A B S T R A C T S

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Human kin recognition is self- rather than family-referential.
Bressan, P. and Zucchi, G.
Biology Letters, 5, 336-338 (2009)

Abstract


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 one's mother and maternal relatives, a unique advantage of self-referent phenotype matching is the possibility of (consciously or unconsciously) identifying one's father and paternal relatives as kin.

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Biologically Costly Altruism Depends on Emotional Closeness Among Step but not Half or Full Siblings
Bressan, P., Colarelli, S. M. and Cavalieri, M. B.
Evolutionary Psychology, 7, 118-132 (2009)

Abstract


We studied altruistic behaviors of varying biological cost (high, medium, and low) among siblings of varying genetic relatedness (full, half, and step). In agreement with inclusive fitness theory, the relative importance of either reliable (such as co-residence) or heuristic (such as emotional closeness) kinship cues depended crucially on the costs of help. When help did not endanger the altruist’s life, thus making reciprocation possible, emotional closeness was the strongest predictor of altruism; perceived physical and psychological similarity to the sibling amplified altruistic behavior via their association with emotional closeness. When help endangered the altruist’s life, thus making reciprocation unlikely, the strongest predictor of altruism was the ancestrally valid kinship cue of co-residence duration. Emotional closeness predicted costly altruism only for step siblings; its effects were non-significant when siblings were genetically related. Our findings support the idea that emotional closeness promotes costly altruistic behavior by serving as a surrogate kinship cue when more reliable cues are missing. 

Full text: PDF file, 236K
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Visual attentional capture predicts belief in a meaningful world.
Bressan, P., Kramer, P. and Germani, M.
Cortex, 44, 1299-1306 (2008)

Abstract


Here we show that the automatic, involuntary process of attentional capture is predictive
of beliefs that are typically considered as much more complex and higher-level. Whereas
some beliefs are well supported by evidence, others, such as the belief that coincidences
occur for a reason, are not. We argue that the tendency to assign meaning to coincidences
is a byproduct of an adaptive system that creates and maintains cognitive schemata, and
automatically directs attention to violations of a currently active schema. Earlier studies
have shown that, within subjects, attentional capture increases with schema strength.
Yet, between-subjects effects could exist too: whereas each of us has schemata of various
strengths, most likely different individuals are differently inclined to maintain strong or
weak ones. Since schemata can be interpreted as beliefs, we predict more attentional
capture for subjects with stronger beliefs than for subjects with weaker ones. We measured
visual attentional capture in a reaction time experiment, and correlated it with scores on
questionnaires about religious and other beliefs and about meaningfulness and surprisingness
of coincidences. We found that visual attentional capture predicts a belief in meaningfulness
of coincidences, and that this belief mediates a relationship between visual
attentional capture and religiosity. Remarkably, strong believers were more disturbed by
schema violations than weak believers, and yet appeared less aware of the disrupting
events. We conclude that (a) religious people have a stronger belief in meaningfulness of
coincidences, indicative of a more general tendency to maintain strong schemata, and
that (b) this belief leads them to suppress, ignore, or forget information that has demonstrably
captured their attention, but happens to be inconsistent with their schemata. 

Full text: PDF file, 436K
(This file is a pre-print version of the manuscript published in Cortex)

The best men are (not always) already taken: Female preference for single versus attached males depends on conception risk.
Bressan, P. and Stranieri, D.
Psychological Science, 19, 145-151 (2008)

Abstract


Because men of higher genetic quality tend to be poorer partners and parents than men of lower genetic quality, women may profit from securing a stable investment from the latter, while obtaining good genes via extrapair mating with the former. Only if conception occurs, however, do the evolutionary benefits of such a strategy overcome its costs. Accordingly, we predicted that (a) partnered women should prefer attached men, because such men are more likely than single men to have pair-bonding qualities, and hence to be good replacement partners, and (b) this inclination should reverse when fertility rises, because attached men are less available for impromptu sex than single men. In this study, 208 women rated the attractiveness of men described as single or attached. As predicted, partnered women favored attached men at the low-fertility phases of the menstrual cycle, but preferred single men (if masculine, i.e., advertising good genetic quality) when conception risk was high.

