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PubMed1976

Differential diagnosis of psychiatric patients with the Minnesota Percepto-Diagnostic Test.

This study investigated whether normals, personality disorders, psychotics and organics could be differentiated by the Minnesota Percepto-Diagnostic Test. There were significant differences between all the groups except the psychotics and personality disorders. It appears that, in general, perceptual disturbance lies along a pathological continuum. Similar performances of psychotics and personality disorders were discussed.

Diagnosis, Differential↗
PubMed1975

[Experiments on perception in schizophrenia (author's transl)].

Acute and chronic schizophrenic subjects were tested with 6 simple experimental tasks of visual stimulus selection. The 2 control groups were a group of non-psychiatric subjects and one of patients with other psychiatric diagnoses. The 6 experimental tasks represented three different types of attention: 1) differentiation between "figure" and "background", 2) concentration; 3) visual integration (Gestalt completion). The main result was that the acute group with paranoidal psychosis and hallucinations made significantly more mistakes in figure-background differentiation (grouping of patterns). But there was no difference between this group and the other patients in the concentration tasks. Both schizophrenic groups performed more poorly in the Gestalt completion task. The results are discussed in light of the information theory (breakdown of a hypothetical filter mechanism) and Sokolow's psychophysiological model of stimulus selection. The hypothesis is put forward that in the acute schizophrenic group a disturbance in an arousal-modulation system is responsible for attenuation of irrelevant input.

Acute Disease↗
PubMed1992

A good-continuation model of some occlusion phenomena.

Occlusion phenomena raise two questions: (1) When will an occluding and a partly occluded object be seen, as opposed to several nonoverlapping objects? (2) What is seen behind the occluding object? Available theories give no satisfactory description of occlusion data. In our view, this situation is at least partially due to the fact that patterns used in occlusion studies are always regular, whereas it is almost unknown which regularities are actually perceived in occlusion patterns. We have therefore collected a complete set of data for a restricted domain of patterns with minimal regularity. Starting from these data, we have developed a model of the perceptual organization of this class of patterns and tested it in a second experiment. The model is a specification of the Gestalt law of good continuation. It assumes that there is a tendency to describe a pattern by the smallest possible number of contour elements and with the smallest possible changes of direction within and between necessary contour elements. The results fit in well with the predictions of the model. It is further demonstrated that the model also describes the preferred interpretations of many regular patterns, published in other studies.

Adult↗
PubMed1993

A progression in the neuropsychological decline of Icelandic patients with probable or possible dementia of the Alzheimer's type: a longitudinal study.

To investigate the nature and rate of cognitive decline in dementia of the Alzheimer's type (DAT), 44 patients with probable or possible DAT (mean age 73.9, range 59-87 years) were given a comprehensive neuropsychological assessment. Twenty-five patients were retested 6 months later, and 11 were tested for the third time another 6 months later. Some tests of mental flexibility and double conceptual tracking ability were beyond the capabilities of the patients, and were left out of the statistical analysis because of floor effect. Poor initial performance on tests of attention, concentration, response speed, general cognitive ability, verbal memory, constructional skills, and perceptual closure ability resulted in nonsignificant changes over time (paired t tests). Tests of expressive speech, visuoperceptual functions and nonverbal memory, on the other hand, showed a significant deterioration over time. These findings indicate that when patients with DAT first receive medical attention, many neuropsychological functions are so severe impaired that there is little room for further decline. To describe the longitudinal course of cognitive decline in DAT, tests should be limited to those that assess the more resistant cerebral functions, and are more sensitive to progressive changes.

Aged↗
PubMed2006

Visual completion and complexity of visual shape in children with pervasive developmental disorder.

Much evidence has been gathered for differences in visual perceptual processing in individuals with Autistic Spectrum Disorder. The presence of the fundamental process of visual completion was tested in a group of children with Pervasive Developmental Disorder (PDD), as this requires perceptually integrating visual structure into wholes. In Experiment 1, it was investigated whether visual completion is present for simple partly occluded shapes in a group of children with PDD and a typically developing group. In Experiment 2, the presence of contextual influences in visual completion was investigated for the two groups. A total of 19 children with PDD and 28 controls who were matched for chronological age and IQ took part in two primed-matching tasks. For both groups, visual completion was present and for both groups, contextual influences were found to be dominant in this process. However, only for the group with PDD no priming effects (PEs) were found from less regular primes on congruent test pairs. The group with PDD did integrate visual information into wholes and did this in a contextually dependent way. However, for more complex shapes, visual completion is weaker for this group.

