We investigated multisensory softness perception using a set of custom-made rubber specimens (compliance 0.11 to 0.96 mm N-1). Participants judged the softness of the stimuli under haptic-only, vision-only and visuo-haptic conditions. In haptic and visuo-haptic conditions participants explored the stimuli without and with vision of their exploratory movements, respectively. In visual conditions, participants watched how another person explored the stimuli. Participants well differentiated between the stimuli under all three modality conditions. Stimuli were judged to be slightly softer under vision-only conditions than under haptic-only conditions; visuo-haptic judgments were in-between (average visual weight: 55%). These findings demonstrate that (a) participants can reliably infer softness from indirect visual information alone, and that (b) such visual information has a major contribution to the visuo-haptic judgments Drewing, K., Ramisch, A., & Bayer, F. (2009). Multisensory softness perception of deformable objects. Perception ECVP abstract, 38, 144-144.
We investigated the effect of stimulus and task properties on the control of exploratory movements in active touch. In Experiment 1 we varied the compliance of silicon rubber stimuli with deformable surfaces. Participants freely explored pairs of lowly compliant stimuli (harder condition) or of highly compliant stimuli (softer condition) with a bare finger, and were asked to select the softer one. Pairs from the two conditions were presented either block-wise, or in randomized order (blocked vs randomized session). In the blocked session, exploratory force was always higher for the harder than for the softer stimuli (long-term adjustment). In randomized sessions force was only higher for the harder stimuli that were explored as second within a trial and it did not differ between softness conditions for the firstly explored stimuli, indicating even short-term movement adjustment. Kaim, L. R., & Drewing, K. (2009). Stimulus compliance influences the force of the exploratory movement. Perception ECVP abstract, 38, 69-69.
In this experiment we investigated the influence of stimulus properties on exploratory movement parameters in active touch. More precisely, we investigated whether and to what extent variations in stimulus compliance influence the executed finger force and velocity of the exploratory movements. Therefore, we varied the compliance of silicon rubber stimuli with deformable surfaces. Participants freely explored pairwise presented stimuli with a bare finger, and were asked to select the softer one. We found that both exploratory force and velocity depended on the compliance of the stimulus. Our results suggest in particular that observers strategically adapt their maximum finger force to the expected softness of the stimulus. L. R. Kaim and K. Drewing, "Finger force of exploratory movements is adapted to the compliance of deformable objects," World Haptics 2009 - Third Joint EuroHaptics conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2009, pp. 565-569, doi: 10.1109/WHC.2009.4810830.
The purpose of this study is to investigate multisensory visual-haptic softness perception using deformable objects. We created a set of rubber specimens, whose compliance varied in a controlled fashion (0.11 to 0.96 mm/N), but which were otherwise indistinguishable. Participants judged the magnitude of the stimuli according to their softness under haptic-only, vision-only and visuo-haptic conditions. In haptic and visuo-haptic conditions participants explored the stimuli without and with vision of their exploratory movements, respectively. In visual conditions, participants watched how another person explored the stimuli. Participants were well able to differentiate between the different stimuli under all three modality conditions. Stimuli were judged to be slightly softer under vision-only conditions than under haptic-only conditions; visuo-haptic judgments were in-between (average visual weight: 55%). These findings demonstrate that (a) participants can reliably infer softness from indirect visual information alone-that is from watching corresponding exploratory movements and stimulus deformations-, and that (b) such visual information has a major contribution to visuo-haptic softness judgments. We further observed that judgments were more variable under visual as compared to haptic conditions; the variability of visuo-haptic judgments was similar to that of haptic ones. The lack of benefit from adding visual to haptic information, and the contrast between the relatively high visual weight in visuo-haptic judgments on the one hand and the low reliability of visual relative to haptic-only information on the other hand, suggest that the integration of visual and haptic judgments was not optimal, but biased towards vision. K. Drewing, A. Ramisch and F. Bayer, "Haptic, visual and visuo-haptic softness judgments for objects with deformable surfaces," World Haptics 2009 - Third Joint EuroHaptics conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2009, pp. 640-645, doi: 10.1109/WHC.2009.4810828.
We present experimental and computational evidence for the estimation of visual and proprioceptive directional information during forward, visually driven arm movements. We presented noisy directional proprioceptive and visual stimuli simultaneously and in isolation midway during a pointing movement. Directional proprioceptive stimuli were created by brief force pulses, which varied in direction and were applied to the fingertip shortly after movement onset. Subjects indicated the perceived direction of the stimulus after each trial. We measured unimodal performance in trials in which we presented only the visual or only the proprioceptive stimulus. When we presented simultaneous but conflicting bimodal information, subjects' perceived direction fell in between the visual and proprioceptive directions. We find that the judged mean orientation matched the MLE predictions but did not show the expected improvement in reliability as compared to unimodal performance. We present an alternative model (probabilistic cue switching, PCS), which is consistent with our data. According to this model, subjects base their bimodal judgments on only one of two directional cues in a given trial, with relative choice probabilities proportional to the average stimulus reliability. These results suggest that subjects based their decision on a probability mixture of both modalities without integrating information across modalities. Drewing, K., & Jovanovic, B. (2010, July). Visuo-haptic length judgments in children and adults. In International Conference on Human Haptic Sensing and Touch Enabled Computer Applications (pp. 438-444). Springer, Berlin, Heidelberg.
We investigated how exploratory movement influences signal integration in active touch. Participants judged the amplitude of a bump specified by redundant signals: When a finger slides across a bump, the finger’s position follows the bump’s geometry (position signal); simultaneously, it is exposed to patterns of forces depending on the gradient of the bump (force signal). We varied amplitudes specified by force signals independently of amplitudes specified by position signals. Amplitude judgment was a weighted linear function of the amplitudes specified by both signals, under different exploratory conditions. The force signal’s contribution to the judgment was higher when the participants explored with the index finger, as opposed to the thumb, and when they explored along a tangential axis, as opposed to a radial one (pivot ≌ shoulder joint). Furthermore, for tangential, as compared with radial, axis exploration, amplitude judgments were larger (and more accurate), and amplitude discrimination was better. We attribute these exploration-induced differences to biases in estimating bump amplitude from force signals. Given the choice, the participants preferred tangential explorations with the index finger—a behavior that resulted in good discrimination performance. A role for an active explorer, as well as biases that depend on exploration, should be taken into account when signal integration models are extended to active touch. Drewing, K., & Kaim, L. (2009). Haptic shape perception from force and position signals varies with exploratory movement direction and the exploring finger. Attention, Perception, & Psychophysics, 71(5), 1174-1184.
