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Results for “FIGURAL AFTEREFFECT”

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At least 955 records · Page 53Linked to original sources
PubMed1983

Short-term reorganization of the cortical network? Some questions from visual psychophysics.

Research into visual system function requires the use of test stimuli as (would-be) neutral probes. Although the risk of transient 'fatigue' is well recognized, e.g. in relation to dark adaptation, we tend otherwise to assume that the system will respond reversibly to stimuli within normal physiological limits. It is on this assumption that gratings of near-parallel lines, for example, are commonly used to determine both physiological and psychophysical response characteristics. This paper reviews evidence suggesting that certain classes of visual stimuli, including gratings in particular, can induce a short-term cooperative reorganization of the visual network that leaves it far from normal in its responsiveness to other inputs. It is suggested that the resulting abnormalities may help to shape our ideas as to the cooperative ensemble properties of cortical neuronal network.

Animals↗
PubMed1984

[Duration of spiral after-effects in psychosomatic patients (a psychophysiologic study and analysis of data using multivariate procedures)].

In a psychophysiological study the spiral after-effect, as measured by means of the Archimedes spiral, was investigated in 182 patients with psychosomatic disorders including duodenal ulcers, ulcerative colitis, anorexia nervosa, asthma and heart neurosis and compared with the results obtained in a control group of healthy volunteers (n = 30). Using multivariate data analysis it was possible to divide the total group of psychosomatic patients into various different subgroups which parallelled the subdivision from the clinical point of view. Moreover, the objectivation of the influence of psychotherapy lasting for 6 weeks on the duration of the after-effect was shown by this technique. These results suggest that the determination of the duration of the spiral after-effect may be of value in clinical psychodiagnostics.

Adolescent↗
PubMed1983

Information processed from brief visual displays by learning-disabled boys.

The spans of apprehension of learning-disabled and normal boys were compared by means of a forced-choice letter-recognition task involving tachistoscopic exposures of letter displays. This task provides an estimate of the span that is relatively insensitive to memory or motivational influences. In Experiment 1, the spans of learning-disabled and normal boys were compared under 4 information conditions: with no noise letters present or with 2, 4, or 8 noise letters present. Experiments 2-4 examined 3 possible interpretations of the deficit in the span of apprehension observed for learning-disabled boys in Experiment 1. In Experiment 2, the possibility that the noise letters were more distracting for learning-disabled boys was examined by varying the amount of physical similarity and redundancy between the signal and noise letters. In Experiment 3, the possibility that the visual afterimage of the letter displays faded more rapidly for the learning-disabled boys was examined. In Experiment 4, the possibility that the learning-disabled boys were slower to pick up information from the decaying afterimages was examined. The results of these three experiments indicated that the decreased spans of apprehension observed for the learning-disabled boys in Experiment 1 resulted either from greater distractiveness or from the slower pickup of information, or both. The implications for visual training are discussed.

Attention↗
PubMed1984

[Clinical psychodiagnosis using psychophysiologic procedures].

The present paper presents several new psychophysiological test methods and measures, which have been developed by the authors for utilization in the field of psychopathology and psychopharmacology. The main advantage of these new techniques seems to lie in the fact, that control and evaluation procedures are microprocessor-assisted which ensures objectivity, reliability and validity. The multidimensionality, e.g. the possibility to concomitantly evaluate several variables at the same time, and the economics, e.g. the short time effort involved in completing the tests, are further advantages. By means of the newly developed techniques several sensitive measures may be obtained which are of great value in the diagnostic process as well as in the assessment of drug effects in clinical psychopharmacology.

Arousal↗
PubMed1983

[A study on simultaneous and successive Delboeuf illusions from the standpoint of the theory of set].

An attempt was made to examine whether or not the simultaneous Delboeuf illusion and the successive one were based on the same perceptual process. By the method of the fixed set, the subject's inner process (set) during the occurrence of the illusions was investigated in Experiment I. The results indicated that his set toward the Delboeuf illusion figure was not changed when only the inducing circle was presented first, but that his set was changed at the moment the inducing circle disappeared and the two circles of identical size were presented. Experiment II examined his perception when there was a time delay between the presentations of the inducing circle of the Delboeuf illusion figure and the other two circles. In that situation, the simultaneous Delboeuf illusion and the successive one should occur successively. The results of Experiment III suggested that the transitional change from the simultaneous Delboeuf illusion to the successive one, which had been observed in the previous study, was due to a change in the judgement of the subject who experienced these two different phenomena successively.

Adult↗
PubMed1983

Cortical processing of visual and tactile stimuli studied by non-invasive rCBF measurements.

Blood flow determinations were made in 32 cortical regions of normal subjects during processing of visual and tactile stimuli. One experiment involved eight subjects who were studied during three conditions of visual stimulation achieved by a Spiral-After-Effect (SAE) apparatus: 1. looking at a stationary spiral, 2. a rotating spiral, and 3. performing the SAE test. Average cortical flow increases during these conditions compared to resting were 5%, 7% and 12% respectively. Local activation was seen in occipital, parietal, temporal, and frontal regions. The magnitude and spread of local flow increases were related to task complexity. In another experiment ten subjects were studied during rest and tactile stimulation of the right hand, left hand, and both. The subjects were instructed either to ignore the stimulation (sensation) or to pay attention to it. Sensation was accompanied by parietal and prefrontal flow increases contralateral to side of stimulation. Attention to the right hand mainly enhanced right hemisphere flow, in the same areas as during sensation. Attention to the left hand was associated with large, diffuse flow increases in both hemispheres. The results support recent proposals of right hemisphere dominance for functions related to attention.

Adult↗
PubMed1982

Visual processing deficits in acute and chronic schizophrenics.

Psychophysical techniques have been used to assess the duration that brief visual stimuli remain in visual memory. At the earliest "iconic" stage the duration depends on several parameters, one of which is spatial frequency. In the present experiment, a two-pulse temporal resolution task was used to evaluate the duration of iconic persistence in schizophrenics as a function of spatial frequency. Normal controls, acute, and chronic schizophrenics viewed achromatic gratings of different spatial frequencies. Their objective was to discriminate between a single or double flash of these gratings. Signal detection analysis was used to control for psychological factors. Repeated measures analyses of variance revealed that schizophrenics (i) do not conform to the typical relationship between iconic persistence and spatial frequency of the grating and (ii) have longer iconic persistence than normals on all spatial frequencies. The results are discussed in terms of the different sensitivities of transient and sustained neurophysiological mechanisms involved in spatiotemporal frequency visual analysis.

Adolescent↗