Full text: PDF file, 272K
(This file is a pre-print version of the manuscript published in Psychological Science)

Gating of remote effects on lightness.
Bressan, P. and Kramer, P.
Journal of Vision, 8(2):16, 1-8 (2008)

Abstract

In various versions of the dungeon illusion (P. Bressan, 2001), we show that grouping between targets and contextual disks determines whether remote luminances affect target lightness or not. In the dungeon illusion, target disks surrounded by contextual disks contrast with them rather than with the immediate background. We formally establish the existence of this illusion and show that it reverses when the luminance of the targets is either lower (double decrement) or higher (double increment) than the luminances of both the background and the contextual disks rather than in between them. On the basis of the double-anchoring theory of lightness (P. Bressan, 2006a), we predict and show that grouping gates the effects of remote luminances in such a way that they go in opposite directions in the double-decrement and double-increment inverted-dungeon illusions. Our results support the double-anchoring theory and demonstrate that luminances that are far away from the targets are irrelevant in some conditions but critical in others.


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Men do not have a stronger preference than women for self-resemblant child faces.
Bressan, P., Bertamini, M., Nalli, A. and Zanutto, A.
Archives of Sexual Behavior, xx, xxx-xxx (2008)

Abstract


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.

Full text: PDF file, 1200K
(This file is a pre-print version of the manuscript in press in Archives of Sexual Behavior)
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Auditory attention causes visual inattentional blindness.
Pizzighello, S. and Bressan, P.
Perception, 37, 859-866 (2008)

Abstract


When engaged in a visual task, we can fail to detect unexpected events that would otherwise be very noticeable. Here we ask whether a common auditory task, such as that of attending to a verbal stream, can also make us blind to the presence of visual objects that we do not anticipate. In two experiments, 120 observers watched a dynamic display while performing either a visual or an auditory attention task, or both simultaneously. When observers were listening to verbal material, in order to either understand it or remember it (auditory task), their probability of detecting an unexpected visual object was no higher than when they were counting bounces of moving items (visual task), although in the former case the observers’ eyes and attention could move around the display freely rather than remaining focused on tracked items. Previous research has shown that attending to verbal material does not affect responses to lights flashing at irregular intervals, suggesting that driving performance is not hampered by listening. The lights, however, were expected. Our data imply that listening to the radio while driving, or to a portable audio player while walking or biking, can impair our reactions to objects or events that we do not expect.

Full text: PDF file, 204K
(This file is a pre-print version of the manuscript in press in Perception)

The attentional cost of inattentional blindness.
Bressan, P. and Pizzighello, S.
Cognition, 106, 370-383 (2008)

Abstract

When our attention is engaged in a visual task, we can be blind to events which would otherwise not be missed. In three experiments, 97 out of the 165 observers performing a visual attention task failed to notice an unexpected, irrelevant object moving across the display. Surprisingly, this object significantly lowered accuracy in the primary task when, and only when, it failed to reach awareness. We suggest that an unexpected stimulus causes a state of alert that would normally generate an attentional shift; if this response is prevented by an attention-consuming task, a portion of the attentional resources remains allocated to the object. Such a portion is large enough to disturb performance, but not so large that the object can be recognized as task-irrelevant and accordingly ignored. Our findings have one counterintuitive implication: irrelevant stimuli might hamper some types of performance only when perceived subliminally.

