signals were estimated in two experiments. The difference between these estimates confirms the time estimate provided by the primed matching task.

Computer Graphics↗
PubMed1997

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 magnitude of p-a, magnitude of q-b, and magnitude of p-q were quantitative conditions of transparency. Metelli has proposed two ordinal conditions of transparency, magnitude of a-b > magnitude of 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 [symbol: see text] (a, q) [or q [symbol: see text] (p,b)]. The results showed that this second condition best predicted the occurrence of transparency.

Contrast Sensitivity↗
PubMed1995

Transparent surfaces and illuminated holes.

A single stimulus determined the alternative perceptions of an illusory transparent grey disk or of an internally illuminated circular hole. A square on a far background was visible through this disk or hole. Subjects rated the grey colour of the transparent disk or the phenomenal illumination inside the hole. The luminance difference relative to the transparent disk and the square and that relative to this disk and its background determined the probability of perceiving the transparent disk or the hole. Rated colour and illumination substantially depended only on this second difference. These results have implications for models of phenomenal transparency and illumination based on the idea that proximal contours activate neural representations of phenomenal attributes.

Humans↗
PubMed1994

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.

Color Perception↗
PubMed1991

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.

Adult↗
PubMed1991

A weighted-average model of achromatic transparency.

A model of achromatic transparency based on the idea that neural representations of transparency are activated by proximal contours is described. It is proposed that the weighted average of the magnitudes of the representations of transparency relative to a perceived continuous transparent surface corresponds to the judgement of the overall degree of transparency of the same surface. Tests of this weighted-average model were carried out with bistable patterns formed by two overlapping surfaces that appeared opaque where they were superimposed on the background and transparent where they were superimposed on each other (partial transparency). In agreement with predictions from the weighted-average model, the rated degrees of transparency of these two surfaces were noncomplementary and independent of background reflectance. Two experiments confirmed the contention of this model that the relevant proximal contours for the judgement of partial transparency of the two overlapping transparent surfaces in a bistable pattern correspond to the part where these surfaces are superimposed.

Form Perception↗
PubMed1989

An explanation for the presentation-order effect in the method of constant stimuli.

The point of subjective equality obtained by the method of constant stimuli depends to a great extent on whether the standard (S) or the variable (V) stimulus occurs first. This presentation-order effect was studied using lines as stimuli. Successive S, V pairs were presented, with inter-stimulus and interpair intervals equal. Observers, who were not told which was S or V, reported whether a given line was longer or shorter than the immediately preceding line. Although the observers' subjective experience was of a train of lines that was not organized into pairs, the presentation-order effect still occurred. This implies that the effect does not depend on the order of presentation of the stimuli in an experienced pair. It was also shown that the observers could categorize line lengths, since they could identify stochastically the most frequent stimulus (S). We propose that the presentation-order effect depends on a decision process based on response probabilities inferred from length categories.

Attention↗