The visual contour in depth

We asked subjects to match points on the surface of a smooth three-dimensional (3-D) shape with points on the surface of another object that was geometrically identical to the first object but was placed in a different pose, was differently textured, and was differently shaded. In all cases, the fiducial point was on the rim of one of the objects (i.e., the boundary of the visible region of the surface), whereas the matching point was well within the silhouette of the other object. This allowed us to draw (preliminary) conclusions concerning the way monocular human observers are able to handle the neighborhood of the rim, where the local slant assumes arbitrarily high values. All experiments were done in real space with real objects (no computer-simulated scenes), the points being indicated with laser beam illumination. The subject was given control over the direction of the laser beams and was thus able to perform the task by adjustment from the vantage position. We studied both consistency (whether the subject’s judgments were invariant against changes of relative pose) and veridicality (whether the depth of the visual contour as calculated from the settings agreed with the true distance as measured by mechanical means). Subjects caught much of the 3-D structure of the contour but did deviate appreciably and apparently idiosyncratically from the true geometry.     

Detection of spatial discontinuities in first-order optical flow fields

We investigated the extent to which the human visual system can detect discontinuities in firstorder optical flow fields. We constructed two types of spatial discontinuities: a circular split field with a straight edge and a disk with annular surround. We used two different first-order optical flow components: an expansion and a rotation. We found an intriguing difference in the detection thresholds for straight and circular discontinuities. Whereas straight discontinuities yielded thresholds of 10%— 50% difference in expansion or rotation, circular discontinuities could, at first, only be detected at extreme differences (>>100%). After a learning period, thresholds for such stimuli decreased, but they remained significantly higher than thresholds for the straight edge. Thresholds rose for stimuli that formed a gradual transition between a circular and a straight edge, and they decreased with increasing eccentricity of the circular discontinuity. Results suggest that symmetry in the stimulus, defined by the coincidence of the center of expansion or rotation and the center of the circular discontinuity, was responsible for the difference in thresholds for circular and straight discontinuities.     

Nasal,retronasal, and gustatory perception: An experimental comparison

Four odor substances (lemon aroma, rum aroma, ethyl butyrate, and amyl acetate) in different concentrations were presented nasally and orally (retronasally) in a four-alternative forced-choice procedure (detection tasks). In a further experimental condition, sucrose was added to the stimuli. Finally, the taste properties of the (nonsugared) odor stimuli were judged on seven semantic scales. In the detection of odor-containing stimuli, there were no significant differences between nasal and retronasal stimulation. In the taste conditions, however, there was a significant decline of “hits” when the stimuli contained sucrose in addition to the odor substances. Furthermore, in semantic scaling of the taste stimuli, a new variant of the taste-smell illusion was observed, namely, a tendency to attribute “suited” basic taste categories (e.g., “sweet”) to pure (nongustatory) odor stimuli.     

Upper bounds for Kruskal's stress

In this paper the relationships between the two formulas for stress proposed by Kruskal in 1964 are studied. It is shown that stress formula one has a system of nontrivial upper bounds. It seems likely that minimization of this loss function will be liable to produce solutions for which this upper bound is small. These are regularly shaped configurations. Even though stress formula two yields less equivocal results, it seems to be expected that minimization of this loss function will tend to produce configurations in which the points are clumped. These results give no clue as to which of the two loss functions is to be preferred.This study has been supported by the Nederlandse Organisatie voor Zuiver-Wetenschappelijk Onderzoek (Netherlands Organization for the Advancement of Pure Research), under grant 56-146.Comments by Willem Heiser and Frank Critichley have been very helpful.The second author presently is employed by the Netherlands Central Bureau of Statistics, Voorburg.     

Growing up with severe learning difficulties: A longitudinal study of young people and their families

The paper reports on a longitudinal study of young people with severe learning difficulties. Two types of comparison are made: changes between Time 1 and Time 2, and comparisons with the younger age group in the study. The young adults acquired considerably more self-help and communication skills between Time 1 and Time 2. They were less likely to require help with self care than the younger age group and their carers were less stressed. Parents' needs for additional service provision fell into three categories: information needs, help with communication and other skills, and practical help. The greatest need was for information. The main concerns of the mothers at Time 1 and Time 2 are documented. The young adults' preparation for leaving school, current day placements at Social Education Centres and employment prospects are discussed. It is concluded that there are few opportunities to move on to less sheltered environments.     

Maternal interactive behaviour towards children with and children without cleft lip and palate

The present study examined qualitative and quantitative differences in maternal interactive behaviour towards infants with and without cleft lip and palate (CLP). Thirty-three mother-child pairs with CLP and 34 pairs without CLP were videotaped at 3, 6, 9, and 12 months of age in two sorts of play situations at home. In addition, the mothers were questioned by letter about their ability to recognize and interpret the child's signals; their willingness to respond to such signals; and the duration of shared daily activities in the context of feeding and play. The results showed that mothers of CLP children are somewhat less sensitive than other mothers. In addition, it appeared that CLP children play less with other people. Longer feeding times for CLP children appeared to be restricted to the age of 3 months. It is suggested that mothers of CLP children may be comparatively directive and stimulating because of uncertainty about additional deficiencies. Furthermore, they may be inclined to keep their children away from the outside world.     

Exploring self-forgiveness

This article presents the results of a phenomenological study of the experience of self-forgiveness. On the basis of in-depth interviews with seven subjects, self-forgiveness is described not as an achievement but rather as a gift where one moves from estrangement and brokenness to a sense of at-homeness.This article is based in part on a paper presented at the Eighth International Human Science Research Conference at the University of Aarhus, Denmark, in August 1989. The authors thank their colleagues Carolyn Grissom and Jodi Kelly for their helpful suggestions.     

SOCIAL VALIDATION OF COMPONENT BEHAVIORS OF FOLLOWING INSTRUCTIONS,ACCEPTING CRITICISM,AND NEGOTIATING

This study evaluated whether behaviors often taught as part of social skills training are judged favorably by others. Community judges evaluated the performances of people in various situations requiring one of three social skills: following instructions, accepting criticism, and negotiating to resolve conflicts. These skills were displayed in videotaped scenes by actors with and without mental retardation who acted out roles that had different types of authority relationships, and when different components or clusters of behavior (nonverbal, specific verbal, or general verbal behaviors) were performed well or poorly. The highest ratings by judges were of videotaped scenes that depicted correct use of all behaviors, regardless of which skill was being examined, whether or not the actor had mental retardation, or what the relationship was between the two actors. The lowest ratings were of videotaped scenes that depicted poor performance of all behaviors, and intermediate ratings were obtained when only some of the behaviors were performed poorly. These results, as well as the verbal responses of judges to questions, indicated that the different behaviors commonly used in teaching the skills of following instructions, accepting criticism, and negotiating are relevant to judgment of social performance, and are likely to be reinforced and maintained by social contingencies.     

The significance of the ergodic decomposition of stationary measures for the interpretation of probability

De Finetti's representation theorem is a special case of the ergodic decomposition of stationary probability measures. The problems of the interpretation of probabilities centred around de Finetti's theorem are extended to this more general situation. The ergodic decomposition theorem has a physical background in the ergodic theory of dynamical systems. Thereby the interpretations of probabilities in the cases of de Finetti's theorem and its generalization and in ergodic theory are systematically connected to each other.This paper is an extended version of footnote 5 of von Plato (1981).