Showing papers on "Foveal published in 1977"

Eye Movements in Curve Negotiation

Abstract: Eye movements and fixations of five drivers were recorded and superimposed on a videotaped recording of the dynamic visual scene as they drove on a two-lane rural road. The results showed that (1) on curved roads, the fixation pattern follows the road geometry, whereas on straight roads, the search behavior is less active, and most of the fixations are close to the focus of expansion. The results indicate that in driving through curves drivers direct foveal fixations to lateral placement cues rather than rely on peripheral vision; (2) the process of curve scanning begins in the approach zone prior to the curve itself, suggesting that perceptually the curve negotiating process precedes the curve by several seconds; (3) the search patterns on right and left curves are not symmetrical; visual excursions to the right on right curves are greater than eye movements to the left on left curves; and (4) fixation duration statistics may be related to accident rates on curves. Implications of this study for the location of curve warning signs are given.

The comparison of small-size rectangle and checkerboard stimulation for the evaluation of delayed visual evoked responses in patients suspected of multiple sclerosis

Abstract: The use of foveal small-size rectangle stimulation to elicit visual evoked responses was compared with VERs elicited by the standard checkerboard pattern. Foveal stimulation achieved a significantly better discrimination of optic nerve lesions in the early diagnosis of multiple sclerosis. Sources of misdiagnosis due to different neurological disorders are discussed.

Peripheral Visual Processing.

Abstract: An attempt was made to examine the development of the ability to identify stimuli presented to peripheral vision in several different tasks. Five- and 8-year-old children and college adults saw, for 20 msec, either a single figure at 1°, 2°, 4°, or 6° of visual angle from the fovea (singleform condition) or an off-foveal figure with an additional figure at the fovea (double-form condition). In the double-form conditions, the subjects were required to identify either the peripheral figure only (double-form presentation) or both figures (double-form report). The main effects of Age, Distance, and Form Condition were significant. Accuracy improved with increasing age and with decreasing distance. The Form Condition effect reflected lower accuracy in the two double-form conditions than in the single-form condition. Interestingly, there was no difference between the two double-form conditions, suggesting that the mere presence of a foveal stimulus, with instructions to ignore it, produces as much decrement in peripheral performance as when subjects are told to fully process and report the foveal stimulus. Also, there was no interaction between Form Condition and Distance, suggesting that the label “tunnel vision” may be misleading, since the presence of the foveal stimulus seems to have an equal effect on all peripheral locations and does not really “restrict” the size of the effective visual field.

Foveal Lesions Seen in Retinitis Pigmentosa

Abstract: • A total of 110 patients with retinitis pigmentosa were prospectively and consecutively evaluated for the presence of foveal lesions. Of these 69 (63%) patients showed one of two types of separate and distinct bilateral foveal lesions. Forty-seven (43%) patients had atrophicappearing lesions of the retinal pigment epithelium within the fovea of both eyes, and an additional 22 (20%) patients showed bilateral foveal cysts or partial-thickness holes. Of the 22 patients in this last group, 16 showed cystoid macular edema evident on fluorescein angiography. ( Arch Ophthalmol 95:1993-1996, 1977)

Color vision in the peripheral retina. I. Spectral sensitivity

Abstract: Spectral sensitivity was measured by heterochromatic flicker photometry both in the fovea and at 45° in the periphery, using a 1200 troland standard At each location, sensitivity functions were obtained using both large and small targets While the foveal functions were normal, the peripheral ones showed a large enhancement in sensitivity to short wavelengths relative to long wavelengths Similar results in the past had been criticized on the ground that they might have been due to differential chromatic adaptation of cone mechanisms In this study such an interpretation was ruled out by additional control experiments including varying luminance and wavelength of the standard light The possibility of a rod contribution to the peripheral functions could not be eliminated although several different techniques, including the Stiles-Crawford effect, were used to try to isolate cone mechanisms

Effect of level of confusability on reporting letters from briefly presented visual displays

Abstract: In a report paradigm, two letters are presented on a trial which are either confusable(e.g., P and R) or nonconfusable (e.g., P and M) in terms of visual features. Across trials, interletter distance, retinal location, duration, and visual field are varied. Identification accuracy on confusable trials was generally lower than on nonconfusable trials, and this effect of level of confusability increased with distance from the fixation point, decreased with duration, and was smaller on the central letter than on the more peripheral letter. A quantitative model, incorporating aspects of the interactive channels model (Estes, 1972) and feature perturbation model (Wolford, 1975), is developed and tested. One parameter of the model measures the effective similarity between two letters after lateral inhibition has occurred, and other parameters measure the probability of feature perturbation in foveal and peripheral directions.

