Incorporating Thermal Feedback in Cutaneous Displays: Reconciling Temporal and Spatial Disparities

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.