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Auteur Harold E. Bedell
Documents disponibles écrits par cet auteur
Ajouter le résultat dans votre panier Affiner la rechercheA Comparison of Foveal and Peripheral Contour Interaction and Crowding / Stephanie M. Marten-Ellis in OVS : Optometry & Vision Science, vol. 98, 01 (Janvier 2021)
[article]
in OVS : Optometry & Vision Science > vol. 98, 01 (Janvier 2021)
Titre : A Comparison of Foveal and Peripheral Contour Interaction and Crowding Type de document : article de périodique Auteurs : Stephanie M. Marten-Ellis ; Harold E. Bedell Année de publication : 2021 Langues : Français (fre) Descripteurs (mots clés) : [Thésaurus Mesh]Acuité visuelle
[Thésaurus Mesh]Rétine
[Thésaurus Mesh]Tests de visionRésumé : SIGNIFICANCE: Performance on clinical tests of visual acuity can be influenced by the presence of nearby targets. This study compared the influence of neighboring flanking bars and letters on foveal and peripheral letter identification. PURPOSE: Contour interaction and crowding refer to an impairment of visual resolution or discrimination produced by different types of flanking stimuli. This study compared the impairment of percent correct letter identification that is produced in normal observers when a target letter is surrounded by an array of four flanking bars (contour interaction) or four flanking letters (crowding). METHODS: Performance was measured at the fovea and at eccentricities of 1.25, 2.5, and 5° for photopic (200 cd/m2 ) and mesopic stimuli (0.5 cd/m2 ) and a range of target-to-flanker separations. RESULTS: Consistent with previous reports, foveal contour interaction and crowding were more pronounced for photopic than mesopic targets. However, no statistically significant difference existed between foveal contour-interaction and crowding functions at either luminance level. On the other hand, flanking bars produced much less impairment of letter identification than letter flankers at all three peripheral locations, indicating that crowding is more severe than contour interaction in peripheral vision. In contrast to the fovea, peripheral crowding and contour-interaction functions did not differ systematically for targets of photopic and mesopic luminance. CONCLUSION: The similarity between foveal contour interaction and crowding and the dissimilarity between peripheral contour interaction and crowding suggest the involvement of different mechanisms at different retinal locations. Permalink : https://bibliotheque.helb-prigogine.be/opac_css/index.php?lvl=notice_display&id= [article]Exemplaires
Cote Support Localisation Section Disponibilité aucun exemplaire Contrast Energy and Contour Interaction / Harold E. Bedell in OVS : Optometry & Vision Science, vol. 96, 12 (Décembre 2019)
[article]
in OVS : Optometry & Vision Science > vol. 96, 12 (Décembre 2019)
Titre : Contrast Energy and Contour Interaction Type de document : article de périodique Auteurs : Harold E. Bedell ; John Siderov ; František Pluhácek Année de publication : 2019 Langues : Français (fre) Descripteurs (mots clés) : [Thésaurus Mesh]Acuité visuelle
[Thésaurus Mesh]Dépistage visuel
[Thésaurus Mesh]Troubles de la visionMots-clés : contour contraste Résumé : SIGNIFICANCE Contour interaction describes an impairment of visual acuity produced by nearby flanking features, which exerts a significant impact in many clinical tests of visual acuity. Our results indicate that the magnitude of interaction depends either on the flanker contrast energy (i.e., the product of flanker contrast and width) or the flanker contrast alone, depending on the contrast energy of the flankers.
PURPOSE The discrimination of acuity targets is impaired by the presence of nearby flanking contours, a phenomenon known as contour interaction.
METHODS In this study, we measured percent correct identification for threshold size, high-contrast Sloan letters at the fovea and at 5° in the inferior visual field for different combinations of flanking-bar width, and Weber contrast corresponding to specific fixed values of contrast energy (width × contrast, in %-min arc).
RESULTS For flanking bars with low-contrast energy, contour interaction exhibited no systematic dependence on the flanking-bar width. However, when the flanking bars had higher contrast energy, narrower high-contrast bars produced significantly greater contour interaction than wider bars of lower contrast.
