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PubMed2003

Radical "visual capture" observed in a patient with severe visual agnosia.

We report the case of a 79-year-old female with visual agnosia due to brain infarction in the left posterior cerebral artery. She could recognize objects used in daily life rather well by touch (the number of objects correctly identified was 16 out of 20 presented objects), but she could not recognize them as well by vision (6 out of 20). In this case, it was expected that she would recognize them well when permitted to use touch and vision simultaneously. Our patient, however, performed poorly, producing 5 correct answers out of 20 in the Vision-and-Touch condition. It would be natural to think that visual capture functions when vision and touch provide contradictory information on concrete positions and shapes. However, in the present case, it functioned in spite of the visual deficit in recognizing objects. This should be called radical visual capture. By presenting detailed descriptions of her symptoms and neuropsychological and neuroradiological data, we clarify the characteristics of this type of capture.

Aged↗

PubMed2002

What geometric visual hallucinations tell us about the visual cortex.

Many observers see geometric visual hallucinations after taking hallucinogens such as LSD, cannabis, mescaline or psilocybin; on viewing bright flickering lights; on waking up or falling asleep; in "near-death" experiences; and in many other syndromes. Klüver organized the images into four groups called form constants: (I) tunnels and funnels, (II) spirals, (III) lattices, including honeycombs and triangles, and (IV) cobwebs. In most cases, the images are seen in both eyes and move with them. We interpret this to mean that they are generated in the brain. Here, we summarize a theory of their origin in visual cortex (area V1), based on the assumption that the form of the retino-cortical map and the architecture of V1 determine their geometry. (A much longer and more detailed mathematical version has been published in Philosophical Transactions of the Royal Society B, 356 [2001].) We model V1 as the continuum limit of a lattice of interconnected hypercolumns, each comprising a number of interconnected iso-orientation columns. Based on anatomical evidence, we assume that the lateral connectivity between hypercolumns exhibits symmetries, rendering it invariant under the action of the Euclidean group E(2), composed of reflections and translations in the plane, and a (novel) shift-twist action. Using this symmetry, we show that the various patterns of activity that spontaneously emerge when V1's spatially uniform resting state becomes unstable correspond to the form constants when transformed to the visual field using the retino-cortical map. The results are sensitive to the detailed specification of the lateral connectivity and suggest that the cortical mechanisms that generate geometric visual hallucinations are closely related to those used to process edges, contours, surfaces, and textures.

Hallucinations↗

PubMed1996

An optical intervention for visual hallucinations associated with visual impairment and dementia in elderly patients.

Onset of visual hallucinations in elderly individuals is a widespread problem with an elusive etiology. Many patients with this problem have visual and cognitive deficits. Intervention with optical aids has not been investigated as a means of treating these hallucinations. The authors report 3 cases in which optical aids were evaluated for efficacy in reducing frequency of visual hallucinations in elderly patients with dementia and visual deficits.

Aged↗

PubMed1989

Visual pigments and the acquisition of visual information.

All the information available to the brain for the interpretation of the visual scene comes from the number of photons absorbed by a very limited number of photoreceptor types which are characterized by their spectral sensitivity. In vertebrates there are considerable differences in the spectral absorption of the rods and cones making up the retinal mosaic of different animals and, in some cases, including fish and primates, there are considerable differences between the cone sets of individuals within a species. Broadly speaking, the spectral sensitivity of the photoreceptors is related to the spectral distribution of the ambient light and this is particularly true of the colour-biased light under water. When an animal migrates from one visual environment to another, its cone complement may change to that suited to the new conditions. However, significant differences between the cone sets of animals living within the same environment and colour vision polymorphism within a species suggest that visual tasks critical to survival or breeding success require particular visual pigment sets. A start has been made in trying to understand what tasks are best served by different pigment sets.

Animals↗

PubMed2006

Change blindness and visual memory: visual representations get rich and act poor.

Change blindness is often taken as evidence that visual representations are impoverished, while successful recognition of specific objects is taken as evidence that they are richly detailed. In the current experiments, participants performed cover tasks that required each object in a display to be attended. Change detection trials were unexpectedly introduced and surprise recognition tests were given for nonchanging displays. For both change detection and recognition, participants had to distinguish objects from the same basic-level category, making it likely that specific visual information had to be used for successful performance. Although recognition was above chance, incidental change detection usually remained at floor. These results help reconcile demonstrations of poor change detection with demonstrations of good memory because they suggest that the capability to store visual information in memory is not reflected by the visual system's tendency to utilize these representations for purposes of detecting unexpected changes.

