6. Exploratory Movement Strategies in Softness Perception

Perception during active touch essentially depends on the executed exploratory movements. Humans use different movement schemes to perceive different haptic properties, the so-called exploratory procedures (EPs). The stereotypically used EPs are normally superior to other EPs in perceiving the associated property and it has been speculated that the EPs are a means of maximising pickup of the relevant sensory information. However, EPs are not always executed identically as they vary in a number of ways. For instance, the peak force and the number of fingers used during exploration are not fixed. This chapter reviews existing findings on the exploratory movement strategies that humans use in softness perception and gives an overview on how different manners of exploration affect the performance in softness tasks. It is shown that observers adapt their movement strategies depending on variations of the stimulus value and the exact conditions of the exploratory task, and that different movement parameters, e.g. the peak exploratory forces, considerably affect performance. Overall, results suggest that humans adjust their exploratory strategies to achieve the highest levels of performance in softness discrimination.