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PubMedDate not supplied

Complex visual hallucinations in the visually impaired: the Charles Bonnet Syndrome.

Visually impaired patients may experience complex visual hallucinations, a condition known as the Charles Bonnet Syndrome. Patients usually possess insight into the unreality of their visual experiences, which are commonly pleasant but may sometimes cause distress. The hallucinations consist of well-defined, organized, and clear images over which the subject has little control. It is believed that they represent release phenomena due to de-afferentation of the visual association areas of the cerebral cortex, leading to a form of phantom vision. Cognitive defects, social isolation, and sensory deprivation have also been implicated in the etiology of this condition. This condition, which is most common in the elderly, frequently goes unrecognized in clinical practice, due to both lack of awareness among doctors and patients' reluctance to admit to hallucinatory experiences, for fear of being labeled mentally unstable. Furthermore, patients who comprehend the unreality of their hallucinations may be distressed by the real fear of imminent insanity. Sensitive and sympathetic history taking is essential to ascertain the existence of hallucinations. Reassurance and explanation that the visions are benign and do not signify mental illness have a powerful therapeutic effect. Hallucinatory activity may terminate spontaneously, on improving visual function or on addressing social isolation. There is no universally effective drug treatment but anticonvulsants may play a limited role in aborting the hallucinations. Physician awareness and empathy are the cornerstones of management.

Anticonvulsants↗
PubMed2001

Perceived length in the central visual field: evidence for visual field asymmetries.

Visual performance for judging the length of a simultaneously presented pair of radial lines, reciprocally opposed by 180 degrees at a central fixation point, was assessed for 24 radial positions of test lines, for three viewing conditions (binocular, left and right monocular) and five different standard line sizes (1.43-7.13 degrees ). Generally, the results showed underestimation of the test line. Furthermore, clear visual field asymmetries were observed between the upper versus lower visual fields and the left versus right visual fields with greater underestimation for test lines presented in the lower and right visual fields. Also, asymmetries tended to be strongest along the 30 and 150 degrees radial orientations. Fourier analysis indicated that these asymmetries are mainly described by summing up the f0, f1, f2 and f5 components.

Adolescent↗
PubMed1978

Does visual deprivation in adult animals affect macromolecular metabolism in visual neurons?

Two-wave-length visible cytospectrophotometry of gallocyanin-stained sections has shown that 30-day-long visual deprivation in adult rats results in an augmentation of RNA content per cell in the neurons of all cell layers in visual cortex. Light stimulation which in normally reared rats brought about an accumulation of RNA in visual cortex neurons gave rise in light-deprived animals to a disappearance of the deprivation-induced increase of neuronal RNA content. In retina ganglion neurons, RNA content per cell was not changed after the visual deprivation as well as after the illumination of the deprived rats although in normal animals this stimulation evoked an increase of RNA content in the retina neurons. The conclusion is made about marked alterations in macromolecular metabolism induced by a long-term hypoactivity in central and peripheral visual neurons of adult animals.

Animals↗
PubMed1982

Visual prognosis for corneal transplantation based on preoperative visual evoked potential and electroretinogram.

Thirty-one corneal transplant cases underwent a visual-evoked potential and electroretinogram examination prior to keratoplasty. There were 12 cases that had a good visual prognosis and 19 cases with a poor visual prognosis based on the preoperative diagnosis and clinical examination. The addition of electrophysiologic testing in the good prognosis cases did not provide additional information, but produced one false negative, whereas tests in poor prognosis cases were helpful in predicting the visual outcome after transplant. These tests were predictive of visual outcome in 71% of all cases and in 58% of the poor prognosis group.

Adolescent↗
PubMed1998

Visual function impairments in relation to gender, age, and visual acuity in patients who undergo cataract surgery.

