The objective of the TOUCH-HapSys Project is the development of new haptic display technology. The present deliverable describes the standard of knowledge in human haptic science and attempts to analyze in how far this knowledge can be used to improve haptic display: We provide a brief overview on existing haptic displays, go on with the sensory foundations of human haptics and, especially, deal with the question how the haptic system derives a representation of the environment from its sensory input. Thereby, we report a couple of principles and illusions in haptic perception which look promising for the future development of haptic display technology and, thus, are worth to be investigated more thoroughly. Drewing, K., Bresciani, J. P., & Ernst, M. O. (2003). Risk analysis on usability of haptic illusions for designing new haptic systems.
Our sensory channels provide us a direct access to several properties of the surrounding environment. A large part of these properties can be redundantly assessed on the basis of two or more of these channels. For instance, both vision and haptics are informative about the shape, the orientation or the texture of a given object. Actually, the different sensory signals are combined in the central nervous system to give rise to a unified percept. The general aim of the present document is to give an overview of the work dealing with the integration of haptic cues and other sensory inputs. More specifically, we will mainly focus on visuo-haptic integration, presenting also some interesting findings in the audio-haptic integration domain. Bresciani, J. P., Drewing, K., & Ernst, M. (2003). Risk analysis for multidimensional illusions for multimodal systems. In Proceedings of the workshop” Touch and Haptics (pp. 4-1).
On a repetitive tapping task, the within-hand variability of intertap intervals is reduced when participants tap with two hands as compared to one-hand tapping. Because this bimanual advantage can be attributed to timer variance (Wing—Kristofferson model, 1973a, b), separate timers have been proposed for each hand, whose outputs are then averaged (Helmuth & Ivry, 1996). An alternative notion is that action timing is based on its sensory reafferences (Aschersleben & Prinz, 1995; Prinz, 1990). The bimanual advantage is then due to increased sensory reafference. We studied bimanual tapping with the continuation paradigm. Participants first synchronized their taps with a metronome and then continued without the pacing signal. Experiment 1 replicated the bimanual advantage. Experiment 2 examined the influence of additional sensory reafferences. Drewing, K., & Aschersleben, G. (2003). Reduced timing variability during bimanual coupling: a role for sensory information. The Quarterly Journal of Experimental Psychology Section A, 56(2), 329-350.
The sense of presence in virtual environments may be greatly improved by the display of haptic virtual reality. Current haptic display technology, however, mostly remains unsatisfying and expensive. One way to overcome existing technical limitations might be to “cheat” the haptic system by exploiting its principles. Importantly, human perception of an environmental property normally relies upon the integration of several different cues, which technologically may-at least partly–be substituted to one another. A recent promising starting point for such substitution is the experimental demonstration that haptic perception of three-dimensional shapes can be evoked by just two-dimensional forces (Robles-de-la-Torre Hayward, 2001: Nature). The experiment dissociated positional and force cues in the perception of small-scale bumps: When sliding a finger across a bump on a surface, the finger follows the geometry of the bump providing positional cues for the shape. At the same time the finger is opposed by forces related to the steepness of the bump. Participants in this experiment reported to feel the shape indicated by the force cues and not by the positional cues. The present study extended this research. We aimed to disentangle the contributions of force and position cues to haptic shape perception more systematically and to explore their integration principles. For that purpose, we constructed a set of virtual standard curves, where we intermixed force and position cues related to curvatures of 0, 8 and 16/m using the PHANToM haptic device. Drewing, K., & Ernst, M. O. (2003). Cue integration in the haptic perception of virtual shapes.
When one slides a finger across a surface with a bump on it, the finger follows the geometry of the bump, providing positional cues for the shape. At the same time, the finger is opposed by forces related to the steepness of the bump. With a specific device, Robles-de-la-Torre and Hayward (2001) dissociated positional and force cues in the haptic perception of small-scale bumps and holes: Participants in this experiment reported feeling the shape indicated by the force cues and not those indicated by the positional cues. We extended this research by systematically disentangling the contributions of these two cues to the perception of curvature. Using the PHANToM haptic device, we presented virtual curves, in which we intermixed force and position cues related to curvatures between 0 and 16/m. Participants compared these with pseudonatural curves. Our results suggest that perceived curvature is a weighted average of both positional and force cues. Drewing, K., & Ernst, M. O. (2003, November). Integration of force and position cues in haptic curvature perception. In 44th Annual Meeting of The Psychonomic Society (p. 112).
