The minimum contrast requirements for stereopsis.

A number of researchers have compared the contrast requirements for stereopsis with those for detection of the stereoscopic stimulus, but they have generally failed to allow for the fact that stereopsis requires a detectable stimulus in both eyes at the same time. It is argued that the most appropriate detection threshold for this comparison is that for simultaneous monocular detection (SMD) of the stereoscopic half images. Experiments in which this comparison threshold has been used are summarised and the hypothesis generated that, on using stimuli that are localised in both space and spatial frequency (e.g. Gabor patches or differences of Gaussians), a range of disparities can always be found over which contrast thresholds for depth identification are less than or equal to this SMD threshold (the SMD hypothesis). It is argued that the success of this hypothesis in describing data obtained with these stimuli is consistent with the notions of labelled lines for disparity sign and the size--disparity correlation. Last, experiments are reported in which contrast thresholds for stereoscopic depth identification (front/back) were measured with interocular differences in contrast. The data obtained are consistent with the presence of both inhibitory and excitatory interactions between the eyes when unequal monocular contrasts are presented. The implications of these results and the SMD hypothesis for theories of stereopsis and binocular function are discussed.     

Perspective based on stereopsis and occlusion

Perspective is usually considered a monocular pictorial cue, distinct from other cues such as occlusion and stereopsis. We cut across these distinctions by asking whether purely binocular (cyclopean) contours, created by stereoscopically shifting a region of homogeneous texture nearer or further than its surround, can act as a linear-perspective cue and whether the contours' ability to do this is influenced by their surface belongingness. We found that the left/right orientation of cyclopean trapezoids nearer than a surround strongly influenced perceived slant, showing that perspective constraints are applied to stereoscopically derived contours. Further regions, however, appeared as surfaces seen through a trapezoidal aperture. Because the aperture "owned" the trapezoidal contours, their orientation had little effect on perceived slant. We conclude that the application of perspective constraints depends critically on how contours are classified by stereo-specified occlusion relationships among surfaces and that perspective, stereopsis, and occlusion are not distinct processing systems.     

Contrast and depth perception: effects of texture contrast and area contrast

Many objects in natural scenes have textures on their surfaces. Contrast of the texture surfaces (the texture contrast) reduces when the viewing distance increases. Similarly, contrast between the surfaces of the objects and the background (the area contrast) reduces when the viewing distance increases. The texture contrast and the area contrast were defined by the contrast between random dots, and by the contrast between the average luminance of the dot pattern and the luminance of the background, respectively. To examine how these two types of contrast influence depth perception, we ran two experiments. In both experiments two areas of random-dot patterns were presented against a uniform background, and participants rated relative depth between the two areas. We found that the rated depth of the patterned areas increased with increases in texture contrast. Furthermore, the effect of the texture contrast on depth judgment increased when the area contrast became low.     

A model for the time-order error in contrast discrimination

Trials in a temporal two-interval forced-choice discrimination experiment consist of two sequential intervals presenting stimuli that differ from one another as to magnitude along some continuum. The observer must report in which interval the stimulus had a larger magnitude. The standard difference model from signal detection theory analyses poses that order of presentation should not affect the results of the comparison, something known as the balance condition (J.-C. Falmagne, 1985, in Elements of Psychophysical Theory). But empirical data prove otherwise and consistently reveal what Fechner (1860/1966, in Elements of Psychophysics) called time-order errors, whereby the magnitude of the stimulus presented in one of the intervals is systematically underestimated relative to the other. Here we discuss sensory factors (temporary desensitization) and procedural glitches (short interstimulus or intertrial intervals and response bias) that might explain the time-order error, and we derive a formal model indicating how these factors make observed performance vary with presentation order despite a single underlying mechanism. Experimental results are also presented illustrating the conventional failure of the balance condition and testing the hypothesis that time-order errors result from contamination by the factors included in the model.     

A model for the time-order error in contrast discrimination

Trials in a temporal two-interval forced-choice discrimination experiment consist of two sequential intervals presenting stimuli that differ from one another as to magnitude along some continuum. The observer must report in which interval the stimulus had a larger magnitude. The standard difference model from signal detection theory analyses poses that order of presentation should not affect the results of the comparison, something known as the balance condition (J.-C. Falmagne, 1985, in Elements of Psychophysical Theory). But empirical data prove otherwise and consistently reveal what Fechner (1860/1966, in Elements of Psychophysics) called time-order errors, whereby the magnitude of the stimulus presented in one of the intervals is systematically underestimated relative to the other. Here we discuss sensory factors (temporary desensitization) and procedural glitches (short interstimulus or intertrial intervals and response bias) that might explain the time-order error, and we derive a formal model indicating how these factors make observed performance vary with presentation order despite a single underlying mechanism. Experimental results are also presented illustrating the conventional failure of the balance condition and testing the hypothesis that time-order errors result from contamination by the factors included in the model.     

