Evaluation of the Tiller Switch Layout of a Tractor Using Eye-Fixation Related Potentials

The human-machine interface (HMI) of a tractor cockpit includes not only the steering wheel and pedals, but also many levers and switches. According to a report from the National Agriculture and Food Research Organization of Japan, the HMI layout often differs from the operator's expectation. This gap between expectations and reality has led to operator errors and market complaints. However, few reports have ergonomically evaluated these arrangements. Our previous work showed that this gap can be evaluated by the amplitude of the P300 component of the event-related potentials (ERPs) for discrimination tasks by using a picture of the vehicle cockpit on the display. However, in real-world driving and operation situations, eye movements occur. In such cases, the eye-fixation related potential (EFRP) may be used. The EFRP appears at the end of a saccade, which is a rapid movement of the eyes between fixation points. Its positive component, called the lambda response, is reported to reflect the human attention level to visual targets. We hypothesize that if the HMI layout differs from the user's expectation, operation becomes difficult and the user's attention to the target during operation will be reduced. In order to confirm this hypothesis, an experiment was conducted during the actual operation of a tractor while changing the tiller switch position. The participants were 13 adult males with experience in tractor operations. The amplitude of the lambda wave was reduced when the switch position was different from the user's expectations, reflecting the decrease in attention caused by the increased difficulty of operating the tiller. We suggest that the amplitude of the lambda response can be used as the evaluation index for optimizing the switch position.