Cross validation of measures of handle/human fit.

The problem of measurement of effectiveness of handle design was addressed directly by scales. Ratings on several subjective scales were used and compared with maximum force exertion capabilities and grip force efficiency. Three of the handles were selected by overall preference ranking and tested using the Point of Subjective Equality (PSE) measure proposed by Hsia and Drury (1986). Factor analysis revealed two orthogonal factors, one related to overall preference and one related to strength. The PSE measure failed to give significant results.

A further note on psychophysical testing of handles.

The psychophysical method of constants was applied to two-handed lifting. A sequence effect was found, with subject's response biased toward which stimulus was presented most recently. This sequence effect drastically reduced the sensitivity of the method for two-handed lifting, so that a further study of comparing sequential and simultaneous lifting was conducted. The results indicated that simultaneous lifting was significantly more sensitive to changes in handle design.

Task analysis for computer-aided design (CAD) at a keystroke level.

The purpose of this research was to develop a new model to describe and predict a computerized task. AutoCAD was utilized as the experimental tool to collect operating procedure and time data at a keystroke level for a computer aided design (CAD) task. Six undergraduate students participated in the experiment. They were required to complete one simple and one complex engineering drawing. A model which characterized the task performance by software commands and predicted task execution time using keystroke-level model operators was proposed and applied to the analysis of the dialogue data. This task parameter model adopted software commands, e.g. LINE, OFFSET in AutoCAD, to describe the function of a task unit and used up to five parameters to indicate the number of keystrokes, chosen function for a command and ways of starting and ending a command. Each task unit in the task parameter model can be replaced by a number of primitive operators as in the keystroke level model to predict the task execution time. The observed task execution times of all task units were found to be highly correlated with the task execution times predicted by the keystroke level model. Therefore, the task parameter model was proved to be a usable analytical tool for evaluating the human-computer interface (HCI).

Speed and accuracy of eye-gaze pointing.

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.

Differential threshold of length and response criterion for inspecting irregular objects.

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.

Ratings of 830 jobs on 45 characteristics: factor and cluster analyses into age-enhanced, age-neutral and age-counteracted, and age-impaired categories.

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.

Aiming accuracy of the line of gaze and redesign of the gaze-pointing system.

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.

Risk for occupational injury of handicapped workers in Taiwan.

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.

A comparison of seven visual fatigue assessment techniques in three data-acquisition VDT tasks.

We compared 7 methods of measuring visual fatigue--accommodation power, visual acuity, pupil diameter, critical fusion frequency (CFF), eye movement velocity, subjective rating of visual fatigue, and task performance--for their sensitivity to visual load. In the experiment, 10 participants performed a monitoring task at 2 viewing distances, read articles under 2 levels of screen contrast, and tracked visual targets at 2 different speeds. The same measurement techniques, excluding pupil diameter and eye movement velocity, were compared by extending the task time from 20 to 60 min with the same VDT tasks to test for possible improvement in sensitivity. The results indicated that sensitivities of accommodation power, visual acuity, and CFF were greatly improved by a longer task period, but these 3 measurement techniques did not distinguish among tasks. Pupil diameter, eye movement velocity, and subjective rating of visual fatigue were sensitive in differentiating tracking from reading and monitoring tasks. Eye movement velocity and subjective rating were sensitive to the changes in target velocity of the tracking task. Although task performance was not directly comparable to other measurement techniques, it helped to ensure that participants maintained the same performance level by devoting more resources to the high-load conditions. Actual or potential applications of this research include using some of these assessment techniques for the design of adaptive displays.