Foveal sparing. New anatomical evidence for bilateral representation of the central retina.

Abstract: • The pattern of retinal ganglion cell projections to the dorsal lateral geniculate nuclei has been demonstrated with horseradish peroxidase neuronography. A 1°-wide strip centered on the vertical meridian has been found in which ipsilaterally and contralaterally projecting ganglion cells intermingle. This strip expands to a width of 3° at the fovea, since mixing of horseradish peroxidase-labeled and unlabeled ganglion cells was found in a band approximately 0.5° wide along both the nasal and temporal rims of the foveola. These labeled ganglion cells rimming the foveal pit in Its entirety represent a possible anatomical basis for "foveal sparing." ( Arch Ophthalmol 95:1445-1447, 1977)

The Neural Control of Saccadic Eye Movements: The Role of the Superior Colliculus

Abstract: Traditionally, the superior colliculus (SC) has been considered a center for producing reflexive movements of the eyes and head in response to visual stimuli. But the suggestion that the SC is a critical or necessary structure for voluntary or involuntary eye movements has been vigorously disputed (Pasik et al., 1966). In recent years, evidence has accumulated which supports earlier suggestions that the SC is involved in coding the location of an object relative to the fovea and in eliciting saccadic movements which produce foveal acquisition of the object. An alternative hypothesis, that the SC is concerned with shifting attention to specific areas of the visual field, has received experimental support as well.

Is the duration of an eye fixation a sufficient criterion referring to information input

Abstract: In experiments on eye movements duration of eye fixations is frequently used as a criterion. In different studies mean duration of eye fixations is relatively constant, amounting approximately to .30 sec., even though duration of a single fixation can vary within a quite large range (cf. Fig. 1). An eye fixation in reference to information-input (Purkinje, 1825) may mean distinguishing between fixations devoted to exploring, processing, and staring according to their durations which should be respectively short, at about average, and long. Even though strict limits were never given, this statement has influenced recent research. If this statement is true, then the distribution of durations must be represented at least by a bimodal vs trimodal curve. For testing this hypothesis the durations of a total of 960 eye fixations, observed on six drivers while steering a car on a straight road, were analyzed as described, elsewhere (Cohen & Fischer, 1977). The mean duration was 0.36 sec. with a standard deviation of 0.22 and a skewness of 2.18; the respective distribution as well as the cumulative frequency are shown in Fig. 1. This figure indicates clearly a unimodal curve. The observed distribution does not allow distinction berween types of eye fixations by their durations only. Furthermore, about 70% of the eye fixations might be approximated by a linear relationship between their cumulative frequency and the respective durations. These data suggest that duration of eye fixation alone is not a sufficient criterion for distinguishing among the three possible purposes of single eye fixations. The duration of a fixation might also depend on the interactions among prior fixations, the am litude of eye movements, characteristics of the fixated point, the present schema of the suiject, as well as his capacity to process information. It might be assumed that detailed information is picked up through foveal vision, while parafoveal vision could be devoted simultaneously to exploration of further points of special interest in the environment to determine the next fixation point prior to beginning the eye movement. This dual function of the eye excludes also a strict distinction between eye fixations devoted only to processing or to scanning.

Stimulus- and response-dependent units from the occipital and temporal lobes of the unanaesthetized monkey performing learnt visual tasks

Abstract: 43% of units recorded from the foveal prestriate cortex, inferotemporal cortex or amygdala of 15 rhesus monkeys performing visual discrimination or serial reversal tasks were responsive to all or some visual stimuli or other aspects of the task. Six units showed activity during movements required for performance of the task. It was not possible to determine whether unit activity could be related to the learnt association of the visual stimuli with reward.