Full text: PDF file, 304K
(This file is a pre-print version of the manuscript published in Cognition)

Dungeons, gratings, and black rooms: a defense of double-anchoring theory and a reply to Howe et al. (2007)
Bressan, P.
Psychological Review, 114, 1111-1115 (2007)

Abstract

The double-anchoring theory of lightness (Bressan, 2006) assumes that any given region  belongs to a set of frameworks, created by Gestalt grouping principles, and receives a provisional lightness within each of them; the region’s final lightness is a weighted average of all these values. In their critique, Howe, Sagreiya, Curtis, Zheng, and Livingstone (2007) (a) show that the target’s lightness in the dungeon illusion (Bressan, 2001) and in White’s effect is not primarily determined by the region with which the target is perceived to group, and (b) claim that this is a challenge to the theory. I argue that Howe et al. misinterpret grouping for lightness by equating it with grouping for object formation, and by ignoring that lightness is determined by frameworks’ weights and not by what appears to group with what. I show that Howe et al.’s empirical findings, together with those on grating induction and all-black rooms that they cite as problematic, actually corroborate rather than falsify the theory.

Full text: PDF file, 196K
(This file is a pre-print version of the manuscript published in Psychological Review)

The place of white in a world of grays: a double-anchoring theory of lightness perception.
Bressan, P.
Psychological Review, 113, 526-553 (2006)

Abstract

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 paper, 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 region's final lightness is a weighted average of the values computed, relative to both anchors, in all frameworks. The new model not only accounts 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.

Full text: PDF file, 1.5 MB
(This file is a pre-print version of the manuscript published in Psychological Review)

Inhomogeneous surrounds, conflicting frameworks, and the double-anchoring theory of lightness.
Bressan, P.
Psychonomic Bulletin & Review, 13, 22-32 (2006)

Abstract

The empirical question of whether the lightness of a region is accounted for purely by the average luminance of its surround has a complex answer, that depends on whether such a region is an increment, a decrement, or intermediate relative to the luminances of the contiguous surfaces. It is shown here that a new model of lightness, based on anchoring principles, predicts and clarifies such intricacies. In the model, the luminance of the target region determines its lightness in two ways: indirectly, by making it group with parts of its surround and thus defining the nested frameworks to which it belongs; and directly, by anchoring it to the highest luminance and to the average surround luminance in each of these frameworks. Inter- and intra-individual differences in lightness assessment are shown to emerge under grouping conditions that create unstable, conflicting frameworks.

Full text: PDF file, 324K (Copyright Psychonomic Society Inc.)
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Simultaneous lightness contrast on plain and articulated surrounds.
Bressan, P. and Actis-Grosso, R.
Perception, 35, 445-452 (2006)

Abstract

Simultaneous lightness contrast is stronger when the dark and light backgrounds of the classic display (where one of the targets is an increment and the other is a decrement) are replaced by articulated fields of equivalent average luminances. Although routinely attributed to articulation per se, this effect may simply result from the increase in highest luminance in the light articulated, vs plain, background; by locally darkening the decremental target, such an increase would amplify the difference between the targets. We disentangled the effects of highest luminance and articulation by measuring, separately, the magnitude of lightness contrast on dark and light plain and articulated backgrounds. We found that highest luminance and articulation contribute separately to the final illusion.

Full text: PDF file, 260K
(This file is a pre-print version of the manuscript published in Perception)

The dark shade of the moon.
Bressan, P.
Clinical and Experimental Ophthalmology, 33, 574 (2005)

Full text: PDF file, 100K
(This file is a pre-print version of the manuscript published in Clinical and Experimental Ophthalmology)

Parental resemblance in one-year-olds and the Gaussian curve.
Bressan, P. and Grassi, M.
Evolution and Human Behavior, 25, 133-141 (2004)

Abstract

Do infants look more like their fathers or their mothers? The available data are contradictory, but were collected through different procedures: either by asking judges to identify the parent in a triplet of adults (straight guess), or by asking them to rate resemblance on a scale and then recoding highest ratings to parents as correct guesses (guess from rating). Here, we used both procedures and compared their results. Eighty judges were asked, first, to estimate the facial resemblance of 40 one-year-olds to each of three adults, and then, to guess which adult in each triplet was the parent. Accuracy was better than chance with both methods, but performance in the guessing task was significantly higher. Judgments of parental resemblance were distributed normally, with a few infants preferentially resembling one parent (father or mother with equal probability), and most resembling father and mother to approximately the same degree.

