Giovanni Bruno Vicario

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.

On experimental phenomenology

Abstract Through an analysis of the literature in the field and a discussion of facts, a tentative definition of experimental phenomenology is proposed. Experimental phenomenology is regarded as true experimentation. Its experimental variables are mental contents of direct experience rather than physical stimuli or physiological processes. Two limits of the phenomenological approach are pointed out, namely, the occurrence of mental facts that do not belong to the phenomenal scene (habits, forgetting) and the actual impossibility of distinguishing which aspects of a mental fact, such as percept, play the role of causes and which those of effects. Despite these limits, experimental phenomenology is regarded as the proper method for psychological research.

Orientation Sensitivity in the Peripheral Visual Field

Orientation sensitivity in the peripheral visual field has been tested in two tasks: (a) setting horizontal the orientation of a grating at various retinal eccentricities, and (b) matching the orientation of a peripherally viewed grating as close as possible to an oblique reference viewed foveally. Both performances fall off with increasing retinal eccentricity. Magnification of the stimulus optimizes peripheral performance. Peripheral performance, optimized by magnification, varies with retinal eccentricity. It approaches, but does not reach, the foveal value (tested by the same method) at 10 deg of eccentricity, and is much lower at 20 and 30 deg of eccentricity.

Wheels: A New Illusion in the Perception of Rolling Objects

A new illusory effect is described which consists of a conspicuous perceptual over-estimation of the speed at which a wheel rolling across an observers visual field appears to be rotating. Wheels appear to revolve much faster than is compatible with their linear displacement. Experimental verification of the genuineness and magnitude of the effect is reported, along with a discussion of some of the variables upon which it may depend.

Another Optical—Geometrical Illusion

A new optical—geometrical illusion is described. The parallelism of short rows of dots is affected by some unknown factor, so that the rows appear as pivoting on their middle point. Some explanations of the illusion are considered, but with no success.

THE OPTICAL-GEOMETRICAL ILLUSION "CORNER POGGENDORFF" RE-EXAMINED

In 1988 Greene noted, if a straight pair of obliques are drawn outside of two orthogonal lines, the segments appear to be angled slightly one relative to the other. This illusion, designated as “corner Poggendorff,” is different from the Poggendorff effect (the two obliques seem to lie on a parallel path). The results of the present experiments (N = 76 students) suggest that the general conditions for the corner Poggendorff are similar to those for the Judd illusion.

On Misoriented Letters

An experiment is reported in which subjects were presented with misoriented letters and asked to identify the transformations to which normal letters had been subjected to produce the misorientation. When two or more transformations were equally justifiable from the geometrical point of view, they did not have necessarily the same relevance from the perceptual standpoint. For instance, it was easier for the subjects to see an upside-down letter R as the outcome of two reflections (one about the horizontal axis and one about the vertical axis) rather than of a 180° rotation in the picture plane. Contrary to expectation, for the same final result a reflection—a movement in three dimensions—was preferred to a rotation—a movement in two dimensions—and two reflections were preferred to a single rotation. To explain the distribution of the responses, a hypothesis on the ‘mode of appearance’ of equivocally oriented objects is presented. This postulates that the directional axes assigned to the objects tend to remain in correspondence with those of the environment. Moreover, the polarization of the up–down axis tends to be preserved, while that of the left-right axis does not. Implications of this simple model for the perception of misorientations are discussed.

TESTIMONY IN A SOCIAL SETTING

80 students aged 19–24 years served as unpaid subjects. Each of them looked at one I9-sec. silent film showing a riot which actually occurred in an Italian stadium after a soccer match. Subjects made a verbal tape-recorded report immediately after having observed the scene. Subjects were divided into two groups of equal numbers. The subjects of the single group viewed the scene individually and individually made their reports. The subjects of the pair group viewed the film in pairs and simultaneously made their reports to two different experimenters in two contiguous rooms separated by a glass wall. Reports were analyzed using the Musatti method (integrated with the Zaretti method). The analysis showed that the reports of the subjects in pairs were more reliable, presenting a significantly smaller number of false elements. The effect is attributed to the different social situation. Subjects who are aware that their reports could be compared with that of another subject are presumably more cautious and avoid inserting doubtful elements.

Forms and Events

In a paper of some years ago,1 I argued about the usefulness of thinking of events in terms of forms. As a student of perception in visual and auditory domains, I referred to those minute facts that are perceptual events, like stroboscopic movements, short melodies, and so on. The conceptual tool I am accustomed to use is Gestalttheorie,and my operational method is experimental phenomenology.2 This tool and method seem well able to provide a reasonable account of the way of appearance (Erscheinungsweise) of objects (events) in the behavioural world, in the sense of the famous question asked by Koffka: “Why do things [events] look as they do”?3 In this paper I shall examine the matter more closely, pointing out some aspects that are relevant to current psychological enquiry into subjective time.

Obliquity Integration: Variations on a Theme of Delbœuf

An optical—geometrical illusion, described by Delbœuf and not familiar to specialists, is investigated. The results of two experiments show that the divergence between a bar filled with parallel slanting lines and a line drawn above it is clearly related to this angle of the lines which fill the bar. The illusion is already present when this angle is 10°, reaches its maximum at 20°, decreases at 30°, and almost disappears at 40°. These results are similar to those found for the tilt illusion, are slightly different from those found for the rod-and-frame illusion, and differ greatly from those found for the Zöllner illusion. The other variables considered—the distance between the slanting lines filling up the bar, the distance between the upper line and the bar, and the width of the bar—do not influence the illusion as much. Since either the line appears as diverging from the bar, or the bar seems inclined in relation to the line, the illusion should be considered a complex one. The small oblique lines inside the bar induce obliquity in the opposite sense in the display, but which of the elements is seen as diverging from the other depends on which of the two is established as the frame of reference.