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PubMed2003

T-junctions and perceived slant of partially occluded surfaces.

Häkkinen and Nyman (1997 Perception 26 29-38) reported that perceived slant is reduced when occlusion is a possible interpretation for the visual system. We present data from three experiments that confirm and expand on their finding. Our stimuli consisted of four types of stereograms depicting white central rectangles flanked on either side by two grey rectangles. The central white rectangles varied in height, thus manipulating the polarity of the T-junction information between the central and flanking rectangles. Perceived slant was smallest or not apparent when T-junction information indicated the central rectangles were nearer than the flanking rectangles and greatest when T-junction information indicated a farther central rectangle. Slant estimates for a stimulus containing a subjective pacmen-induced central rectangle were biased towards a depth step when an occlusion interpretation was possible.

Depth Perception↗
PubMed2006

Does the use of natural stimuli facilitate amodal completion in pigeons?

Three experiments were carried out to investigate whether amodal completion in pigeons can be facilitated by the use of colour photographs instead of highly artificial stimuli such as geometrical shapes. Ten pigeons were trained in a go/no-go procedure to discriminate between photographs of complete and of incomplete pigeon figures. In the subsequent test, the birds classified pictures of partly occluded pigeons as though they were complete (experiment 1). However, we found evidence that classification was based on spurious stimulus features that paralleled the intended class rule of figural completeness versus incompleteness. In particular, classification was shown to be guided by white background gaps that separated the parts of the fragmented pigeon figures (experiment 2), as well as by cues related to overall Gestalt (experiment 3). In summary, the present results indicate that the use of more natural stimuli such as photographs instead of geometrical shapes is insufficient for providing amodal completion in pigeons. It is suggested that a combination of various cues, including, eg, 3-D information and common motion in addition to surface and contour properties, may be required to induce a perceptual bias favouring visual completion of occluded portions.

Animals↗
PubMed2006

Development of modal and amodal completion in infants.

Visual completion has been divided into two types: modal and amodal. While psychophysical studies with adults provided several common properties between modal and amodal completion, studies with infants showed differential trends in the development of these perceptual abilities. In the present study, we further examined the development of these two kinds of visual completion in infants aged 3 to 6 months. We created a display composed of a partially overlapping circle and square. The display induced either modal or amodal completion depending on the colour. Infants were familiarised with either the modal or the amodal display. After this familiarisation, the infants were tested on their discrimination between the complete figure and the broken figure. If the infants could perceptually complete the figures in the familiarisation display, they were expected to show a novelty preference for the broken figure. A total of thirty-two infants participated in the present study. Our results suggest that modal completion develops by 3-4 months of age, whereas amodal completion develops by 5-6 months of age.

Child Development↗
PubMed2004

Amodal completion as reflected by gaze durations.

In two experiments amodal completion of partly occluded shapes was investigated by recording eye movements in a directed visual-search task. Participants searched arrays of shapes in a prescribed order for target figures that could partly be occluded. Longer gaze durations were found on occlusion patterns than on truncated control patterns for targets but not for non-targets. This effect of occlusion was restricted to a subset of the stimuli. A second experiment was carried out to establish whether this restriction resulted from structural properties of the stimuli or their familiarity. Occlusion patterns in this experiment were ambiguous with respect to structure, allowing both local and global completions. One of the completions was always less familiar than the other. The results showed longer gazes only for the less familiar completions, irrespective of whether they were local or global.

Adult↗
PubMed2005

Perceptual grouping in pigeons.

Animal studies reveal that many species perceive partially occluded objects in the same way as do humans. Pigeons have been a notable exception. We re-investigated this anomaly of pigeon perception using a different approach from previous studies. With our method, we show that pigeons perceive occluded objects in the same manner as do other species. In addition, we report that pigeons can recognize perceptually transparent surfaces when the effect is induced by the same perceptual mechanisms as occlusion. These results give behavioral evidence that the perception of both occlusion and transparency is a common visual function shared by pigeons and humans, despite the structural differences between their visual systems.

Animals↗
PubMed2006

Who owns the contour of a visual hole?

