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PubMed1984

VEPs in humans reveal high and low spatial contrast mechanisms.

The effect of contrast on visual evoked potential (VEP) amplitude was examined in nine observers. A 6.0 cycles/deg (cpd) grating was modulated in an "on-off" mode at 7.5 Hz. The VEP response contains significant first and second harmonic components: their growth with contrast is parallel, each function consisting of two limbs. The data are consistent with the hypothesis that the pattern VEP obtained with "on-off" presentation may reflect the contributions of "low" and "high" contrast neuronal populations demonstrated in physiological studies of the primate.

Evoked Potentials, Visual↗
PubMed1983

Relationships between speed, accuracy of performance and hemispheric superiorities for visuo-spatial pattern processing in the two sexes.

The aim of this study was to investigate the relationship between visual field differences in tachistoscopic recognition of visuo-spatial patterns and overall proficiency in the two sexes. The results demonstrated a left visual field advantage in males but not in females. A female subgroup showed opposite rather than lacking visual field superiorities without affecting speed and accuracy of performance. These data warn against explaining differences in performance in the two sexes in terms of different hemispheric asymmetries.

Achievement↗
PubMed1984

Complex visual discrimination of tridimensional patterns in rats: progressive learning improves discriminative and recognition capacities.

The purpose of these experiments was to evaluate the rat's discriminative capacities when facing tridimensional patterns. The behavioral approach involved 3 steps: (1) After establishing a brightness discrimination in a Y-maze (S+ = dark, S- = bright), tridimensional objects were introduced into the goal boxes. (2) Brightness differences were gradually attenuated during the course of the fading procedure and correct responding to the tridimensional patterns was obtained. (3) This procedure had a second fading phase where configurational differences between these patterns were progressively reduced. All animals trained with this method of successive approximations learned the discrimination to a 90% criterion; whereas control animals, given the same complex discrimination without any shaping procedure, failed to learn. These experiments show that success or failure in the acquisition of a visual task is specific to the training method used. Our fading procedure produced complex discrimination behavior.

Animals↗
PubMed1975

Visual recogition of dot-pattern bigrams: an extension and replication.

The study examined visual recognition of bigrams, each formed from a pair of "random" dot patterns, as a function of stimulus offset asynchrony and duration. The results replicate and extend those of an earlier study by showing that the effect of backward masking in vision, where the mask is actually a part of the preceding composite target, is limited to about 250 to 300 msec. This time interval is suggested as that required to complete the processing of that composite target. The results may be understood in terms of an interruption hypothesis, with selective attention and/or discontinuity detectors as mechanisms possibly involved in the masking process.

Adolescent↗
PubMed1990

Interference with visual short-term memory.

Working memory (Baddeley and Hitch 1974) incorporates the notion of a visuo-spatial sketch pad; a mechanism thought to be specialized for short-term storage of visuo-spatial material. However, the nature and characteristics of this hypothesized mechanism are as yet unclear. Two experiments are reported which examined selective interference in short-term visual memory. Experiment 1 contrasted recognition memory span for visual matrix patterns with that for visually presented letter sequences. These two span tasks were combined with concurrent arithmetic or a concurrent task which involved manipulation of visuo-spatial material. Results suggested that although there was a small, significant disruption by concurrent arithmetic of span for the matrix patterns, there was a substantially larger disruption of the letter span task. The converse was true for the secondary visuo-spatial task. Experiment 2 combined the span tasks with two established tasks developed by Brooks (1967). Span for matrix patterns was disrupted by a visuo-spatial task but not by a secondary verbal task. The converse was true for letter span. These results suggest that the impairment in short-term visual memory resulting from secondary arithmetic reflects a small general processing load, but that the selective interference due to mode of processing is by far the stronger effect. Results are interpreted as being entirely consistent with the notion of a specialized visuo-spatial mechanism in working memory.

Adult↗
PubMed1982

Hemispheric functionality patterns between dextrals and sinistrals in tactile-visual tasks at lower or higher level of mental processes.

