Minimal information to determine affine shape equivalence

Participants judged the affine equivalence of 2 simultaneously presented 4-point patterns. Performance level (d') varied between 1.5 and 2.7, depending on the information available for solving the correspondence problem (insufficient in Experiment 1a, superfluous in Experiment 1b, and minimal in Experiments 1c, 2a, 2b) and on the exposure time (unlimited in Experiments 1 and 2a and 500 ms in Experiment 2b), but it did not vary much with the complexity of the affine transformation (rotation and slant in Experiment 1 and same plus tilt in Experiment 2). Performance in Experiment 3 was lower with 3-point patterns than with 4-point patterns, whereas blocking the trials according to the affine transformation parameters had little effect. Determining affine shape equivalence with minimal-information displays is based on a fast assessment of qualitatively or quasi-invariant properties such as convexity/ concavity, parallelism, and collinearity.     

Human sensitivity to phase perturbations in natural images: a statistical framework

Fourier-phase information is important in determining the appearance of natural scenes, but the structure of natural-image phase spectra is highly complex and difficult to relate directly to human perceptual processes. This problem is addressed by extending previous investigations of human visual sensitivity to the randomisation and quantisation of Fourier phase in natural images. The salience of the image changes induced by these physical processes is shown to depend critically on the nature of the original phase spectrum of each image, and the processes of randomisation and quantisation are shown to be perceptually equivalent provided that they shift image phase components by the same average amount. These results are explained by assuming that the visual system is sensitive to those phase-domain image changes which also alter certain global higher-order image statistics. This assumption may be used to place constraints on the likely nature of cortical processing: mechanisms which correlate the outputs of a bank of relative-phase-sensitive units are found to be consistent with the patterns of sensitivity reported here.     

Developmental psychology and public policy: progress and prospects

This article outlines a framework for developmentally oriented policy research. Drawing from U. Bronfenbrenner's (1995) dynamic developmental systems theory, the authors suggest ways in which the key tenets of process, persons, context, and time can inform policy research in developmental psychology and can be used to support a causal interpretation of the results of those analyses. Conceptualizing public policies from a dynamic developmental systems perspective has a variety of implications for future research, and this article considers some of these implications.     

Concurrent second-order schedules: some effects of variations in response number and duration

To examine the effects on concurrent performance of independent manipulations of response-unit duration and number, 6 hens were exposed to concurrent second-order schedules of reinforcement. Each first-order operant unit required completion of a fixed-ratio schedule within the time specified by a fixed-interval schedule, with one further response completing the fixed-interval schedule. The fixed-ratio and fixed-interval requirements comprising the first-order operant units were systematically and independently varied under three pairs of concurrent variable-interval schedules to produce differences in the first-order response and duration requirements (response and duration differentials). These manipulations produced consistent changes in response, time, and operant-unit biases. A 1:4 response differential biased the time and operant-unit measures towards the smaller fixed ratio, but to a degree less than the imposed response differential. The response-based biases favored the larger fixed ratio. Duration differentials of 4:1 and 8:1 biased the response and operant-unit measures towards the shorter fixed interval, again less than the imposed duration differential, but the time biases remained close to zero. Both sorts of differentials acted to bias operant-unit completions more systematically than the other measures, but undermatching to the differentials occurred. The undermatching appears to have arisen from a pattern of fix and sample (in which visits to the less preferred alternative involved only a single completed operant unit) under combinations of unequal operant-unit requirements and reinforcer rates. The response and time bias measures appeared to arise as by-products of the changes in operant-unit completions.     

Is self special? A critical review of evidence from experimental psychology and cognitive neuroscience

Varied research findings have been taken to support the claim that humans' representation of the self is "special," that is, that it emerges from systems that are physically and functionally distinct from those used for more general purpose cognitive processing. The authors evaluate this claim by reviewing the relevant literatures and addressing the criteria for considering a system special, the various operationalizations of self, and how the studies' findings relate to the conclusions drawn. The authors conclude that many of the claims for the special status of self-related processing are premature given the evidence and that the various self-related research programs do not seem to be illuminating a unitary, common system, despite individuals' subjective experience of a unified self.     

Perceptual limits on low-dimensional models of Munsell reflectance spectra

Some experimental and theoretical approaches to surface-colour perception depend on approximating surface reflectance spectra by low-dimensional models. In the psychophysical experiment reported here, observers had to discriminate between patterns of Munsell surfaces and their spectral approximations under either the same or different illuminants. The approximations were produced by principal component analysis, by independent component analysis, and by artificial neural networks trained with a supervised-learning rule. In all experimental conditions, observers required, on average, at least 5 basis functions for discrimination performance to be at chance, thus placing a lower limit on the dimensionality of models of Munsell reflectance spectra.     

Minimalist surface-colour matching

Some theories of surface-colour perception assume that observers estimate the illuminant on a scene so that its effects can be discounted. A critical test of this interpretation of colour constancy is whether surface-colour matching is worse when the number of surfaces in a scene is so small that any illuminant estimate is unreliable. In the experiment reported here, observers made asymmetric colour matches between pairs of simultaneously presented Mondrian-like patterns under different daylights. The patterns had either 49 surfaces or a minimal 2 surfaces. No significant effect of number was found, suggesting that illuminant estimates are unnecessary for surface-colour matching.     

Competition between antecedent and between subsequent stimuli in causal judgments

In the analysis of stimulus competition in causal judgment, 4 variables have been frequently confounded with respect to the conditions necessary for stimuli to compete: causal status of the competing stimuli (causes vs. effects), temporal order of the competing stimuli (antecedent vs. subsequent) relative to the noncompeting stimulus, directionality of training (predictive vs. diagnostic), and directionality of testing (predictive vs. diagnostic). In a factorial study using an overshadowing preparation, the authors isolated the role of each of these variables and their interactions. The results indicate that competition may be obtained in all conditions. Although some of the results are compatible with various theories of learning, the observation of stimulus competition in all conditions calls for a less restrictive reformulation of current learning theories that allows similar processing of antecedent and subsequent events, as well as of causes and effects.     

Parent and Adolescent Responses to PovertyRelated Stress: Tests of Mediated and Moderated Coping Models

We tested several models of the associations among economic strain, life stress, coping, involuntary stress responses, and psychological symptoms in a sample of 57 parent-adolescent dyads from rural, lower-income families. Economic strain and life stress predicted symptoms for both parents and adolescents. Stressor-symptom specificity was found for parents, such that economic strain uniquely predicted depression, whereas negative life events predicted hostility. Involuntary stress responses were associated with higher levels of symptoms for both parents and the adolescent children. Secondary control coping was associated with fewer symptoms for both parents and adolescents. Results support a mediational role of coping and responses to stress during adolescence, with a shift to moderational status in adulthood. Implications of these results are discussed with regard to developmental coping theory and potential interventions with at-risk families.