Part Of Visual Field Research Articles

Combined contributions of feedforward and feedback inputs to bottom-up attention.

In order to deal with a large amount of information carried by visual inputs entering the brain at any given point in time, the brain swiftly uses the same inputs to enhance processing in one part of visual field at the expense of the others. These processes, collectively called bottom-up attentional selection, are assumed to solely rely on feedforward processing of the external inputs, as it is implied by the nomenclature. Nevertheless, evidence from recent experimental and modeling studies points to the role of feedback in bottom-up attention. Here, we review behavioral and neural evidence that feedback inputs are important for the formation of signals that could guide attentional selection based on exogenous inputs. Moreover, we review results from a modeling study elucidating mechanisms underlying the emergence of these signals in successive layers of neural populations and how they depend on feedback from higher visual areas. We use these results to interpret and discuss more recent findings that can further unravel feedforward and feedback neural mechanisms underlying bottom-up attention. We argue that while it is descriptively useful to separate feedforward and feedback processes underlying bottom-up attention, these processes cannot be mechanistically separated into two successive stages as they occur at almost the same time and affect neural activity within the same brain areas using similar neural mechanisms. Therefore, understanding the interaction and integration of feedforward and feedback inputs is crucial for better understanding of bottom-up attention.

Effects of hemiretinal form deprivation on central refractive development and posterior eye shape in chicks

We determined effects of hemiretinal form deprivation (i.e., form-depriving half of the retina) on central refractive development and posterior eye shape in chicks. Seventy-seven White Leghorn chicks were randomly assigned to receive superior (SRD, “Superior Retinal Deprivation” or inferior visual field deprivation, same principle applies for the following abbreviations, n=17), inferior (IRD, n=14), temporal (TRD, n=23) or nasal hemiretinal (NRD, n=23) form deprivation monocularly from day 5 to day 26. Central refractive errors, expressed as interocular difference in spherical equivalent (M), J0 and J45 astigmatic components, were measured using Hartinger refractometer at the beginning and weekly after treatment for 3weeks. At the end of the treatment period, eyes of a subset of birds were enucleated and eye shape profile was photographed along four different meridians. These digital images were later processed to extract axial length (AL), equatorial diameter (ED), and AL/ED. For comparison purposes, the eye shape profile was also acquired from a separate group of birds reared with monocular full-retinal form deprivation (FRD, n=10). The four hemiretinal form deprivations altered central ametropia and posterior eye shape to different degrees. The biggest contrast in M was found between SRD and IRD groups (mean±SE after 3weeks: SRD=−4.14±0.71 D vs. IRD=+1.24±0.36 D; p<0.05), whereas subtle differences in J0 and J45 components were found across the four treatment groups (both p⩽0.03). SRD group also showed significantly higher AL/ED ratio compared to IRD and NRD groups (0.76±0.05 vs. 0.74±0.07 and 0.75±0.04; both p⩽0.03). Furthermore, M was significantly correlated with AL/ED ratio in the treated eyes of hemiretinal treated chicks (r=−0.55, p<0.001). Our results suggest that mechanism regulating central ametropia can be influenced by selectively interrupting the visual experience at different parts of visual field.

An epidemiological approach for the estimation of disease onset in Central Europe in central and peripheral monogenic retinal dystrophies

To study clinical patterns of disease onset in monogenic retinal dystrophies (MRD), using an epidemiological approach. Records of patients with MRD, seen at the University Eye Hospital Tuebingen from 1994 to 1999, were selected from a database and retrospectively reviewed. For analysis, patients were divided into 2 groups by predominant part of visual field (VF) involvement: group 1 (predominantly central involvement) included Stargardt disease (ST), macular dystrophy (MD), and central areolar choroidal dystrophy (CACD), and group 2 (predominantly peripheral involvement) included Bardet-Biedl syndrome (BBD), Usher syndrome (USH) I and II, and choroideremia (CHD). Age, sex, age of first diagnosis, age of visual acuity (VA) decrease and VF emergence, night blindness and photophobia onset, types of VF defects and age of its onset, color discrimination defects and best corrected VA were analyzed. Records of 259 patients were studied. Men were more prevalent than women. Mean age of the patients was 47.2 (SD = 15.6) years old. Forty-five patients in the first group and 40 in the second were first diagnosed between 21 and 30 years of age. Ninety-four patients in the first group had VA decrease before 30 years of age; in the second group, 68 patients had VA decrease onset between 21 and 40 years of age. Forty-four patients in the first group noticed VF at an age between 21 and 30 years, and 74 patients between 11 and 30 years in the second group. Central scotoma was typical for the first group, and was detected in 115 patients. Concentric constriction was typical for the second group, and was found in 81 patients. Half of patients in both groups preserved best-corrected VA in the better eye at a level of 20/40 or better; 7% in the first group and 6% in the second group were registered as legally blind according to WHO criteria, having VA <1/50 or VF <5 degrees . Diagnosis frequency was USH I and II-34%, ST-31%, MD-18%, CHD-14%, BBD-5%. An epidemiological approach to the estimation of the disease onset of various subtypes of monogenic retinal degenerations will be useful for detection of disease duration, its prognosis, rehabilitation and the researching of future treatment possibilities.