Autistic Disorder↗
PubMed1989

The effects of kinetic occlusion and categorization on amodal completion. A comment on Gerbino and Salmaso (1987).

The experimental study of Gerbino and Salmaso (1987) focused on the process of amodal completion, i.e. the process that leads to the impression of a total pattern in the absence of information about all parts of the pattern. One of the questions that they have attempted to answer with respect to this process is whether or not it depends on the categorization of the modal part (i.e. the part about which visual information is present) as a modification of a complete prototype. The major conclusion of their experiments is that amodal completion does not depend upon categorization. Furthermore, they interpret their results as indicating that neither the truncated form of the occluded part nor the unification/segregation of contour segments are phenomenally real. We designed some variants of the tunnel effect to demonstrate (1) that the explicit categorization of some parts of the input can have an influence on amodal completion and (2) that the truncated form of a pattern can be phenomenally real. Our results corroborate these hypotheses and can, therefore, interpreted as refuting two rather central claims of Gerbino and Salmaso (1987). The conclusion of our experiment must be that amodal completion is not as primary as they have supposed but can be influenced by kinetic occlusion and categorization stored in visual memory.

Adult↗
PubMed1990

Object superiority: a comparison of complete and part probes.

Previous research on object superiority effects has shown that certain contexts enhance the recognition of an object part. However, those contexts would not normally be called objects. The present study discusses object superiority within more general issues of object recognition. By using what we call 'complete' probes, superiority effects were extended to exposure durations much longer than those used in previous research. Experiments 1 and 2 found that complete probes gave stable superiorities at 250 msec and even 2-sec stimulus exposures. These object superiority effects were found for both objects (faces and chairs) investigated. Experiment 3 showed that object superiorities established with complete probes were not necessarily greater than those for part probes. The experiments stress the role of spatial arrangement of object parts in accessing stored information. It is argued that a successful match of a structural description to a representation in long-term memory influences stimulus processing by allowing the formation of higher level features.

Adult↗
PubMed2004

Mental rotation depends on the number of objects rather than on the number of image fragments.

It is often intuitively assumed that disconnected image fragments result in a representation of separate objects. When objects are partly occluded, disconnected image fragments can still result in a representation of a single object, based on visual completion. In a simultaneous matching task, displays showing one object, partly occluded objects, or two objects were compared with each other. When only a translation was required to match pairs of displays, one-object displays were matched faster than both occluded-object and two-object displays, which did not differ significantly from each other. When mental rotation and translation were required, the one-object displays were again matched the fastest. In addition, an advantage for occluded-object displays compared with two-object displays was found. We conclude that when the generation of a mental representation is likely, object-based connectedness determines object matching. Mental rotation then seems to depend on the number of objects rather than on the number of image fragments.

Adolescent↗
PubMed2005

Pigeons do not perceptually complete partly occluded photos of food: an ecological approach to the "pigeon problem".

Humans routinely complete partly occluded objects to recognize the whole objects. However, a number of studies using geometrical figures and even conspecific images have shown that pigeons fail to do so. In the present study, we tested whether pigeons complete partially occluded objects in a situation simulating a natural feeding context. In Experiment 1, we trained pigeons to peck at any photograph of food and not to peck at any containing a non-food object. At test, we presented both photos of food partly occluded by pigeon's feather and photos simply truncated at the same part. We predicted that if the pigeons perceptually completed the occluded portion, then they would discriminate the photos of occluded food better than the truncated photos. The result was that the pigeons pecked at the truncated photos earlier than the occluded photos. Placing the occluder next to all of the stimuli in Experiment 2 or substituting indented lozenge for the feather in Experiment 3 did not affect the results. Thus, even in a simulated ecologically significant situation, pigeons continued to not show evidence of perceptual completion.

Animals↗
PubMed2004

Rapid completion effects in human high-order visual areas.

Object completion is an inherent property of visual recognition in which objects can be accurately perceived in the presence of substantial obstructions. We have previously shown [Cereb. Cortex 12 (2002) 163] that high-order human object areas are driven partially by local object fragments and partially by global completion effects. Here we explored, through a backward masking paradigm, whether the balance of local and global processing is time dependent, that is, to what extent completion effects evolve at a different time compared to local image representations. In two separate experiments, subjects were presented with three types of images: (a) unobstructed line drawings of animal shapes ("whole"), (b) the same shapes obstructed by a set of parallel stripes ("grid"), and (c) a scrambled version of b in which the stripe position was shifted horizontally, disrupting the relative position of image regions but maintaining the local feature distribution ("scrambled"). Images were presented either for 60 or 250 ms followed by a mask. Both behavioral and fMRI findings from high-order occipitotemporal object areas showed consistently that object selectivity emerges at the same time as the local feature representation. Thus, object completion effects were evident at the same relative magnitude (LO: 0.5 +/- 0.3 and 0.58 +/- 0.04; pFs: 0.62 +/- 0.3 and 0.6 +/- 0.04; 60 and 250 ms, respectively) even at the short presentation durations when overall object activation was greatly reduced.