PURPOSE: This study aimed to determine the relationship between visual function impairment in 776 patients who had extracapsular cataract extraction with posterior chamber intraocular lens implantation and gender, age, preoperative visual acuity (VA) of both the operative and the contralateral eye, and presence of other ocular disease in the operative eye. DESIGN: Retrospective cross-sectional study. PARTICIPANTS: 1139 patients whose medical records were abstracted and who had cataract surgery performed at 1 of 10 participating academic medical centers in 1990. MAIN OUTCOME MEASURE: In the 776 patients who had explicit statements about impairment of visual function documented in their medical records, univariate and multivariable logistic analyses were used to assess the above relationship. RESULTS: The most severe visual functional deficit that justified the cataract operation varied in relation to gender, age, and VA. On bivariate analysis, men were more likely to have impairment with employment, driving, and glare, whereas women were more likely to have impairment with activities of daily living and recreational activities. Significant findings between visual impairment and the independent variables from the logistic regression models included: (1) employment limitation and male gender (odds ratio [OR], 1.92; 95% confidence interval [CI], 1.08-3.40); (2) employment limitation and younger age (OR, 0.12; 95% CI, 0.050-0.28 for ages 70-79); (3) recreational impairment and older age (OR, 2.77; 95% CI, 1.64-4.70 for ages 80+); (4) impairment in performing activities of daily living and female gender (OR, 0.72; 95% CI, 0.53-0.98 for male gender); (5) impairment in performing activities of daily living and worse VA in the operative eye (OR, 5.13; 95% CI, 2.93-9.00 for VA < 20/100); (6) glare-associated impairment and younger age (OR, 0.40; 95% CI, 0.24-0.69 for age 80+); and (7) glare-associated impairment and better VA (OR, 0.16; 95% CI, 0.067-0.38 for VA < 20/100). CONCLUSION: When deciding whether to perform cataract surgery, functional impairment must be considered in relation to the age and the gender of the patient, for the type of functional impairment varies in association with age and gender.

Activities of Daily Living↗
PubMed2003

Goal-related activity in V4 during free viewing visual search. Evidence for a ventral stream visual salience map.

Natural exploration of complex visual scenes depends on saccadic eye movements toward important locations. Saccade targeting is thought to be mediated by a retinotopic map that represents the locations of salient features. In this report, we demonstrate that extrastriate ventral area V4 contains a retinotopic salience map that guides exploratory eye movements during a naturalistic free viewing visual search task. In more than half of recorded cells, visually driven activity is enhanced prior to saccades that move the fovea toward the location previously occupied by a neuron's spatial receptive field. This correlation suggests that bottom-up processing in V4 influences the oculomotor planning process. Half of the neurons also exhibit top-down modulation of visual responses that depends on search target identity but not visual stimulation. Convergence of bottom-up and top-down processing streams in area V4 results in an adaptive, dynamic map of salience that guides oculomotor planning during natural vision.

Animals↗
PubMed2000

The human visual system is optimised for processing the spatial information in natural visual images.

A fundamental tenet of visual science is that the detailed properties of visual systems are not capricious accidents, but are closely matched by evolution and neonatal experience to the environments and lifestyles in which those visual systems must work. This has been shown most convincingly for fish and insects. For mammalian vision, however, this tenet is based more upon theoretical arguments than upon direct observations. Here, we describe experiments that require human observers to discriminate between pictures of slightly different faces or objects. These are produced by a morphing technique that allows small, quantifiable changes to be made in the stimulus images. The independent variable is designed to give increasing deviation from natural visual scenes, and is a measure of the Fourier composition of the image (its second-order statistics). Performance in these tests was best when the pictures had natural second-order spatial statistics, and degraded when the images were made less natural. Furthermore, performance can be explained with a simple model of contrast coding, based upon the properties of simple cells in the mammalian visual cortex. The findings thus provide direct empirical support for the notion that human spatial vision is optimised to the second-order statistics of the optical environment.

Adult↗
PubMed2006

Feature-based memory-driven attentional capture: visual working memory content affects visual attention.