CONCLUSIONS The results are consistent with the interpretation that contour interaction depends primarily on the contrast energy of flanking contours when their contrast energy is low. As the contrast energy of the flanking contours increases, the magnitude of contour interaction depends on the flanker contrast. For high-contrast flanking contours, the magnitude of contour interaction saturates when the width of the flanking contours is approximately 20% of letter size.Permalink : https://bibliotheque.helb-prigogine.be/opac_css/index.php?lvl=notice_display&id= [article]Exemplaires
Cote Support Localisation Section Disponibilité aucun exemplaire High- and Low-contrast Letter Acuity during Image Motion in Normal Observers and Observers with Infantile Nystagmus Syndrome / Harold E. Bedell in OVS : Optometry & Vision Science, vol. 98, 02 (Février 2021)
[article]
in OVS : Optometry & Vision Science > vol. 98, 02 (Février 2021)
Titre : High- and Low-contrast Letter Acuity during Image Motion in Normal Observers and Observers with Infantile Nystagmus Syndrome Type de document : article de périodique Auteurs : Harold E. Bedell ; Sop Song Année de publication : 2021 Langues : Français (fre) Descripteurs (mots clés) : [Thésaurus HELB]:Photographie:contrastes
[Thésaurus Mesh]Acuité visuelle
[Thésaurus Mesh]Enfant
[Thésaurus Mesh]Lecture
[Thésaurus Mesh]Nystagmus physiologiqueMots-clés : syndrome du nystagmus infantile Résumé : SIGNIFICANCE: High-contrast acuity in individuals with infantile nystagmus syndrome (INS) is poorer than
expected from their ongoing retinal image motion, indicating a sensory loss. Conversely, acuity for larger
low-contrast letters in these observers may be limited by image motion alone.
PURPOSE: The aim of this study was to assess visual acuity for letters of different contrast in normal observers and
individuals with idiopathic INS under conditions of comparable retinal image motion.
METHODS: Visual acuity was measured using projected Landolt C charts in 3 normal observers and 11 observers
with presumed idiopathic INS. Normal observers viewed each chart after reflection from a front-surface mirror that
underwent continuous 4-Hz ramp motion with amplitudes ranging from 4 to 9.6° and simulated foveation durations of 20 to 80 milliseconds. Observers with INS viewed the charts directly. By reciprocally varying the luminance
of the projected charts and a superimposed veiling source, Landolt C's were presented on a background luminance
of 43 cd/m2 with Weber contrasts between −12 and −89%.
RESULTS: Whereas normal observers' high-contrast acuity during imposed image motion depends only on the duration of the simulated foveation periods, acuity for low-contrast optotypes also worsens systematically as motion intensity (frequency amplitude) increases. For comparable parameters of retinal image motion, high-contrast acuity in
all but one of the observers with INS was poorer than in normal observers. On the other hand, low-contrast acuity
in the two groups of observers was similar when the retinal image motion was comparable.
CONCLUSIONS: Reduced high-contrast acuity in observers with INS appears to be attributable primarily to a sensory deficit. On the other hand, the reduction of low-contrast acuity in observers with INS may be accounted for on
the basis of retinal image motion.Permalink : https://bibliotheque.helb-prigogine.be/opac_css/index.php?lvl=notice_display&id= [article]Exemplaires
Cote Support Localisation Section Disponibilité aucun exemplaire Spatial Interactions in Interocular and Monocular “Blur Suppression” / Jin Qian in OVS : Optometry & Vision Science, vol. 99, 12 (Décembre 2022)
[article]
in OVS : Optometry & Vision Science > vol. 99, 12 (Décembre 2022)
Titre : Spatial Interactions in Interocular and Monocular “Blur Suppression” Type de document : article de périodique Auteurs : Jin Qian ; Saumil S. Patel ; Harold E. Bedell Année de publication : 2022 Langues : Français (fre) Descripteurs (mots clés) : [Thésaurus Mesh]:O:Oeil:Oeil / métabolisme
[Thésaurus Mesh]Vision binoculaire
[Thésaurus Mesh]Vision monoculaire