Adult↗

PubMed2003

Structural and functional analyses of the occipital cortex in visual impaired patients with visual loss before 14 years old.

Single photon emission tomography (SPECT) perfusion images of the brain of individuals with complete visual loss before the age of 14 were carried out and compared to those of visually normal subjects, in order to assess hypothetical differences in brain structural and metabolism between the two groups. Study group was comprised by 2 females and 3 males, aged 30 +/- 10 years. Controls were composed by 6 females and 5 males aged 41.5 +/- 3.8 years. All individuals were submitted to physical and neurological examinations, and to MRI and to SPECT. Blind subjects presented larger perfusion measurements bilaterally in their medial temporal lobes (p=0.030, right side; p=0.01, left side), but smaller perfusion measurements in their left frontotemporal area than controls (p=0.026). Intragroup analysis of the study group disclosed asymmetric perfusion, lesser in the left temporal and parietal areas (p=0.026 and p<0.0001, respectively) compared to the right side. In the healthy controls, reduced perfusion was also noted at the left parietal areas when compared to the right side (p=0.035). The study revealed that completely blind patients that became visually impaired before the age of 14 in spite of not having MRI detectable changes in their brain's anatomy do present increases in perfusion of their left and right medial temporal lobes, and a reduction in the perfusion of the left frontotemporal area, as compared to normal controls. While the increases in blood flow may reflect compensatory mechanisms for visual deprivation, the significance of the diminished perfusion in the left frontotemporal area remains elusive.

Adolescent↗

PubMed1985

Drinking-induced changes in fowl adrenocortical activity: effect of visual and non-visual stimuli.

The deprivation of drinking water for 30 h resulted in increased corticosterone concentrations in the plasma of 8- to 10-week-old chickens. When water-deprived birds were allowed to drink ad libitum the corticosterone concentration declined within 45 min, to the level in hydrated controls, and remained suppressed thereafter. Similar reductions in the corticosterone concentrations were also observed in water-deprived chicks which were allowed to drink for only 5 min, 1 min or 5 s. The involvement of visual stimuli in mediating this adrenocortical response was demonstrated by a comparable decline in the corticosterone concentration in water-deprived birds which were presented with water but not allowed access to it. Non-visual stimuli also appeared to be causally involved in the adrenocortical suppression after drinking, since the intraperitoneal injection of tap water (40 ml per bird) also resulted in a lowering of the corticosterone level. However, in the absence of appropriate reinforcement from metabolic stimuli, a rebound in the corticosterone concentration was observed in birds prevented from drinking, in birds unable to satiate their thirst and in birds rehydrated (orally or intraperitoneally) without feeding. These results demonstrate adrenocortical suppression in water-deprived chickens after free access to food and water and the involvement of visual and non-visual stimuli in mediating this response. The maintenance of adrenocortical suppression is dependent upon metabolic stimuli associated with food and water intake.

Adrenal Cortex↗

PubMed1977

Imposed delay of response: effects on aphasics auditory comprehension of visuality and non-visually cued material.

Two groups of aphasics were administered an auditory comprehension task under conditions of 0-, 5-, and 10-sec. imposed delay of response. The auditory-visual group received auditory and visual cues; the auditory group received only auditory cues. Comprehension for the auditory-visual group was significantly better than for the auditory group. Increase in delay time significantly improved comprehension for the auditory-visual group but not for the auditory group.

Adult↗

PubMed1978

Suppression of visual observing by rhesus monkeys produced by conditioned aversive visual stimuli.

Nine rhesus monkeys were tested in a visual observing situation to determine the influence of conditioned aversive visual stimulation. A set of meaningless visual stimuli was selected on the basis of cumulative frequency and cumulative duration of observing during a pretest phase of the experiment. Three subsets of stimuli (low, medium, high) were formed indicating level of observing during pretesting. A portion of the "medium" category of slides then served as conditioned stimuli in a classical conditioning procedure by being paired with electric shock. Following conditioning the entire set of stimuli was again presented in a visual observing situation. The results showed a significant decrease in both frequency and duration of observing of the slides with conditioned aversive qualities, relative to non-shock control slides. These findings support an aversion-produced suppression of observing relatively unconfounded by methodological, procedural, and other differences existing among previous reports on the role of fear or anxiety in this context.