In 7 experiments, the authors explored whether visual attention (the ability to select relevant visual information) and visual working memory (the ability to retain relevant visual information) share the same content representations. The presence of singleton distractors interfered more strongly with a visual search task when it was accompanied by an additional memory task. Singleton distractors interfered even more when they were identical or related to the object held in memory, but only when it was difficult to verbalize the memory content. Furthermore, this content-specific interaction occurred for features that were relevant to the memory task but not for irrelevant features of the same object or for once-remembered objects that could be forgotten. Finally, memory-related distractors attracted more eye movements but did not result in longer fixations. The results demonstrate memory-driven attentional capture on the basis of content-specific representations.

Adolescent↗
PubMed2003

Semantic interference from visual object recognition on visual imagery.

A new technique for examining the interaction between visual object recognition and visual imagery is reported. The "image-picture interference" paradigm requires participants to generate and make a response to a mental image of a previously memorized object, while ignoring a simultaneously presented picture distractor. Responses in 2 imagery tasks (making left-right higher spatial judgments and making taller-wider judgments) were longer when the simultaneous picture distractor was categorically related to the target distractor relative to unrelated and neutral target-distractor combinations. In contrast, performance was not influenced in this way when the distractor was a related word, when a semantic categorization decision was made to the target, or when distractor and target were visually but not categorically related to one another. The authors discuss these findings in terms of the semantic representations shared by visual object recognition and visual imagery that mediate performance.

Humans↗
PubMed2004

Selective reconfiguration of layer 4 visual cortical circuitry by visual deprivation.

Visual deprivation during a developmental sensitive period markedly alters visual cortical response properties, but the changes in intracortical circuitry that underlie these effects are poorly understood. Here we use a slice preparation of rat primary visual cortex to show that 2 d of prior visual deprivation early in life increases the excitability of layer 4 circuitry. Slice recordings showed that spontaneous activity of layer 4 star pyramidal neurons increased 25-fold after 2 d of visual deprivation between postnatal days (P) 15 and P17. This effect was mediated by increased net excitatory and decreased net inhibitory synaptic drive. Paired recordings showed that excitatory connections between star pyramidal neurons doubled in amplitude, whereas inhibitory connections decreased or increased depending on the interneuron class. These effects reversed when vision was restored. This dynamic adjustment of the excitation-inhibition balance may allow the networks within layer 4 to maintain stable levels of activity in the face of variable sensory input.

Animals↗
PubMed1986

[The papilla and visual field in glaucoma. Relation between planimetrically determined papilla and visual field changes].

From 126 patients with ocular hypertension and/or primary open-angle glaucoma, those (n = 18) who had an untreated intraocular pressure of at least 25 mm Hg or a cup/disk ratio of at least 0.8 were selected for this study. The course of the disease was followed by means of photos of the disk and visual field examinations performed with an automated perimeter. The area of the neuroretinal rim was measured planimetrically. The mean period of observation was 3.7 years, in the course of which the size of neuroretinal rim became decreased in 10 patients, merely fluctuated in 6 patients, and increased in 2 patients. No definite correlation between the course of the visual fields and that of changes in the neuroretinal rim could be demonstrated at either the first or the last examination. Nonetheless, when the visual field changes were juxtaposed to those in the neuroretinal rim, a tendency to a decrease in rim area and an increase in visual field losses was noted. However, numerous exemplary cases showed that one cannot necessarily predict visual field losses from the size of the rim and vice versa. Comparison of estimated rim areas with those determined planimetrically obviously verifies that planimetry provides more accurate results.

Aged↗
PubMed1977

Auditory-visual interactions and the correspondence between perceived auditory space and perceived visual space.

Changes in the physical rate of a clicking or fluttering sound caused changes in the rate at which a simultaneously viewed light appears to flicker, even though the physical flicker rate remains constant. Perceived flicker rate increases in response to a rate of change of flicker frequency, and this auditory 'driving' does not depend on whether the auditory and visual sources have the same location. Visual evoked potentials do not correlate with 'driving'. Thus, the effect of auditory flutter upon perceived visual frequency is not due to the properties of Morrell-type bimodal neurons, nor does it reflect the activities of neurons responsible for maintaining correspondence between perceived auditory space and perceived visual space. The effect is possibly due to modification of a subjective criterion rather than, as previously suggested, to the entrainment or time-locking of physiological signals in the visual pathway.

