Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Perceptual Closure”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources
PubMed2003

Depression and cognitive functioning in alcoholism.

AIMS: Studies on cognitive processes in alcoholism have reported changes with respect to executive functions and memory, which have been interpreted within the context of different neuropsychological models. The aims of the present study were to investigate (1) the validity of these models and (2) the influence of depression on cognitive functioning in alcoholism. DESIGN, SETTING AND PARTICIPANTS: In the present investigation, patients suffering from alcoholism (Alc; n = 30), patients with depression but without alcoholism (Dep; n = 28) and healthy controls (HC; n = 28) were compared on a neuropsychological test battery. MEASUREMENTS: The test battery included measurements of mood, memory and executive functions. The possible cumulative effect of alcohol and depression was analysed by comparison of depressed alcoholic patients (Dalc) and non-depressed alcoholic patients (NDAlc). FINDINGS: Group comparisons revealed impairments of alcoholic patients with respect to response inhibition, reasoning and free recall, irrespective of depression. Priming, short-term memory as well as verbal fluency abilities were unaffected. Depressive patients showed verbal fluency as well as free recall deficits. However, there was no difference in performance between depressed and non-depressed alcoholics. CONCLUSIONS: The specific pattern of neuropsychological deficits of the alcoholic patients supports the frontal lobe hypothesis. The results of the present investigation suggest that these deficits are not generally exacerbated by comorbid depressive symptoms. Further studies, however, are desirable to investigate the relation between executive deficits and depression in alcoholics with evidence of major depression.

Adult↗
PubMed2004

Early neural activity in Necker-cube reversal: evidence for low-level processing of a gestalt phenomenon.

Normally we experience the visual world as stable. Ambiguous figures provide a fascinating exception: On prolonged inspection, the "Necker cube" undergoes a sudden, unavoidable reversal of its perceived front-back orientation. What happens in the brain when spontaneously switching between these equally likely interpretations? Does neural processing differ between an endogenously perceived reversal of a physically unchanged ambiguous stimulus and an exogenously caused reversal of an unambiguous stimulus? A refined EEG paradigm to measure such endogenous events uncovered an early electrophysiological correlate of this spontaneous reversal, a negativity beginning at 160 ms. Comparing across nine electrode locations suggests that this component originates in early visual areas. An EEG component of similar shape and scalp distribution, but 50 ms earlier, was evoked by an external reversal of unambiguous figures. Perceptual disambiguation seems to be accomplished by the same structures that represent objects per se, and to occur early in the visual stream. This suggests that low-level mechanisms play a crucial role in resolving perceptual ambiguity.

Adult↗
PubMed1978

Op art and visual perception.

An attempt is made to list the visual phenomena exploited in op art. These include moire frinlude moiré fringes, afterimages, Hermann grid effects, Gestalt grouping principles, blurring and movement due to astigmatic fluctuations in accommodation, scintillation and streaming possibly due to eye movements, and visual persistence. The historical origins of these phenomena are also noted.

Afterimage↗
PubMed1978

Illusory contours can arise in dot figures.

Frisby and Clatworthy have suggested that subjective contours depend on special contrast effects acting at the tips of lines and at right angles to the lines. Their suggestion depends in part on the absence of such contours in dot figures. However, if the dots are grouped regularly and make a 'good figure', strong subjective contours appear, including a pattern comparable to Kaniza's triangle. The kind of contrast explanation required for these figures would be one in which individual dots create small contrast effects which are only manifest in perception when the effects are grouped together, by Gestalt form indicators, overlap cues, or the like.

Form Perception↗
PubMed1978

The Penrose triangle and a family of related figures.

Starting from a study of the Penrose triangle, the theory is advanced that our perception of the relative spatial positions of parts of a figure is mediated by a set of significant directions (or axes). Illustration and exploration of the theory in this paper revolves around examples drawn mostly from a family of figures related to the Penrose triangle. This family is defined partly in terms of the common nature of its members' anomalies, and partly by the feature that they are seen as configurations of 'beams'. This feature and the conditions for it are also examined by the use of examples.

Depth Perception↗
PubMed1979

The nonequivalence of abrupt and diffuse illusory contours.