A probabilistic contrast model of causal induction

Deviations from the predictions of covariational models of causal attribution have often been reported in the literature. These include a bias against using consensus information, a bias toward attributing effects to a person, and a tendency to make a variety of unpredicted conjunctive attributions. It is contended that these deviations, rather than representing irrational biases, could be due to (a) unspecified information over which causal inferences are computed and (b) the questionable normativeness of the models against which these deviations have been measured. A probabilistic extension of Kelley's analysis-of-variance analogy is proposed. An experiment was performed to assess the above biases and evaluate the proposed model against competing ones. The results indicate that the inference process is unbiased.     

Infant pattern vision: A new approach based on the contrast sensitivity function

Current approaches to the study of infant pattern vision have yielded interesting findings but have not yielded a set of data or principles from which general predictions can be drawn. We propose an alternative approach based on measurements of the contrast sensitivity function (CSF). This approach has been successfully applied to the study of adult vision. In principle, the approach allows one to predict the detectability of a wide variety of two-dimensional patterns if one knows the observer's CSF. Two experiments were conducted. In Experiment 1, CSFs of 1-, 2-, and 3-month infants were measured using a fixation preference paradigm. The results indicated noteworthy development between 1 and 3 months particularly in sensitivity to high spatial frequencies (fine stripes). The low-frequency attenuation characteristic of adult vision is observed at 2 and 3 months but not always at 1. In Experiment 2, CSFs of 2-month infants were measured at a lower luminance level. The results indicated that low-frequency attenuation became less pronounced as would be predicted if it were a manifestation of lateral inhibitory processing. The manner in which the CSF can be used to make general predictions is described. The CSFs of Experiment 1 are then used to successfully predict infants' detection of patterns used in two frequently cited experiments. We also propose a simple model of infant pattern preference and show that the model accurately predicts the results of a number of well-known experiments.     

A note on the measurement of reversals of perspective

The contradictory findings in the classical literature on the rate of reversal of perspective illusions stem, at least partly, from a failure to isolate three major sources of variance: set, subjects, and sequence. This paper provides a model for the statistical isolation of these variables. It consists of the square-root transformation of reversible data which appear to constitute a Poisson distribution. Such a transformation permits the full utilization of the analysis of variance.     

The theory of psychological reversals: A review and critique

The main elements in the new theory of psychological reversals are examined. One application of the theory, in the crisis-counselling field, is explored to illustrate its practical implications. A number of problems associated with the recent development of the theory are identified.     

A simple cell model with dominating opponent inhibition for robust contrast detection

Ein Modell kortikaler Einfachzellen mit dominanter opponenter Inhibition zur robusten Kontrastdetektion Zusammenfassung. Im primären visuellen Pfad wird Information in zwei getrennten, komplementären Domänen repräsentiert, den on- und off-Zellen. In dieser Arbeit untersuchen wir die Interaktion von on- und off-Zellen zur Generierung der Eingabe für eine kortikale Einfachzelle. Basierend auf physiologischen Studien schlagen wir einen Mechanismus vor, bei dem eine kortikale Einfachzelle aus beiden Domänen eine Eingabe erhält, wobei die Eingabe aus dem opponenten Pfad stärker gewichtet wird. Mit diesem Mechanismus der dominanten opponenten Inhibition können Antworten von kortikalen Einfachzellen auf Hell-Dunkel-Balken simuliert werden, die im primären visuellen Kortex der Katze gemessen wurden. Bei der Verarbeitung synthetischer und natürlicher Bilder können mit dem neuen Modell schärfere Antworten und bessere Rauschunterdrückung erreicht werden. Wir geben eine stochastische Analyse der Rauschunterdrückungscharakteristika des vorgeschlagenen Mechanismus und präsentieren detaillierte numerische Simulationen mit systematischen Parametervariationen. Die Resultate zeigen, dass das Modell kortikaler Einfachzellen mit dominanter opponenter Inhibition robuster gegenüber verrauschten Eingaben wird, weitgehend unabhängig von der Stärke des Rauschens. Diese Eigenschaft ist möglicherweise der Grund für die physiologisch gemessene dominante Inhibition und für die Repräsentation von Kontrastinformation in zwei komplementären Domänen. Basierend auf diesen Ergebnissen stellen wir die Hypothese auf, dass dominante opponente Inhibition im visuellen System verwendet wird, um in verrauschten Umgebungen Kontraste robust extrahieren zu können. Summary. In the primary visual pathway, information is represented in two distinct, complementary domains, namely "on" and "off" cells. In this work we examine how on and off cells may interact to form the input to simple cell subfields. On the basis of physiological evidence, we propose a mechanism of dominating opponent inhibition, where a simple cell subfield is driven by both on and off domains, receiving more heavily weighted input from the opponent pathway. We demonstrate that the model can account for physiological data on luminance gradient reversal recorded from simple cells in cat striate cortex. Next, we use the model for the processing of synthetic and natural images, showing that sharpness of response and robustness to noise can be increased by dominating opponent inhibition. Finally, we present a stochastic analysis of the noise-suppression characteristics of the proposed mechanism accompanied by detailed simulations with systematic parameter variations. Results show that dominating opponent inhibition makes the simple cell responses more robust to noise, largely independently of the amount of noise added. This property may give a rationale for the strong inhibition measured physiologically and for the representation of contrast information in two complementary domains. On the basis of these findings, we hypothesize that the visual system uses dominating opponent inhibition in order to robustly extract features in noisy environments.     

