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SummaryVisual acuity was tested and the anterior portion of the eye inspected among the Gidra in Lowland Papua New Guinea, who depend on hunting for their animal food. The visual acuity of the youths and adults was as high as that of hunters and gatherers; 88% of the males and 81% of the females had an acuity of 1·2 or better. The elders had far lower acuity, correlated with the advance of cataract. The senescent (...) class='Hi'>visual acuity is discussed in relation to little practice and low productivity of the elders' hunting, and to the Gidra traditional age-grade system. (shrink)

After a discourse about the literature on visual acuity before Hume, I discuss how the "size" of visual objects is defined and determined. I shall then present circumstantial, but commanding, evidence for the influence of James Jurin's Essay upon Distinct and Indistinct Vision on Hume's thought. This work contains well-supported findings incompatible with claims made in T 1.2, "Of the ideas of space and time," and elsewhere. Specifically, the prominent principle of the Treatise, "[w]hat consists of parts (...) is distinguishable into them, and what is distinguishable is separable" (T 1.2.1.3; SBN 27) is shown to be false. A powerful principle, it is a premise to the most important arguments of the Treatise, but is shunned in the Enquiry and later writings because, I believe, Hume had read Jurin. (shrink)

Sensory substitution devices (SSDs) aim to compensate for the loss of a sensory modality, typically vision, by converting information from the lost modality into stimuli in a remaining modality. “The vOICe” is a visual-to-auditory SSD which encodes images taken by a camera worn by the user into “soundscapes” such that experienced users can extract information about their surroundings. Here we investigated how much detail was resolvable during the early induction stages by testing the acuity of blindfolded sighted, naïve (...) vOICe users. Initial performance was well above chance. Participants who took the test twice as a form of minimal training showed a marked improvement on the second test. Acuity was slightly but not significantly impaired when participants wore a camera and judged letter orientations “live”. A positive correlation was found between participants' musical training and their acuity. The relationship between auditory expertise via musical training and the lack of a relationship with visual imagery, suggests that early use of a SSD draws primarily on the mechanisms of the sensory modality being used rather than the one being substituted. If vision is lost, audition represents the sensory channel of highest bandwidth of those remaining. The level of acuity found here, and the fact it was achieved with very little experience in sensory substitution by naïve users is promising. (shrink)

Optic neuropathies are conditions that cause disease to the optic nerve, and can result in loss of visual acuity and/or visual field defects. An improved understanding of how these conditions affect the entire visual system is warranted, to better predict and/or restore the visual loss. In this article, we review visually-driven functional magnetic resonance imaging (fMRI) studies of optic neuropathies, including glaucoma and optic neuritis (ON); we also discuss traumatic optic neuropathy (TON). Optic neuropathy-related vision (...) loss results in fMRI deficit within the visual cortex, and is often strongly correlated with clinical severity measures. Using predominantly flickering checkerboard stimuli, glaucoma studies indicated retinotopic-specific cortical alteration with more prominent deficits in advanced than in early glaucoma. Some glaucoma studies indicate a reorganized visual cortex. ON studies have indicated that the impacted cortical areas are briefly hyperactive. For ON, brain deficits are greater in the acute stages of the disease, followed by (near) normalization of responses of the LGN, visual cortex, and the dorsal visual stream, but not the ventral extrastriate cortex. Visually-driven fMRI is sensitive, at least in ON, in discriminating patients from controls, as well as the affected eye from the fellow eye within patients. The use of a greater variety of stimuli beyond checkerboards (e.g., visual motion and object recognition) in recent ON studies is encouraging, and needs to continue to disentangle the results in terms of change over time. Finally, visually-driven fMRI has not yet been applied in TON, although preliminary efforts suggest it may be feasible. Future fMRI studies of optic neuropathies should consider using more complex visual stimuli, and inter-regional analysis methods including functional connectivity. We suggest that a more systematic longitudinal comparison of optic neuropathies with advanced fMRI would provide improved diagnostic and prognostic information. (shrink)

