Foveal

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

Foveal cone pigment density difference and reflectance in retinitis pigmentosa

Abstract: • Cone pigment density difference refers to a change in light absorption by cones before and after bleaching of their visual pigments. With a television ophthalmoscope image processor, we measured the foveal cone pigment density difference in patients with retinitis pigmentosa (RP), good central vision, and no clinically apparent foveal lesion. Foveal reflectance was obtained at 12 different wavelengths of illumination. Compared with similar-aged normal subjects, most patients with dominantly inherited RP had normal or minimally reduced cone pigment density difference within the central fovea, relatively lower than normal density difference at the foveal margin, and increased foveal reflectance. Compared with these normal subjects, patients with recessively inherited RP had significantly reduced cone pigment density difference within the central fovea, relatively more normal density difference at the foveal margin, and normal foveal reflectance.

Chapter 4 – Saccadic Selectivity During Visual Search: The Influence of Central Processing Difficulty

Abstract: Publisher Summary This chapter examines the robustness of guidance of eye movements during visual search. Visual search is one of the dominant paradigms used for investigating visual attention. In a typical visual search task, participants have to decide whether a search display contains a designated target among distractors (nontarget elements). Consistent with major visual search theories, experiments discussed in the chapter demonstrate that participants direct their saccades selectively during the search process, revealing a strong correspondence between target-distractor similarity and saccadic frequency toward the respective distractors. While the duration of current fixations increased with increasing target-distractor similarity, there was no evidence that saccadic selectivity was influenced by the target-distractor similarity of the previously fixated display item or the duration of the previous fixation. These findings are inconsistent with the predictions by the waiting-room model. The chapter manipulates the difficulty of the central discrimination by introducing a concurrent visual task and presenting a gaze-contingent moving foveal mask. Although manipulations substantially degraded the overall visual search performance, the magnitude of peripheral selection was not affected. This is not consistent with the notion that the central discrimination and the peripheral analysis share the same pool of attentional resources as suggested by the foveal load model. Thus, these experiments provide convergent evidence that peripheral selection is a robust process, largely independent of the central processing difficulty.

Foveal vs. parafoveal attention-grabbing power of threat-related information.

Abstract: We investigated whether threat words presented in attended (foveal) and in unattended (parafoveal) locations of the visual field are attention grabbing. Neutral (nonemotional) words were presented at fixation as probes in a lexical decision task. Each probe word was preceded by 2 simultaneous prime words (1 foveal, 1 parafoveal), either threatening or neutral, for 150 ms. The stimulus onset asynchrony (SOA) between the primes and the probe was either 300 or 1,000 ms. Results revealed slowed lexical decision times on the probe when primed by an unrelated foveal threat word at the short (300-ms) delay. In contrast, parafoveal threat words did not affect processing of the neutral probe at either delay. Nevertheless, both neutral and threat parafoveal words facilitated lexical decisions for identical probe words at 300-ms SOA. This suggests that threat words appearing outside the focus of attention do not draw or engage cognitive resources to such an extent as to produce interference in the processing of concurrent or subsequent neutral stimuli. An explanation of the lack of parafoveal interference is that semantic content is not extracted in the parafovea.

Visual evoked potentials (VEP) elicited by checkerboard versus foveal stimulation in multiple sclerosis. A clinical study in 235 patients.

Abstract: In 235 patients with suspected multiple sclerosis (MS) the diagnostic value of visual evoked potentials (VEP) elicited by checkerboard and central foveal stimulation was compared. No significant difference was found. Both methods are supplementary in diagnostic value. Foveal stimulation may provide an additional diagnostic clue. Normal VEPs do not exclude a prior retrobulbar neuritis. Electronystagmography and examination of CSF are at least essential for the diagnosis of MS as VEPs. The combination of these methods increase the accuracy of diagnosis.

The avascular zone and neuronal remodeling of the fovea in Parkinson disease.

Abstract: Inner foveal thinning and intracellular alpha-synuclein were demonstrated in the retina in Parkinson disease. While pathognomonic alpha-synuclein is associated with embryonic dopaminergic (DA) neurons, postmortem studies in the nervous system and retina show prominent effect also in non-DA neurons. We evaluated foveal capillaries and foveal thickness in 23 Parkinson disease subjects and 13 healthy controls using retinal fluorescein angiography and optical coherence tomography. The size of the foveal avascular zone inversely correlates with foveal thinning. Foveal thinning highly correlates with motor impairment and also disease duration. Quantifying capillary and neuronal remodeling could serve as biological markers.