[Thésaurus Mesh]Vision oculaireMots-clés : image floue Interactions spatiales Résumé : SIGNIFICANCE: The suppression of blurred images in one eye by clear images in the other eye is thought to contribute to the success of monovision correction. We show that interocular suppression occurs also for low-contrast targets that are not blurred and, to a lesser extent, when clear and low-contrast targets are presented to the same eye. PURPOSE: A blurred target presented to one eye may be suppressed when a clear target is presented to the other eye. We sought to determine how this interocular suppression varies according to the separation between the blurred and clear targets and the magnitude of imposed blur. In addition, we examined whether a similar suppression occurs when the clear and blurred targets are imaged in the same eye. METHODS: Subjects (N = 4) viewed a clear 20/40 Sloan letter surrounded by four 2 10 min-arc flanking bars. In different blocks of trials, the gap between the letter and flanking bars varied from 0.5 to 4 bar widths. In addition, the flanking bars were either clear or spatially filtered to simulate 0.5 to 2 D of blur. The contrast required to detect the flanking bars was determined when the letter and flanking bars were presented either dichoptically or monoptically and compared with the thresholds for the bar targets presented alone. RESULTS: In both dichoptic and monoptic viewing conditions, detection thresholds for the blurred flanking bars are highest for the smallest spatial gap and decrease systematically as the gap increases. Thresholds are uniformly higher during dichoptic than monocular viewing, but the proportional change with the bar-to-letter separation is similar in both conditions. Surprisingly, the magnitude of imposed blur has very little influence on the magnitude of threshold elevation in either the dichoptic or monoptic viewing conditions. CONCLUSIONS: Because threshold elevation is nearly the same in the presence of 0 to 2 D of blur, we prefer to designate the phenomenon we studied as “contrast suppression.” The similar spatial characteristics of suppression during dichoptic and monoptic viewing are consistent with contributions from a common neural mechanism. Permalink : https://bibliotheque.helb-prigogine.be/opac_css/index.php?lvl=notice_display&id= [article]Exemplaires
Cote Support Localisation Section Disponibilité aucun exemplaire Stereothresholds during Voluntary Head Movement and Disconjugate Image Motion / Harold E. Bedell in OVS : Optometry & Vision Science, vol. 99, 01 (Janvier 2022)
[article]
in OVS : Optometry & Vision Science > vol. 99, 01 (Janvier 2022)
Titre : Stereothresholds during Voluntary Head Movement and Disconjugate Image Motion Type de document : article de périodique Auteurs : Harold E. Bedell ; Dorcas K. Tsang ; Michael T. Ukwade Année de publication : 2022 Langues : Français (fre) Descripteurs (mots clés) : [Thésaurus Mesh]Mouvements de la tête
[Thésaurus Mesh]Optométrie
[Thésaurus Mesh]Perception visuelle tridimensionnelle
[Thésaurus Mesh]Vision oculaireRésumé : SIGNIFICANCE
Stereothresholds increase in the presence of disconjugate image motion, whether this motion results from vergence errors that occur during active head movements or is imposed externally.
PURPOSE
During rapid voluntary oscillations of the head, vergence eye position has been reported to vary with a peak-to-peak amplitude of about 0.5°—a considerably greater amplitude than when the head is still. Concurrently, stereopsis was reported to be unaffected by voluntary head motion. In the present study, we measured stereothresholds during voluntary side-to-side head movements and during imposed disconjugate image motion with the head stationary, to simulate that produced during active head movement.
METHODS
Stereothresholds were measured for a pair of 30-arcmin bright vertical lines presented on an oscilloscope and viewed through a custom mirror haploscope. Data were obtained from four normal observers during voluntary side-to-side head movements at temporal frequencies up to 1.5 Hz and also while the head remained still. In addition, stereothresholds were measured with the head stationary when opposite rotations of the galvanometer-driven mirrors in each channel of the haploscope created disconjugate image motion to simulate vergence variability during active head movement.
RESULTS
During head motion, average stereothresholds increased from about 10 to about 14 arcsec. With imposed disconjugate image motion, stereothresholds rose systematically to about 35 arcsec when the peak-to-peak motion amplitude was 0.5°. Stereothresholds depend primarily on the amplitude of imposed motion and only marginally on variations of the disjunctive-motion wave form.
CONCLUSIONS
Stereothresholds are elevated modestly during active head movements. The results obtained with imposed disjunctive image motion are consistent with a previously proposal that stereothresholds vary according to the unsigned, time-averaged deviation of the stereotarget from the plane of the horopter.Permalink : https://bibliotheque.helb-prigogine.be/opac_css/index.php?lvl=notice_display&id= [article]Exemplaires
Cote Support Localisation Section Disponibilité aucun exemplaire Technical Report: The Mechanism of Contour Interaction Differs in the Fovea and Periphery / František Pluhácek in OVS : Optometry & Vision Science, vol. 97, 12 (Décembre 2020)
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