S.M. Berman

Human electroretinogram responses to video displays, fluorescent lighting, and other high frequency sources.

Time-averaged human electroretinogram (ERG) responses were determined for several workplace visual stimuli which are temporally modulated at rates exceeding the perceptual critical fusion frequency (CFF). A clearly identifiable synchronous response was in evidence for a video display terminal (VDT) stimulus operating with a refresh rate as high as 76 Hz. A directly viewed fluorescent luminaire with controllable driving frequency elicited a synchronous response at rates as high as 145 Hz. In addition, an intense stimulus created by modulating the light from a slide projector produced responses at least as high as 162 Hz. The implications of these high-frequency responses are representing a potential basis for visual symptoms are discussed.

Luminance-Controlled Pupil Size Affects Word Reading Accuracy

(510) 486-5682, Fax# (510) 486-6940 Neurobehavioral Laboratory Software 41 Rhinestone Terrace San Rafael CA 94121 2 Abratech Corporation 475 Gate Five Road, #255 Sausalito CA 94965 The present study extends our prior visual performance studies to word reading tasks presented at fixed high contrast (black print on white background), but with varying character size. Word reading is a complex resolution task which is representative of tasks in typical workplace environments. In the study presented below, we are examining the effect of pupil size on the letter sizeacuity function. Word reading acuity has been extensively used in vision research as a measure of visual performance and has been shown to correlate well with face recognition and other complex recognition tasks. In this study, the task is shielded from the surround lighting, allowing surround and task luminance to be controlled independently. Two pupil size conditions are compared, where pupil size is controlled by high or low luminance levels of a single surround illuminant. We chose to use a single illuminant to control pupil size to avoid changes in induced color which occur when pupil size is changed by varying the surround spectrum. The results here for 9 subjects ages 23 to 59 years replicate and extend our Landolt C studies and show again, that smaller pupils improve visual performance even though task -retinal illuminance is markedly reduced. In the study reported here, the improvement in visual performance with smaller pupils also more than compensates for increased disability glare present in the high luminance surround condition. LUMINANCE CONTROLLED PUPIL SIZE AFFECTS WORD READING ACCURACY S. Berman, G. Fein1, D. Jewett2, B. Benson2, T. Law2, and A. Myers2 Lawrence Berkeley Laboratory 1Neurobehavioral Laboratory Software University of California 41 Rhinestone Terrace Berkeley, CA 94720 San Rafael, CA 9412

PUPILLARY SIZE DIFFERENCES UNDER INCANDESCENT AND HIGH PRESSURE SODIUM LAMPS

Eight healthy young adult subjects produced significantly larger steady state pupil areas, as measured by infra-red pupillometry, when exposed to indirect lighting from high frequency high pressure sodium lamps compared to photopically matched levels of indirect incandescent lamps at three levels of luminance: 30, 60 and 90 candelas per meter squared (cd/m2). Three additional intensities were studied, which were not matched photopically between lamps. Analysis of all data showed that a scotopic spectral distribution accounted for pupil size better than either a photopic spectrum or an Alpern-Campbell pupillary response spectrum. Because pupil size can affect visual functioning, these results suggest that control of pupil size should be considered in lighting design and that the scotopic spectral output from lamps should be important in determining the effectiveness of a lighting environment. 14 refs., 15 figs., 3 tabs.

Energy and lighting

Advances in research for new types of lighting with increased efficacies (lumens/watt) are discussed in the following areas: (1) high‐frequency, solid‐state ballasts, (2) isotopic enhancement of mercury isotopes, (3) magnetic augmentation, (4) electrodeless, ultra‐high frequency, (5) tuned phosphors, (6) two‐photon phosphors, (7) heat mirrors, and (8) advanced control circuits to take advantage of daylight and occupancy. As of 1985, improvements in efficacy have been accomplished on an economic basis to save energy for (1) high frequency ballasts (25%), (2) isotopic enhancement (5%), and (8) advanced control circuits (up to 50%). Most of these advances depend on a deeper understanding of the weakly ionized plasma as a radiating and diffusing medium.

Spatial adaptation to text on a video display terminal

We employed vertical sinusoidal test gratings to search for spatial adaptation to lower‐case text presented on a standard video display terminal. The parameters of the contrast sensitivity test were selected on the basis of waveform analysis of horizontal spatial luminance profiles of the text. We found that subjects exhibited a small (4–5dB), but significant, frequency‐specific spatial adaptation consistent with the frequency spectrum of the stimulus. The theoretical and practical significance of this finding is discussed.

Visual performance at video display terminals--effects of screen color and illuminant type.

A limited set of illuminants and phosphor colors are commonly used in video display terminal (VDT) working environments. This study attempts to identify any combinations of such conditions that influence performance on a visually demanding counting task. Experiments were performed to test whether the phosphor color, ambient lighting spectrum, or temporal frequency characteristics of the display and ambient lighting could alter performance. Under conditions where potentially contaminating variables such as reflectance level and screen glare patterns were equalized, no significant differences in performance were produced by the particular sets of stimulus conditions tested. The results suggest that displays and illuminant types that are in common use allow substantially equivalent visual performance.

Location of nonlinear processes within the pupillary pathway

The pupil oscillates in synchrony with a slow beat produced by adding two lights flickering at slightly different frequencies. This behavior shows that nonlinear processes are present within the pathway. To localize these processes, a light of one frequency was presented to one eye, while a light of a different frequency was presented to the other. No pupil oscillations were seen in response to the beat in these dichoptic conditions, but when both lights were superimposed and presented to the same eye a powerful pupillary response was produced. We conclude that the nonlinearity giving rise to the pupils beat response occurs before the pathways from the two eyes join and hence is neural rather than muscular in origin. Furthermore, the lack of a pupil response in the dichoptic conditions suggests that the signals from the two eyes may combine linearly.

Spatial Adaptation On Video Display Terminals

Spatial adaptation, in the form of a frequency-specific reduction in contrast sensitivity, can occur when the visual system is exposed to certain stimuli. We employed vertical sinusoidal test gratings to investigate adaptation to the horizontal structure of text presented on a standard video display terminal. The parameters of the contrast sensitivity test were selected, on the basis of waveform analysis of spatial luminance scans of the text stimulus. We found. that subjects exhibited a small, but significant, frequency-specific adaptation consistent with the spatial frequency spectrum of the stimulus. Theoretical and practical significance of this finding are discussed.

A New Look at Models of Visual Performance

In this paper the authors argue that performance-visibility models are meaningless if “performance” is not strictly defined. The authors argument implies that there are serious conceptual problems in the new CIE visual performance model (CIE 19/2). They analyzed 1) optimization of performance with respect to time, 2) the problem of multiple tasks, and 3) the significance of ambiguous targets. The performance-visibility fits presented in CIE 19/2 are not correctly based on a physical model, and therefore in their present form should not be used as a basis for lighting recommendations.