Filling-in percepts produced by luminance modulation.

M A Paradiso; S Hahn

doi:10.1016/0042-6989(96)00033-8

Home/Archive/PubMed

PubMed · 8917752

Filling-in percepts produced by luminance modulation.

M A Paradiso·S Hahn

View original source ↗Export metadata ↓

Abstract

We report that when the luminance of a homogeneous spot of light is gradually increased or decreased, there are conditions in which the brightness of the spot is spatially nonuniform. When the spot luminance is increased, brightness changes in the spot's center lag behind changes at the edge and brightness appears to sweep inward. Conversely, if the luminance of the spot is decreased, there is a relative lag in the darkening toward the center of the spot and darkness seems to spread inward. In Experiment 1 we found that with both increasing and decreasing luminance sweeps, the strength of the brightness filling effects was strongest with luminance sweep durations of 0.25-0.5 sec. In Experiment 2, the sweep duration was held constant at 0.5 sec; the filling effect was seen when the dwell time spent at each luminance step was less than about 100 msec, but nonuniformities were not observed at longer dwell times. In Experiment 3, a spot of light was positioned to surround the optic disk in one eye. Surprisingly, when the spot was luminance modulated from bright to dark, darkness appeared to sweep from the edge to the center of the modulated disk, even though most of the disk's interior was imaged on a portion of the retina devoid of photoreceptors. These findings are consistent with the hypothesis that a neural filling-in mechanism in visual cortex plays a key role in brightness perception.

Explore related subjects

Darkness Humans Light Male Optic Disk Time Factors Vision, Binocular Vision, Monocular Visual Perception Journal Article Research Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

M A Paradiso, S Hahn. 1996. Filling-in percepts produced by luminance modulation.. https://doi.org/10.1016/0042-6989(96)00033-8

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2006

Reactive oxygen species generation through NADH oxidation by 6-formylpterin derivatives in the dark.

6-formylpterin (6FP) has been reported to produce reactive oxygen species (ROS) such as *O2- and H2O2 from O2 in the presence of NADH under light condition. In the present study, we prepared a variety of 6FP derivatives and found that 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-pivaloylpteridin-4-one and 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-methylpteridin-4-one, in which the 2-amino groups are modified by a dimethylaminomethylene group and the 3-positions by pivaloyl and methyl groups and 2-amino-6-formyl-3-methylpteridin-4-one in which the amino group at the 2-position is free and the 3-position is modified by a methyl group generated H2O2 from O2 on oxidation of NADH to NAD+ in the dark. However, 6FP and 2-(N,N-dimethylaminomethyleneamino)-6-formylpteridin-4-one, in which the 3-position is free did not yield H2O2. These results indicate that modification of the 3-position is essential to make the activities of 6FP available in the dark and would be suggestive for designing pharmaceutical compounds that generate appropriate and controllable amounts of ROS in vivo.

Darkness↗

PubMed2006

Very strong UV-A light temporally separates the photoinhibition of photosystem II into light-induced inactivation and repair.

When organisms that perform oxygenic photosynthesis are exposed to strong visible or UV light, inactivation of photosystem II (PSII) occurs. However, such organisms are able rapidly to repair the photoinactivated PSII. The phenomenon of photoinactivation and repair is known as photoinhibition. Under normal laboratory conditions, the rate of repair is similar to or faster than the rate of photoinactivation, preventing the detailed analysis of photoinactivation and repair as separate processes. We report here that, using strong UV-A light from a laser, we were able to analyze separately the photoinactivation and repair of photosystem II in the cyanobacterium Synechocystis sp. PCC 6803. Very strong UV-A light at 364 nm and a photon flux density of 2600 micromol photons m(-2) s(-1) inactivated the oxygen-evolving machinery and the photochemical reaction center of PSII within 1 or 2 min before the first step in the repair process, namely, the degradation of the D1 protein, occurred. During subsequent incubation of cells in weak visible light, the activity of PSII recovered fully within 30 min and this process depended on protein synthesis. During subsequent incubation of cells in darkness for 60 min, the D1 protein of the photoinactivated PSII was degraded. Further incubation in weak visible light resulted in the rapid restoration of the activity of PSII. These observations suggest that very strong UV-A light is a useful tool for the analysis of the repair of PSII after photoinactivation.

Darkness↗

PubMed2006

Does seasonal variation affect hallucinations in PD? A longitudinal study.

The objective of this study was to examine the chronobiology of visual hallucinations in Parkinson's disease (PD) patients to test whether hallucinations are more severe during darker months (winter) than summer months. We extracted longitudinal data on the UPDRS Thought Disorder (TD) score, taken as part of regular patient management on sequential visits through a 1-year cycle in hallucinating PD patients. To reduce the confounding effects of medication adjustments, analysis was restricted to patients with a baseline evaluation that did not involve a medication change. The primary outcome was the seasonal change in hallucination severity, defined as a change in TD score or neuroleptic use. Using Wilcoxon rank-sum tests, we compared the exacerbation of hallucination by season, focusing on winter (December through February) versus summer (June through August). A total of 51 hallucinating patients met entry criteria, and their longitudinal data were analyzed. There was no difference in hallucination severity with changing season; the level of wintertime exacerbation was no greater than summertime exacerbation (P = 0.42). Although hallucinations frequently develop in dimmed environments and evening hours, the darkness of wintertime does not exacerbate hallucinations in PD subjects on stable medications. Because we found no evidence of seasonal variations, we cannot recommend phototherapy or other strategies affecting chronobiological systems as research priorities to treat PD hallucinations. (c) 2006 Movement Disorder Society.

Darkness↗