Full text: PDF file, 128K
(This file is a pre-print version of the manuscript published in Evolution and Human Behavior)
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Antigravity hills are visual illusions.
Bressan, P., Garlaschelli, L. and Barracano, M.
Psychological Science, 14, 441-449 (2003)

Abstract

Antigravity hills, also known as spook hills or magnetic hills, are natural places where cars put into neutral are seen to move uphill on a slightly sloping road, apparently defying the law of gravity. We show that these effects, popularly attributed to gravitational anomalies, are in fact visual illusions. We re-created all the known types of antigravity spots in our laboratory using tabletop models; the number of visible stretches of road, their slant, and the height of the visible horizon were systematically varied in four experiments. We conclude that antigravity-hill effects follow from a misperception of the eye level relative to gravity, caused by the presence of either contextual inclines or a false horizon line.

Full text: PDF file, 296K
(This file is a pre-print version of the manuscript published in Psychological Science)
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A fair test of the effect of a shadow-incompatible luminance gradient on the simultaneous lightness contrast. Comment.
Bressan, P.
Perception, 32, 721-723 (2003)

A fair test of the effect of a shadow-incompatible luminance gradient on the simultaneous lightness contrast. Reply to Logvinenko's reply.
Bressan, P.
Perception, 32, 725-730 (2003)

Abstract

Shadow-compatibility of simultaneous lightness contrast is discussed by Alexander D Logvinenko and Paola Bressan, with examples claiming to provide a test of the hypothesis.

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Chromatic induction in neon colour spreading.
Da Pos, O. and Bressan, P.
Vision Research, 43, 697-706 (2003)

Abstract

Neon colour spreading occurs when sections of a lattice are replaced by segments of a different colour. This colour appears to
diffuse out of the segments, and produce a slightly tinted transparent surface floating above the lattice. In two of the four experiments reported here, observers varied the colour of an area in a test display, until it matched the neon colour perceived in a corresponding (illusory) area in a comparison display. We found that the neon colour is an additive mixture of the colour of the segments and the colour complementary to the lattice, as suggested by Bressan (Vision Research 35 (1995) 375). In the other two experiments,we separately manipulated the presence and alignment of lattice and segments, to test whether the neon effect is fully predicted by a combination of colour diffusion and simultaneous colour contrast. We found that the colour induced in a neon figure is more saturated than the colour induced in a comparable non-neon figure. We discuss the implications of these results on our current understanding of the mechanisms of neon colour spreading.

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Talis pater, talis filius: perceived resemblance and the belief in genetic relatedness.
Bressan, P. and Dal Martello, M.F.
Psychological Science, 13, 213-218 (2002)

Abstract

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.

Full text: PDF file, 48K
(This file is a pre-print version of the manuscript published in Psychological Science)

Why babies look like their daddies: paternity uncertainty and the evolution of self-deception in evaluating family resemblance.
Bressan, P.
Acta Ethologica, 4, 113-118 (2002)

Abstract

It has been suggested that, in a socially monogamous system where fathers invest in their mates' offspring but paternity is far from certain, it will be adaptive on the part of infants to conceal their fathers' identity; but the opposite claim  has also been made that this is against the genetic interests of the fathers, and a high frequency of adulterine births will select instead for paternal resemblance. In this paper, I present a simple theoretical model that suggests that neonatal anonymity benefits fathers, mothers and children. Once anonymity becomes established, however, all babies start paying the cost of paternity uncertainty, that is of the reduction in paternal care due to fathers not knowing whether they have truly sired their mates' offspring. By diminishing the fitness of babies, such cost bounces back as lowered fitness for parents as well. We should then expect the evolution of maternal strategies directed to decrease paternity uncertainty, in the form of instinctive and unsolicited comments on babies' resemblance to their putative fathers. In contradiction with the widespread belief that it would be in fathers' interest to be sceptical of these allegations, the model suggests that, under conditions of infant anonymity, fathers will actually promote their own fitness by believing their spouses.

