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.

在研究触觉柔软感的研究中，通常会指导参与者通过用食指压入来探索柔软的物体。相反，很少研究其他手指的演奏。我们想知道在自发探索中使用了哪些手指，以及手指之间的性能差异是否可以解释自发使用。在实验1中，参与者辨别了两种橡胶刺激物的柔软度，而手指运动几乎没有任何限制。结果表明，人类在探索过程中使用不同手指和手指组合的连续阶段，偏爱食指，中指和（在较小程度上）无名指。在实验2中，我们比较了条件之间的区分阈值，参与者使用了优势手的四个手指之一。参与者在两次间隔的强制选择辨别任务中比较了橡胶刺激的柔软性。与无名指和小指相比，食指和中指的性能更好，小指最差。在实验3中，我们再次比较了辨别阈值，但要求参与者使用恒定的峰值力。小指的表现最差，而其他手指的表现没有差异。我们得出的结论是，在自发探索中，食指，中指和部分无名指的组合的偏好似乎是很好的选择，这是由自发使用的手指的性能提高所表明的。更好的表现似乎是基于两种不同的产生力的运动能力（主要与使用食指和中指有关）以及不同的感官敏感性，