Material-illumination ambiguities and the perception of solid objects

The appearance of objects depends on their material, shape, and on the illumination conditions. Conversely, object appearance provides us with cues about the illumination and the material. This so-called inverse problem is basically underdetermined and therefore we expect that material and illumination perception are confounded. To gain insight into the relevant mechanisms, we rendered a set of artificial spheres for vastly different canonical light fields and reflectance functions. We used four physics-based bidirectional reflectance distribution functions (BRDFs) representing glossy, pitted, velvety, and matte material. The six illumination conditions were collimated illumination from four directions, hemispherical diffuse illumination, and fully diffuse (Ganzfeld) illumination. In three sub-experiments we presented pairs of stimuli and asked human observers to judge whether the material was the same, whether the illumination was the same, and for a subset in which either the illumination or the material was the same to judge which of the two was constant. We found that observers made many errors in all sub-experiments. In experiment 2 the illumination direction was chosen at random. Using an interactive interface, we asked human observers to match the illumination direction of a sphere of one of the four materials with that of a Lambertian sphere. We found systematical material-dependent deviations from veridical performance. Theoretical analysis of the radiance patterns suggests that judgments were based mainly on the position of the shadow edge. In conclusion, we found no evidence for 'material constancy' for perception of smooth rendered spheres despite vast quantitative and qualitative differences in illumination and in BRDF between the stimuli. Although human observers demonstrated some 'illumination constancy', they made systematic errors depending on the material reflectance, suggesting that they used mainly the location of the shadow edge. Our results suggest that material perception and light-field perception are basically confounded.     

Contribution to the mathematical biophysics of visual perception with special reference to the theory of aesthetic values of geometrical patterns

On the basis of previous mathematico-biophysical studies, a theory of visual perception is outlined. The theory is applied to the aesthetic values of polygonal patterns and found in fair agreement with experimental results.     

Approaching the religious patient in forensic psychiatry,with special focus on ethnic minority patients

ABSTRACT

Ethnic minority patients are overrepresented in Danish forensic psychiatry and knowledge is needed on how these patients are approached in relation to religious and cultural issues. The aim of this study was to investigate how psychiatrists in Danish forensic psychiatry approach religious ethnic minority patients. The study revealed positive approach towards religious ethnic minority patients. However, unless religion features as part of the illness, the tendency is to not incorporate the patients’ religiosity in treatment. The study finds that the hospital chaplain is regarded by the psychiatrists as an important part of the ward and expressed the desire for a more formal cooperation with religious specialists to be developed. Finally, the study finds that religious practices such as Ramadan, common prayer, and Islamic edicts on food and unlawful touch are areas where more knowledge is needed, especially in relation to anxiety, potential stress, and conflict situations.     

Culture, control, and perception of relationships in the environment

East Asian cognition has been held to be relatively holistic; that is, attention is paid to the field as a whole. Western cognition, in contrast, has been held to be object focused and control oriented. In this study East Asians (mostly Chinese) and Americans were compared on detection of covariation and field dependence. The results showed the following: (a) Chinese participants reported stronger association between events, were more responsive to differences in covariation, and were more confident about their covariation judgments; (b) these cultural differences disappeared when participants believed they had some control over the covariation judgment task; (c) American participants made fewer mistakes on the Rod-and-Frame Test, indicating that they were less field dependent; (d) American performance and confidence, but not that of Asians, increased when participants were given manual control of the test. Possible origins of the perceptual differences are discussed.     

Men's perception of premenstrual changes on the premenstrual assessment form

Outcome research has shown that partner-spouse support can enhance the therapeutic outcome in a number of clinical problems. In the area of premenstrual tension, studies of treatment have apparently overlooked this issue of partners' support. This study was designed to address how men perceive premenstrual changes. 99 undergraduate men were asked whether they believed that women had premenstrual changes reflected on the 18 unipolar scales of the Premenstrual Assessment Form. Responses suggest that young men acknowledge that some women experience dysphoric features like hostility, mood swings, and low self-esteem as well as physical discomfort and behavioural changes. Clinical implications are outlined.     

