Approach to Common Visual Complaints Presenting to the Outpatient Neurologist

Visual complaints are commonly encountered by the practicing neurologist. We review assessment of vision loss, diplopia, and positive visual phenomena, all of which require a thoughtful evaluation to localize disease and refine management. While many causative entities are unlikely to cause poor visual outcomes, including dry eyes, migraine, and congenital strabismus, others may threaten vision, life, or both, such as posterior communicating artery aneurysms, pituitary apoplexy, or temporal arteritis. A systematic approach to vision loss and diplopia is reviewed along with focused differential diagnoses.

On the Spatiotemporal Nature of Vision, as Revealed by Covered Bridges and Puddles: A Dispatch from Vermont

Retinal painting, anorthoscopic perception and amodal completion are terms to describe visual phenomena that highlight the spatiotemporal integrative mechanisms that underlie primate vision. Although commonly studied using simplified lab-friendly stimuli presented on a computer screen, this is a report of observations made in a novel real-world context that highlight the rich contributions the mechanisms underlying these phenomena make to naturalistic vision.

Occipito-temporal infarction manifesting as isolated visual perceptual abnormalities: A rare case of posterior cerebral artery stroke

Ischemic stroke in the Posterior Cerebral Artery (PCA) territory is an uncommon entity. Majority present with visual field defects while isolated visual perceptual abnormalities are an exceptional manifestation. About 60 year old hypertensive patient presented with vague symptoms of blurring of vision and palinopsia. Defective color vision was recorded in superior quadrants. Perimetry revealed bilateral congruous left superior quadrantanopia. Magnetic Resonance Imaging (MRI) disclosed right PCA infarct involving occipito-temporal region. This case highlights a rare presentation of PCA stroke with palinopsia and cerebral dyschromatopsia. Perimetric examination coupled with urgent neuroimaging helps the clinician in prompt diagnosis of neurological event causing unexplained visual phenomena.

Cortical Circuits for Top-down Control of Perceptual Grouping

A fundamental characteristic of human visual perception is the ability to group together disparate elements in a scene and treat them as a single unit. The mechanisms by which humans create such groupings remain unknown, but grouping seems to play an important role in a wide variety of visual phenomena, and a good understanding of these mechanisms might provide guidance for how to improve machine vision algorithms. Here, we build on a proposal that some groupings are the result of connections in cortical area V2 that join disparate elements, thereby allowing them to be selected and segmented together. In previous instantiations of this proposal, connection formation was based on the anatomy (e.g., extent) of receptive fields, which made connection formation obligatory when the stimulus conditions stimulate the corresponding receptive fields. We now propose dynamic circuits that provide greater flexibility in the formation of connections and that allow for top-down control of perceptual grouping. With computer simulations we explain how the circuits work and show how they can account for a wide variety of Gestalt principles of perceptual grouping and two texture segmentation tasks. We propose that human observers use such top-down control to implement task-dependent connection strategies that encourage particular groupings of stimulus elements in order to promote performance on various kinds of visual tasks.

Visual hallucinations in psychiatry – what aren’t we seeing?

Objective: To increase awareness of practising clinicians and researchers to the phenomenological distinctions between visual hallucinations and trauma-based, dissociative, visual re-experiencing phenomena seen in psychiatric disease. Conclusions: The experience of visual hallucinations is not exclusive to psychotic disorders in psychiatry. Different forms of experiences that resemble visual hallucinations may occur in patients with a trauma background and may potentially affect diagnosis. Given the paucity of literature around the subject, it is imperative that further research aims to characterise the distinction between visual hallucinations in psychosis and visual phenomena associated with trauma.

