Feature search in persons with severe visual impairment.

Feature search performance was measured in visually impaired (VI) and age-matched controls with normal vision (NV). All VI subjects were legally blind. The task was to search for a 2 degrees x 2 degrees square target among smaller 1 degrees x1 degrees distracters. Targets and distracters were white and presented on a dark background that subtended 69 degrees by 58 degrees . Three field-sizes (10 degrees , 20 degrees , and 40 degrees ) and three set sizes (8-, 16-, and 32-items) were tested. The VI subjects searched more slowly than the NV subjects, but the reaction time of both groups of subjects did not rise with increasing number of items. The latter is consistent with a parallel search. Both groups searched more slowly when field-size increased, but the VI group was affected more by the increase than the NV group.

Colour thresholds in dichromats and normals.

Studies indicate dichromats detect large, long duration spectral increments presented on bright white backgrounds with a blue-yellow colour opponent mechanism. Since opponent processes signal colour, we hypothesized that under these viewing conditions dichromats should perceive spectral increments as coloured at detection threshold. Psychophysical detection and colour discrimination thresholds were determined for normal and dichromatic humans. Test stimuli were 2 degrees, 200 ms increments presented upon a white, 1000 td, spatially coincident background. As expected, normal observers were able to discriminate between white and spectral flashes at intensities near detection threshold intensities. Dichromatic observers required suprathreshold ( approximately 0.30 log units) stimulus intensities to discriminate between the white and spectral flashes. The results do not support our hypothesis and alternative explanations for the elevated colour discrimination thresholds in dichromats are discussed.

Aging-related foveal flicker sensitivity losses in normal observers.

Photopic flicker sensitivity for healthy subjects over 60 years of age was compared with that of subjects in their 20s and 30s. The stimulus was achromatic and viewed foveally through a 2.0-mm artificial pupil which assured a constant pupil size in all subjects. As a group, older subjects had lower flicker sensitivity than younger subjects. This was found even when the retinal illuminance difference between age groups that arises from increased lens absorption in older adults was taken into account. The results indicate that a reduction in retinal illuminance with age cannot account for all the flicker sensitivity losses in older adults.

Effect of short wavelength absorbing filters on Farnsworth-Munsell 100 Hue test and hue identification task performance.

The influence of four short wavelength absorbing filters (yellow filters) on performance of the Farnsworth-Munsell 100-Hue test and three hue identification tasks was assessed in 10 color-normal observers. The yellow filters included the NoIR 40% Amber, Vuarnet No. 4006, Corning CPF 550, and Blu Blocker. A neutral density filter and a no-filter condition served as comparisons. Results showed that the Vaurnet, CPF 550, and Blu Blockers significantly lowered performance on the Farnsworth-Munsell 100-Hue test and the color-dependent tasks below levels obtained in either the neutral-density filter or no-filter conditions.

D-15 performance with short wavelength absorbing filters in normals.

Short wavelength absorbing filters (SWAF's) have become very popular in the prescription and commercial sunglass markets. Like other chromatic filters SWAF's have the potential to alter color vision. Performance on the Farnsworth Panel D-15 (D-15) test was measured to determine whether any of 4 popular SWAF's, in the form of sunglasses, produced color vision changes in 22 color normal adults. Using standard illuminant C, observers were tested under the following conditions: wearing no filter, a 1.0 log unit neutral density filter (NDF), or one of the following SWAF's: Corning CPF 550; NolR Amber 40%; Blu Blocker; and Vuarnet 4006. In addition, the Vuarnets were tested outdoors in shaded daylight to determine the effects of increased illumination. The NDF served as the control and had no effect on D-15 performance. Compared to it, only the Blu Blockers and Vuarnets affected D-15 cap arrangements for these SWAF's significantly. Blu Blocker error patterns had no predominant axis, whereas the predominant axis of errors in both Vuarnet conditions was tritan. Results of quantitative analysis performed on three factors confirmed these findings and indicated the Blu Blockers and Vuarnet SWAF's caused moderate and moderate-to-severe levels of color confusion, respectively. Increasing the illumination level improved performance with the Vuarnets, but it remained significantly outside the normal range.