We reviewed the current state of knowledge regarding visual function and its suitability as part of medical examinations for driving licenses. We focused only on Group 1 drivers. According to previous studies, visual acuity, which is the most common test, is weakly associated with a higher risk of road accidents, with a greater role of visual field. The inclusion of the visual field test in medical examinations is therefore important, but the actual limit value is (...) still unclear and further research in specific situations is needed. Color vision impairment was not found a threat to traffic safety. Contrast sensitivity decreases with age and is affected by abnormal eye conditions. Resulting glare can lead to an increased risk of traffic accidents during night driving in the elderly and others with conditions that impair contrast sensitivity. However, the universal cut-off limits have not been established either. The current European Union (EU) regulations therefore reflect minimum common denominator across the member states which may not entirely translate to optimal driving safety. Due to these open questions, standardized testing in simulators or on polygons that simulate real life conditions would be needed to better determine safe limits of visual function in different conditions. As there is a need to have better standardization across Europe regarding the requirements and rules regarding driving licenses in European countries, we first analyzed existing rules and compared them with each other, also in terms of deviations from the EU directive itself. We reviewed the literature in this field and prepared proposals for a more optimal regulation of the rules in the future. Particular attention is paid to the new method of examining the visual field that was created to respect the European directive. The paper can serve as a basis of information for research teams to design further protocols, as it gathers research findings to date on the importance and impact of various visual functions on driving safety, as well as a starting point for a debate on revising existing rules for obtaining and maintaining licenses, as it compares the current regulations in European countries and differences between them. (shrink)

In amblyopia, abnormal visual experience during development leads to an enduring loss of visual acuity in adulthood. Physiological studies in animal models suggest that intracortical GABAergic inhibition may mediate visual deficits in amblyopia. To better understand the relationship between visual cortical γ-aminobutyric acid (GABA) and perceptual suppression in persons with amblyopia (PWA), we employed magnetic resonance spectroscopy (MRS) to quantify GABA levels in both PWA and normally-sighted persons (NSP). In the same individuals, we obtained psychophysical (...) measures of perceptual suppression for a variety of ocular configurations. In PWA, we found a robust negative correlation between the depth of amblyopia (the difference in visual acuity between the amblyopic and non-amblyopic eyes) and GABA concentration that was specific to visual cortex and was not observed in a sensorimotor cortical control region. Moreover, lower levels of visual cortical GABA were associated with weaker perceptual suppression of the fellow eye by the amblyopic eye and stronger suppression of the amblyopic eye by the fellow eye. Taken together, our findings provide evidence that intracortical GABAergic inhibition is an important component of the pathology of human amblyopia and suggest possible therapeutic interventions to restore vision in the amblyopic eye through enhancement of visual cortical GABAergic signaling in PWA. (shrink)

We experience our own body through both touch and vision. We further see that others’ bodies are similar to our own body, but we have no direct experience of touch on others’ bodies. Therefore, relations between vision and touch are important for the sense of self and for mental representation of one’s own body. For example, seeing the hand improves tactile acuity on the hand, compared to seeing a non-hand object. While several studies have demonstrated this visual enhancement (...) of touch effect, its relation to the ‘bodily self’, or mental representation of one’s own body remains unclear. We examined whether VET is an effect of seeing a hand, or of seeing my hand, using the rubber hand illusion. In this illusion, a prosthetic hand which is brushed synchronously—but not asynchronously—with one’s own hand is felt to actually be one’s hand. Thus, we manipulated whether or not participants felt like they were looking directly at their hand, while holding the actual stimulus they viewed constant. Tactile acuity was measured by having participants judge the orientation of square-wave gratings. Two characteristic effects of VET were observed: cross-modal enhancement from seeing the hand was inversely related to overall tactile acuity, and participants near sensory threshold showed significant improvement following synchronous stroking, compared to asynchronous stroking or no stroking at all. These results demonstrate a clear functional relation between the bodily self and basic tactile perception. (shrink)

It has long been suggested that emotion, especially threatening emotion, facilitates early visual perception to promote adaptive responses to potential threats in the environment. Here, we tested whether and how fearful emotion affects the basic visual ability of visual acuity. An adapted Posner’s spatial cueing task was employed, with fearful and neutral faces as cues and a Vernier discrimination task as the probe. The time course of the emotional attention effect was examined by varying the stimulus (...) onset asynchrony of the cue and probe. Two independent experiments consistently demonstrated that the brief presentation of a fearful face increased visual acuity at its location. The facilitation of perceptual sensitivity was detected at an SOA around 300 ms when the face cues were presented for both 250 ms and 150 ms. This effect cannot be explained by physical differences between the fearful and neutral faces because no improvement was found when the faces were presented inverted. In the last experiment, the face cues were flashed very briefly, and we did not find any improvement induced by the fearful face. Overall, we provide evidence that emotion interacts with attention to affect basic visual functions. (shrink)