Holes are useful in the study of shape, contour curvature, and border ownership. Several authors have suggested that holes have figural or quasi-figural status. I discuss three criteria to test the evidence that holes behave more like figures than like ground: (i) holes perceived as such; (ii) similar performance for holes and figures; (iii) different performance for holes and other ground regions. Using these criteria, I review the literature and conclude that holes do not have figural status in relation to border ownership. I also argue that holes are ideal stimuli to study figure-ground organisation.

Contrast Sensitivity↗
PubMed2005

Visual extrapolation of contour geometry.

Computing the shapes of object boundaries from fragmentary image contours poses a formidable problem for the visual system. We investigated the extrapolation of contour shape by human vision. Measurements of extrapolation position and orientation were taken at six distances from the point of occlusion, thereby yielding a detailed representation of the extrapolated contours. Analyses of these measurements revealed that: (i) extrapolation curvature increases linearly with the curvature of the inducing contour, although there is individual bias in the slope; (ii) the precision with which an extrapolated contour is represented is roughly constant, in angular terms, with increasing distance from the point of occlusion; (iii) there is a substantial cost of curvature, in that the overall precision of an extrapolated contour decreases systematically with curvature; (iv) the shapes of visually extrapolated contours are characterized by a nonlinear decrease in curvature, asymptoting to zero; and (v) this decaying pattern of curvature is explained by a Bayesian model in which, with increasing distance from the point of occlusion, the prior tendency to minimize curvature gradually dominates the likelihood tendency to minimize variation in curvature.

Bayes Theorem↗
PubMed2001

On a common circle: natural scenes and Gestalt rules.

To understand how the human visual system analyzes images, it is essential to know the structure of the visual environment. In particular, natural images display consistent statistical properties that distinguish them from random luminance distributions. We have studied the geometric regularities of oriented elements (edges or line segments) present in an ensemble of visual scenes, asking how much information the presence of a segment in a particular location of the visual scene carries about the presence of a second segment at different relative positions and orientations. We observed strong long-range correlations in the distribution of oriented segments that extend over the whole visual field. We further show that a very simple geometric rule, cocircularity, predicts the arrangement of segments in natural scenes, and that different geometrical arrangements show relevant differences in their scaling properties. Our results show similarities to geometric features of previous physiological and psychophysical studies. We discuss the implications of these findings for theories of early vision.

Gestalt Theory↗
PubMed2002

Facial identity and facial emotions: speed, accuracy, and processing strategies in children and adults.

As yet, nearly all studies in face and facial affect recognition typically provide only data on the accuracy of processing, invariably also in the absence of reference data on abstract information processing. In this study, accuracy and speed of abstract visuo-spatial processing, face recognition, and facial emotion recognition were investigated in normal school children (7-10 years) and adults (25+/-4 years). In the age range of 7-10 years, accuracy of facial processing hardly increased, while speed did substantially increase with age. Adults, however, were substantially more accurate and faster than children. Differences between facial and abstract information processing were related to type of processing strategy, that is, configural or holistic processing versus featural or piecemeal processing. Improvement in task performance with age is discussed in terms of an enhanced efficiency of the configural organization of facial knowledge (facial information processing tasks), together with a further increase in processing capacity (all tasks). The differential developmental course of speed and accuracy levels indicates that speed is a more sensitive measure when children get older. Moreover, it also suggests that speed of performance, in addition to accuracy, might be successfully used in the assessment of clinical deficits, as has recently been demonstrated in children with autistic disorders of social contact.

Adult↗
PubMed1976

Differences in the sequential integration of form as a function of age and interstimulus interval.

The sequential integration of visual stimuli was studied in 12 young (18-28 years) and 12 old (51-62 years) men and women. Stimuli were constructed as corresponding word halves and inter-stimulus intervals (ISI's) of varied duration (0-150 msec.) were introduced between the presentation of the two halves. Correct word identification was found to be an inverse function of ISI for both young and old subjects. The number of stimuli correctly identified was significantly lower for the older subjects at all levels of ISI. None of the interactions of age, sex, and ISI was significant. The data appear to question the "stimulus persistence" model as applied to age differences in the temporal organization of form.

Adult↗
PubMed2000

A developmental trajectory in implicit memory is revealed by picture fragment completion.

