Background: When we use our fingers to explore the fine surface (spatial
features smaller than 200 m) of an object, the relevant temporal features are
encoded by cutaneous mechanoreceptor afferents that are widely believed to lead to
the perception of roughness. However, whether visual input influences the haptic
perception of fine surfaces and how the haptic and visual modalities interact with
each other are questions that remain unanswered.
Objective: In the present study, fifteen healthy volunteers participated in a series of
unimodal (haptic-haptic (HH) task and visual-visual (VV) task) and bimodal (haptic-
haptic & visual (HHv) task and visual-visual & haptic (VVh) task) fine surface
roughness estimation tasks.
Methods: The subjects were asked to estimate the roughness of a test surface that they compared to a
standard surface in the HH and VV tasks. In the HHv and VVh tasks, the task procedures were the
same as those in the unimodal tasks, but both haptic and visual surfaces were presented simultaneously.
Results: Our results suggest that both the visual and haptic roughness estimations were influence by
information from the other modality.
Conclusion: In conclusion, we propose that humans store a modality-independent and dimensionless
quantity in the brain when estimating the roughness of a fine surface.