Infants' perception of concavity and convexity of shaded objects

The discriminative sensitivities of 30 4‐month‐old and 30 8‐month‐old infants for concave and convex objects were measured using the preferential‐looking method. Five cylinder‐like objects with different magnitudes of concave or convex shaded surfaces and outline contours were presented to the infants in pairs. The results indicated that the 4‐month‐old infants could discriminate better between object convexities than between object concavities. In contrast, the 8‐month‐old infants were able to equally discriminate between object concavities and object convexities, and their sensitivity to both object concavity/convexity was much higher than that of the 4‐month‐old infants. This difference in the sensitivity to object concavity and convexity suggested that younger and older infants might have differential abilities for cue utilization for recovering object structures.     

The concavity effect is a compound of local and global effects

Using a change detection paradigm, Barenholtz, Cohen, Feldman, and Singh (2003) found that changes in concave regions of a contour are more easily detected than changes in convex regions. In a series of three experiments, we investigated this concavity effect using the same paradigm. We observed the effect in wire-like stimuli as well as in silhouettes (Experiment 1) and in complex, smoothed images as opposed to angular polygons (Experiment 2). We also observed a systematic effect of the magnitude of the change (Experiment 1). Furthermore, we find that the effect cannot be attributed to either local or global processing effects, but rather to a combination of both "mere" concaveness and an effect due to changes in the perceived part structure of the stimulus object (Experiment 3). For our data analysis, we used a nonparametric bootstrap method, which greatly increases sensitivity (compared to more traditional analyses like ANOVA).     

A prior for global convexity in local shape-from-shading

To solve the ill-posed problem of shape-from-shading, the visual system often relies on prior assumptions such as illumination from above or viewpoint from above. Here we demonstrate that a third prior assumption is used--namely that the surface is globally convex. We use complex surface shapes that are realistically rendered with computer graphics, and we find that performance in a local-shape-discrimination task is significantly higher when the shapes are globally convex than when they are globally concave. The results are surprising because the qualitative global shapes of the surfaces are perceptually unambiguous. The results generalise findings such as the hollow-potato illusion (Hill and Bruce 1994 Perception 23 1335-1337) which consider global shape perception only.     

Sets of probability distributions, independence, and convexity

This paper analyzes concepts of independence and assumptions of convexity in the theory of sets of probability distributions. The starting point is Kyburg and Pittarelli??s discussion of ??convex Bayesianism?? (in particular their proposals concerning E-admissibility, independence, and convexity). The paper offers an organized review of the literature on independence for sets of probability distributions; new results on graphoid properties and on the justification of ??strong independence?? (using exchangeability) are presented. Finally, the connection between Kyburg and Pittarelli??s results and recent developments on the axiomatization of non-binary preferences, and its impact on ??complete?? independence, are described.     

The role of convexity in perception of symmetry and in visual short-term memory

Visual perception of shape is affected by coding of local convexities and concavities. For instance, a recent study reported that deviations from symmetry carried by convexities were easier to detect than deviations carried by concavities. We removed some confounds and extended this work from a detection of reflection of a contour (i.e., bilateral symmetry), to a detection of repetition of a contour (i.e., translational symmetry). We tested whether any convexity advantage is specific to bilateral symmetry in a two-interval (Experiment 1) and a single-interval (Experiment 2) detection task. In both, we found a convexity advantage only for repetition. When we removed the need to choose which region of the contour to monitor (Experiment 3) the effect disappeared. In a second series of studies, we again used shapes with multiple convex or concave features. Participants performed a change detection task in which only one of the features could change. We did not find any evidence that convexities are special in visual short-term memory, when the to-be-remembered features only changed shape (Experiment 4), when they changed shape and changed from concave to convex and vice versa (Experiment 5), or when these conditions were mixed (Experiment 6). We did find a small advantage for coding convexity as well as concavity over an isolated (and thus ambiguous) contour. The latter is consistent with the known effect of closure on processing of shape. We conclude that convexity plays a role in many perceptual tasks but that it does not have a basic encoding advantage over concavity.     

Monotonicity,convexity, and other qualitative psychophysical laws

General methods are described for directly testing qualitative psychophysical laws, such as monotonicity and convexity. These methods consist of estimating lower and higher orders of derivatives and procedures for verifying qualitative laws involving these derivatives. The quantitative power law hypothesis is compared for goodness of fit with the qualitative hypothesis that the psychophysical function is monotone and convex, in application to bisection brightness data. Other topics include discussion of a possible topological formulation of the distinction between qualitative and quantitative laws; the search for psychophysical invariants; and the failure of qualitative laws such as convexity to conform to Luce's invariance-theoretic principles of theory construction.     

Memory and aging in context

Much research has indicated that aging is accompanied by decrements in memory performance across a wide variety of tasks and situations. A dominant perspective is that these age differences reflect normative changes in the integrity and efficiency of the information-processing system. Contextual perspectives of development, however, argue for consideration of a broader constellation of factors as determinants of both intraindividual change and interindividual variation in memory functioning. The validity of the contextual perspective in characterizing the relationship between aging and memory is examined through a review of studies exploring a variety of alternative mechanisms associated with age differences in performance. It is concluded that a more multidimensional approach to the study of aging and memory is warranted.     