A distinction is drawn between diffuse regions of apparent brightness and illusory, but abrupt, brightness gradients. Differences between the two phenomena are sufficient to disqualify conclusions about one based on observations about the other. It is suggested that diffuse contours may be attributable to peripheral mechanisms while sharp contours may be central or cognitive in origin.

Adult↗
PubMed1980

Perception at the blind spot and tilt aftereffect.

Black and white stripes were used to induce a tilt aftereffect near the blind spot. Stripe fragments on either side of the blind spot were seen as being completed across the blind spot, but the magnitude of the tilt aftereffect they induced suggested that the perceptually "filled-in" portions of the stripes did not contribute to the aftereffect. So perceptually filled-in lines seem not to be fully potent percepts.

Adult↗
PubMed1980

Quantitative studies of some dynamic visual effects.

The viewing of rotating or rapidly approaching one-dimensional periodic structures results in the perception of a high-contrast band on a uniform structureless surround. For rotating gratings, the width of the generated band is inversely proportional to the angular speed of rotation and the orientation of the band lags behind the direction perpendicular to the grating lines for both clockwise and anticlockwise rotation of the pattern. The amount of lag is proportional to the angular speed of rotation. The width of the band perceived during the viewing of an approaching or receding grating is inversely proportional to its speed, and the orientation of the generated band is along the direction of the lines in the grating. A model is proposed which explains and predicts the effects observed during the viewing of one-dimensional periodic structures in terms of temporal luminance integration in the visual system. The extent to which temporal luminance integration is responsible for the perception of frame or element movement in multielement stimulus frames is also examined. The results obtained with monocularly or dichoptically presented multielement stimulus frames, as well as other relevant psychophysical and physiological data, suggest that the temporal integration responsible for the observed effects is associated with mechanisms of early-stage visual processing which must be located prior to the lateral geniculate nucleus level.

Brain Mapping↗
PubMed1983

How many trees does it take to make a forest?

In order to study the relative perceptual availability of global and local features in very sparse patterns, subjects were asked to make 'same'/'different' judgments on pairs of geometrical figures and the times needed to detect global and local differences were compared. With triangular patterns a global precedence was found which could be attributed to size differences. With rectangular patterns global precedence was larger, not accounted for by size differences, and indifferent both to the number of elements and to their spacing. Thus it was demonstrated that global precedence may hold for patterns with as few as four elements. Patterns with smooth edges could be compared much more quickly than patterns with serrated eges. It is proposed that configurational properties of some of the patterns interfered with the encoding of their global structures or with comparing them. It is argued that the results support a principle of global addressability which postulates that visual schemata are mainly addressed through their global constituents.

Discrimination Learning↗
PubMed1983

The multiple determination of illusory contours: 2. An empirical investigation.

Judgments of contour strength or saliency for twenty-four illusory-contour configurations were subjected to a confirmatory factor analysis. A four-factor model that posited the involvement of simultaneous contrast, linear effects (assimilation and dissimilation), depth/completion cues, and feature analyzers accounted for a substantial proportion of the variance in judgments of illusory-contour strength. The hierarchical addition of a fifth factor, diffuse illusory contours, significantly improved the overall fit of the model, but added little to the proportion of explained variance. The taxonomic approach adopted provides support for a multiprocess model of illusory-contour perception.

Adolescent↗
PubMed1983

Evidence relating subjective contours and interpretations involving interposition.

Subjective contours, according to one theory, outline surfaces that are apparently interposed between the viewer and background (because of the disruption of background figures, sudden termination of lines, and other interposition 'cues') but are not explicitly outlined by intensity discontinuities. This theory predicts that if the cues are not interpreted as evidence of interposition, no intervening surface need be postulated, hence no subjective contours would be seen. This prediction, however, is difficult to test because observers normally interpret the cues as interposition evidence and normally see the subjective contours. Tests are reported on a patient with visual agnosia who is unable to make the usual interposition interpretations and unable to see subjective contours, but has normal ability to interpret standard visual illusions, stereograms, and in particular, stereogram versions of the standard subjective contour figures, which elicit to him strong subjective edges in depth (corresponding to the subjective contours viewed in the monocular versions of the figures.

Aged↗