Two different patterns of unilateral tactile-visual recognition tasks with random shapes were administered to 64 subjects, 32 right-handed (16 males, 16 females) and 32 left-handed (16 males, 16 females). The main effects were found in the over-all performance: dextral subjects performed better than sinistral subjects; males performed better than females. On the task at a lower level of mental process dextral subjects performed better over-all than the sinistral subjects; however, neither group showed superiority of one hand over the other. On the task at a higher level of mental process performance of sinistral subjects improved to a level equivalent to that of the dextral subjects. Dextral subjects tended to perform better with their left hands, whereas the sinistral subjects scored equally with both hands. The findings are discussed in terms of quantitative and qualitative differences in patterns of hemispheric functionality between dextral and sinistral subjects, and the more specific cerebral activation for tasks at a higher level of mental process is hypothesized.

Adolescent↗
PubMed1978

Visual short-term memory, age, and imaging ability.

Visual short-term memory of young and older adults was studied in relation to imaging ability. Both recall and recognition memory tasks were used and additional variables included stimulus complexity and response delay (recognition tasks) and stimulus complexity and visual masking (recall tasks). Young and older participants were matched on visual discrimination, verbal intelligence, and imaging ability. Stimuli consisted of abstract visual patterns. Age-related decrements in recognition and recall were observed but performance was related to imaging ability only with recall tasks and only for older adults. The results were discussed with reference to mediational strategies and locus of occurrence of age-related decrements in short-term memory.

Adolescent↗
PubMed1991

[Pattern-reversal visual evoked potentials and electroretinography in the early diagnosis of chronic simple glaucoma].

For differential, therapeutic, and prognostic reasons the recognition of early lesions in glaucoma chronicum simplex is very important. Besides sophisticated ophthalmological investigations optic nerve and retinal functions can be tested by flash and pattern-reversal evoked visual potentials and electroretinograms. 38 glaucomatous eyes were investigated by VEP and ERG applying single and flicker flashes as well as transient pattern-reversal stimuli of different check sizes. The results related to the degree of visual field disturbances show the damage of retinal and neuronal elements in a descending order affecting first of all the macular cones, then the rod system, and later on the elements of the second retinal neuron. The ganglion cells seems to be affected after all.

Chronic Disease↗
PubMed1988

Tracking multiple independent targets: evidence for a parallel tracking mechanism.

There is considerable evidence that visual attention is concentrated at a single locus in the visual field, and that this locus can be moved independent of eye movements. Two studies are reported which suggest that, while certain aspects of attention require that locations be scanned serially, at least one operation may be carried out in parallel across several independent loci in the visual field. That is the operation of indexing features and tracking their identity. The studies show that: (a) subjects are able to track a subset of up to 5 objects in a field of 10 identical randomly-moving objects in order to distinguish a change in a target from a change in a distractor; and (b) when the speed and distance parameters of the display are designed so that, on the basis of some very conservative assumptions about the speed of attention movement and encoding times, the predicted performance of a serial scanning and updating algorithm would not exceed about 40% accuracy, subjects still manage to do the task with 87% accuracy. These findings are discussed in relation to an earlier, and independently motivated model of feature-binding--called the FINST model--which posits a primitive identity maintenance mechanism that indexes and tracks a limited number of visual objects in parallel. These indexes are hypothesized to serve the function of binding visual features prior to subsequent pattern recognition.

Algorithms↗
PubMed1988

[Distribution of spatial attention in position recognition].

Spatial limitation in visual information processing was examined with dot-in-matrix patterns by using a probe recognition procedure. The independent variables were the number (1-16 dots) and the position of target dots. Subjects were four undergraduate students. The data were analyzed and discussed from three points of view; span of attention, spatial limitation of recognition and visual attention. The following became clear: First, the span of position recognition was 4.8. Second, "spatial span of attention" was defined as the range of dot positions at which subjects can perceive target dots with 75% or more accuracy. It extended around the fixation point and shrinked with the increase of the number of target dots. Finally, the distribution of spatial attention was estimated for each target dot condition under the assumption that the hit RT at each probe position reflects the amount of attention allocated there. Distributions estimated were cone-shaped, and the height and extent changed with the number of target dots. It was suggested that spatial limitation (i.e. spatial span of attention) in the processing of spatial positions can be explained by the notion of distribution of spatial attention.

