Ruifeng Yu

Assessment of grip force and subjective hand force exertion under handedness and postural conditions

The Borg CR-10 scale has been used to quantify the perception of physical exertion. An experiment was conducted to test the grip force of males on four levels of the CR-10 scale under experimental conditions. It was found that the subjects applied higher grip forces than they perceived at levels 2, 5, and 7 on the scale. The grip forces between dominant and non-dominant hands at low CR-10 levels were negligible. The grip forces were significantly different between the two hands at level 10. Similar results were found for the postural conditions. A follow-up experiment was conducted to estimate the subjective rating when applying a pre-determined grip force under the same conditions. Regression models were established to link the relationship between the subjective rating and hand force. The estimated ratings were lower than those actual values under all the tested conditions, even though the models have high R² values.

Effect of display polarity and luminance contrast on visual lobe shape characteristics

The effect of display polarity and luminance contrast on visual lobe (effective visual field) shape characteristics was studied using three levels of luminance contrast with combinations of positive and negative polarities. The binocular effective visual field for a detection task, with a peripherally presented target (V) embedded in a homogeneous competing background (Xs), was mapped on 24 imaginary axes passing through the fixation point. The results showed that visual lobes mapped using positive polarity were statistically larger in area, rounder and more regular in shape than those for negative polarity. The medium contrast condition lobes were more symmetric and regular than low contrast condition lobes, and lobe area and perimeter increased with increasing luminance contrast ratio. Under the interaction of positive polarity and high luminance contrast, visual lobes were found to be larger, smoother and rounder. The high level of luminance and contrast however resulted in a higher degree of visual discomfort. The results indicated that positive polarity and contrast of medium (26:1) to high (41:1) levels are possible display settings for better visual lobe characteristics and better anticipated search performance. Practitioner Summary: The effect of display polarity and luminance contrast on visual lobe shape characteristics was examined with uniform stimulus materials in this study. The results help to identify the optimum display settings for luminance contrast and display polarity to enhance lobe shape characteristics and hence search performance in industrial inspection tasks.

Validating the Random Search Model for Two Targets of Different Difficulty

A random visual search model was fitted to 1,788 search times obtained from a nonidentical double-target search task. 30 Hong Kong Chinese (13 men, 17 women) ages 18 to 33 years (M = 23, SD = 6.8) took part in the experiment voluntarily. The overall adequacy and prediction accuracy of the model for various search time parameters (mean and median search times and response times) for both individual and pooled data show that search strategy may reasonably be inferred from search time distributions. The results also suggested the general applicability of the random search model for describing the search behavior of a large number of participants performing the type of search used here, as well as the practical feasibility of its application for determination of stopping policy for optimization of an inspection system design. Although the data generally conformed to the model, the search for the more difficult target was faster than expected. The more difficult target was usually detected after the easier target and it is suggested that some degree of memory-guided searching may have been used for the second target. Some abnormally long search times were observed and it is possible that these might have been due to the characteristics of visual lobes, nonoptimum interfixation distances and inappropriate overlapping of lobes, as has been previously reported.

Auditory stimulus-response compatibility and control-display design

This study investigated spatial stimulus-response (S-R) compatibility effects for auditory signals, in order to suggest interface design recommendations. The auditory signals were presented in transverse and longitudinal orientations relative to the listener. The results showed that stimulus-response correspondence was the prime factor contributing to spatial compatibility and that there were spatial compatibility effects for both orientations. Relatively longer reaction times (RTs) and higher error percentages (EPs) were found for the longitudinal orientation than for the transverse one. The results suggest that the longitudinal orientation should not be used for getting attention and soliciting responses when using auditory signals. Transverse orientation signals produced quicker and more accurate responses. For faster reaction times, auditory signals should be positioned on the right hand side of right-handed operators. The length of warning time interval between an alerting visual message and the presentation of an auditory signal was shown to affect reaction time in the transverse stimulus orientation. To shorten reaction times, people should be given a greater than 1-s, and preferably a 3-s, forewarning period before being asked to make a response. For both orientations, reaction times varied with assigned hand posture, indicating that the layout of response keys on, for example, a control console should be compatible with the hand posture of the operators. Uncrossed hand posture should be assigned in the transverse orientation and the right and left hands should be used for the rear and front keys, respectively, in the longitudinal orientation. This study showed that in man–machine interface design, in addition to spatial S-R compatibility, hand position and an appropriate warning time should also be considered.

Age-related changes in visual lobe shape characteristics and their relationship to visual search performance

Visual lobe shape plays an important role in visual search performance, but little is known about the age-related changes in visual lobe shape. The age-related changes in visual lobe shape characteristics and their relationships to visual search performance were investigated in this study. A total of 96 participants aged 15–64 years participated in this study. Their visual lobes were mapped on a uniform 2-D test field composed of 24 regularly spaced meridians passing through the centre of the visual field, and their search performances were also measured. The results showed that in general, age significantly affected visual lobe size, visual lobe shape and search time. As age increased, the visual lobe size decreased; in addition, the roundness, boundary smoothness, symmetry and regularity of the visual lobe deteriorated, and the search time increased. Moreover, significant correlations between visual lobe shape, search time and age were found. Regression analyses indicated that age was important in determining visual lobe shape and search time, suggesting that age differences should be considered when predicting search time and when designing tasks and products that involve visual search in our daily lives and work. Practitioner Summary: Age-related changes in visual lobe shape characteristics and their relationships to visual search performance were investigated in this study. The results help to explain how tasks and products involving visual search in our daily lives and work should be designed for target audiences of different ages.