Effects of surface texture on weight perception when lifting objects with a precision grip

In this paper, we show that, when lifting an object using a precision grip with the distal pads of the thumb and index finger at its sides, the perceived weight depends on the object’s surface texture. The smoother the surface texture, the greater the perceived weight. We suggest that a smoother object is judged to be heavier because the grip force, normal to the surface, required to prevent it from slipping is greater. The possibility of there being an influence of surface texture per se is excluded by a second experiment that employed a variant of the precision grip in which the thumb supports the weight of the object from underneath. With the grip oriented in this way, there is no need to match grip force to surface texture and, under these conditions, there is no effect of surface texture on weight perception. In the first two experiments, the test and comparison weights were lifted successively by the same hand. In a third experiment, the effect of surface texture was replicated for sequential lifts made with separate hands. Thus, the effect is not restricted to comparisons made with the same hand.     

Effects of 3-D complexity on the perception of 2-D depictions of objects

In a recent study, Pelli (1999 Science 285 844-846) performed a set of perceptual experiments using portrait paintings by Chuck Close. Close's work is similar to the 'Lincoln' portraits of Harmon and Julesz (1973 Science 180 1194-1197) in that they are composite images consisting of coarsely sampled, individually painted, mostly homogeneous cells. Pelli showed that perceived shape was dependent on size, refuting findings that perception of this type is scale-invariant. In an attempt to broaden this finding we designed a series of experiments to investigate the interaction of 2-D scale and 3-D structure on our perception of 3-D shape. We present a series of experiments where field of view, 3-D object complexity, 2-D image resolution, viewing orientation, and subject matter of the stimulus are manipulated. On each trial, observers indicated if the depicted objects appeared to be 2-D or 3-D. Results for face stimuli are similar to Pelli's, while more geometrically complex stimuli show a further interaction of the 3-D information with distance and image information. Complex objects need more image information to be seen as 3-D when close; however, as they are moved further away from the observer, there is a bias for seeing them as 3-D objects rather than 2-D images. Finally, image orientation, relative to the observer, shows little effect, suggesting the participation of higher-level processes in the determination of the 'solidness' of the depicted object. Thus, we show that the critical image resolution depends systematically on the geometric complexity of the object depicted.     

On the psychophysical discriminability of somatosensory nerve action potential patterns with irregular intervals

In this paper we consider the problem of whether or not a series of irregularities in the interpulse intervals in a train of nerve action potentials can be discriminated better than a single gap in a regular train. We also consider the corollary problem-does an increase in the number of impulses in a burst with irregular intervals lead to a decrease in the threshold for irregularity, thus indicating some integrative capacity of the relevant neural decoding mechanism. Answers to these questions are obtained by means of a psychophysical test and are affirmative in both cases. This suggests that the irregularities which have been observed in the intervals between nerve action potentials in animal preparations are true information-carrying codes within a restricted temporal region. Because of certain critical points in the functions relating this sensitivity to the basic frequency of the nerve impulses, a group of seiveral temporal regions is postulated in which time is dealt with differently by the somatosensory system.     

Effects of the orientation of moving objects on the perception of streaming/bouncing motion displays

In this study, we examined the contribution of the orientation of moving objects to perception of a streaming/bouncing motion display. In three experiments, participants reported which of the two types of motion, streaming or bouncing, they perceived. The following independent variables were used: orientation differences between Gabor micropatterns (Gabors) and their path of motion (all the experiments) and the presence/absence of a transient tone (Experiment 1), transient visual flash (Experiment 2), or concurrent secondary task (Experiment 3) at the coincidence of Gabors. The results showed that the events at coincidence generally biased responses toward the perception of bouncing. On the other hand, alignment of Gabors with their motion axes significantly reduced the frequency of bounce perception. The results also indicated that an object whose orientation was parallel to its motion path strengthened the spatiotemporal integration of local motion signals along a straight motion path, resulting in the perception of streaming. We suggest that the effect of collinearity between Gabors and their motion path is relatively free from the effect of attention distraction.     

On the theory of relations based on the theory of objects

Summary The theory of relations presented in this article consists of the general and the special theory of relations. The formulae of the former are meaningful and its laws valid for relations of any type. The meaningfulness of expressions and the validity of laws of the latter are restricted to relations of a certain special type. The special theory of relations is distinguished from the applied theory of relations. The applied theory of relations is the general theory applied to relations of a special type, the difference between the general and the applied being in the form of the variables. The special theory of relations and the applied theory, when concerned with relations of the same special type, may differ with respect to the form of constants without differing with respect to variables.     

