94 research outputs found
R_Contrast: Rapid measurement of recognition contrast thresholds.
R_Contrast is a program for the rapid assessment of recognition contrast thresholds on the PC
Visual attention outperforms visual-perceptual parameters required by law as an indicator of on-road driving performance
Purpose: A variety of visual and psychometric tests have been developed for assessing on-road driving performance and fitness to drive. The diagnostic power of a state of the art psychometric test battery (Vienna Test System) combined with a set of standard visual parameters recommended for assessing fitness to drive is investigated using an on-road driving test. The study aimed to determine whether a psychometric test battery could predict older adults' on-road driving performance. The relevance of visual standards required by law is discussed. Methods Vision impairment is more prevalent in later adulthood and many studies on visual and cognitive impact on driving safety and performance therefore focus on adults above 60 years of age. We therefore acquired an extensive set of driving-related visual and psychometric performance parameters in a group of elderly drivers (N = 84, median age 69, SD 6.6 years). Visual assessment included foveal acuity, perimetric field size, and dynamic aspects of peripheral vision (termed "PP") in the computer-based Vienna Test System (VTS;Schuhfried), as well as letter contrast thresholds in foveal and parafoveal vision in a separate setup. A selection of psychometric driving-aptitude tests that demonstrated the battery's capacity to predict aspects of driving performance and safety were further conducted on the VTS. Driving performance was assessed in a standardized on-road driving test. Two independent observers rated driving performance using a fixed scoring system assessing the number of driving errors in pre-defined traffic situations. In addition, globalized driving competence scores were assigned on a 6-point scale. Results: The test battery performed excellent in identification of good drivers but failed in the prediction of bad driving performance. Visual performance indicators required by German law were less indicative of driving ability than psychometric assessment. Selective and divided attention turned out to be much more important for predicting fitness to drive than either visual acuity, size of the visual field, or contrast sensitivity. Conclusion Predicting fitness to drive by means of visual and psychometric tests is an ambitious challenge. On the one hand sensitivity of a multi-disciplinary test-battery is too low to predict reliable driving ability in diagnostic settings which require an unambiguous interpretation of test results for individual drivers. Low sensitivity and low predictive values are incompatible with that objective. On the other hand, the results are valuable for a routine screening of fitness to drive. For that case, the assessment of attentional abilities in particular appears to be promising. Performance measures of divided and selective attention showed themselves to be the most predictive for fitness to drive in a sample pre-screened for clear visual deficits. Visual performance parameters required by law, in contrast, had no meaningful impact on driving performance, indicating a gap between mandatory regulations of state authorities and research results. Our results suggest that visual acuity tests designed for clinical diagnosis and monitoring of eye diseases should not at all be the choice for a screening of fitness to drive
Ewald Hering's (1879) "On Muscle Sounds of the Eye":A translation and commentary
Investigations of eye movements were transformed by Ewald Hering in 1879. He developed a novel method for recording them using the muscular sounds attendant on their rapid movements. Brief "clapping" sounds could be heard with the aid of a device like a stethoscope placed on the eyelid and they occurred when afterimages or "floaters" were seen to move. Hering applied the technique to record eye movements during reading and he called the rapid eye movements Rucke (jerks in English). Hering published a long review of eye movements and spatial vision later in 1879, but without a description of the muscle sounds. Hering's insightful article has been overlooked and a translation of it into English is presented.</p
James Jurin (1684-1750):a pioneer of crowding research?