Adult↗
PubMed2006

TMS over right posterior parietal cortex induces neglect in a scene-based frame of reference.

Although damage to right posterior parietal cortex (RPPC) produces bias in line bisection, Karnath et al. [Karnath, H.-O., Berger, M. F., Küker, W., & Rorden, C. (2004). The anatomy of spatial neglect based on voxelwise statistical analysis: A study of 140 patients. Cerebral Cortex, 14, 1164-1172] claim that it plays little role in spatial neglect, which is better measured by target cancellation. We used a detection task (approximating cancellation in requiring detection) to investigate this claim by compromising the parietal cortex with transcranial magnetic stimulation (TMS). Two outline shapes, one on each side of fixation, were briefly displayed before a mask. The target was a discontinuity in the left or right of the outline of one of these perceptual objects. Subjects indicated position or absence of target as fast as possible. Stimulus-mask onset asynchrony was adjusted individually to yield 75% detection. TMS was delivered over left posterior parietal cortex (LPPC), RPPC and Vertex, with Sham TMS over RPPC as a baseline control. Target detection was near ceiling and fastest at central positions and worst and slowest at the far right. Detection was significantly reduced at the far left position by TMS over RPPC. No other effects were obtained and latency was not affected by TMS. Disruption of RPPC by TMS does produce left neglect as measured by detection. Given the pattern of performance and since it was disrupted on one side of the display rather than on one side of each shape, attention and neglect were in a scene-based rather than object-based reference frame.

Adult↗
PubMed2006

Perceptual grouping in disorganized schizophrenia.

This study evaluated visual perceptual grouping in schizophrenia to test the hypothesis that the disorganization syndrome in schizophrenia is related to a deficit in cognitive coordination. Perceptual grouping was examined with three psychophysically well-controlled tasks in patients with disorganized schizophrenia (n=11), non-disorganized schizophrenia (n=24), psychotic disorders other than schizophrenia (n=31) and non-psychotic psychiatric disorders (n=35). These measures assessed processing of both concurrent and preceding stimulus context. Deficits in perceptual grouping were observed on all three tasks in disorganized schizophrenia patients. Dysfunctional perceptual grouping mechanisms produced both enhanced and impaired task performance suggesting that the pattern of performance observed was the result of a specific deficit in the grouping of stimulus elements. We interpret these data as further support for the hypothesis that the disorganization syndrome in schizophrenia reflects a widespread deficit in the cognitive coordination of contextually related stimuli, leading to dysfunctional grouping of stimulus features in vision, thought and language.

Adult↗
PubMed2004

Asymmetry between horizontal and vertical illusory lines in determining the depth of their embedded surface.

To investigate how the visual system integrates disparity information from horizontal and vertical edges and conveys it to the regions without any depth cues, we introduce a new phenomenon of subjective surface formation in an Ehrenstein-style configuration with inducing elements at different depths, and without explicit monocular occlusion zones. Different sets of experiments by separate groups of subjects suggest that when a subjective (illusory) square forms, it is at the depth of vertical illusory sides rather than horizontal ones. When the vertical side inducers are stereoscopically behind the horizontal ones, subjective surface formation is less likely. In depth assignment, we interpret the dominance of vertical sides over horizontal ones geometrically: vertical orientation can convey the horizontal disparity--a critical factor for Wheatstone (classic) stereopsis--but horizontal orientation per se lacks horizontal disparity information. Therefore, in the disparity integration, vertical illusory sides play a dominant role and their depth information influences the embedded subjective surface as well as the horizontal illusory sides.

Cues↗
PubMed2005

The recognition of partially visible natural objects in the presence and absence of their occluders.

The visual system is adept at compensating for the missing information in scenes that results from occlusion, but how this is done is not fully understood. In particular, the role of the occluding object in visual processing and its effect on the subsequent recognition of the occluded object is unclear. We report three human behavioral experiments suggesting that the recognition of partially visible objects is facilitated when the missing object information is replaced by an occluder rather than simply removed. Furthermore, we provide EEG evidence suggesting that the processes responsible for facilitated recognition occur relatively early in the visual stream.

