The previous research has been summarized and classified in terms of defining a design solution for the desired value concerning human sensory function. We have found that the data are not sufficient to define the design solution systematically. Therefore, in this study, a systematic procedure based on the process of how humans react to an external stimulation was proposed. The design solution is obtained from the sensory evaluation value by determining the physical amount of the external stimulus quantitatively and obtaining correlations of the sensory evaluation value and the design value with the physical amount of stimulus. This procedure enabled us to find a corresponding design solution from the targeted sensory evaluation value. We also have confirmed validity of this procedure by applying this to “sensory intensity on the strength of warm water jet” and “dependence of easiness in turning over in bed on performance of pillows.” Verification of the effectiveness of this technique in a large number of cases is required.
In this study, two different “event-related brain potentials (ERPs)” were examined to assess mental workload. Eye-fixation-related potentials (EFRPs) associated with the occurrence of fixation pause can be obtained from averaging electroencephalograms (EEGs) at the offset of saccades. An EFRP is a kind of event-related brain potential (ERP), which has a relationship with visual attention and the physical properties of visual stimulus. Auditory P300 is the ERP elicited from probe stimuli in a secondary task. The amplitude of a late positive wave (P300) is inversely proportioned to the amount of perceptual-central processing resources allocated to a primary task. In this experiment, the lambda responses of EFRPs and auditory P300 (irrelevant probe technique) were examined concurrently with multiple tracking tasks to compare the effects of tasks of different difficulties. Eighteen participants were assigned six different types of tracking task, each for 5 min. The workload under each tracking condition was different in the task quality (the difficulty of perceptual-motor and/or perceptual-central levels). As a result, the peak amplitude of lambda responses decreased with the level of perceptual-motor workload, while the peak amplitude of P300 didn't decrease with the level of both workloads. The results suggested that the brain physiological indexes should be used in a usability testing with due consideration of reaction characteristics and the limits of measuring technique.