1,721,081 research outputs found
Test of models of achromatic transparency
No full textConsider 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
Storia e problemi della psicofisica
No full textThis paper illustrates the problems of psychophysics through an historical analysis. The analysis begins with noting that, about 150 years before Christ, Hipparchus of Rhodes was the first to use a psychophysical method to measure the intensity of the sensation of stellar brightness. Astronomers discovered that the relation between this intensity and the corresponding quantity of light measured by the photometer was approximately logarithmic. Fechner proposed that such a logarithmic relation was a psychophysical law valid for all sensations. Alternatively, Plateau proposed that a power function described the psychophysical law. An analysis of these laws shows, however, that they are arbitrary. This conclusion leads to the redefinition of the objectives of psychophysics. These new objectives are illustrated in the context of Anderson’s theory of information integration. Besides the problem of measuring sensory intensity, modern psychophysics faces both the problem of discovering the laws governing the integration of information involved in the generation of sensations and the problem of measuring such information. Curiously, the psychophysical method found today to be adequate for this purpose is the method used by Hipparchus more than 2000 years ago. Finally, philosophical analysis shows that physics and psychophysics share the objective of explaining perceived objects and that, to make these explanations possible, each of these sciences is compelled to make use of imperceptible explanatory principles
The time it takes to stratify two phenomenal surfaces
No full textThe 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
Test of Petter’s rule for perceived surface stratification
No full textPetter's rule applies to two-dimensional patterns formed by two overlapping surfaces that alternately 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
Luminance determinants of perceived surface stratification in two-dimensional achromatic transparent patterns
No full text- …