Full text: PDF file, 60K
Published online: 25 October 2001, DOI: 10.1007/s10211-001-0053-y
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Explaining lightness illusions.
Bressan, P.
Perception, 30, 1031-1046 (2001)

Abstract

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 organization 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.

Full text: PDF file, 404K
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Going round in circles: shape effects in the Ebbinghaus illusion.
Rose, D. and Bressan, P.
Spatial Vision, 15, 191-203 (2002)

Abstract

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.

Full text: PDF file, 196K
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Simultaneous lightness contrast with double increments.
Bressan, P. and Actis-Grosso, R.
Perception, 30, 889-897 (2001)

Abstract

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.

Full text: PDF file, 124K
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The connection between random sequences, everyday coincidences, and belief in the paranormal.
Bressan, P.
Applied Cognitive Psychology, 16, 17-34 (2002)

Abstract

This paper argues against the theory that people interpret unusual coincidences as paranormal because they misunderstand the probability of their occurring by chance. In the two studies reported here, 214 subjects were given a questionnaire on the frequency of coincidences in their lives, a series of probabilistic problems and a scale assessing their belief in the paranormal. Believers reported more coincidences than disbelievers. Believers made more errors than disbelievers in tasks reflecting sensitivity to the relationship between expected distribution of chance events and total number of occurrences; and avoided repetitions of identical alternatives in a random sequence to a greater extent. However, the last two effects completely disappeared in a subsample of university students. It is proposed that a more frequent experience of coincidences on the one hand, and a more biased representation of randomness on the other, are independent consequences of a stronger propensity of paranormal believers to connect separate events.

Full text: PDF file, 208K
Published online: 21 December 2001, DOI: 10.1002/acp.754
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The barberpole illusion depends on contrast.
Vezzani, S. and Bressan, P.
Ricerche di Psicologia, 23, 69-81 (1999)

Abstract

An array of parallel bars drifting behind an elongated aperture appears to move in the direction of the longer axis of the aperture (barberpole illusion). We examined the luminance conditions under which the barberpole effect occurs. Our results show that aperture-driven motion is a direct function of the contrast between the aperture's edge and the background. These data suggest that models of the aperture problem should take into account the contribution of both grating and edge contrast to the analysis of visual motion.

NOTE: The work reported in this paper was done in 1995.

Full text: PDF file, 102K
(This file is a pre-print version of the manuscript published in Ricerche di Psicologia)

Neon color spreading: a review.
Bressan, P., Mingolla, E., Spillmann, L., and Watanabe, T.
Perception, 26, 1353-1366 (1997)

Contents

1 Introduction
2 Phenomenology
    2.1 Color
    2.2 Transparency
    2.3 Glow
3 Psychophysics: Conditions for the occurrence of neon color spreading
    3.1 Figure
    3.2 Depth
    3.3 Color
4 Relation of neon color spreading to other perceptual phenomena
    4.1 Assimilation
    4.2 Illusory contours
    4.3 Motion and depth
    4.4 Texture and disparity
5 Physiology: The neural basis of neon color spreading
    5.1 Illusory contours
    5.2 Apparent contrast reduction
    5.3 Neon flanks and color diffusion
6 Analysis of neon color spreading with the use of a model of early vision
    6.1 Spreading as a metaphor and mechanism
    6.2 Brightness boosting

Full text: PDF file, 153K
(This file is a pre-print version of the manuscript published in Perception)
Look at the figures

The authors during their Team Residency at the Rockefeller Foundation's Study and Conference Center in Bellagio, Italy (June 1995). Left to right: Mingolla, Bressan, Spillmann, Watanabe.