Feeling good and feeling close: Affective influences on the perception of intimate relationships

Two experiments investigated the role of short-term affective states on the way people perceive various aspects of their personal relationships. Using an unobtrusive mood induction in a field setting, Experiment 1 found significant mood congruency in evaluative judgments about well-established intimate relationships. Experiment 2 used a controlled laboratory procedure and found that evaluations of the relationship and the partner, as well as preferred styles of conflict resolution were all significantly affected by the respondents' transient mood state. Increasing relationship longevity did not reduce affective influences on judgments in either study. The results arc discussed in terms of the role of affective states in cognition and judgments, and the influence of affect on everyday judgments about personal relationships is considered.     

Kinematic form and scaling: further investigations on the visual perception of lifted weight

Observers are able to judge accurately the weight lifted by another person when only the motions of reflective patches attached to the lifter's major limb joints and head can be seen (Runeson & Frykholm, 1981). What properties of these complex kinematic patterns allow judgments of weight to be made? The pattern of variation in velocity of the lifted object over position is explored as a source of information for weight: It is found to provide limited information. How are variations in kinematic patterns scaled to allow judgments of weight, a kinetic quantity? The possibility of a source of information for scaling in the kinematics is investigated. Judgments based only on patch-light displays are accurate to a degree that is improved by an extrinsic scaling basis. Finally, the sensitivity to scaling of alternative metrics used in judging is explored. Intrinsic metrics are discovered to be less sensitive to the absence of an extrinsic basis for scaling.     

Common and relative components of reflected light as information about the illumination, colour, and three-dimensional form of objects

Abstract.— A model for perceptual analysis of the proximal stimulus into common and residual components, earlier described in a series of papers by Johansson and his co-workers for motion and space perception, is applied to colour perception. Though still premature, this application seems to make colour constancy a natural result of the analysis in the same way as size and form constancy is solved by Johansson's vector analysis in the frame of reference of projective geometry. Applications of the model to Land's Mondrian experiments, to simultaneous contrast, and to the Cornsweet-OBrien effect are outlined. The information from variations and invariances in reflected light (besides the geometrical projection) is discussed with reference to Gibson's ecological optics.     

The perception of false self scale for adolescents: Reliability,validity, and longitudinal relationships with depressive and anxious symptoms

A scale assessing generalized false self‐perceptions (Perceptions of False Self, POFS) was developed and tested across three studies involving a total of 331 adolescents (11–16 years). In Study 1, interviews were conducted to develop items for the scale. In Study 2, psychometric techniques were used to derive a scale composed of 16 items. Study 2 also assessed the validity of the scale: depressive symptoms were found to increase POFS across 10 weeks, whereas false self‐perceptions had a reciprocal effect on anxiety. In Study 3, the convergent validity of the POFS scale was established. Overall, the evidence suggests that the POFS scale is a reliable and valid measure of generalized false self‐perceptions.     

An examination of social and psychological influences on academic learning: a focus on self-esteem,social relationships,and personal interest

The present study focused on an examination of both global and domain-specific self-esteems in secondary mathematics learning. The extent to which self-esteem, in general, would account and explain educational success through social relationships with teachers and peers, and personal interest in learning tasks is the main inquiry of this correlational investigation. Two hundred and eighty-three year 10 students (128 girls, 155 boys) were asked to respond to a number of Likert-scale inventories. Causal modeling procedures, aided by the statistical software MPlus 7.3, were used to analyze the data and to test the hypothesized model. A series of a posteriori analyses yielded a modified model for discussion, producing a number of key findings, namely: (a) the differential influences of both global (e.g., →relationship with teachers) and domain-specific (e.g., →relationship with peers) self-esteems, (b) the positive influences of social relation with teachers (e.g., →exam result) and interest in learning tasks (e.g., →end-of-school term grade), and (c) the mediating functioning of relationship with peers and interest in learning tasks. This evidence, overall, provides additional theoretical insights into the operational nature and trajectories of effective learning.