Foveal

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

Visual consequences of the foveal pit

Abstract: When viewing a uniform field through a small aperture moved circularly before the pupil of the eye, many observers report a diffuse dim spot subtending roughly 1 degree visual angle, which rolls around the fixation point in synchrony with the motion of the aperture. Measurements of the Stiles-Crawford maximum for different locations within the fovea confirm that small but systematic shifts in foveal directional sensitivity are responsible for this entoptic effect. A quantitative model is developed which accounts for the directional sensitivity shifts on the basis of refraction of light at the sloping sides of the foveal pit. Supporting evidence for the model is provided by a second entoptic phenomenon: fundal scatter from the image of a glare source on the eccentric retina is reflected by the foveal pit in such a way as to render it visible. Estimates of the slope of the foveal pit from this effect agree well with that predicted from the observed shifts in directional sensitivity.

Foveal Load Affects the Functional Field of View

Abstract: The results of three tachistoscopic experiments are reported, which suggest that the functional or useful field of view is very sensitive to foveal demands (load). As the foveal primary task becomes more difficult, peripheral information extraction is perturbed, and it is perturbed increasingly as the retinal eccentricity of the peripheral information increases. This is the case even when compensatory adjustments are made for acuity loss. The results are discussed in terms of tunnel vision and general interference models.

Ocular fixation and visual activity in the monkey lateral intraparietal area.

Abstract: The macaque lateral intraparietal area (LIP) has been implicated in visuospatial attention and saccade planning. Since area LIP also contains a representation of the central visual field, we investigated its possible role in fixation and foveal attention in a visual fixation task with gap (momentary disappearance of fixation point). In addition to the expected visual neurons (n=119), two main categories were identified: (1) cells responding tonically both during the presence and momentary absence of the fixation stimulus(n=47); a subset of these neurons studied in a saccade task showed perisaccadic inhibition in half of the cases (14/27). The timing of this inhibition, however, is only loosely related to saccade timing; (2) cells responding mainly to the absence of the fixation stimulus, with either abrupt or gradual onset of activity during the gap (n=62). During saccades, these neurons showed presaccadic buildup and/or postsaccadic activity, which was spatially tuned in about half of the tested cells (28/53). Ninety-one percent of the cells in the first category and 59% of the cells in the second category were located in the dorsal portion of area LIP (LIPd). These results are consistent with the hypothesis of an oculomotor-attentional network contributing to fixation engagement and disengagement in a subregion of LIP.

Retinal locus for scanning text.

Abstract: --A method of mapping the retinal location of text during reading is described in which text position is plotted cumulatively on scanning laser ophthalmoscope retinal images. Retinal locations that contain text most often are the brightest in the cumulative plot, and locations that contain text least often are the darkest. In this way, the retinal area that most often contains text is determined. Text maps were plotted for eight control subjects without vision loss and eight subjects with central scotomas from macular degeneration. Control subjects' text maps showed that the fovea contained text most often. Text maps of five of the subjects with scotomas showed that they used the same peripheral retinal area to scan text and fixate. Text maps of the other three subjects with scotomas showed that they used separate areas to scan text and fixate. Retinal text maps may help evaluate rehabilitative strategies for training individuals with central scotomas to use a particular retinal area to scan text. Key words: eccentric viewing, fixation, fixation PRL, preferred retinal locus, reading, reading rehabilitation, retinal function mapping, scanning laser ophthalmoscope, text scanning, text-scanning PRL INTRODUCTION When individuals without vision loss read, their fast saccadic eye movements sequentially shift the characters in a line of text onto the fovea, the retinal area of highest acuity, where they are held in place and visually processed. This typical reading process is disrupted when foveal vision is lost because of macular disease. Normal reading rates usually exceeding 150 words a minute can drop to approximately 25 words a minute or less [1]. Individuals with foveal vision loss resulting in dense central scotomas use a peripheral retinal area (preferred retinal locus [PRL]) adjacent to the scotoma to fixate and inspect small visual objects, such as single letters. They may also use this fixation PRL (fPRL) to scan extended sentences and paragraph text. Over the past 25 years, various rehabilitative strategies have been proposed for enhancing use of eccentric (i.e., PRL) viewing and improving reading rates [2-4]. These rehabilitative measures have met with some success but may be less than optimal. One impediment to the development of effective reading rehabilitation strategies has been the lack of a means to adequately characterize the retinal area used for scanning text. Determining the fPRL for inspecting small visual objects such as fixation targets, letters, or short words is relatively straightforward because these visual stimuli are spatially discrete. Consequently, their positions on the retina are readily characterized with multiple scanning laser ophthalmoscope (SLO) images. Mapping the retinal locus for scanning multiple words in paragraphs is more problematic, however, since the text is spatially extensive and occupies a much larger retinal area. For example, Figure 1 shows an SLO image of paragraph text on a retina with a hypothetical scotomatous central lesion. The text extends beyond the scotoma on all sides. In this hypothetical example, the retinal area being used to inspect the text at the moment the SLO image was made is impossible to determine. As shown by the ovals with question marks, many possibilities exist (Figure 1). One cannot assume that the fPRL for inspecting small objects was also used for scanning the extended text. [FIGURE 1 OMITTED] Here we report a method for mapping the retinal area that subjects used to scan text during reading. This method is based on an earlier graphical method [5]. The present method cumulatively plots text position on an SLO retinal image. In the cumulative plot, retinal areas that contained text most often will be the brightest, and those that contained text least often will be the darkest. In this way, we can determine the retinal region that most often contains text. In essence, the method is like a time exposure of film in a camera. …