Animals↗

PubMed1986

Influence of auditory or visual warning on visual reaction time with variations of subjects' alertness.

The purpose of the study was to determine the effect of visual and auditory warning on visual reaction time with variations of subjects' alertness. An experimental group of 30 subjects was tested with an auditory or visual warning signal; foreperiods lasted 3, 2, and 4 sec. Reaction time was shorter as alertness improved and with an auditory warning signal. Comparable measures in a control group showed that visual reaction time was shorter when an auditory warning signal was used.

Adult↗

PubMed1998

Partial cross-validation of low correlation for scores on the Test of Visual-Motor Integration and the Beery-Buktenica Developmental Test of Visual-Motor Integration.

The aim of this study was to further investigate the correlation between a well established test, the Beery-Buktenica Developmental Test of Visual-Motor Integration and a new copying test, the Test of Visual-Motor Integration. For scores on the tests of 71 children from a public school in Italy, the correlation is .34, which is consistent with earlier evidence and indicates that the Test of Visual-Motor Integration is not a substitute for the Beery-Buktenica Developmental Test of Visual-Motor Integration.

Child↗

PubMed1985

The relationship between visual seizures and visual evoked potentials.

We have studied a patient (pt) in status epilepticus with visual seizures (szs) arising focally from the right occipital area and have recorded the visual evoked potential (VEP) to three different stimuli under three different conditions (during, between and with no szs). The pt experienced "sparkling" in the contralateral visual field as the sz and the intensity of the "sparkling" was directly related to the frequency of the ictal activity recorded on the EEG. During the szs the VEPs could still be recorded, but the amplitude of the P100 was higher on the contralateral side with pattern reversal (PR) stimuli, and with flashes (FL) the positive peak after the P100 was less evident on the ipsilateral side. Latencies to these latter two positivities were generally shorter than in normals, with much greater standard deviations ipsilaterally with FL and contralaterally with PR, especially during the actual szs. The relationship between VEP generation and visual sz phenomena is discussed.

Adult↗

PubMed1982

Optokinetic visual detection in the rat visual centres. A [14C]-2-deoxy-D-glucose study.

Following forty-five min of binocular optokinetic stimulation (OKS) the autoradiographic maps of [14C]-2-deoxy-D-glucose (2DG) assumption of Long-Evans brain reveal clearly different patterns of optical density within visual centres. The most superficial layers of superior colliculus (SC) and a pretectal area including the nucleus of the optic tract (NOT) appear symmetrically, strongly darker than other visual structures such as lateral geniculate nucleus (LGN) and visual cortex (VC). Whereas the lack of metabolic increase at LGN and VC levels entirely confirms the non-involvement of the geniculo-cortical path in mediating the optomotor response following OKS in Rodents, it is postulated that the symmetrical increase of 2DG uptake even upon unidirectional OKS found even at pretectal level may represent a commissural transfer of visual information between homologous pretectal areas like the nuclei of the optic tract.

Animals↗

PubMed2005

Influence of visually induced expectation on perceived motor effort: a visual-proprioceptive interaction at the Santa Cruz Mystery Spot.

It is known that dense objects seem heavier than larger, less dense objects of the same weight. We have investigated a related illusion, in which visual context biases the apparent weight of a single object. The apparatus is a cabin on a steep hillside near Santa Cruz, CA, tilted 17 degrees from vertical. From its ceiling hangs a weight on a chain. The cabin's tilt makes the weight appear suspended at an angle. Pushing the weight toward the visually based vertical is perceived as difficult, whereas pushing it away from the visual vertical is perceived as easy. Seven subjects pushed the weight in both directions, judging required effort on a double-anchored 1-10 scale. All experienced the effort illusion, with no significant subject effect. When subjects' eyes were closed, the effect was smaller but still present. Apparently proprioceptive and skin inputs, equal for both directions, are ignored or underweighted as visually based expectations influence perceived effort.

Humans↗

PubMed2003

Visual marking: a convergence of goal- and stimulus-driven processes during visual search.