Foveal letters and parafoveal recognition of and words by dyslexics and by average readers

Abstract: In adult readers, parafoveal recognition of words is limited by strong interferences between letters. In the present study subjects were 20 dyslexic children and 20 average readers (9-14 yr). Recognition scores of isolated letters, of embedded letters and of words were compared both in foveal and in parafoveal vision. The groups did equally well on isolated letters whereas the dyslexics generally stayed behind on embedded letters and on words. Individual scores of embedded letters and of words were moderately correlated as were word score and reading level. It is advocated that research on dyslexia is directed at possible deficits in reading processes such as eye control, word recognition, and storage not only as separate factors but rather in their intimate relationships.

Visual Acuity and Checkerboard Potentials with Defocusing Lenses

Abstract: Mainly because of the topography of the visual cortex, the VECPs reflect to a large extent the function of the posterior pole (Van Lith & Henkes, 1970). This is not only the case for pattern evoked potentials, but also for luminance evoked potentials. Despite this, the latter give hardly any information about one of the main foveal functions, viz. the visual acuity. One of the reasons is that the evoked potentials are highly variable; another reason is that luminance evoked potentials and visual acuity represent two totally different functions, the former being a measure of light sensitivity whereas the latter also includes a contrast function. Cortical potentials evoked by a pattern stimulus represent both functions, luminance and contrast, in a variable relation depending on checksize and contrast between the checks.

Power Boat Operators' Visual Behavior Patterns

Abstract: Power boat operators' visual characteristics were recorded with a corneal reflection eye movement system in order to determine their foveal fixations. Data were collected while three (3) subjects p...

The Foveal Local Erg Response to Transient and Steady State Flickering Stimuli

Abstract: The photoreceptors are the first neural elements in the visual system, and an appreciation of their response characteristics can greatly assist our understanding of higher order neural processes. The extent to which photoreceptor activity can be monitored in primates by means of a nearly normal preparation will directly effect our ability to attain this goal It was in pursuit of such a preparation that this study was undertaken.

Foveal Threshold of One Eye When Illuminated by Contralateral Steady Light

Abstract: Summary.-The effect of luminance of the contcalatecal steady light upon the foveal threshold was examined in the siruation where both test-field and contralateral background (or surround) appeared to be completely fused when both were exposed simultaneously. The relation between the test threshold (defined as log Lt/Lco) and the luminance of the contralateral badground (or surround) (I) was expressed by log (Lt/Lto) = a(l -e-"'" I), where a and b are constants. It has been debated whether interocular effects can be found in dark adaptation. Generally speaking, it is known that the adaptations of the two retinae are independent. In this sense, dark adaptation is supposed to be a completely peripheral process. Since previous investigators have reported some contradictory results, a problem, however, still remains to be settled. Beitel (1936), Crawford (1940), and Ivanoff (1947; cited by Bouman, 1955) deny any effect of the state of adaptation or glare of one eye on the absolute or differential thresholds of the other. Bouman (1955) measured contrast and increment thresholds (foveal and peripheral) with the presentation of the test stimulus to one of the eyes, adapting fields of mutually different brightness and colors being incident in both eyes. No essential influence was found on threshold under such stimulation of the non-measured eye. To the contrary, according to Fiorentini and Radici ( 1961), the increment threshold in a parafoveal area of one eye is depressed by strong illumination of a disparate area of the other eye. That is to say, the parafoveal increment threshold measured in one eye simultaneously with the onset of a conditioning stimulus to the other eye was higher than the threshold measured in the absence of the contralateral stimulus. Also, Fiorentini and Bittini (1963) investigated the temporal course of sensitivity on one eye before and during stimulation of the other eye by a method similar to that used in the monocular experiment, wherein the test flash and the conditioning field were presented to the same eye. By comparing their data with the data obtained by Batcersby and Wagman (1759) in an experiment in which the test stimulus and conditioning field were presented to the same eye, they suggested that central processes could be involved in the changes in sensitivity occurring at the early negative intervals 'The author wishes to express sincere gratirude to Dr. S. Torii of University of Tokyo for his helpful advice concerning the manuscript. Wailing address: 2-15-10 Kame-yama, Fujisawa, 251 Japan.