-
Journal of Cognitive Psychology (Hove,... 2014Participants were asked to search for a complete in an array consisting of eight clusters of four Landolt s (i.e., s with a gap) arranged in a ring. The size of the gap...
Participants were asked to search for a complete in an array consisting of eight clusters of four Landolt s (i.e., s with a gap) arranged in a ring. The size of the gap in the s varied from cluster to cluster but was held constant within a cluster. The manual response time data were consistent with a serial self-terminating search. More importantly, eye movement data supported a serial processing model as (a) clusters were fixated serially (either clockwise or counterclockwise) on most trials and (b) fixation times on a cluster reflected processing time on that cluster and were unaffected by the gap size of either the prior or succeeding cluster. Furthermore, the pattern of fixation times on a cluster was similar to the pattern of response times in a secondary task where a single cluster was presented at fixation. These data extend the findings of Williams and Pollatsek (2007) in which search was through a linear sequence of clusters, and indicate that a serial search pattern through clusters of these kinds of objects is not confined to reading-like linear arrays.
PubMed: 24527204
DOI: 10.1080/20445911.2013.865630 -
Yonsei Medical Journal Dec 2003This study both measured and compared the mesopic contrast sensitivity function and the visual acuity in both normal and amblyopic eyes from amblyopic children using an...
This study both measured and compared the mesopic contrast sensitivity function and the visual acuity in both normal and amblyopic eyes from amblyopic children using an ACV (visual acuity analyzer). Twenty one amblyopic children (mean age, 8.48 years; S.D., 1.68 years), 11 strabismic amblyopes and 10 anisometropic amblyopes, were tested. Based on a display of the standard optotypes, the minimal contrast level, at which the optotypes were correctly read for all sizes of displays from a distance of 1m, was measured. The contrast ranged from 1% to 99% and the spatial frequencies ranged from 0.6 to- 30cpd using a Landolt ring composed of low (0.6- 2.9 c.p.d.), intermediate (3.0 - 12.9 c.p.d.) and high level (13.0- 30.0 c.p.d.) frequencies. As the visual acuity decreased, the mesopic contrast sensitivity function decreased along the contrast sensitivity axis. However, the peak sensitivity was noted at the same spatial frequencies. A comparison between the normal eye and the corresponding amblyopic eye showed that under mesopic conditions, the contrast sensitivity functions decreased more in the intermediate spatial frequencies than in the other spatial frequencies. The mesopic contrast sensitivity function decreased in the amblyopic eyes, which suggests the possibility of its use an adjunct to an evaluation of amblyopia.
Topics: Amblyopia; Case-Control Studies; Child; Contrast Sensitivity; Female; Humans; Male; Visual Acuity
PubMed: 14703607
DOI: 10.3349/ymj.2003.44.6.995 -
Vision Research Dec 2001Hess et al. (Vision Res. 40 (2000) 365) found that the peak frequency of the amplitude difference spectrum (ADS) of a Landolt C/flanking bar configuration was higher...
Hess et al. (Vision Res. 40 (2000) 365) found that the peak frequency of the amplitude difference spectrum (ADS) of a Landolt C/flanking bar configuration was higher than that of an isolated C. They believed that this mismatch in the dominant frequency components could account for the foveal crowding effect. The following empirical and theoretical studies were conducted to evaluate this new explanation. First, the foveal crowding effect between a Landolt C and four flanking bars was measured under same- and mixed-polarity conditions. Significant crowding was found under the mixed-polarity condition. This result is different from the data that Hess et al. used to support their explanation of the foveal crowding effect. Second, analytical expressions for the Fourier transforms of C/flanking bar configurations were derived. ADS for various ring/bar separations and contrast polarities were calculated using these expressions. This analysis showed several discrepancies between ADS peak frequency predictions and empirical data. Therefore, the ADS peak frequency of the stimulus configuration does not provide an adequate explanation for the foveal crowding effect.
Topics: Fourier Analysis; Fovea Centralis; Humans; Models, Neurological; Photic Stimulation; Psychophysics; Visual Acuity
PubMed: 11712983
DOI: 10.1016/s0042-6989(01)00221-8 -
The Expansion of RPE Atrophy after the Inverted ILM Flap Technique for a Chronic Large Macular Hole.Case Reports in Ophthalmology Jan 2014To report a case of the expansion of submacular retinal pigment epithelium (RPE) atrophy after using the inverted internal limiting membrane (ILM) flap technique for a...
PURPOSE
To report a case of the expansion of submacular retinal pigment epithelium (RPE) atrophy after using the inverted internal limiting membrane (ILM) flap technique for a persisting, large, stage IV macular hole (MH).
CASE REPORT
A 79-year-old woman presented with a chronic large MH that remained open despite pars plana vitrectomy (PPV). The surgery was performed twice for the MH closure 14 years earlier. ILM peeling was not performed during the previous surgeries. The best-corrected visual acuity (BCVA) with the Landolt ring chart was 0.08 at her visit. The minimum MH diameter was 1,240 μm. Inverted ILM flap technique with 20% SF6 gas tamponade was performed for the MH closure. For the inverted ILM flap technique, 25-gauge PPV and ILM staining with indocyanine green were used. The ILM was peeled off for 2 disc diameters around the MH, but the ILM was not removed completely. The ILM was then inverted and covered the MH.
RESULTS
One month after surgery, the MH was closed, accompanied by glial cell proliferation spreading from the inverted ILM flap (as reported before). On the other hand, the area of the submacular RPE atrophy, which was already observed 1 week after surgery, gradually increased in size. BCVA improved to 0.3 six months after the surgery.
CONCLUSIONS
The inverted ILM flap technique may be promising even for persisting large MH which were not closed in previous surgeries, but long-term observation is needed because the detailed behavior of the inverted ILM and the Müller cells after surgery is not yet known.
PubMed: 24707278
DOI: 10.1159/000360693 -
The Open Ophthalmology Journal Nov 2007Visibility of a simple stimulus is known to be determined not only by its physical contrast, but also by the configuration of surrounding stimuli. In this study, we...
Visibility of a simple stimulus is known to be determined not only by its physical contrast, but also by the configuration of surrounding stimuli. In this study, we investigated the surrounding modulation of foveal visibility of a blurred target. Subjects were instructed to respond to the gap orientation of a Gaussian-blurred Landolt ring presented at a fixation point with a surrounding stimulus. The correct response rate was measured as a metric of the foveal visibility. Results were subsequently compared among different surrounding stimulus conditions. Results showed an improvement in the subjects' performance when low-pass white noise filtered with the same Gaussian function used for the target was presented in the surrounding area, although no effect was observed using high-contrast white noise. A performance improvement was observed when the surround stimulus had an intermediate contrast in the spatial frequency band necessary for identifying the target orientation.
PubMed: 19478859
DOI: 10.2174/1874364100701010004