Size,convexity, and curvature magnitude estimations of curvilinear forms

Groups of Os made magnitude estimates of size, convexity, and curvature of patterns along a shape continuum. College Os repeated the procedure for a given physical measure in three successive sessions, but high school Os made only one set of estimates. The apparent size for the patterns was found to grow with an exponent between .700 and .755 for high school and college Os. The magnitude estimates for convexity and curvature were less reliable than the size estimates both between college and high school Os and within college Os over successive sessions. The magnitude estimates from the high school and college Os showed a faster apparent growth of curvature than of convexity.     

Concreteness and item-to-list context associations in the free recall of items differing in context variability

Context variability can be defined as the number of preexperimental contexts in which a given concept appears. Following M. Steyvers and K. J. Malmberg's (2003) work, the authors have shown that concepts that are experienced in fewer preexperimental contexts generally are better remembered in episodic memory tasks than concepts that are experienced in a greater number of preexperimental contexts. The purpose of this article is to demonstrate that low context variability confers its memorial advantage because of stronger item-to-list context associations as compared with high context variability. Three experiments that use environmental context changes from study to test demonstrate that the low context variability advantage is eliminated when item-to-list context associations are not available because of environmental changes at test. In addition, the low context variability advantage is eliminated when inward processing at study prevents the formation of item-to-list context associations.     

Career in context

Mainstream career theories have been criticised for their scanty conceptualisation of the environment that influences individuals' careers. There are few foundations upon which to build an appropriate conceptualisation of the dramatically changing environment of career today. The implications of Pepper's contextualist world hypothesis are discussed. Compared with orthodox approaches, the world as seen from this perspective is as different as the Internet is from a library; its understanding of the environment, and indeed career, is also significantly different. The contextualist perspective upon career research, theory and practice is outlined and the possibility of its adoption in the mainstream of the career field is explored     

Counseling in context

In these tense times of campus turmoil the expertise of the counselor is more needed than ever, but as an agent of change he should emerge from the closet of his office and be involved in group counseling in contexts where student and faculty feelings are starting to ferment. This would require expanding his role to include collaborating with teachers to improve the psychological settings in their classrooms, conducting informal “rap sessions” with both faculty or students, and setting up opportunities for group guidance activities both in and out of the classroom.     

Similarity in context

Similarity comparisons are highly sensitive to judgment context. Three experiments explore context effects that occur within a single comparison rather than across several trials. Experiment 1 shows reliable intransitivities in which a target is judged to be more similar to stimulus A than to stimulus B, more similar to B than to stimulus C, and more similar to C than to A. Experiment 2 explores the locus of Tversky’s (1977) diagnosticity effect in which the relative similarity of two alternatives to a target is influenced by a third alternative. Experiment 3 demonstrates a new violation of choice independence which is explained by object dimensions’ becoming foregrounded or backgrounded, depending upon the set of displayed objects. The observed violations of common assumptions to many models of similarity and choice can be accommodated in terms of a dynamic property-weighting process based on the variability and diagnosticity of dimensions.     

Latent inhibition, context specificity, and context familiarity

In two appetitive licking experiments, thirsty rats were pre-exposed to two stimuli prior to conditioning sessions in which one or both of these stimuli were paired with water. Consistent with other results, latent inhibition was disrupted when conditioning took place in a context different from that in which stimulus pre-exposure had occurred. But in animals given prior exposure to the context of stimulus pre-exposure before the start of stimulus pre-exposure, substantial and equivalent latent inhibition was evident whether or not there was a change of context between stimulus pre-exposure and conditioning. These results are discussed in terms of current theories of latent inhibition.     

Closure and context

The aim of this paper is to explain why imaginativeness is valuable. Recent discussions of imaginativeness or creativity (which I regard as the same property) have paid relatively little attention to this important question. My discussion has three parts. First, I elucidate the concept of imaginativeness by providing three conditions a product or act must satisfy in order to be imaginative. This account enables us to explain, among other things, why imaginativeness is associated with inspiration, why it is associated with the faculty of imagination, and why it is relative to persons and to contexts. Second, in the light of this account, I say what the imaginativeness of persons is. Philosophical discussions of the imaginativeness of persons usually treat it as a capacity. In fact, it is a tendency or disposition of a certain kind. Third, I give reasons why the imaginativeness of persons has the value it does. I begin by saying what the basic facts about its value are. When a person's imaginativeness is valuable, it is either (i) a good thing about a person, (ii) good for the person, or (iii) good for others. I provide explanations of each of these facts. I conclude by addressing the difficult question of whether a person's imaginativeness is non-instrumentally good for her. On Romantic and Romantic-inspired views, imaginativeness is non-instrumentally good for a person because of its connection with self-realization. I reject this claim. However, I argue that, often, imaginativeness is indeed non-instrumentally good for the imaginative person.     

Recognizing faces in and out of context

Two experiments are reported which examined the influence of context on face recognition accuracy for novel and familiar faces respectively. Context was manipulated by varying the physical background against which the faces appeared. In Experiment I, 80 student subjects observed 18 faces before attempting to recognize them in a sequence of 36 al ternatives , For half the subj ects, the backgrounds changed from study to test, while for the remainder they stayed the same. In addition, for half the subjects, both the pose and expression of the face also changed, while for the others it remained constant. Changes in pose plus expression and context significantly reduced recognition accuracy for the target faces. Experiment 11 used an identical design, except that the faces of celebrities replaced the novel faces. The influence of context was eliminated but the effects of pose and expression were maintained. However, when only faces which were actually identified by subjects were considered, the effects of pose and expression, too, were eliminated. The significance of these findings for theories of contextual memory are discussed.