A closer look at the dependence of neon color spreading on wavelength and illuminance.
Bressan, P.
Vision Research, 35, 375-379 (1995)

Abstract

Ejima, Redies, Takahashi and Akita [(1984) Vision Research, 24, 1719-1726], studying the dependence of the neon colour spreading effect on wavelength and illuminance, found a number of relationships that appeared of difficult interpretation. This paper shows that these relationships can all be logically predicted within Grossberg and Mingolla’s [(1985) Psychological Review, 92, 173-211] approach to the neon spreading problem, with no need of making ad hoc assumptions.

Full text: PDF file, 400K
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Solving occlusion indeterminacy in chromatically homogeneous patterns.
Tommasi, L., Bressan, P., and Vallortigara, G.
Perception, 24, 391-403 (1995)

Abstract

Overlapping figures can produce consistent depth stratification even when chromatically homogeneous. Since neither T-junctions nor X-junctions are present in these patterns, the problem arises of what rules determine the direction of depth stratification, ie which surfaces appear in front and which behind. In a series of demonstrations and formal experiments involving perception of stereopsis, motion, transparency, motion in depth, and reversible figures, the validity of the principle that the visual system tends to minimise the formation of interpolated modal contours was tested. The reason why larger surfaces tend to be seen modally in front, rather than behind, would reflect the geometrical property that when, in overlapping objects, larger surfaces are closer there will be shorter occluding boundaries than when smaller surfaces are closer. It is shown that  this constraint is independent of the empirical depth cue of relative size. An example is also given of a simple computational strategy that extracts, from chromatically homogeneous patterns, occluding subjective contours corresponding to those perceived by human observers.

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A new motion illusion related to the aperture problem.
Bressan, P., and Vezzani, S.
Perception, 24, 1165-1176 (1995)

Abstract

A previously unreported motion illusion is described. Oblique lines that drift smoothly on the retina in a vertical direction appear to be displaced laterally. The effect occurs both for moving lines under fixation and for stationary lines under ocular tracking of an external target. Orientation, length, and homogeneity of the obliques affect the magnitude of illusory displacement. We propose that this illusion is associated with a misregistration of the direction of displacement occurring, in lines slanted relative to the axis of their motion, because of the aperture problem.

Occlusion, transparency, and stereopsis: a new explanation for stereocapture.
Vallortigara, G. and Bressan, P.
Vision Research, 34, 2891-2896 (1994)

Abstract

Stereo capture occurs when a regular pattern of repeating elements with zero disparity is superimposed on a disparate subjective figure. The elements enclosed within the subjective contours, but not those outside them, are perceptually captured and pulled on the same depth plane of the disparate figure. The phenomenon has been interpreted as the result either of a spreading of disparity signals from the subjective figure or of the attribution of the depth of certain salient image features to the finer texture elements enclosed in them. We suggest here that, instead, the fact that stereo capture is limited to the texture elements lying within the boundaries of the subjective figure is simply due to ambiguous occlusion information at the monocular level. When the texture elements occlude the inducers of the subjective figure as well, the elements lying outside the boundaries of the subjective figure are also captured. We propose that stereo capture arises as the solution to a conflict between information provided by retinal disparity and occlusion, and show how this effect is related to other previously observed phenomena of conflicting cues to depth.

What induces capture in motion capture?
Bressan, P. and Vallortigara, G.
Vision Research, 33, 2109-2112 (1993)

Abstract

The phenomenon of 'motion capture' has been demonstrated by presenting, one after the other, two identical Kanizsa squares spatially separated and superimposed on a regular matrix of dots. For appropriate temporal intervals, one illusory square  is seen to jump from one location to the other and the dots in it appear to move with it even though they are physically stationary. The standard explanation of the effect is that motion signals from the subjective figure are spontaneously attributed to the static elements laying on it. We have found, however, that if alternative removal of right-angle sectors (required to obtain apparent motion of the illusory square) is not accompanied by alternative appearance and disappearance of a few dots, motion capture does not occur. This suggests that the basic mechanism underlying capture is not the motion of the subjecive figure per se, but the spreading of motion signals arising from those texture elements that alternately go on and off between frames. On the other hand, subjective contours do play a role by confining the spreading of motion signals to the texture elements located on the figure.