Auditory Perception↗
PubMed2002

Revision: is visual perception a requisite for visual imagery?

Vision is the most highly developed sense in man and represents the doorway through which most of our knowledge of the external world arises. Visual imagery can be defined as the representation of perceptual information in the absence of visual input. Visual imagery has been shown to complement vision in this acquisition of knowledge--it is used in memory retrieval, problem solving, and the recognition of properties of objects. The processes underlying visual imagery have been assimilated to those of the visual system and are believed to share a neural substrate. However, results from studies in congenitally and cortically blind subjects have opposed this hypothesis. Here I review the currently available evidence.

Blindness↗
PubMed2004

The capacity of visual short-term memory is set both by visual information load and by number of objects.

Previous research has suggested that visual short-term memory has a fixed capacity of about four objects. However, we found that capacity varied substantially across the five stimulus classes we examined, ranging from 1.6 for shaded cubes to 4.4 for colors (estimated using a change detection task). We also estimated the information load per item in each class, using visual search rate. The changes we measured in memory capacity across classes were almost exactly mirrored by changes in the opposite direction in visual search rate (r2=.992 between search rate and the reciprocal of memory capacity). The greater the information load of each item in a stimulus class (as indicated by a slower search rate), the fewer items from that class one can hold in memory. Extrapolating this linear relationship reveals that there is also an upper bound on capacity of approximately four or five objects. Thus, both the visual information load and number of objects impose capacity limits on visual short-term memory.

Adolescent↗
PubMed1991

Promotion of visual development of severely visually impaired babies: evaluation of a developmentally based programme.

A developmentally based programme (PVD) to promote the visual development of babies with severe visual impairment was evaluated in 58 infants aged between one month and 13 months of age. Progress in nine aspects of visual development was significantly greater for babies receiving the programme. This benefit extended to those with severe learning disability, or with minimal or apparently no vision at entry. The PVD favourably influenced visual outcome when introduced at any time during the first 13 months of life, although earlier introduction enabled greater benefit to be derived from the improved vision. Therefore, it is recommended that infants are referred to a developmental centre as soon as severe visual impairment is suspected.

Attention↗
PubMed1993

Visual evoked potentials and visual processing in stimulant drug-exposed infants.

Prenatal exposure to cocaine and amphetamines has been associated with many adverse effects in infants, including neurological abnormalities. Recent evidence shows that the visual system may be useful in infancy to evaluate neurological functioning. Visual evoked potentials (VEPs) and visual recognition memory testing were carried out on eight infants with prenatal drug-exposure and eight controls, matched for ethnicity and socio-economic status. The drug-exposed infants performed significantly worse on the visual recognition test. However, there were no differences between groups on VEP testing and no correlations between tests. The results suggest that the difficulties found in visual recognition memory of drug-exposed infants are not related to neurological maturity, as measured by VEPs.

Amphetamines↗
PubMed2005

Connecting the past with the present: how do humans match an incoming visual display with visual memory?

Extensive cognitive research has been devoted to the sensitivity of the visual system to invariant statistical information. For example, many studies have shown that performance improves when a visual display is presented repeatedly. But what allows humans to connect the current visual input to previous memory? Is the connection made only when the entire incoming display matches with a previous memory, or can retrieval rely on an incomplete match between the input and a learned display? Using a visual search task, we show that (1) once a repeated display is learned, subjects can retrieve it even when an incoming display only matches it in 3-4 locations; (2) however, early during learning, repetition of a small proportion of a display is not enough to establish a strong memory trace for the repeated locations. We suggest that the retrieval of a well-established visual memory can proceed even if an incoming display partly matches the previous memory.

Adolescent↗