Watson and Humphreys (1997) proposed that visual marking is a goal-directed process that enhances visual search through the inhibition of old objects. In addition to the standard marking case with targets at new locations, included in Experiment 1 was a set of trials with targets always at old locations, as well as a set of trials with targets varying between new and old locations. The participants' performance when detecting the target at old locations was equivalent to their performance in the full-baseline condition when they knew the target would be at old locations, and was worse when the target appeared at old locations on 50% of the trials. Marking was observed when the target appeared at new locations. In Experiment 2, an offset paradigm was used to eliminate the influence of the salient abrupt-onset feature of the new objects. No significant benefits were found for targets at new locations in the absence of onsets at new locations. The results suggest that visual marking may be an attentional selection mechanism that significantly benefits visual search when (1) the observer has an appropriate search goal, (2) the goal necessitates inhibition of old objects, and (3) the new objects include a salient perceptual feature.

Goals↗

PubMed1996

Effects of a visual frame and of low radial accelerations on the visually perceived eye level.

The purpose of this study was to determine how the combined effects of a reference frame and of very low gravito-inertial forces produced by centrifugation affect the visually perceived eye level (VPEL). Twenty subjects were instructed to set a luminous target to the VPEL under various experimental conditions involving two main factors: (1) visual context (frameless, frame centered, frame moved down 50 mm, and frame moved up 50 mm) and (2) gravito-inertial context (motionless, Gi1 = 9.81001 m/sec2 and Gi2 = 9.95 m/sec2). The visual context significantly reduced the lowering of VPEL in darkness as caused by radial acceleration; this confirms the prevailing role of vision versus propriosomesthesis. However, under condition Gi2, there was a significant effect on the VPEL in spite of the presence of the luminous frame; this demonstrates that VPEL processing involves both visual and propriosomesthesic information. Furthermore, the VPEL varied linearly with the vertical shift of the luminous frame for any of the gravito-inertial conditions used in this study, but, under condition Gi2, the VPEL was shifted downward.

Acceleration↗

PubMedDate not supplied

A comparison of visual-perceptual and visual-motor skills between Palestinian and Israeli children.

PURPOSE: This pioneer study examines the visual-motor and visual-perceptual performance of Israeli and Palestinian children, and makes comparisons among these respective populations according to age, place of residence, and parental education. In addition, the study evaluates the validity of standardized assessment tools for use with Palestinian children, with the view of establishing a sound assessment battery for this underserved population. METHODS: Participants included 101 Israeli and 125 Palestinian children from kindergarten, first grade, and second grade who underwent visual-motor and visual-perceptual tests. RESULTS: Significant differences were found between the two cultural groups in all assessments. Results also refer to grade, place of residence, and parents' education variables. CONCLUSIONS: Although culture influences children's performance, children from different societies should be screened and, when necessary, evaluated and treated in order to enable their optimal functioning at school. The validity of the assessment tools used, expressed in the ability to differentiate between Israeli and Palestinian children, should be further studied in order to suggest that these assessments may be considered as part of an evaluation battery for determining the school readiness and ability to advance in grade level among Palestinian children.

Age Factors↗

PubMed2002

[Visual impression of photographic density of the brain in head CT images: verification of optical illusion by visual subjective evaluation of medical images].

The purpose of this study was to clarify the psychological influence of optical illusion on the photographic density of the brain in head CT images. In this study, I attempted to compare the visual impression of photographic density of the brain using visual subjective evaluation according to observers and cases. The results showed that the visual impression of photographic density of the brain at cerebellar CT depended upon the mode of appearance of the optical illusion (assimilation, contrast, picture frame effect, etc.). In addition, that impression varied according to differences in cases (difference of picture pattern) and observers. Further, it was clarified that the optical illusion had been observed according to individual differences among observers. Moreover, cases could be divided into two main classes. Some cases were recognized as a kind of outline figure (the white skull was recognized as an induction color, and the brain as a non-induction color) with assimilation, and consequently the brain seemed whitish. In other cases (the white skull was not recognized as an induction color) in which there was no assimilation, the brain did not seem whitish. This was considered to have occurred because the degree of influence of the skull on the visual impression of the photographic density of the brain had changed according to differences in cases.

Brain↗