Biomedical subjects

Esther G González

Publications and source records attributed to Esther G González.

8 recordsLinked to original sources

PubMed2006

Peripheral fading with monocular and binocular viewing.

This study measured the fading times of peripheral targets as a function of whether viewing was monocular or binocular, and of brightness contrast. Data from a binocularly normal group showed Troxler fading to be significantly faster with monocular (i.e., patched) than with binocular viewing. In contrast, one-eyed observers showed significantly longer fading times than the two-eyed observers viewing monocularly and equivalent times to their binocular viewing. A control experiment showed that these findings were not due to worse fixation stability, larger pupil sizes, or an unusually large blinking rate in the enucleated group. The enucleated group actually exhibited a slight miosis, equivalent fixation stability, and a normal blinking rate. In both experiments, the times to fading of all observers were a function of brightness contrast. We conclude that in binocularly normal observers patching or closing one eye does not produce monocular vision but rather a condition of weak binocular rivalry, and that the absence of inhibitory binocular interactions in the enucleated group may explain, in part, their resistance to fading and their superior performance in other contrast-defined tasks.

Adolescent↗

PubMed2006

Binocular interactions in patients with age-related macular degeneration: acuity summation and rivalry.

This study examined two aspects of binocular function in patients with age-related macular degeneration (AMD): summation/inhibition of visual acuity and rivalry. The performance of 17 patients with AMD was compared with that of 17 elderly controls and 21 young people. Monocular and binocular acuities were measured using a multiple-E optotype test. Binocular ratios, defined as the better-eye acuity divided by the binocular acuity, were calculated. We also measured eye dominance during rivalry (proportion of time the participants reported perceiving the input to each eye) and rivalry rates (number of alternations per minute). The results showed that while overall binocular ratios were similar for the three groups, the frequency distributions of people who experienced inhibition, equality or summation were different for the young and AMD groups. In the rivalry test, patients experienced more piecemeal perception than the elderly and young controls, but time dominance from the better-seeing eye was comparable for the three groups. Rivalry rates decreased with age and further with pathology. Moreover, rivalry time dominance of the worse-seeing eye was negatively correlated with interocular acuity differences for the AMD group.

Adult↗

PubMed2006

Fixation stability using radial gratings in patients with age-related macular degeneration.

BACKGROUND: The fixation stability of patients with macular atrophy is generally worse than that of people without pathology. METHODS: The effects of 2 types of high-contrast fixation stimuli on fixation stability were compared between patients with longstanding age-related macular degeneration (AMD) and control subjects with normal vision. One stimulus was a 9-cycle square-wave radial grating measuring 5 degrees in diameter and the other a white 0.5 degrees disc. A video-based infrared eye tracker with remote optics was used to record eye position while participants fixated the stimuli in primary position of gaze for 6 to 7 s. Fixation stability was measured with a bivariate contour ellipse area (BCEA). RESULTS: For patients with AMD, fixation stability for the radial grating was largely independent of visual acuity, whereas fixation stability for the disc diminished with acuity. For the control observers, there were no differences in fixation stability for the 2 kinds of stimuli. INTERPRETATION: In clinical and research settings, radial gratings can be useful targets for fixation for patients with macular disease since they provide enough visual information to help maintain fixation stability. These findings have important implications for the design of clinical tests and procedures such as perimetry, multifocal electroretinography, and optical coherence tomography for patients with macular atrophies.

Adult↗

PubMed2006

Binocular function in patients with age-related macular degeneration: a review.

Normally sighted observers typically benefit from binocular viewing when monocular sensitivities are equivalent. Age-related macular degeneration (AMD) not only destroys the foveal vision, however, but it also affects the 2 eyes unequally, providing grounds for impairment of binocular function. The aim of the present article is to provide a review of the current research on the effect of AMD on binocular vision. The main findings to date reveal that a high proportion of patients show characteristics of binocular contrast inhibition at low and medium spatial frequencies. Yet binocular acuity gain is not different from that of age-matched control participants without AMD. Additional findings show that rivalry processes are severely disrupted in patients with AMD. The effects of the disease on other binocular functions have yet to be explored. Knowledge of binocular function in AMD may one day help clinicians decide on the most appropriate management and rehabilitation techniques.

Contrast Sensitivity↗

PubMed2005

Kanizsa's shrinkage illusion produced by a misapplied 3-D corrective mechanism.