Optic neuropathy refers to disease of the optic nerve and can result in loss of visual acuity and/or visual field defects. Combining findings from multiple fMRI modalities can offer valuable information for characterizing and managing optic neuropathies. In this article, we review a subset of resting-state functional magnetic resonance imaging (RS-fMRI) studies of optic neuropathies. We consider glaucoma, acute optic neuritis (ON), discuss traumatic optic neuropathy (TON), and explore consistency between findings from RS and visually driven fMRI (...) studies. Consistent with visually driven studies, glaucoma studies at rest also indicated reduced activation in the visual cortex and dorsal visual stream. RS-fMRI further reported varying levels of functional connectivity in the ventral stream depending on disease severity. ON patients show alterations within the visual cortex in both fMRI techniques. Particularly, higher-than-normal RS activity is observed in the acute phase and decreases as the disease progresses. A similar pattern is observed in the visual cortex of TON-like, open globe injury (OGI), patients. Additionally, visually driven and RS-fMRI studies of ON patients show recovery of brain activity in the visual cortex. RS-fMRI suggests recovery of signals in higher-tier visual areas MT and LOC as well. Finally, RS-fMRI has not yet been applied to TON, although reviewing OGI studies suggests that it is feasible. Future RS-fMRI studies of optic neuropathies could prioritize studying the fine scale RS activity of brain areas that visually driven studies have identified. We suggest that a more systematic longitudinal comparison of optic neuropathies with advanced fMRI would provide improved diagnostic and prognostic information. (shrink)

BackgroundCerebral Visual Impairment is a very common finding in children affected by Cerebral Palsy. In this paper we studied the characteristics of CVI of a large group of children with CP and CVI, describing their neurovisual profiles according to three different age subgroups.MethodsWe enrolled 180 subjects with CP and CVI for the study. We carried out a demographic and clinical data collection, neurological examination, developmental or cognitive assessment, and a video-recorded visual function assessment including an evaluation of ophthalmological (...) characteristics, oculomotor functions, and basic visual functions. In school-aged children, we also performed an evaluation of their cognitive-visual profiles.ResultsThere were signs of CVI in all the three subgroups. Subgroup 1 and subgroup 2 were different for fixation, visual acuity and contrast sensitivity, being more frequently impaired in younger children. Comparing subgroup 2 with subgroup 3, the older children presented more frequently myopia while the younger ones esotropia and alteration in smooth pursuit and saccades. Furthermore, fixation, smooth pursuit, visual acuity, contrast sensitivity and visual filed were more frequently impaired in younger children compared to the older ones. Multiple correspondence analysis confirmed the different neurovisual profiles according to age: younger children with CP showed more signs of CVI compared to the older ones. 34 out of 68 children belonging to subgroup 3 underwent the cognitive visual evaluation; an impairment of cognitive visual skills was detected in 21 subjects.ConclusionYounger children with CP showed more signs of CVI compared to the older ones, likely for the physiological maturation of visual system and mechanisms of neuroplasticity. In this direction, we suggest an early neurovisual evaluation to detect any weak visual functions. (shrink)

PurposeThis study investigated the impact of age and myopia on visual form perception among Chinese school-age children.MethodsThis cross-sectional study included 1,074 students with a mean age of 12.1 ± 4.7 years. The mean spherical equivalence refraction of the participants was −1.45 ± 2.07 D. All participants underwent distance visual acuity, refraction measurement and local and global visual form perception test including orientation, parallelism, collinearity, holes and color discrimination tasks.ResultsThe reaction times of emmetropes were slower than those (...) of myopic and high myopic groups on both local and global discrimination tasks. A reduction in reaction times was found with increasing age on both local and global discrimination tasks. Age was significantly associated with both local and global visual perception performance after adjusting for gender, visual acuity and SER.ConclusionsThis study revealed that both local and global visual perception improve with age among Chinese children and that myopes seem to have better visual perception than emmetropes. (shrink)