The longer the first stimulus is explored in softness discrimination the longer it can be compared to the second one.

Abstract

In haptic perception information is often sampled serially over a certain interval of time. For example, a stimulus is repeatedly indented to repeatedly estimate its softness. Albeit such redundant estimates are equally reliable, they seem to contribute differently to the overall haptic percept in a comparison task. When comparing the softness of two silicon rubber stimuli, the within-stimulus weights of estimates of the second stimulus' softness decrease during the exploration. Here we test the hypothesis that such decrease of weights depends on the representation strength of the first stimulus' softness. We varied the length of the first stimulus' exploration. Participants subsequently explored two silicon rubber stimuli by indenting the first stimulus (comparison) 1 or 5 times and the second stimulus (standard) always 3 times. We assessed the weights of indentation-specific estimates from the second stimulus by manipulating perceived softness during single indentations. Our results show that the longer the first stimulus is explored the more estimates of the second stimulus' softness can be included in the comparison of the two stimuli. This suggests that the exploration length of the first stimulus determines the strength of its representation which influences the decrease of weights of indentation-specific estimates of the second stimulus.