Foveal

About: Foveal is a research topic. Over the lifetime, 2652 publications have been published within this topic receiving 94120 citations.

Attention alters spatial integration in macaque V1 in an eccentricity-dependent manner

Abstract: Attention can selectively enhance neuronal responses and exclude external noise, but the neuronal computations that underlie these effects remain unknown. At the neuronal level, noise exclusion might result in altered spatial integration properties. We tested this proposal by recording neuronal activity and length tuning in neurons of the primary visual cortex of the macaque when attention was directed toward or away from stimuli presented in each neuron's classical receptive field. For cells with central-parafoveal receptive fields, attention reduced spatial integration, as demonstrated by a reduction in preferred stimulus length and in the size of the spatial summation area. Conversely, in cells that represented more peripheral locations, attention increased spatial integration by increasing the cell's summation area. This previously unknown dichotomy between central and peripheral vision could support accurate analysis of attended foveal objects and target selection for impending eye movements to peripheral objects.

Abnormal Foveal Morphology in Ocular Albinism Imaged With Spectral-Domain Optical Coherence Tomography

Abstract: Objectives To evaluate the spectrum of foveal architecture in pediatric albinism and to assess the utility of spectral-domain optical coherence tomography (OCT) in ocular imaging of children with nystagmus. Methods Spectral-domain OCT imaging was performed on study subjects in 3 groups: subjects with ocular albinism (OA) or suspected OA with foveal hypoplasia, with nystagmus, and with or without iris transillumination; a subject with oculocutaneous albinism and Hermansky-Pudlak syndrome; and control subjects. Dense volumetric scans of each fovea were captured using standard and handheld spectral-domain OCT devices. Images were postprocessed and scored for the presence and configuration of each retinal layer across the fovea. Results High-quality spectral-domain OCT images obtained from each subject revealed a range of abnormalities in subjects with OA or suspected OA and the subject with oculocutaneous albinism and Hermansky-Pudlak syndrome: persistence of an abnormal, highly reflective band across the fovea, multiple inner retinal layers normally absent at the center of the fovea, and loss of the normally thickened photoreceptor nuclear layer at the fovea when compared with that in control subjects. The optic nerve was elevated in multiple eyes of subjects with OA or suspected OA and the subject with oculocutaneous albinism and Hermansky-Pudlak syndrome. Conclusions A spectrum of foveal morphological abnormalities is seen in subjects with OA or suspected OA, which in some cases contrasted with previous studies using time-domain OCT. These OCT findings clarify the morphology of foveal hypoplasia seen clinically. This imaging modality may be useful in evaluating children.

Early Foveal Involvement and Generalized Depression of the Visual Field in Glaucoma

Abstract: • We selected for study 35 patients with glaucomatous visual field loss or cupping that was asymmetric between the two eyes, concentrating on cases in which the glaucomatous damage was mild. We found that 15 patients had a reduced foveal sensitivity usually associated with either a scotoma impinging on fixation or a depression in the central field. In addition, 19 of the 35 patients had a subtle reduction in visual acuity. Thus, the fovea is often mildly affected early in glaucoma, even though the point of fixation is typically among the last regions of visual field to have a severe loss of visual sensation. We also observed that there is often a diffuse visual field loss early in glaucoma, represented as a generalized depression, and this may occur before there are discrete nerve fiber-bundle defects (paracentral scotomas and the like).

Colour Perception with the Peripheral Retina

Abstract: Until recently, descriptions of peripheral colour perception have been largely qualitative. The present paper reports a quantitative determination of the colours of peripherally presented lights, in which a foveal mixture field is used for comparison. Observations were made under dark adaptation conditions by two observers. The colour changes are analysed in terms of hue and saturation. In addition, spectral sensitivity curves are derived from the colour-matching data. Some subsidiary experiments are reported which indicate effects due to light adaptation, test luminance and exposure time. The results indicate a progressive deterioration in colour perception with distance from the fovea: tending, under the conditions of the experiment, to dichromatism at 25°-30° and to monochromatism at 40°–50°. The roles of (a) rod vision, (b) the fusion of nerve pathways, and (c) the depletion of the cone population are discussed.