Comparative research on response stereotypes for daily operation tasks of Chinese and American engineering students

A group of Mainland Chinese engineering students were asked to respond to 12 questions by indicating their design conventions and expectations about operations, directions-of-motion, and descriptions of movement for items such as doors, keys, taps, and knobs. Chi-square tests demonstrated strong response stereotypes for tasks of all 12 questions. A comparison of the stereotype strengths found here with that of Hong Kong Chinese and American engineering students reported earlier indicated that stereotype strengths of engineering students from the three regions were generally different. For some cases stereotype characteristics of two regions were more alike than the other, and also for some subjects in the three regions performed similarly. The Mainland and Hong Kong Chinese were more alike in making their choices on questions of conceptual compatibility, while more consistent preferences on movement compatibility and spatial compatibility were noted between the Mainland Chinese and American students than Hong Kong Chinese.

Modeling of predictive muscular strength for sustained one-handed carrying task.

BACKGROUND Manual materials handling (MMH) tasks are common. They are considered major contributors of musculoskeletal injuries and are the sources of financial burden for industries in terms of lost work days and worker compensation costs. One-handed carrying is common and could result in arm fatigue. OBJECTIVE The purpose of this study was to establish predictive models for one-handed carrying strength considering weight handed and handedness conditions. METHODS Twenty male subjects were recruited for the study. The subject carried a weight of 6 or 12 kg using either dominant or non-dominant hand lasting a time period of 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, or 4 minutes. RESULTS The results showed that handedness (p <  0.0001), weight (p <  0.05), and time period (p <  0.0001) were all significant factors affecting single arm carrying strength. Predictive models of single arm carrying strength were established under handedness and weight conditions. The MADs of these models ranged from 0.39 to 2.19 kgf. CONCLUSION The exponential function based predictive models may be adopted to describe the single arm carrying strength with reasonable predictive errors. The trend of the carrying strength after carrying a load for a certain period may be employed to describe muscular fatigue for sustained carrying tasks.

Perceived floor slipperiness and floor roughness in a gait experiment

BACKGROUND Slips and falls contribute to occupational injuries and fatalities globally. Both floor slipperiness and floor roughness affect the occurrence of slipping and falling. Investigations on fall-related phenomena are important for the safety and health of workers. OBJECTIVE The purposes of this study were to: compare the perceived floor slipperiness before and after walking on the floor; compare the perceived floor slipperiness with and without shoes for males and females; discuss the perceived floor roughness based on barefoot walking; and establish regression models to describe the relationship between perceived floor slipperiness and actual friction of the floors. METHODS Male and female subjects walked on 3 m walkways with or without shoes. The perceived floor slipperiness ratings both before and after their walk were collected. RESULTS The perceived floor slipperiness both before and after walking were significantly affected by both floor and surface conditions. Gender, floor, surface, and footwear conditions were all significant factors affecting the adjustment of perceived floor slipperiness. The subjects made more adjustment on perceived floor slipperiness rating when they had shoes on than when they were barefooted. CONCLUSION Regression models were established to describe the relationship between perceived floor slipperiness and floor coefficient of friction. These models may be used to estimate perceived floor slipperiness, or in reverse, the coefficient of friction of the floor, so as to prevent slipping and falling in workplaces.

Quasi-Likelihood for Right-Censored Data in the Generalized Linear Model

This article proposes a method for estimation in a generalized linear model with right-censored data. Consider the model , μ i (β) = g(β T X i ), where v and g are known functions, e i , i = 1,…,n are identically and independently distributed with mean 0 and finite variance φ2, but the distribution is unspecified. We use Kaplan–Meier estimates to replace the censored observations and employ quasi-likelihood to estimate the parameters. Consistency and asymptotic normality of the parameter estimates are derived. The performance of the proposed method for small sample sizes is investigated by simulation study. The new method is illustrated with the Stanford heart transplant data.

Effects of Target Prevalence and Speech Intelligibility on Visual Search Performance

Visual search is commonly performed in the control rooms of several industries such as nuclear power plants, flight control, security screening, and monitoring. In this study, the effects of target prevalence and speech intelligibility on visual search performance were investigated. A 2 (target prevalence: low versus high) × 3 (speech transmission index = 0 versus 0.51 versus 0.69) mixed design experiment was conducted. Target prevalence was a between-subject variable, whereas the speech transmission index was a within-subject variable. A total of 32 participants participated in simulated X-ray screening tasks in different speech intelligibility conditions. Results revealed that both the target prevalence and the speech transmission index level had significant effects on visual search performance. The reaction time was shorter and the miss error rate was higher under low target prevalence condition than in high target prevalence condition. Compared with no speech condition (speech transmission index = 0), the reaction time of the participants increased significantly with the presence of intelligible speech in an acoustic environment. Performance loss was greatest when the speech transmission index was 0.51. The interaction effect of target prevalence and speech transmission index level was also significant. Proper measures should be taken to reduce unfavorable effects of low target prevalence and intelligible speech in acoustic environment on visual search performance in control rooms.