James Jurin wrote an extended essay on distinct and indistinct vision in 1738. In it, he distinguished between "perfect,'' "distinct,'' and "indistinct vision'' as perceptual categories, and his meticulous descriptions and analyses of perceptual phenomena contained observations that are akin to crowding. Remaining with the concepts of his day, however, he failed to recognize crowding as separate from spatial resolution. We present quotations from Jurin's essay and place them in the context of the contemporary concerns with visual resolution and crowding
Ewald Hering's (1879) "On Muscle Sounds of the Eye":A translation and commentary
Investigations of eye movements were transformed by Ewald Hering in 1879. He developed a novel method for recording them using the muscular sounds attendant on their rapid movements. Brief "clapping" sounds could be heard with the aid of a device like a stethoscope placed on the eyelid and they occurred when afterimages or "floaters" were seen to move. Hering applied the technique to record eye movements during reading and he called the rapid eye movements Rucke (jerks in English). Hering published a long review of eye movements and spatial vision later in 1879, but without a description of the muscle sounds. Hering's insightful article has been overlooked and a translation of it into English is presented.</p
Blind und sehend in einer Person
Es wird der Fall einer Patientin mit Dissoziativer Identitätsstörung vorgestellt, die nach 15-jähriger, als kortikal diagnostizierter Blindheit im Laufe einer psychotherapeutischen Behandlung schrittweise wieder zu sehen begann. Zunächst konnten nur einige wenige Persönlichkeitsanteile wieder sehen, während andere weiterhin blind waren. Dies konn-te durch elektrophysiologische Untersuchungen bestätigt werden, in denen die noch blinden Persönlichkeitsanteile ausbleibende, die sehenden Persönlichkeitsanteile hin-gegen völlig unauffällige, reguläre evozierte Potentiale aufwiesen. Das Umschalten zwi-schen sehenden und blinden Anteilen konnte übergangslos geschehen. Als neuronale Grundlage der psychogenen Blindheit kommt eine „top-down“ Modulation der Aktivität der primären Sehbahn, auf Ebene des Thalamus oder primären visuellen Kortex, in Be-tracht. Mittels VEP-Untersuchungen kann daher eine psychogene Blindheit nicht von organischen Ursachen einer Unterbrechung der Sehbahn abgegrenzt werden. Zusam-menfassend scheint psychogene Blindheit den Zufluß visueller Information auf früher Stufe zu blockieren
Peripheral vision and pattern recognition:a review
We summarize the various strands of research on peripheral vision and relate them to theories of form perception. After a historical overview, we describe quantifications of the cortical magnification hypothesis, including an extension of Schwartz's cortical mapping function. The merits of this concept are considered across a wide range of psychophysical tasks, followed by a discussion of its limitations and the need for non-spatial scaling. We also review the eccentricity dependence of other low-level functions including reaction time, temporal resolution, and spatial summation, as well as perimetric methods. A central topic is then the recognition of characters in peripheral vision, both at low and high levels of contrast, and the impact of surrounding contours known as crowding. We demonstrate how Bouma's law, specifying the critical distance for the onset of crowding, can be stated in terms of the retinocortical mapping. The recognition of more complex stimuli, like textures, faces, and scenes, reveals a substantial impact of mid-level vision and cognitive factors. We further consider eccentricity-dependent limitations of learning, both at the level of perceptual learning and pattern category learning. Generic limitations of extrafoveal vision are observed for the latter in categorization tasks involving multiple stimulus classes. Finally, models of peripheral form vision are discussed. We report that peripheral vision is limited with regard to pattern categorization by a distinctly lower representational complexity and processing speed. Taken together, the limitations of cognitive processing in peripheral vision appear to be as significant as those imposed on low-level functions and by way of crowding
Blur Unblurred - A Mini Tutorial
Optical blur from defocus is quite frequently considered as equivalent to low-pass filtering. Yet that belief, although not entirely wrong, is inaccurate. Here, we wish to disentangle the concepts of dioptric blur, caused by myopia or mis-accommodation, from blur due to low-pass filtering when convolving with a Gaussian kernel. Perhaps surprisinglyif well known in optometrythe representation of a blur kernel (or point-spread function) for dioptric blur is, to a good approximation and disregarding diffraction, simply a cylinder. Its projection onto the retina is classically referred to as a blur circle, the diameter of which can easily be deduced from a light-ray model. We further give the derivation of the relationship between the blur-disk's diameter and the extent of blur in diopters, as well as the diameter's relation to the near or far point, and finally its relationship to visual acuity
A matter of time: improvement of visual temporal processing during training-induced restoration of light detection performance
The issue of how basic sensory and temporal processing are related is still unresolved. We studied temporal processing, as assessed by simple visual reaction times (AT) and double-pulse resolution (DPR), in patients with partial vision loss after visual pathway lesions and investigated whether vision restoration training (VRT), a training program designed to improve light detection performance, would also affect temporal processing. Perimetric and campimetric visual field tests as well as maps of DPR thresholds and RI were acquired before and after a 3 months training period with VRT. Patient performance was compared to that of age matched healthy subjects. Intact visual field size increased during training. Averaged across the entire visual field, DPR remained constant while RI improved slightly. However, in transition zones between the blind and intact areas (areas of residual vision) where patients had shown between 20 and 80% of stimulus detection probability in pre-training visual field tests, both DPR and RI improved markedly. The magnitude of improvement depended on the defect depth (or degree of intactness) of the respective region at baseline. Inter-individual training outcome variability was very high, with some patients showing little change and others showing performance approaching that of healthy controls. Training-induced improvement of light detection in patients with visual field loss thus generalized to dynamic visual functions. The findings suggest that similar neural mechanisms may underlie the impairment and subsequent training-induced functional recovery of both light detection and temporal processing
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