Attention↗
PubMed1988

'Real-motion' cells in visual area V2 of behaving macaque monkeys.

Extracellular recordings were made in area V2 of behaving macaque monkeys. Neurons were classified into three groups: non-oriented cells, oriented cells with antagonistic areas and oriented cells without antagonistic areas in their receptive field. All neurons were tested with standard visual stimulations in order to assess whether they gave different responses to the movement of a stimulus and to the movement of its retinal image alone, when the stimulus was motionless and the animal voluntarily moved its eyes. To do this, neuronal responses obtained when a moving stimulus swept a stationary receptive field (during steady fixation) and when a moving receptive field swept a stationary stimulus (during tracking eye movements), were compared. The receptive field stimulation at retinal level was physically the same in both cases, but only in the first was there actual movement of the visual stimulus. Control trials, where the monkeys performed tracking eye movements without any intentional receptive field stimulation, were also carried out. Out of a total of 263 neurons isolated in the central 10 deg representation of area V2, 101 were fully studied with the visual stimulation described above. Most of these (83/101; 82%) gave about the same response to the two situations. About 14% (14/101) gave a good response to stimulus movements during steady fixation and a very weak one to retinal image displacements of stationary stimuli during visual tracking. We have called neurons of this type "real-motion cells" (cf. Galletti et al. 1984). None of the non-oriented cells was a real-motion one, while about an equal percentage of real-motion cells was found among the oriented cells with and without antagonistic areas. Finally, we found only 4 neurons which showed behaviour opposite to that of real-motion cells, i.e. they showed a better response to displacement of the retinal image of stationary stimuli than to actual movement of stimuli. We suggest that real-motion cells might contribute to correctly evaluating movement in the visual field in spite of eye movements and that they might allow recognition of the movement of an object even if it moves across a non-patterned visual background. Present data on area V2, together with similar results observed in area V1 (Galletti et al. 1984; Battaglini et al. 1986), support the view that these two cortical areas analyse the movement in a parallel fashion along with many other characteristics of the visual stimulus.

Animals↗
PubMed1983

Visual recognition impairment following medial thalamic lesions in monkeys.

Monkeys with surgical lesions which removed the medial portions of the medial and anterior thalamic nuclei were markedly impaired on a test of object recognition. The same animals were able to learn visual pattern discriminations and a spatial delayed response task at a normal rate. These findings indicate that lesions in the medial thalamus produce a selective impairment in visual recognition memory in monkeys and, consequently, may provide an experimental model for human "diencephalic amnesia".

Animals↗
PubMed1988

Patterns of visual-spatial performance and 'spatial ability': dissociation of ethnic and sex differences.

Is there a common basis for the ethnic and sex differences that are characteristically obtained on psychometric tests of spatial ability? Three experiments approached this question by observing subject differences in the recognition and reconstruction of visual-spatial displays. The pattern of performance on these experimental tasks was compared with that on a traditional spatial ability test. In the first experiment, two samples of 40 students, balanced for sex, from Zimbabwe and Scotland respectively, attempted a forced-choice recognition task for meaningful scenes. Both ethnic groups and both sexes showed equivalent performance. The same subjects then undertook a task involving the reproduction of an arrangement of blocks into two-dimensional plan and elevation views. On this task, involving spatial reorientation, the Zimbabweans made over three times as many errors as the Scots. In a third experiment the requirement for spatial reorientation was added to the original recognition task and this was performed by a further 40 subjects. A significant difference between ethnic groups now emerged and this effect covaried with spatial ability. Again, however, no sex difference was observed. The overall pattern of results points to spatial reorientation as a major factor in the cross-ethnic differences. The absence of a sex difference on the experimental tasks contrasts with its appearance in both samples on the spatial ability test and represents a puzzling obstacle to our current understanding. This dissociation of sex and ethnic differences provides evidence against the hypothesis that they stem from the same source.

Adult↗