In order to include the monocular areas from the left and the right eye in the cyclopean view, the visual system displaces the occluded elements which would result in a horizontal elongation of the shape but does not occur thanks to a correction mechanism which preserves the shape. We hypothesised that this mechanism causes Kanizsa's amodal shrinkage illusion (the apparent elongation of a partially occluded square) when it is incorrectly applied by the visual system to a two-dimensional stimulus. Four experiments tested this hypothesis: (i) one-eyed observers were less susceptible to the illusion than people with normal binocular vision because, for them, the correction for shape is unnecessary; (ii) the illusion was stronger with binocular than with monocular vision since binocularity induces the visual system to correct for the shape distortion; (iii) the illusion diminished when the stimulus was rotated 90 degrees given that displacement and compression are not required for vertical occlusion; (iv) the magnitude of the illusion was a function of the width of the occluder because, as previous research has shown, the edges of a partially occluded square are less displaced the farther they are from the edges of the occluder. The data from the four experiments support our hypothesis even though no condition was able to eliminate the illusion; other possible causes are discussed.

Adolescent↗

PubMed2004

Global shape discrimination at reduced contrast in enucleated observers.

Previous research has shown that observers with early unilateral enucleation have selectively better sensitivity to luminance contrast than monocular viewing controls [González et al., 2002; Vision Research 36 (1) (1996) 175; Vision Research 36 (1996) 3011; Vision Research 37 (17) (1997) 2465]. We asked whether unilateral enucleation specifically enhances all levels of luminance processing. Enucleated observers, as well as binocular and monocular viewing controls, detected global shape in radial frequency (RF) patterns [Vision Research 38 (1998) 2555] at low contrast. Control observers were tested in two monocular conditions in which the stimulus was presented to one eye, while the fellow eye: (1) viewed a luminance-matched grey field or (2) was covered by a dark eye patch. Sensitivity to low-contrast global shape was equivalent in enucleated observers and binocular controls. More importantly, enucleated observers showed superior performance to that of controls in either monocular condition. At low contrast, the dichoptic control group was more sensitive than controls wearing an eye patch, which suggests that dichoptic viewing is a superior method of testing when comparing monocular control performance to that of monocularly deprived populations. The previously reported enhanced sensitivity to luminance-defined form in early enucleated observers also occurs for low-contrast global shape discrimination.

Adolescent↗

PubMed2002

Foveal and eccentric acuity in one-eyed observers.

The purpose of these two experiments was to examine the effects of enucleation on the foveal and near-periphery acuity of human observers. In Experiment 1, using high contrast illiterate-E optotypes, we measured foveal and 7-degree eccentric (nasal and temporal) acuity in the remaining eye of unilaterally enucleated children and adults. The data were compared to those of the fellow or 'good eye' of age-matched non-amblyopic and amblyopic strabismic observers-a different kind of monocular deprivation-and binocularly normal subjects. The main finding was that the 7-degree eccentric acuity of enucleated observers and normal controls was best, followed by that of the non-amblyopic and lastly, the amblyopic subjects. There were no naso-temporal asymmetries. In Experiment 2, foveal and 7-degree eccentric acuities of enucleated and binocularly normal subjects were tested at 96, 13.5 and 4.7% contrast levels using the same kind of stimuli. The foveal acuity of the enucleated observers was better than the monocular acuity of controls at all contrasts, and equivalent to their binocular acuity. The eccentric acuity of the enucleated observers was better at the two low contrast levels. No naso-temporal asymmetries were found in either group at any contrast level. These findings suggest that, in humans, visual deprivation from unilateral enucleation does not result in a naso-temporal asymmetry in the near periphery.

Adolescent↗

PubMed2002

Early unilateral enucleation disrupts motion processing.

Previous research has shown that unilaterally enucleated observers demonstrate better luminance-defined form perception compared to monocularly viewing controls, and similar performance to control observers viewing binocularly (Vision Res. 37(17) (1997) 2465). In Experiment 1 we asked whether the perception of form, where form is defined by other attributes than luminance, is also improved compared to monocularly viewing controls. We tested 16 enucleated observers and 25 controls viewing monocularly and binocularly for their ability to detect and recognize form from texture (texture-defined (TD) form) and form from motion (motion-defined (MD) form). There was no difference between the three groups for TD form perception. However, enucleated observers had significantly poorer MD form perception than did binocularly viewing controls. In Experiment 2 we asked whether poor performance on the perception of MD form might be due to a general reduction in motion processing abilities. To examine this possibility, we used a motion coherence task. We tested eight unilaterally enucleated and 14 monocularly and binocularly viewing control observers on a horizontal coherent motion discrimination task. The monocularly viewing controls showed no naso-temporal asymmetry in direction discrimination for coherent motion. In contrast, the enucleated group showed an asymmetry in direction discrimination where temporalward motion coherence thresholds were significantly higher than those for nasalward motion. These latter findings are discussed in terms of the absence of binocular competition during the development of motion processing pathways.

Adolescent↗