Search for: All records

Multisensory cutaneous displays have been developed to enhance the realism of objects touched in virtual environments. However, when stimuli are presented concurrently, tactile stimuli can mask thermal perception and so both these modalities may not be available to convey information to the user. In this study, we aim to determine the simultaneity window using the Simultaneity Judgment Task. A device was created that could present both tactile and thermal stimuli to the thenar eminence of the participant’s left hand with various stimulus onset asynchronies (SOA). The experimental results indicated that the simultaneity window width was 639 ms ranging from -561 ms to 78 ms. The point of subjective simultaneity (PSS) was at -242 ms, indicating that participants perceived simultaneity best when the thermal stimulus preceded the tactile stimulus by 242 ms. These findings have implications for the design of stimulus presentation in multisensory cutaneous displays. 

There are fundamental differences between the tactile and thermal sensory systems that must be accommodated when designing multisensory cutaneous displays for use in virtual or teleoperated robotic environments. In this review we highlight the marked temporal and spatial differences between the senses of cold and warmth as revealed in psychophysical experiments. Cold and warmth are distinct senses with marked differences in the time taken to respond to stimulation and in their temporal filtering processes. Such variations must be taken into account when time-varying profiles of thermal stimulation are delivered to the skin concurrent with tactile stimulation since the resulting sensations will not be perceived on the same time scale. Although it is often reported that the thermal senses are markedly inferior to the sense of touch with respect to their spatial acuity, it is also clear that there is considerable variability across the body in the accuracy with which thermal stimuli can be localized. The distal to proximal gradient in thermal acuity suggests that locations other than the palmar surface of the hand are better suited for displaying thermal cues, in contrast to the situation for tactile inputs. As was noted for temporal processes, there are differences between localizing warmth and cold stimuli, with localization being superior for cold. These properties provide benchmarks that can be used in designing thermal and multisensory displays. 

A number of haptic displays based on smart fluidic materials such as electrorheological (ERFs) and magnetorheological fluids (MRFs) have been fabricated. These displays are relevant to medical virtual environments where it is important to create realistic simulations of soft tissues with varying stiffness. In this paper a new haptic device is described that was designed in consideration of the limitations of an earlier MRF display. The new prototype consists of 400 permanent magnets (PMs) arranged in a 20x20 array that is underneath a chamber filled with MRF. The magnetic field within the fluid is controlled by 400 PM stepping motors that move the magnets vertically. The magnetic behavior of the device was simulated using FEM which indicated that its spatial resolution was substantially improved when compared to the earlier prototype and that objects as small as 10 mm can be rendered. The device was fabricated and assembled and measurements demonstrated the accuracy of the FE model. Its novelty is demonstrated by the increased intensity of the magnetic field produced and the enhanced spatial resolution. These features will enable the dynamic presentation of haptic information such as object shape and compliance which will be characterized in future psychophysical experiments.