Optimising the glaucoma signal/noise ratio by mapping changes in spatial summation with area-modulated perimetric stimuli

Identification of glaucomatous damage and progression by perimetry are limited by measurement and response variability. This study tested the hypothesis that the glaucoma damage signal/noise ratio is greater with stimuli varying in area, either solely, or simultaneously with contrast, than with conventional stimuli varying in contrast only (Goldmann III, GIII). Thirty glaucoma patients and 20 age-similar healthy controls were tested with the Method of Constant Stimuli (MOCS). One stimulus modulated in area (A), one modulated in contrast within Ricco's area (C R ), one modulated in both area and contrast simultaneously (AC), and the reference stimulus was a GIII, modulating in contrast. Stimuli were presented on a common platform with a common scale (energy). A three-stage protocol minimised artefactual MOCS slope bias that can occur due to differences in psychometric function sampling between conditions. Threshold difference from age-matched normal (total deviation), response variability, and signal/noise ratio were compared between stimuli. Total deviation was greater with, and response variability less dependent on defect depth with A, AC, and C R stimuli, compared with GIII. Both A and AC stimuli showed a significantly greater signal/noise ratio than the GIII, indicating that area-modulated stimuli offer benefits over the GIII for identifying early glaucoma and measuring progression

Color comparisons and interpersonal variation

An important challenge to color objectivists, who hold that statements concerning color are made true or false by objective (non-subject-involving) facts, is the argument from interpersonal variation in where normal observers locate the unique hues. Recently, an attractive objectivist response to the argument has been proposed that draws on the semantics of gradable adjectives and which does not require defending the idea that there is a single correct location for each of the unique hues (Gómez-Torrente, 2016). In Hansen (2015), I argued that the recent objectivist response doesn’t apply to comparative occurrences of color adjectives, so a revised, comparative, version of the argument from interpersonal variation remains a powerful objection to certain types of objectivism. In this paper, I address several unsatisfactory objectivist replies to the comparative version of the argument from interpersonal variation, and offer what I think is a more plausible objectivist reply to the comparative argument from interpersonal variation

Additivity of spatially induced blackness.

Tests of additivity of the postreceptoral pathways that mediate the perception of blackness were conducted under conditions of spatial contrast. Observers increased the radiance of a surrounding annulus until a broadband (white) test center appeared completely black. Additivity tests with heterochromatic flicker photometry (HFP) and direct brightness matching were also conducted for each observer. The results indicated that the luminance level of the annulus required to induce blackness did not change with variations in spectral composition. Results consistent with additivity were also obtained for HFP, but the results from brightness matching were not consistent with additivity. The data support the view that the perception of blackness is mediated by neural mechanisms that additively combine the input of middle- and long-wave photoreceptors

Perception of blackness.

We sought to measure the mechanisms underlying the perception of blackness in the following way. A central spot (45') of fixed luminance was surrounded by a dark ring (7.5'), and surrounding all was an annular zone (30') of light. This stimulus was presented in Maxwellian view for 0.5 sec every 3 sec. The radiance of the annulus required to make the central area (spot and ring) appear uniformly black was measured for different wavelengths (440-660 nm) of the annulus. These measurements were made for test spots that were either broadband or of wavelength 480, 500, 580, or 660 nm. In all conditions the measured spectral efficiency of induced blackness matched the inverse of the V lambda function. Using the same stimulus, we have also measured increment-threshold functions. For a fixed luminance of the spot, the radiance of the surrounding annulus required to bring the central spot to threshold was measured. These increment-threshold functions do not match the V lambda or blackness functions. Our results show that induced blackness is inversely related to the luminous efficiency function and that the spectral efficiency of induced blackness is distinct from the increment-threshold function measured under these conditions. Furthermore, blackness appears to be independent of the wavelengths of the inducing annulus as well as of the central spot. Thus these results link induced blackness to the luminance pathway and argue against the involvement of the chromatic pathways in the perception of blackness