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This study evaluated the potential effectiveness of screen filters in relieving visual fatigue. Critical flicker frequency (CFF), accommodation power, visual acuity, and subjective rating of visual fatigue were evaluated at four different stages: without screen filter, screen filter use of 2.5 mo., 5 mo., and 12 mo. For each stage, all measurements were taken before and after an 8-hr. workday. Analysis of variance was performed to test whether the screen filter use or measurement time had a significant effect on any of the visual fatigue measurements. The results indicated visual acuity was significantly improved after the use of a screen filter, while after the screen filter was installed, the CFF reading showed visual fatigue was more pronounced. Significant improvement in subjective ratings of double vision on screen was found after the screen filter use of 2.5 mo., but improvements disappeared after continuous use at 5 too. A Hawthorne effect could have contributed to the short-term relief in visual fatigue and inconsistent findings in other visual performance measurements. Sorting out frequently used questions into a few definable areas and data sets might reduce the screen viewing time and visual fatigue more effectively.

The study derived seven descriptors from the pixel matrices of both the uppercase and lowercase forms of the 26 letters in the English alphabet in the regular and italic versions of the most commonly used font, Times New Roman. A factor analysis of the seven descriptors showed that a two-factor solution of letter width and height explained 76.6% of the variance. Legibility threshold of the 26 letters in the regular and italic Times Roman font and in two-case forms were collected to specify effects of letter width and height. 20 university students, 10 women and 10 men, with a mean age of 24.1 yr. (SD = 1.6) participated. They identified letters displayed initially on a PC screen at a minimum font size and enlarged gradually until the participant correctly recognized the letter. Analysis showed letters of greater width or height were more legible than those of smaller width or height. Given an oblique effect, letters in the italic Times Roman font had significantly greater width but were less legible than those in the regular font.

Potential ergonomic hazards for 27 disabled call center agents engaged in computer-telephone interactive tasks were evaluated for possible associations between the task behaviors and work-related disorders. Data included task description, 300 samples of performance, a questionnaire on workstation design, body-part discomfort rating, perceived stress, potential job stressors, and direct measurement of environmental factors. Analysis indicated agents were frequently exposed to prolonged static sitting and repetitive movements, together with unsupported back and flexed neck, causing musculoskeletal discomforts. Visual fatigue (85.2% of agents), discomfort of ears (66.7%), and musculoskeletal discomforts (59.3%) were the most pronounced and prevalent complaints after prolonged working. 17 of 27 agents described job pressure as high or very high, and dealing with difficult customers and trying to fulfill the customers' needs within the time standard were main stressors. Further work on surrounding noise, earphone use, possible hearing loss of experienced agents, training programs, feasible solutions for visual fatigue, musculoskeletal symptoms, and psychosocial stress should be conducted.

The current experiment tested the aiming accuracy of the eye for targets at nine different positions and of two different sizes. The left eye was tracked to record the line of gaze with an infrared eye-monitoring device. For each subject, horizontal shift, vertical shift, standard deviations of the X and Y coordinates, and 95th percentile of the horizontal and vertical shifts from the nine target centers were calculated to indicate the precision, accuracy, and possible design limits of the gaze points. Analysis showed that the target's position had a strong effect on the vertical shift, standard deviations of the Y coordinate, and 95th percentile of the vertical shift. The effect of target size was not significant on any of the dependent measures. The research findings have important implications for the redesign of the gaze-pointing device. Visual targets appearing below the horizontal line of sight should be larger than those above. based on the 95th percentile of the horizontal and vertical shifts, targets should be approximately 2.0 [degrees] wide and 2.4 [degrees] long above or coinciding with the horizontal line of gaze and 2.6 [degrees] wide and 3.9 [degrees] (cm) long below the horizontal line of gaze.

The current experiment examined the speed-accuracy trade-off of saccadic movement between two targets. Ten subjects looked alternately at two targets as fast and as accurately as possible for 2 min. under different conditions of target size, distance between targets, and direction of eye movement. Saccadic movement of the left eye was tracked and recorded with an infrared eye monitoring device to compute the starting position, ending position, and duration of each saccadic movement. Eye-movement time was significantly related to target size and distance between targets, but the speed-accuracy trade-off was significantly different from that predicted by Fitts' Law. Reaction time was not significantly changed by the direction of eye movement.

This research investigated human visual sensitivity and bias in inspecting irregular objects. A preliminary study was conducted using the method of constants to determine the threshold value for judgment of size. A factorial experiment was conducted using payoffs, rate of defective items, and detectability in the signal-detection theory as the factors. In total, eight experimental conditions were tested. 10 college students were recruited as subjects. Each subject was asked to compare 40 teapot shapes to a standard teapot shape under eight experimental conditions. Defective shapes were generated by lengthening the vertical dimension of a standard teapot shape by a factor of 1.01 and 1.04 for 'low' and 'high' detectability. The decision time and responses of 'identical' or 'different' were collected under all experimental conditions. Analysis indicates that the decision-making strategy used to inspect this irregular object was very close to maximizing the accuracy of decision-making by considering the rate of defective items. This result is different from most research findings in signal-detection theory in which responses of human beings are similar to degraded Bayes optimizers. The standard deviation of the signal distribution was about 1.30 and 1.41 times that of the noise distributions for 'low' and 'high' detectability.

The current study investigated occupational risk of handicapped workers relative to nonhandicapped workers and used the standardized mortality ratio as an index that handicapped workers were at elevated risk for occupational injury. A total of 6,327 records of disabling occupational injuries beyond first aid treatment from January to December, 1999 were collected and analyzed. The ratio of the standardized mortality ratio of the handicapped vs nonhandicapped workers indicated that occupational injury risk of handicapped workers must be seriously examined for the reasons for this unexpectedly high occupational risk.

The current study measured the critical elements of jobs and characterized the jobs' suitability for aging workers based on ratings of those elements. The sample consisted of 830 job titles collected by the Employment and Vocational Training Administration in Taiwan. For each job the ratings of 45 specific variables, falling into three major classes, were factor analyzed, using principal components analysis with varimax rotation. A nine-factor solution explained 50.1% of the variance. Using a nonhierarchical clustering procedure, 830 jobs were classified into three homogeneous clusters which were significantly different on nine factors except for Manual Dexterity. Mapping the ratings on the 9 factors and the characteristics of aging workers, the four job clusters were defined as Age-enhanced, Age-neutral, and Age-counteracted, and Age-impaired to describe the suitability for aging workers.