Revisitation of the luminance conditions for the occurrence of the achromatic neon color spreading illusion.
Bressan, P.
Perception & Psychophysics, 54, 55-64 (1993)

Abstract

This paper develops the idea (Bressan, 1993) that neon spreading derives from the perceptual scissioning of ordinary assimilation color, a process identical to that occurring with nonillusory colors in phenomenal transparency. It is commonly held that the critical elements in achromatic neon spreading patterns must be of luminance intermediate between that of the embedding lines and of the background. The interpretation of neon spreading on the basis of color scissioning, however, predicts that neon spreading should also be observed for different luminance hierarchies, provided that these are compatible with transparency. This prediction found experimental support in the present work. The results suggest that (1) the widespread notion that chromatic and achromatic neon spreading must be mediated by separate mechanisms is unwarranted; (2) the widespread notion that color spreading in ordinary assimilation patterns and color spreading in neon patterns must be mediated by separate mechanisms is unwarranted; (3) other than pointing to the way in which the overall organization of a scene affects the mode of color appearance, the neon spreading effect may not convey any extra theoretical relevance.

Neon colour spreading with and without its figural prerequisites.
Bressan, P.
Perception, 22, 353-361 (1993)

Abstract

Neon colour spreading has been shown to disappear if certain figural conditions are not met. Evidence is presented which suggests that these conditions are only incidentally related to the neon spreading effect; in particular, that they can be violated as long as the structure remains compatible with the interpretation of a transparent surface. It is proposed that neon spreading and classical colour assimilation share the same basic mechanism, and that the peculiar perceptual attributes of the former derive from the perceptual scissioning of ordinary assimilation colour. This process is identical to that occurring with nonillusory colours in phenomenal transparency.

Motion aftereffects with rotating ellipses.
Bressan, P., Tomat, L., and Vallortigara, G.
Psychological Research, 54, 240-245 (1992)

Abstract

The perceptual outcome and the motion-aftereffect duration generated by the rotation on the frontal plane of an ellipse with a bar depend on whether the bar is placed along the major or the minor axis. When the bar is placed along the minor axis, a stereokinetic transformation occurs, and the pattern looks like a tilting ring with a perpendicular bar moving rigidly with it. Placing the bar along the major axis prevents the stereokinetic transformation: subjects report deformations and relative motion of the bar with respect to the ellipse. We found that motion aftereffects last longer when the bar is placed along the minor rather than the major axis. A series of experiments was carried out to investigate whether differences in aftereffect duration are related to the stereokinetic transformation. Results seem to suggest that they are not.

Illusory depth from moving subjective figures and neon colour spreading.
Bressan, P. and Vallortigara, G.
Perception, 20, 637-644 (1991)

Abstract

If a pattern of concentric circles, interrupted so as to produce the perception of a subjective bar extending from the centre to the periphery of the pattern, was slowly rotated in a plane perpendicular to the line of sight, observers reported seeing the bar slanted in depth and moving over complete and stationary concentric circles. When the interrupted concentric circles were completed by red segments -- thereby giving rise to a neon colour-spreading effect -- observers reported seeing a reddish bar, which sometimes appeared to be slanted in depth, moving behind the plane of the concentric circles. A combination of the two patterns was found to originate a compelling percept of a unitary bar slanted in depth: part of the bar (the subjective half) appeared to be located in front of its inducing elements, whereas the other part (the neon-like half) appeared to continue behind them. When translatory instead of rotary motion was used, the bars did not look slanted in depth: however, the neon bar appeared either behind or in front of the inducing lines, depending on the luminance contrast between the segments and the inducing lines themselves.

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