Adolescent↗
PubMed1998

Perceiving topological structure of 2-D patterns.

Four experiments investigated observers' sensitivity to the topological structure of visual stimuli. Three factors were taken to capture the topological structure of 2-D patterns: The number of disconnected components, the number of holes (connections), and inclusion relationships. If studied in isolation, any given topological property is typically confounded with the presence of particular features such as line terminations and contour length, or with Gestalt principles of perceptual organization. We went beyond existing studies and attempted to systematically remove potential confounds from the stimulus displays. Results showed that processing speeds for two-dimensional patterns are a function of their topological properties. The more patterns differ in their topological structure the easier they can be discriminated. Not only do all three topological factors contribute to pattern discriminability, they also can be combined to provide an overall measure of structural complexity. Forced choice comparison techniques agreed well with similarity judgments. Topological structure thus contributed to discriminability above and beyond many confounding variables. Claims suggesting a general topological analyzer in visual processing are discussed.

Adult↗
PubMed1999

Investigating global effects in visual occlusion: from a partly occluded square to the back of a tree-trunk.

'Classic' occlusion examples, such as a square partly occluded by a rectangle, have given rise to so-called local and global accounts of amodal completion. Without denying the influence of local configurations, I take the position that, in the long run, any theory of amodal completion should account for global properties. After a brief review of local and global accounts, two extensions of the stimulus domain are proposed to further illustrate the necessity of global accounts. The first is the domain of so-called fuzzy regularities, i.e., regularities which are not based on metrical identities. It is argued and demonstrated that observers are even susceptible to these fuzzy regularities and that they complete partly occluded shapes accordingly. The second extension is towards 3D object completion. Theories of object representation that describe intrinsic regularities of objects appear to be most suitable to predict relative preferences of alternative object completions. Consequently, fuzzy object completions, such as the completion of the back of a tree-trunk, can be explained better by global constraints.

Depth Perception↗
PubMed1999

Complete mergeability and amodal completion.

When image fragments are taken to correspond to the visible portions of a single occluded object, the object is said to 'amodally complete' behind the occluder. Kellman and Shipley (Kellman, P. J., & Shipley, T. F. (1991). A theory of visual interpolation in objective perception. Cognitive Psychology, 23, 144-221) argued that when the virtual contour extensions of such image fragments subtend an obtuse or right angle, the contours are 'relatable' and therefore complete. However, edge and surface relatability are neither necessary nor sufficient for completion to be perceived (Tse, P. U. (1999) Volume completion. Cognitive Psychology). Evidence is offered that completion is not driven directly by image cues such as contour relatability, but is driven, rather, by intermediate representations, such as volumes that are inferred from global image cue relationships. Evidence suggests that several factors, none of which is necessary for amodal completion to occur, contribute to the perceived strength of amodal completion, including similarity of pattern or substance, proximity, and good volume continuation or complete mergeability. Two partially occluded volumes are completely mergeable when they can be extended into occluded space along the trajectory defined by their visible surfaces such that they merge entirely with each other. Mergeability is not measurable in the image because it describes an inferred relationship among volumes that must themselves be inferred from the image.

Adult↗
PubMed1999

Synchronous change and perception of object unity: evidence from adults and infants.

Adults and infants display a robust ability to perceive the unity of a center-occluded object when the visible ends of the object undergo common motion (e.g. Kellman, P.J., Spelke, E.S., 1983. Perception of partly occluded objects in infancy. Cognitive Psychology 15, 483-524). Ecologically oriented accounts of this ability focus on the primary of motion in the perception of segregated objects, but Gestalt theory suggests a broader possibility: observers may perceive object unity by detecting patterns of synchronous change, of which common motion is a special case. We investigated this possibility with observations of adults and 4-month-old infants. Participants viewed a center-occluded object whose visible surfaces were either misaligned or aligned, stationary or moving, and unchanging or synchronously changing in color or brightness in various temporal patterns (e.g. flashing). Both alignment and common motion contributed to adults' perception of object unity, but synchronous color changes did not. For infants, motion was an important determinant of object unity, but other synchronous changes and edge alignment were not. When a stationary object with aligned edges underwent synchronous changes in color or brightness, infants showed high levels of attention to the object, but their perception of its unity appeared to be indeterminate. An inherent preference for fast over slow flash rates, and a novelty preference elicited by a change in rate, both indicated that infants detected the synchronous changes, although they failed to use them as information for object unity. These findings favor ecologically oriented accounts of object perception in which surface motion plays a privileged role.

Adult↗