Paola Bressan

The perception of 3-dimensional affine structure from minimal apparent motion sequences

The research described in the present article was designed to identify the minimal conditions for the visual perception of 3-dimensional structure from motion by comparing the theoretical limitations of ideal observers with the perceptual performance of actual human subjects on a variety of psychophysical tasks. The research began with a mathematical analysis, which showed that 2-frame apparent motion sequences are theoretically sufficient to distinguish between rigid and nonrigid motion and to identify structural properties of an object that remain invariant under affine transformations, but that 3 or more distinct frames are theoretically necessary to adequately specify properties of euclidean structure such as the relative 3-dimensional lengths or angles between nonparallel line segments. A series of four experiments was then performed to verify the psychological validity of this analysis. The results demonstrated that the determination of structure from motion in actual human observers may be restricted to the use of first order temporal relations, which are available within 2-frame apparent motion sequences. That is to say, the accuracy of observers’ judgments did not improve in any of these experiments as the number of distinct frames in an apparent motion sequence was increased from 2 to 8, and performance on tasks involving affine structure was of an order of magnitude greater than performance on similar tasks involving euclidean structure.

The Place of White in a World of Grays: A Double-Anchoring Theory of Lightness Perception.

The specific gray shades in a visual scene can be derived from relative luminance values only when an anchoring rule is followed. The double-anchoring theory I propose in this article, as a development of the anchoring theory of Gilchrist et al. (1999), assumes that any given region (a) belongs to one or more frameworks, created by Gestalt grouping principles, and (b) is independently anchored, within each framework, to both the highest luminance and the surround luminance. The regions final lightness is a weighted average of the values computed, relative to both anchors, in all frameworks. The new model accounts not only for all lightness illusions that are qualitatively explained by the anchoring theory but also for a number of additional effects, and it does so quantitatively, with the support of mathematical simulations.

Neon color spreading: a review

This paper is about a phenomenon that combines a delicate beauty with a profoundsignificance for understanding visual perception. The neon-like glow of a color that escapesthe boundaries of a real figure and fills the surrounding area until it is halted by theboundaries of an illusory figure has an ethereal quality unlike any other brightness and coloreffect. It also has substantial implications regarding the way in which our visual system usesseemingly incomplete stimuli to generate meaningful percepts, segregate objects from theirbackgrounds, and provide them with color and depth.As it so often happens in science, the effect was discovered and then independentlyrediscovered in the span of a few years. In 1971, Dario Varin of the University of Milanpublished a monograph on Ochromatic contrast and diffusionO whose front cover isreproduced in figure 1. A circular transparent veil can be seen to extend over four sets ofconcentric rings partly composed of blue arcs. It has a subtle bluish tinge and is luminescent,as if it emitted a weak light, or as if it were a colored spot of light cast by some off-screenlamp. This veil is illusory, in the sense that a point-by-point description of the reflectancespectrum of the white background would not reveal any changes corresponding to it.

Explaining Lightness Illusions

Grey looks darker when set against white than when set against black. In some complex figures this illusion becomes startling, and can be shown to depend on the perceptual organisation of regions within the image. The most widely accepted explanations of such effects are based on the analysis of the junctions formed where the boundaries of nearby regions meet. Even theories where junctions are not the subject of special concern underline their importance as grouping cues. In this paper I present several new families of figures that challenge both views, and conclude that junctions do not play any crucial role in lightness estimation.

Talis Pater, Talis Filius: Perceived Resemblance and the Belief in Genetic Relatedness

People hardly ever realize that their belief in their high rate of success in detecting family resemblances is affected by their knowledge of the actual genetic link between individuals. In the three studies reported here, 100 men and 100 women were requested to estimate the facial resemblance of photographically portrayed child-adult pairs, while being given either truthful or deceitful information, or no information, about their relatedness. Believing that the members of a pair were parent and offspring was the main predictor of the perceived similarity between them. Men and women agreed in judging children as more similar to female than to male adults, except when the pair members were believed to be related; in this case, men judged the child as resembling the alleged parents equally. Common remarks on family resemblance thus appear to ensue less from a conscious desire to please or reassure the parents than from general hypothesis-testing biases in human reasoning, made perhaps more specific in men by a concern with the problem of uncertain paternity.

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.

Going round in circles: shape effects in the Ebbinghaus illusion

The Ebbinghaus illusion has traditionally been considered as either a sensory or a cognitive illusion, or some combination of these two. Cognitive contrast explanations take support from the way the illusion varies with the degree of shape similarity between the test and inducing elements; we show, however, that contour interaction explanations may account for this result too. We therefore tested these alternative theories by measuring the illusion with different test shapes as well as different inducer shapes, in all combinations. We found that for angular or hexagonal test shapes there is no similarity effect, and for some shape combinations there is no significant illusion, in contradiction to both of the traditional hypotheses. Instead, we suggest that an integrated model of visual processing is needed to account for the illusion.

Men Do not Have a Stronger Preference than Women for Self-resemblant Child Faces

Are men more likely than women to take into account a child’s facial resemblance to themselves when making hypothetical parental investment choices? The benefits of self-resemblance in decreasing relatedness uncertainty are larger in men than in women for direct descendants. However, they are identical in men and women for collateral relatives, such as siblings, cousins, nephews, and nieces; these individuals can also be the recipients of parental-like altruism, which comes primarily from women. Published data are contradictory. In the present study, 14 men and 14 women were shown child faces and asked to judge their attractiveness, adoptability, and familiarity. The faces had been digitally manipulated to resemble (at three different resemblance levels, two of which were under recognition threshold) either the experimental participant, an acquaintance, or strangers. We found a significant preference for self-resemblant children in women, but not in men. This was not an artefact of women being better at detecting self-resemblance, given that at the highest resemblance level more men than women recognized themselves. Overall, face preference increased with face familiarity; for self-resemblant faces, this correlation was not mediated by conscious self-recognition. We discuss how the fast-response, multiple-question procedure used in previous experiments may have led to reports of a much larger self-resemblance preference in men than in women.

Human kin recognition is self- rather than family-referential

Inclusive fitness theory predicts that organisms will tend to help close kin more than less related individuals. In a variety of birds and mammals, relatives are recognized by comparing their phenotype to an internal representation or template, which might be learned through either repeated exposure to family members or self-inspection. Mirrors are ubiquitous now, but were absent during our evolutionary history; hence it is hard to predict, and empirically unknown, whether human kin recognition is family- or self-referential. Here we put this issue to the strongest possible test by comparing nepotistic behaviour towards self- versus co-twin-resemblant individuals. Seventy monozygotic and dizygotic twins were shown same-sex faces, covertly manipulated to resemble either themselves or their co-twin, and indicated which individual they would prefer in two prosocial contexts. Self-resemblant faces were significantly preferred to twin-resemblant faces, showing that visual information about the self supersedes that about close family members in the kin-recognition template. Because, under conditions of paternal uncertainty, a reliable family-referent template could be based only on ones mother and maternal relatives, a unique advantage of self-referent phenotype matching is the possibility of (consciously or unconsciously) identifying ones father and paternal relatives as kin.

Simultaneous Lightness Contrast with Double Increments

In this paper we demonstrate the existence of simultaneous lightness contrast in displays in which the target patches are both more luminant than their surrounds. These effects are not predicted by theories of lightness that assume that the highest luminance in a scene is perceived as white, and anchors all the other luminances. We show that the strength of double-increment illusions depends crucially on the luminance of both the surrounds and the target patches. Such luminance prerequisites were not met in previous studies, which explains why simultaneous contrast with incremental targets has so far been regarded as extremely weak or nonexistent.