/pdf/collision-course-the-hazards-of-lighted-structures-and-43glfuzipo.pdf

Collision Course: The Hazards of Lighted Structures and Windows to Migrating Birds

The schematic eye ofStrix aluco, a nocturnal owl species, is described. A comparative and ecological context is used to examine the relationships between optical parameters of the eye and its light gathering and resolving powers. It is concluded that the essentially ‘nocturnal’ feature of the owl eye does not lie in either its light gathering power or the sensitivity of individual rod receptors. Differences in visual performance at low light levels between the owl and the diurnal pigeon appear to be attributable to differences in the retinal neural integration mechanisms of the two species. However, it is hypothesised that the neural mechanisms which mediate the extraction of spatial information from the retinal image throughout the nocturnal luminance range, can function in the owl eye only because of its absolutely large sized retinal image. Thus the primarily nocturnal feature of the owl eye is its absolutely large posterior nodal distance, retinal image brightness is maximised only as a secondary feature.

An owl's eye: Schematic optics and visual performance inStrix aluco L.

On the localization of troxler's effect in the visual pathway

1. Extrafoveal decremental and incremental visual thresholds have been measured with a circular test-object of 57′ diameter, an exposure time of 0·1 sec and background luminance ranging from 2·5 to 7·3 log. quanta (equivalent to 507 nm) per second per square degree at the cornea.

2. The decremental threshold is lower than the incremental threshold by factors up to 0·4 log. unit when the background luminance is low; and the two thresholds are virtually the same when the background luminance is high.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1966.sp008007

Decremental and incremental visual thresholds

The squint response corresponding to photophobia (light-induced discomfort) was assessed via electromyography as a function of stimulus size, retinal locus (superior, inferior, temporal, nasal), and retinal eccentricity in three subjects. These results were compared to the same subjects' psychophysically-determined spatial distributions of macular pigment, to examine in detail the attenuation of photophobia by macular pigment. Results indicate that the photophobia response is preferentially biased to prevent the fovea from exposure to potentially damaging short-wavelength light. In this regard, macular pigment appears to act as a spatially-integrated filter, serving to attenuate photophobia to a great extent. Photophobia and macular pigment therefore appear to serve a "tandem" function of foveal photoprotection. Spatial summation for photophobia to long-wavelength "orange" light was found to be linear and somewhat greater than that dictated by Piper's law. The spatial summation functions derived from broadband xenon-white lights are more complicated, with two or perhaps three different branches. It is suggested that xenon-white light, which contains much short-wave energy, interacts with macular pigment (which absorbs short-wave energy) to give rise to the different branches of summation found in this function. The present study provides data that are suggestive of the pathways that gives rise to the photophobia response. A close correspondence was found between the degree of spatial summation determined for photophobia and the dendritic area of two kinds of retinal ganglion cell, parasol and small bistratified. Moreover, the spatial densities of parasol and small bistratified ganglion cells were found to decline in a fashion commensurate with the photophobia response, as a function of retinal eccentricity. These findings suggest that photophobia is mediated via a combination of parasol and small bistratified ganglion cells; hence the magnocellular and koniocellular visual pathways are implicated as channeling the visual signals that eventually give rise to photophobia.

/pdf/spatial-properties-of-photophobia-48k5xdpiz4.pdf

O'doherty Ef

Papers

Individual differences in night-vision efficiency.