title: Integrating force and position: testing model predictions.
abstract: In this study, we investigated the integration of force and position information in a task in which participants were asked to estimate the center of a weak force field. Two hypotheses, describing how participants solved this task, were tested: (1) by only using the position(s) where the force reaches the detection threshold, and (2) by extrapolating the force field based on perceived stiffness. Both hypotheses were also described formally, assuming a psychophysical function obeying a power law with an exponent smaller than one. The hypotheses were tested in two psychophysical experiments, in which 12 participants took part. In Experiment 1, an asymmetric force field was used and the presence of visual feedback about hand position was varied. In Experiment 2, a unilateral force field was used. For both experiments, hypothesis 1 predicts biases between (Experiment 1) or at (Experiment 2) the position(s) of the force detection threshold, while hypothesis 2 predicts smaller biases. The measured data show significant biases in both experiments that coincide with the biases predicted by using force detection thresholds from the literature. The average measured responses and their variabilities also fitted very well with the mathematical model of hypothesis 1. These results underline the validity of hypothesis 1. So, participants did not use a percept of the stiffness of the force field, but based their estimation of the center of the force field on the position(s) where the force reached the detection threshold. This shows that force and position information were not integrated in this task.
authors.affiliation: Department of Behavioural and Human Movement Sciences, MOVE Research Institute Amsterdam, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands. f.e.van.beek@vu.nl.
authors.forename: Femke E
authors.identifier: 0000-0003-4741-6196
authors.initials: FE
authors.lastname: van Beek
authors.affiliation: Department of Behavioural and Human Movement Sciences, MOVE Research Institute Amsterdam, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
authors.forename: Wouter M
authors.initials: WM
authors.lastname: Bergmann Tiest
authors.affiliation: Department of Behavioural and Human Movement Sciences, MOVE Research Institute Amsterdam, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
authors.forename: Astrid M L
authors.initials: AM
authors.lastname: Kappers
authors.affiliation: Department of Robotics, Brain and Cognitive Sciences (RBCS), Istituto Italiano di Tecnologia, Genoa, Italy.|Faculty of Psychology, Universitá Vita-Salute San Raffaele, Milan, Italy.|Experimental Psychology Unit, Ospedale San Raffaele, Milan, Italy.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Baud-Bovy
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D005260:Female; D007839:Functional Laterality; D006225:Hand; D006801:Humans; D008297:Male; D008960:Models, Psychological; D010465:Perception / Q000502:physiology*; D011434:Proprioception / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D011601:Psychophysics; D012684:Sensory Thresholds; D014110:Touch; D055815:Young Adult
keywords: Bisection model; Force field; Haptic perception; Psychophysics; Sensory integration