The force exerted during manual tasks is a dominant risk factor for upper-limb musculoskeletal disorders. To identify tasks that may lead to fatigue over a shift, or increase the risk of injury, the demands placed on the hand and forearm system must be quantified and predicted. The purpose of this research was to determine how different ways of simulating manual tasks affected the estimate of demand on the hand and forearm and how well normative data could be used to provide an estimate of that demand. The forces and moments required to perform 20 manual tasks were measured and simulations with three different levels of realism developed, ranging from simple feedback, with real parts, postures and timing to more controlled simulations with simplified parts, standard postures and 5s static exertions. 11 workers hired from a temporary employment agency each performed the simulated tasks and their physical demand was determined using perceived effort, the muscle activity of 8 hand and forearm muscles, and grip (or pinch) force matching. Based on these criteria, the best simulation was that with the same handle size, shape and orientation as the criterion version of the task using simple feedback to match one or two forces. Over the variety of tasks studied here, perceived effort, grip force matching and extensor digitorum activation provided the most similar demand estimate to the criterion task of all measured parameters. The more controlled simulation had the highest correlation compared with normative demand. Overall, the more changes in hand-object interface made between the task of interest and a simulation or normative data, the greater the discrepancy in demand. Normative data tended to underestimate demand, thus underestimating the risk of fatigue and injury. The use of simulations and task specific normative data to estimate hand task demand, with an accuracy useful for field measurements by ergonomists, was supported.

The force exerted during manual tasks is a dominant risk factor for upper-limb musculoskeletal disorders. To identify tasks that may lead to fatigue over a shift, or increase the risk of injury, the demands placed on the hand and forearm system must be quantified and predicted. The purpose of this research was to determine how different ways of simulating manual tasks affected the estimate of demand on the hand and forearm and how well normative data could be used to provide an estimate of that demand. The forces and moments required to perform 20 manual tasks were measured and simulations with three different levels of realism developed, ranging from simple feedback, with real parts, postures and timing to more controlled simulations with simplified parts, standard postures and 5s static exertions. 11 workers hired from a temporary employment agency each performed the simulated tasks and their physical demand was determined using perceived effort, the muscle activity of 8 hand and forearm muscles, and grip (or pinch) force matching. Based on these criteria, the best simulation was that with the same handle size, shape and orientation as the criterion version of the task using simple feedback to match one or two forces. Over the variety of tasks studied here, perceived effort, grip force matching and extensor digitorum activation provided the most similar demand estimate to the criterion task of all measured parameters. The more controlled simulation had the highest correlation compared with normative demand. Overall, the more changes in hand-object interface made between the task of interest and a simulation or normative data, the greater the discrepancy in demand. Normative data tended to underestimate demand, thus underestimating the risk of fatigue and injury. The use of simulations and task specific normative data to estimate hand task demand, with an accuracy useful for field measurements by ergonomists, was supported.

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The overall aim of this current research was to investigate effects of individual differences and task demand on co-speech gestures in communication. Specifically, we examined whether gesture use affected speakers' information content, and whether individual differences in working memory (WM) profiles and lexical retrieval, and task demand could account for variability in gesture use. Forty-four speaker-listener pairs of Mandarin-speaking adults participated in a video description task. The speaker watched and described motion event videos to the listener, who had two options to choose from. The speaker's descriptions were transcribed and coded for motion element type (manner, path, source, goal, and trajectory), modality use (speech vs. gesture), gesture type (deictic vs. iconic), gestures' relation to speech (complementary vs. supplementary), and information type carried by gesture (spatial vs. semantic). A WM profile/discrepancy was measured by a difference between visuo-spatial and verbal working memory using Automated Working Memory Asessment (Alloway, 2007). Lexical retrieval was measured using a semantic fluency task (naming `animals' or `foods' in a one-minute interval). Task demand was manipulated by changing number of motion elements to be described in each video, ranging from two to four. The results of an ANOVA showed that speakers did not include more information when they chose to gesture, although they sometimes used supplementary gestures that carried information absent from speech. However, a series of mixed model regression analyses showed that spatial complementary gestures decreased with task demand, whereas spatial supplementary gestures increased with task demand. Also, Individual differences in WM discrepancy and spatial WM capacity, not lexical retrieval, predicted production of semantic supplementary gestures. The interaction between task demand and WM discrepancy predicted spatial complementary gestures. Also, the interaction between task demand and WM discrepancy predicted semantic supplementary gestures. Most importantly, we found that verbal dominant speakers produced fewer spatial complementary gestures when task demand was high, whereas spatial dominant speakers used these gestures similarly across task demands. Also, spatial dominant speakers tended to use more semantic supplementary gestures than verbal dominant speakers when task demand was low, but no such differences were found when task demand was high. Taken together, our findings reveal that individuals' gesture production is a complex process, in which speaker-internal factors, such as WM, and speaker-external factors, such as task demand, and even interactions between the two factors could play a role. Given that communication is dynamic and complex, instead of restricting to one factor at a time, we may need to expand our scope to more influencing factors and their interactions to fully understand the underlying mechanism of multi-modal communication.

This study investigated the effects of cross-modality warning presentation and retention in a dual-task paradigm in a simulated military environment under various task-induced stress levels. It was also intended to determine what role working memory played in the mode of warning presentation that resulted in the highest retention and subsequent compliance. An all within participant design was created in order to determine if scores on working memory span tasks predicted performance across the varying forms of warning presentation. Furthermore, task-induced stress levels were varied over the course of the experiment to identify if workload transitions affected performance. Results revealed that when the presentation format and the response format matched (e.g., verbal-verbal), behavioral compliance was greater then when presentation and response format were mismatched (e.g., verbal-pictorial). Thus, it is not necessarily the presentation type that affects compliance, but the combination of presentation and response mode. Analysis also revealed that the pictorial-pictorial warning combination resulted in greater behavioral compliance compared to verbal-verbal or written-written combinations. The format of warning presentation did not affect performance on the operational tasks as predicted. Thus, the visual/spatial operational task, regardless of its complexity was not interrupted in timesharing with intra-modal warning presentations or cross-modal time-sharing. As predicted, task based stress affected the WCCOM task in all experimental procedures. Results further revealed that as task demand increased, performance on the WCCOM task decreased. Task demand did affect the operational tasks, the shooting and the navigation tasks. The shooting task, which was less complex than the navigation task was not affected by lower levels of task demand, but at the greatest level of demand (eight warnings) performance in the operational task, degraded. Degradations in performance on the more complex task, the navigation task, materialized at a moderate level of task demand (four warnings). For subjective ratings, task demand did affect workload ratings. As the task demand increased, the subjective workload ratings also increased, revealing a true association between workload and subjective ratings. The working memory separability hypothesis was supported by the working memory span tasks, but consequently they were not predictive of the warning presentation format.