A Systematic Comparison of Perceptual Performance in Softness Discrimination with Different Fingers
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A Systematic Comparison of Perceptual Performance in Softness Discrimination with Different Fingers Aaron C. Zoeller 1 & Knut Drewing 1
# The Author(s) 2020
Abstract In studies investigating haptic softness perception, participants are typically instructed to explore soft objects by indenting them with their index finger. In contrast, performance with other fingers has rarely been investigated. We wondered which fingers are used in spontaneous exploration and if performance differences between fingers can explain spontaneous usage. In Experiment 1 participants discriminated the softness of two rubber stimuli with hardly any constraints on finger movements. Results indicate that humans use successive phases of different fingers and finger combinations during an exploration, preferring index, middle, and (to a lesser extent) ring finger. In Experiment 2 we compared discrimination thresholds between conditions, with participants using one of the four fingers of the dominant hand. Participants compared the softness of rubber stimuli in a two-interval forced choice discrimination task. Performance with index and middle finger was better as compared to ring and little finger, the little finger was the worst. In Experiment 3 we again compared discrimination thresholds, but participants were told to use constant peak force. Performance with the little finger was worst, whereas performance for the other fingers did not differ. We conclude that in spontaneous exploration the preference of combinations of index, middle, and partly ring finger seems to be well chosen, as indicated by improved performance with the spontaneously used fingers. Better performance seems to be based on both different motor abilities to produce force, mainly linked to using index and middle finger, and different sensory sensitivities, mainly linked to avoiding the little finger. Keywords Psychophysics . Perception . Softness discrimination . Active exploration
Introduction In everyday life, haptic perception is essential for interacting with our surroundings, because it allows us to identify and discriminate relevant properties of objects that cannot really be distinguished by other senses. The compliance of an object is one important property that can be determined most exactly through haptic exploration (Lederman & Klatzky, 1987). Its perceptual correlate is softness. To assess softness, we use specifically optimized exploratory movements. For example, when we judge the ripeness of an avocado in the supermarket, or how comfortable a cushion is, we indent the surface of that object to gather softness information (Lederman & Klatzky, 1987). In typical studies on softness perception, participants * Aaron C. Zoeller [email protected] 1
Department of General Psychology, Justus-Liebig University Giessen, Building F1, Room 307, Otto-Behaghel-Str. 10F, D-35394 Giessen, Germany
are constrained to explore objects using only the index or only the middle finger (e.g., Friedman et al., 2008; Fujita & Ohmori, 2001; Kaim & Drewing, 2011; S
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