Ability of deutan color defectives to perform simulated air traffic control tasks.

Air traffic controllers perform a variety of tasks which require them to identify, discriminate, and name colors. Qualification standards for this occupation require applicants and incumbents to have normal color vision. The validity of this standard has been questioned and is currently under review. In this study, 22 deutans and 78 normals were tested on a set of tasks which simulated critical tasks performed daily by air traffic controllers. The four tasks included discriminating red from black pencil marks on flight progress strips, color-naming of 1 degree and 0.1 degree discs, and identification of colored line segments embedded in a multicolored background. Deutans classified as mild were found to perform all tasks as well as normals. Moderate deutans performed only the large disc color-naming task as well as normals, whereas severe deutans performed none of the tasks as well as normals. Different methods for scoring the color vision tests were explored to determine their value as predictors of task performance. The D-15 relative error score was found to be the single best predictor of performance on the tasks (r-square = 0.602). It is concluded that mild deutan color defectives have adequate color vision for safe performance of several critical air traffic control tasks. Moderate and severe deutans do not. In addition, the results of several methods for scoring color vision tests can be used to predict group, but not individual, performance with high reliability.

The ability of protan color defectives to perform color-dependent air traffic control tasks.

Air traffic controllers perform a variety of tasks which require them to identify, discriminate and name colors. Qualification standards for this occupation require applicants to have normal color vision. Although the validity of this standard has been questioned, Adams and Tague recently presented evidence in this Journal (1985;62:744-50) that protanopes cannot perform color-dependent air traffic control tasks reliably. In our study, the results of 7 severe and 2 moderate protans are compared to those of 78 normals on a set of tasks which simulated critical tasks performed daily by air traffic controllers. The four tasks included discriminating red from black pencil marks on flight progress strips, color-naming of 1(0) and 0.1(0) discs, and identification of colored line segments embedded in a multi-colored background. The severe protans we tested performed none of the tasks as well as normals. While the performance of the moderate protans was better, statistical conclusions could not be drawn. Our set of tasks bears many similarities to the set used by Adams and Tague and it appears we were trying to answer the same questions. The results of the two studies are similar and the conclusions are the same: severe protans cannot perform color-dependent air traffic control tasks reliably.

Effects of monocular deprivation on the lateral geniculate nucleus in a primate.

In many mammalian species, rearing with one eyelid closed produces a loss of vision in the deprived eye and a change in cell size in the lateral geniculate nucleus (LGN). In cats, the reduction in the size of deprived LGN cells has been correlated with a loss of one functional class of cells, Y cells. In primates, such as galago, LGN cells also exhibit marked changes in size with deprivation. In the present study we recorded from single cells in the LGN of monocularly deprived galagos to determine if such changes in cell size would be accompanied by changes in physiological properties. The results revealed no alterations in the distribution or functional properties of any cell class. The differences in the effects of monocular deprivation on the function of LGN cells in cats and primates are most easily explained by a fundamental difference in visual system anatomy. In cats, different classes of retinal afferents (X vs. Y) are in a position to compete for postsynaptic LGN neurons: in primates, segregation of cell classes into different layers may preclude such developmental interactions.

Spectral sensitivity of the peripheral retina to large and small stimuli.

Increment-threshold spectral sensitivity functions were taken foveally and at four other retinal locations with different sized test stimuli. For the fovea and parafovea at 4 degrees, a 1 degree, 250 msec stimulus of variable wavelength, flashed on a 1000 td white background yielded spectral sensitivity curves with three distinct maxima located near 455, 530-540 and 600 nm. As eccentricity increased so did the minimum spot size needed to produce spectral curves with three peaks. In particular, the 2 degrees 10' spot at 20 degrees, 4 degrees 10' at 30 degrees and 5.5 degrees at 45 degrees gave this result. Smaller stimuli in the periphery yielded curves with a minor peak at 455 nm, present under some conditions, and a major broad peak at 560 nm that resembled the CIE photopic luminosity function. Two different systems subserve detection: the three-peaked curves indicate mediation by the opponent-color system while the other type of function can be attributed to the non-opponent system.