Comparison based satisfaction: contrast and empathy

The paper (1) presents a new contrast–empathy model to capture affective reactions following a social comparison, and (2) supports the applicability of the value function to social comparisons. Relationship quality and relevance of the comparison dimension are assumed to influence the interplay between contrast and empathy effects. The application of the value function to the contrast–empathy model leads to the predictions that (a) dissatisfaction looms larger than satisfaction and that (b) pity looms larger than empathetic joy. Three studies test the validity of the contrast empathy model. In all studies participants rated their satisfaction with income comparisons. Study 1 demonstrates the applicability of the value function to social comparisons. Study 2 extends the self‐evaluation model and supports the validity of the contrast–empathy model. Study 3 replicates parts of Study 2 in a between‐subjects design. Copyright © 2000 John Wiley & Sons, Ltd.     

Lightness from contrast: a selective integration model

As has been observed by Wallach (1948), perceived lightness is proportional to the ratio between the luminances of adjacent regions in simple disk-annulus or bipartite scenes. This psychophysical finding resonates with neurophysiological evidence that retinal mechanisms of receptor adaptation and lateral inhibition transform the incoming illuminance array into local measures of luminance contrast. In many scenic configurations, however, the perceived lightness of a region is not proportional to its ratio with immediately adjacent regions. In a particularly striking example of this phenomenon, called White's illusion, the relationship between the perceived lightnesses of two gray regions is the opposite of what is predicted by local edge ratios or contrasts. This paper offers a new treatment of how local measures of luminance contrast can be selectively integrated to simulate lightness percepts in a wide range of image configurations. Our approach builds on a tradition of edge integration models (Horn, 1974; Land & McCann, 1971) and contrast/filling-in models (Cohen & Grossberg, 1984; Gerrits & Vendrik 1970; Grossberg & Mingolla, 1985a, 1985b). Our selective integration model (SIM) extends the explanatory power of previous models, allowing simulation of a number of phenomena, including White's effect, the Benary Cross, and shading and transparency effects reported by Adelson (1993), as well as aspects of motion, depth, haploscopic, and Gelb induced contrast effects. We also include an independently derived variant of a recent depthful version of White's illusion, showing that our model can inspire new stimuli.     

New axioms for the contrast model of similarity

An additive version of Tversky's (1977, Psychological Review84, No. 4, 327–352) contrast model of similarity is discussed, and an axiomatization proposed for it. A representation theorem for the new system is derived on the basis of results drawn from Krantz et al. (1971, Foundations of Measurement, Vol. 1, New York: Academic Press).     

A model for mastery learning based on dynamic equilibrium theory

A theoretical model is developed based on dynamic equilibrium theory, which suggests a quantitative explanation for the basic idea in mastery learning that individuals of different aptitude reacting in an ideal environment to the same total quantity of material will ultimately reach the same mastery status, or gain equal increments of status starting from the same base, in time spans inversely proportional to the aptitude. The approach incorporates two widely used mechanisms, one for growth in learning and intelligence and one for loss through forgetting, into a single model that treats acquisition and loss as opposing, but simultaneously occuring processes. Operational definitions for acquisition and loss rate constants that would enable the model to account exactly for the basic assumption of mastery learning and at the same time yield a growth pattern identical to that implicit in the Stanford Binet ratio IQ are identified. An analysis of the extent to which the requirements of the model are confirmed by the available experimental evidence reveals that the basic idea of mastery learning is a useful and convenient approximation, which applies with some validity to the growth of mental ability as well as to the growth in school achievement.     

When stereotypes hurt: Three studies of penalties for sex-role reversals

Three studies that demonstrate penalties for sex-role reversals are reported. In each study, subjects evaluated men and women who behaved either in line with sex-role stereotypes or counter to them. The results show that popularity ratings and perceived psychological adjustment of both passive-dependent men and aggressive-assertive women were adversely affected. The findings are discussed in terms of their contribution to recent theories about women's achievement motivation.     

Hiring you makes me look bad: Social-identity based reversals of the ingroup favoritism effect

The current research attempts to explain reversals of ingroup favoritism in terms of one of the prevalent mechanisms generally used to account for positive ingroup bias: Tajfel’s social identity theory. We propose that individuals strategically evaluate ingroup targets in order to maximize their own self-esteem and to avoid costly errors. This strategic evaluation typically results in ingroup favoritism toward an ingroup target member. However, if a positive evaluation of the target poses a significant self-esteem threat, denigration of the target will result. Two studies examined how ingroup and outgroup targets were evaluated when applicants were qualified versus unqualified (Study 1), or when the ingroup target might confirm a negative ingroup stereotype (Study 2). Study 1 results indicated that participants showed ingroup favoritism only toward qualified applicants. Study 2 demonstrated that, when a marginally qualified ingroup applicant has the potential to confirm a negative stereotype, bias against the ingroup is observed. Results of both studies both confirm and provide explanations for ingroup denigration.