There are three research areas of fatigue in the research literature. Once there is psychic fatigue, visual fatigue, and physical fatigue with a great weight between the examined fields.
Psychic fatigue is defined as the decreasing ability of information processing standing in direct proportion with the level of load. In this case, the employee is not capable of maintaining the appropriate level of attention needed for the task completion (Holtzer et al., 2010). This type of fatigue not only worsens the quality of information processing, but the reaction abilities are corrupted as well (Techera et al., 2016). Based on the previous facts the decreasing level of attention and the increased level of task-completion together can result in the drop of quality in the production process. (Buckley et al., 2016).
Some include visual fatigue in the category of psychic fatigue others handle the decrease in visual abilities separately. Visual fatigue results in a decrease of visual capacity accompanied by the feeling of discomfort (Megaw, 1995).
The fatigue of vision is caused by long-term visual activities that affect the level of watchfulness too. The oculomotor nerve is responsible for the slow and difficult completion of tasks resulting in the decrease of resources for the adaptation processes. (Ukai and Howarth, 2008).
Physical fatigue is the waning of the physical power responsible for metabolic problems, nerve-muscle transmission problems, and problems in the system of proteins responsible for muscle contraction. Physical fatigue can be related to the changes in the central nervous system that cause symptoms around the spine. (Behm, 2004). Physical fatigue is described as the decreased amount of muscle force, the decrease in the control of motor functions (Gates and Dingwell, 2008), untrue sensing of the positions of body parts (Björklund et al., 2000). These may be responsible for decreased productivity and low quality. (Hammarskjöld and Harms-Ringdahl, 1992).
Since we cannot talk about purely mental or physical fatigue, we have to consider each situation complex, and we have to think about them jointly. Their effects should be understood collectively.
For example, ACT-R theory considers that an assembly process is done by the visual, manual, and execution parts of the brain (Anderson et al., 2004). The visual unit is responsible for the position of the object and sends back relevant information for the execution, then a response is chosen and sent to the manual unit. The choice of the response is based on previous observations and happens fast. But in case of fatigue is analyzed in the virtual space it is harder to determine the position of the object, the response is slower. (Arthur et al., 1997; Witmer and Kline, 1998; Keyson, 2000; Armbrüster et al., 2008). That is how fatigue can affect the sensing processes of the brain and with that the whole process. Therefore, it is extremely important to know fatigue for health and economic reasons as well.
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