Dissociations between performance on implicit and explicit tasks have often been taken as evidence that different neural structures subserve the two types of memory. One such dissociation involves developmental differences that emerge in explicit tasks, but which appear to be absent in implicit tasks. Such findings are consistent with the idea that implicit memory is subserved by a more primitive system that evolves earlier at both phylogenetic and ontogenetic levels. The present paper reviews previous studies that claimed to find evidence that implicit memory is fully developed in very young children. Issues of measurement error, ceiling effects, and insufficient power brought up questions about those studies with respect to the developmental issue. The present study compares performance on implicit (picture fragment completion) and explicit (free recall and recognition) memory tasks with groups ranging in age from 5-28 years. We find a reliable developmental trend in both implicit and explicit performance in which the former cannot be attributed to the operation of explicit memory processes. Thus, we conclude that implicit memory, like explicit memory, develops with age.

Adolescent↗
PubMed1975

Hemispheric specialization in normal man studied by bilateral measurements of the regional cerebral blood flow. A study with the 133-Xe inhalation technique.

Changes of regional cerebral blood flow (rCBF) during mental activation have so far only been studied unilaterally by means of the intracarotid 133Xe injection technique. In the present study bilateral rCBF measurements were made by the 133Xe inhalation technique during mental activities supposed to engage the hemispheres selectively. The study was carried out on 24 normal right-handed male volunteers by the short 133Xe inhalation method. Fourteen scintilation detectors were placed in parallel overcorresponding regions of the two hemispheres. Four rCBF measurements were made on each subject during three randomized conditions: (1) Rest (two studies); (2) Verbal test (Miller Analogy Test), and (3) Spatial test (Street). The recordings were separated by at least one hour to avoid contamination from previous measurement. The answers to the problems were given either by raising the fingers of the left hand (Verbal test) or after the study (Spatial test). In order to investigate the effects of increased motivation 12 of the subjects were promised an extra money reward in addition to the basic payment, if they performed above a certain level on the tests. Small but statistically significant differences between the average hemisphere flows were recorded during the two tests. In the highest motivated (paid) group the verbal test increased the flow in the left hemisphere by 16 per cent while the right-sided increase was significantly smaller, 13 per cent (P less than 0-001). The corresponding figures for the spatial test were: left 7 per cent, right 10 per cent (P less than 0-01). The same tendencies were seen in the less motivated group although the hemisphere differences were smaller and statistically not significant. Analysis of the regional results showed that the largest interhemispheric differences (about 5 per cent) were seen in occipital and parietal regions during the verbal test and in frontal and parietal regions during the spatial test. It is concluded that bilateral measurements of rCBF can be used with advantage in the study of lateralization of mental functions in the human brain.

Adolescent↗
PubMed1985

Aging and similarity grouping in visual search.

It has been argued that principles of perceptual organization play an important role in the representation of a visual stimulus and that elderly adults may be deficient in perceptual unit formation. The present study examined the extent to which the Gestalt principles of grouping by proximity and similarity predicted the formation of large perceptual units that could affect performance in a visual search task. The verbal reaction time to determine the presence or absence of a target letter in arrays of 1, 5, or 9 elements was determined for young (20 years) and elderly (69 years) adults. Both age groups could take advantage of the organization implied by Gestalt principles in finding a target in the context of a small implied group. The elderly adults, however, were not able to organize a single perceptual unit composed of eight elements. Thus, although the visual search performance of the age groups was similar, the elderly adults did yield evidence of a perceptual organization deficit.

Adolescent↗
PubMed1980

Family studies of schizophrenia: an update and commentary.

Recent family studies of schizophrenia which address the question of etiology are reviewed. The majority of these studies continue to focus on two major aspects of family life, deviant role relationships and disordered communication processes among family members. By and large the research on role relationships has not gone beyond demonstrating that correlations exist between these family variables and the occurrence of schizophrenia in an offspring. By contrast, recent research on disordered communication has begun to employ methodologies appropriate to testing the direction of the relationship between these family interaction patterns and schizophrenia. On a limited scale, some investigators have also begun to consider the etiologic role of family communication variables within more complex causal models, incorporating factors outside the domain of family interaction. To date greatest attention has been given to the combined role of genetic and family interaction variables. The need for multivariate and longitudinal approaches which examine the moderating effects of the social context of the family on relations between family variables and schizophrenia is discussed.

Adolescent↗