97/03634 Process for producing lubricating base oils

We determined effects of hemiretinal form deprivation (i.e., form-depriving half of the retina) on central refractive development and posterior eye shape in chicks. Seventy-seven White Leghorn chicks were randomly assigned to receive superior (SRD, “Superior Retinal Deprivation” or inferior visual field deprivation, same principle applies for the following abbreviations, n = 17), inferior (IRD, n = 14), temporal (TRD, n = 23) or nasal hemiretinal (NRD, n = 23) form deprivation monocularly from day 5 to day 26. Central refractive errors, expressed as interocular difference in spherical equivalent (M), J0 and J45 astigmatic components, were measured using Hartinger refractometer at the beginning and weekly after treatment for 3 weeks. At the end of the treatment period, eyes of a subset of birds were enucleated and eye shape profile was photographed along four different meridians. These digital images were later processed to extract axial length (AL), equatorial diameter (ED), and AL/ED. For comparison purposes, the eye shape profile was also acquired from a separate group of birds reared with monocular full-retinal form deprivation (FRD, n = 10). The four hemiretinal form deprivations altered central ametropia and posterior eye shape to different degrees. The biggest contrast in M was found between SRD and IRD groups (mean ± SE after 3 weeks: SRD = −4.14 ± 0.71 D vs. IRD = +1.24 ± 0.36 D; p < 0.05), whereas subtle differences in J0 and J45 components were found across the four treatment groups (both p ⩽ 0.03). SRD group also showed significantly higher AL/ED ratio compared to IRD and NRD groups (0.76 ± 0.05 vs. 0.74 ± 0.07 and 0.75 ± 0.04; both p ⩽ 0.03). Furthermore, M was significantly correlated with AL/ED ratio in the treated eyes of hemiretinal treated chicks (r = −0.55, p < 0.001). Our results suggest that mechanism regulating central ametropia can be influenced by selectively interrupting the visual experience at different parts of visual field.

Binocular vision in strabismic humans with alternating fixation

Grating acuity, interocular suppression and binocular interaction were evaluated at different positions in the visual field of strabismic humans with alternating fixation. In all cases, the suppression of the deviated eye was most intense in a region corresponding to the fovea of the fixating eye, but reduced or absent in the periphery. In addition, suppression was found in part of the peripheral visual field of the fixating eye. For most subjects, the monocular properties of both eyes were normal. However, for one subject with a strong preference for one of the eyes, visual acuity and luminance detection were selectively impaired in the chronically suppressed regions of the non-preferred eye. Regardless of which eye was currently used for fixation, the visual information available to the subject came from both eyes. In parts of the visual field, the two eyes tended to replace each other. In the far periphery, and especially in the upper and lower hemifield, signals from the two eyes were often combined in a binocular perception of depth.

The Gelb Effect: Brightness Contrast Plus Attention

Early in twentieth century, a new approach to understanding of visual perception began to develop. This approach stressed importance of relations among parts of visual field and insisted that percept could not be explained in terms of elements impinging on retina. This is point inherent in writings of von Ehrenfels (1890) on 'Gestaltqualitat,' in early work of Wertheimer on phi phenomenon (1912), in formulation by Koffka (1935) of principles of organization of visual world, and in many demonstrations produced by 'Gestalt psychology.' The essence of point has been summed up in often quoted, and sometimes misquoted, statement that the whole is different from sum of its parts.

Characteristics of suppression in strabismus.

The ability of human beings to suppress or inhibit a part of the binocular visual field in strabismus, and only that part of the visual field which is confusing to visual orientation, is a remarkably subtle property. It is a wellknown fact that patients may have full binocular fusion in one position of gaze but, because of extraocular muscle noncomitancy, such as an overactive inferior oblique, may suppress a part of the binocular field in another position of gaze. The suppression is called upon only when needed. In concomitant strabismus, the region of suppression may be shown to have a border at the vertical decussation line through the macula (hemiretinal), which is its most constant, interesting, and clinically useful characteristic. It is the purpose of this paper to emphasize the clinical advantage of simplicity in testing procedures in the determination of the characteristics of suppression in strabismic patients, to outline

Traumatic Retinal Detachment Hypertension, Part of Visual Field Retained

An eye struck with a baseball showed dimness of vision that increased for two months when only light perception remained. A year later tension was increased but was brought below normal by iridectomy. After needling of lens the detached retina was seen but there was still light perception in the temporal field. Read before the Chicago Ophthalmological Society.