Chromatic Induction in Migraine

The human visual system is not a colorimeter. The perceived colour of a region does not only depend on its colour spectrum, but also on the colour spectra and geometric arrangement of neighbouring regions, a phenomenon called chromatic induction. Chromatic induction is thought to be driven by lateral interactions: the activity of a central neuron is modified by stimuli outside its classical receptive field through excitatory–inhibitory mechanisms. As there is growing evidence of an excitation/inhibition imbalance in migraine, we compared chromatic induction in migraine and control groups. As hypothesised, we found a difference in the strength of induction between the two groups, with stronger induction effects in migraine. On the other hand, given the increased prevalence of visual phenomena in migraine with aura, we also hypothesised that the difference between migraine and control would be more important in migraine with aura than in migraine without aura. Our experiments did not support this hypothesis. Taken together, our results suggest a link between excitation/inhibition imbalance and increased induction effects.

Migraine-Like Positive Visual Phenomena Related to Focal Cortical Lesions with Undetectable Visual Field Defects

Migraines are commonly associated with a visual aura that has a characteristic clinical presentation. Cortical lesions within or in close proximity to the retrochiasmal visual pathways may also present in a manner that mimics migrainous visual phenomena and, in some cases, may be too small to manifest with a visual field defect on formal testing. We present 4 patients (3 females and 1 male) with an average age of 48.5 (range 28–67) years who had migraine-like visual disturbances related to a right temporal meningioma, occipital cavernoma, occipital lobe infarction, and demyelination in the optic radiations, which was the presenting sign of multiple sclerosis. No patient underwent neurosurgical intervention, and 1 patient (occipital lobe infarct) had complete resolution of the symptom after initial presentation. All patients had normal visual fields at follow-up and no thinning evident on optical coherence tomography. Our cases emphasize the importance of a history in assessing patients with transient positive visual phenomena and identify pathology that may present without visual field defects. Clinical features that should raise a doubt about a diagnosis of migraine visual aura include the absence of headache, brief visual disturbance lasting <5 min or those lasting >60 min, and age >40, especially with no past medical history of migraine.

Precedent Names in Russian Political Advertising: Representation of Value-Based Standards and Cultural Symbols

The article considers the specificity of precedent proper names as universal value-based standards and cultural symbols in the texts of Russian political advertisement. The axiological aspect is at the core of the pragmatic impact made by political advertising on the target audience. The research material involves political advertising texts issued during presidential and parliamentary campaigns in Russia in 1993–2018. The author distinguishes between the notions of ‘standard’ and ‘symbol’ as ways of conveying value-based meanings. In the first case, it is the connotative use of proper names and the “rating scale” of evaluation that matter the most. In the second case, both denotative and connotative ways of using precedent names are possible while the rating features are optional. Moreover, unlike names-standards, symbolic names express a particular idea implicitly, not explicitly. Precedent names with value meanings can be rendered both verbally and by means of precedent visual phenomena having an associative link with onomastic units. A significant role in forming value-based connotations is played by the context in which proper names are used. The study has allowed to reveal the following axiological categories represented by precedent names and non-verbal signs: standards of hero, heroic deed, creator, scientist, positive traits of character and beauty; symbols of heroism, patriotism, Russian culture and art. It is demonstrated that proper names connected with the latter three values are most frequent in Russian political advertising texts. A special role is played by names associated with the Great Patriotic War and space exploration as well as names conveying orthodox values.

The Principles of Visual Perception Within The Context of Visual Illusions

In the transformation of the low-level, ambiguous retinal signal into a vivid and meaningful phenomenological experience, certain aspects are as essential as the input coming from the external environment. The semantic knowledge stored in memory, figure-background segmentation, grouping principles, and current mood and expectations of the person are equally important. Visual illusions, which might be described as the discrepancy between the objective properties of the external world and their subjective representations, is a common feature of the visual perception that provides meaningful insights with regards to the structure and function of the complex information processor in the brain. In this context, visual illusions are the end results of the optimization strategies that allow the effective use of limited neuronal and metabolic resources, and thus reflect the natural working principles while coping with these limitations, rather than restrictions inflicted upon the system. In this review, we present a compilation of illusions and summarize the key principles of visual perception on the basis of these visual phenomena. In the final section, we also discuss a number of recent topics within the context of Bayesian inference and psychopathology, illusions and alpha brain oscillations and time perception to describe the current directions in the field. Keywords Visual perception, visual illusions, visual system