VTechWorks staff will be away for the winter holidays starting Tuesday, December 24, 2024, through Wednesday, January 1, 2025, and will not be replying to requests during this time. Thank you for your patience, and happy holidays!

Browsing by Author "Bangor, Aaron W."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Display Technology and Ambient Illumination Influences on Visual Fatigue at VDT Workstations
    Bangor, Aaron W. (Virginia Tech, 2000-12-19)
    The concept of "visual fatigue" has been studied for 70 years or more. In that time, no single metric of measuring visual fatigue nor one agreed-upon set of tasks to induce visual fatigue has been settled upon. Not even a robust definition of visual fatigue has been established. This research worked to solve some of those problems. This research first set out to develop an index of visual fatigue that could be used effectively in quantifying the subjective experience of visual fatigue. Then it sought to create a set of measurable tasks, representative of office work, that would induce visual fatigue. Taking these two developments, an experiment using human participants was conducted to validate these developments and work toward solving two issues in the visual fatigue field: how visual display technology and ambient illumination affect the onset of visual fatigue. A 4x4 within-subjects design was developed and executed to study how these two independent variables affected ratings of visual fatigue, performance on the task battery, subjective image quality judgments, and contrast sensitivity shifts. Two cathode ray tube (CRT) and two active-matrix LCD (AMLCD) monitors were used in this study. While many instances of the monitors as a whole caused significant differences in reports of visual fatigue, performance, subjective image quality, and contrast sensitivity loss, only a slight effect of display technology was found. Four of eleven visual fatigue and two of eight subjective image quality dimensions showed that the LCD monitors induced more visual fatigue and were rated poorer than the CRT monitors. Ambient illumination levels of 0, 300, 600, and 1200 lux affected all four groups of dependent variables. On the whole, lighting caused visual fatigue, with "watery eyes" and "glare from lights" being adversely affected by brighter lighting. The 0 and 1200 lux were associated with the worst performance, while 300 lux was associated with the best performance. Subjective image quality was affected by lighting, with increasing lighting causing bothersome screen reflections and more temporal (e.g., flicker and jitter) distortions; 600 lux induced more reports of image sizing anomalies. Finally, it caused significantly worse shifts at the 6.0 c/deg spatial frequency on the contrast sensitivity test. The data show that lighting of 300 lux is the best of these four illumination levels. The results of this study not only contribute to the body of research in the areas of display technology and ambient illumination, but several developments of this research are offered to the research community: a complete survey metric of visual fatigue, a standardized battery of tasks for studying visual fatigue and image quality, and a comprehensive subjective image quality survey.
  • Thumbnail Image
    Improving Access to Computer Displays: Readability for Visually Impaired Users
    Bangor, Aaron W. (Virginia Tech, 1998-08-06)
    In the field of human factors engineering the issue of how to present electronic text to people has been studied intensely for over 35 years. However, one major consideration that has largely been overlooked in these studies is how visual impairments affect reading of computer text. Specifically, the issue of how text can be modified to improve readability of CRTs for individuals with low vision. A 2x5x2x3 (visual capability, font size, polarity, and contrast) mixed-factor, repeated-measures experimental design was used to determine if changes in font size, contrast polarity, and/or contrast can improve reading speeds and reduce error rate for people with low vision. The results of this experiment show that alterations in text can be made that do not affect unimpaired vision readers while dramatically improving the reading capabilities of the impaired vision population. For character size, 12 and 14 point font sizes were found to be too small for the visually impaired population examined. In general, 18 and 30 point font sizes were equal to each other and to the 24 point font size, but for some interactions these two were found to produce longer response times and higher error rates. Thus, a 24 point font size is recommended. Unlike previous research with visually impaired participants, this experiment found that negative (white-on-black) polarity worsened reading performance. It is thought that this discrepancy is a result of polarity's interaction with small font sizes. For this reason, it is recommended that for font sizes of 18 points and below, positive polarity should be used. For 24 and 30 point sizes either polarity is satisfactory, though previous research (Legge, Pelli, Rubin, and Schleske, 1985b; NRC, 1995; Rubin and Legge, 1989) suggests negative polarity might be better for some visually impaired readers.. Contrasts of 3:1, 7:1, and 18:1 were used in this experiment and had no significant effect for either vision group. However, contrast did significantly interact with both font size and polarity. For font sizes of 18 points or below, it is recommended that contrasts of 18:1 be used for either polarity, but this is very important if negative polarity is used. The above recommendations are based on a small group of impaired vision readers. Visual impairments vary widely and the sample used in this experiment represented only a portion of them, with respect to both cause and severity. Wherever possible, computer text should be tailored to the unique needs of its users.