The impact of cognitive load on prospective and retrospective time estimates at long durations: An investigation using a visual and memory search paradigm

As human beings, we are bound by time. It is essential for daily functioning, and yet our ability to keep track of time is influenced by a myriad of factors (Block & Zakay, 1997, Psychonomic Bulletin & Review, 4[2], 184-197). First and foremost, time estimation has been found to depend on whether participants estimate the time prospectively or retrospectively (Hicks et al., 1976, The American Journal of Psychology, 89[4], 719-730). However, there is a paucity of research investigating differences between these two conditions in tasks over two minutes (Tobin et al., 2010, PLOS ONE, 5[2], Article e9271). Moreover, estimates have also been shown to be influenced by cognitive load. We thus investigated participants' ability to keep track of time during a visual and memory search task and manipulated its difficulty and duration. Two hundred and ninety-two participants performed the task for 8 or 58 minutes. Participants in the prospective time judgment condition were forewarned of an impending time estimate, whereas participants in the retrospective condition were not. Cognitive load was manipulated and assessed by altering the task's difficulty. The results revealed a higher overestimation of time in the prospective condition compared with the retrospective condition. However, this was found in the 8-minute task only. Overall, participants significantly overestimated the duration of the 8-minute task and underestimated the 58-minute task. Finally, cognitive load had no effect on participants' time estimates. Thus, the well-known cross-over interaction between cognitive load and estimation paradigm (Block et al., 2010, Acta Psychologica, 134[3], 330-343) did not extend to a longer duration in this experiment.

Differences in spinal moments, kinematics and pace during single-task and combined manual material handling jobs

This study compared the spinal moments (i.e., peak and cumulative moments acting on the L5/S1 joint), kinematics (i.e., peak trunk and knee angles) and work pace of workers, when either removing a box from a shelf or depositing a box on a shelf, under two conditions: as a single task or as part of a combined task. An experiment was conducted, in which the subjects performed the tasks and were recorded using a motion capture system. An automated program was developed to process the motion capture data. The results showed that, when the removing and depositing tasks were performed as part of a combined task (rather than as single tasks), subjects experienced smaller peak and cumulative spinal moments and they performed the tasks faster. The results suggest that investigations into the separate tasks that comprise a combination have a limited ability to predict kinematics and kinetics during the combined job.

Effects of display curvature and task duration on proofreading performance, visual discomfort, visual fatigue, mental workload, and user satisfaction

This study examined the effects of display curvature and task duration on proofreading performance, visual discomfort, visual fatigue, mental workload, and user satisfaction. Five 27″ rear-screen mock-ups with distinct curvature radii (600R, 1140R, 2000R, 4000R, and flat) were used. Ten individuals per display curvature completed a series of four 15 min comparison-proofreading trials at a 600 mm viewing distance. Only proofreading speed benefited from display curvature, with 600R providing the highest mean proofreading speed. Proofreading speed increased and accuracy decreased for all display curvatures over the 1 h proofreading period. Visual discomfort, visual fatigue, and mental workload increased during the first 15 min of proofreading. A decrease in critical fusion frequency during that period indicated increases in visual fatigue and mental workload. A short break between 15 min proofreading tasks could be considered to prevent further degradation of task performance and ocular health.

Muscle activity, time to fatigue, and maximum task duration at different levels of production standard time

[Purpose] This study investigated the variations in muscle fatigue, time to fatigue, and maximum task duration at different levels of production standard time. [Methods] Twenty subjects performed repetitive tasks at three different levels of production standard time corresponding to "normal", "hard" and "very hard". Surface electromyography was used to measure the muscle activity. [Results] The results showed that muscle activity was significantly affected by the production standard time level. Muscle activity increased twice in percentage as the production standard time shifted from hard to very hard (6.9% vs. 12.9%). The muscle activity increased over time, indicating muscle fatigue. The muscle fatigue rate increased for the harder production standard time (Hard: 0.105; Very hard: 0.115), which indicated the associated higher risk of work-related musculoskeletal disorders. Muscle fatigue was also found to occur earlier for hard and very hard production standard times. [Conclusion] It is recommended that the maximum task duration should not exceed 5.6, 2.9, and 2.2 hours for normal, hard, and very hard production standard times, respectively, in order to maintain work performance and minimize the risk of work-related musculoskeletal disorders.

Work organization on smallholder dairy farms: a process unique to each farm

The way smallholder farms organize and carry out work impacts their ability to secure their livelihoods and meet growing demand for agricultural products. This study investigates the way dairy family farms in Brazil manage their workforce to achieve their objectives of production and income. Fifteen smallholder farms were surveyed using the QuaeWork method to understand the work organization on each farm. A high diversity of workloads was found, but these do not appear to be strictly related to the farms' production systems. The high variability of workloads is linked to the available workforce, technical choices, and the delegation of tasks to an external workforce. Farmers can decrease their workload by adopting milking mechanization, silage, hiring labor, and increasing the duration of the work day. Work organization depends on a farmer's personal choices, rendering the whole issue of workforce management a process unique to each farm.