Thermosensory reversal effect quantified

Material Recognition via Heat Transfer Given Ambiguous Initial Conditions

Humans and robots can recognize materials with distinct thermal effusivities by making physical contact and observing temperatures during heat transfer. This works well with room temperature materials, yet research has shown that contact with distinct materials can result in similar temperatures and confusion when one material is heated or cooled. To thoroughly investigate this form of ambiguity, we designed a psychophysical experiment in which a participant discriminates between two materials given initial conditions that result in similar temperatures (i.e., ambiguous initial conditions). In this article, we conducted a study with 32 human participants and a robot. Humans and the robot confused the materials. We also found that robots can overcome this ambiguity using two temperature sensors with different temperatures prior to contact. We support this conclusion based on a mathematical proof using a heat transfer model and empirical results in which a robot achieved 100% accuracy compared to 5% human accuracy. Our results also indicate that robots with a single temperature sensor can use subtle cues to outperform humans. Overall, our work provides insights into challenging conditions for material recognition via heat transfer, and suggests methods by which robots can overcome these challenges.

Effect of thermal control of dry fomites on regulating the survival of human pathogenic bacteria responsible for nosocomial infections

We monitored the survival of human pathogenic bacteria [Escherichia coli (ATCC), extended-spectrum β-lactamase-producing E. coli (Clinical isolate), New Delhi metallo-β-lactamase-producing E. coli (clinical isolate), Staphylococcus aureus (ATCC)] on dry materials (vinyl chloride, aluminum, plastic, stainless steel) at distinct temperatures (room temperature or 15°C–37°C). These bacteria favored a lower temperature for their prolonged survival on the dry fomites, regardless of the material type. Interestingly, when mixed with S. aureus, E. coli survived for a longer time at a lower temperature. Cardiolipin, which can promote the survival of S. aureus in harsh environments, had no effect on maintaining the survival of E. coli. Although the trends remained unchanged, adjusting the humidity from 40% to 60% affected the survival of bacteria on dry surfaces. Scanning electron microscopic analysis revealed no morphological differences in these bacteria immediately before or after one day of dry conditions. In addition, ATP assessment, a method used to visualize high-touch surfaces in hospitals, was not effective at monitoring bacterial dynamics. A specialized handrail device fitted with a heater, which was maintained at normal human body core temperature, successfully prohibited the prolonged survival of bacteria [Enterococcus faecalis (ATCC), E. coli (ATCC), Pseudomonas aeruginosa (ATCC), S. aureus (ATCC), Acinetobacter baumannii (clinical isolate), and Serratia marcescens (clinical isolate)], with the exception of spore-forming Bacillus subtilis (from our laboratory collection) and the yeast-like fungus Candida albicans (from our laboratory collection)] on dry surfaces. Taken together, we concluded that the tested bacteria favor lower temperatures for their survival in dry environments. Therefore, the thermal control of dry fomites has the potential to control bacterial survival on high-touch surfaces in hospitals.

Material recognition based on thermal cues: Mechanisms and applications

Some materials feel colder to the touch than others, and we can use this difference in perceived coldness for material recognition. This review focuses on the mechanisms underlying material recognition based on thermal cues. It provides an overview of the physical, perceptual, and cognitive processes involved in material recognition. It also describes engineering domains in which material recognition based on thermal cues have been applied. This includes haptic interfaces that seek to reproduce the sensations associated with contact in virtual environments and tactile sensors aim for automatic material recognition. The review concludes by considering the contributions of this line of research in both science and engineering.

Perceived Cooling Using Asymmetrically-Applied Hot and Cold Stimuli

Temperature perception is a highly nonlinear phenomenon with faster rates of change being perceived at much lower thresholds than slower rates. This paper presents a method that takes advantage of this nonlinear characteristic to generate a perception of continuous cooling even though the average temperature is not changing. The method uses multiple thermal actuators so that a few are cooling quickly while the rest of the actuators are heating slowly. The slowly-heating actuators are below the perceptual threshold temperature change and hence are not perceived, while the quickly-cooling actuators are above the perceptual temperature change, hence are perceived. As a result, a feeling of decreasing temperature was elicited, when in fact, there was no net change in the temperature of the skin. Three sets of judiciously designed experiments were conducted in this study, investigating the effects of actuator sizes, forearm measurement locations, patterns of actuator layout, and various heating/cooling time cycles. Our results showed that 19 out 21 participants perceived the continuous cooling effect as hypothesized. Our research indicates that the measurement location, heating/cooling cycle times, and arrangement of the actuators affect the perception of continuous cooling.

Salient material properties and haptic volume perception: the influences of surface texture, thermal conductivity, and compliance

We investigated the influences of surface texture, thermal conductivity, and compliance on the haptic perception of the volume of small cubes. It was hypothesized that an object containing highly salient material properties would be perceived as larger in volume than the same object without these properties. Blindfolded subjects were asked to explore pairs of cubes differing in their material properties and to select the one with the larger volume. The results showed that, counterintuitively, a smooth cube was perceived as being significantly larger than a rough cube of the same physical volume, with average biases of about 19 %. Furthermore, cubes with a higher thermal conductivity were perceived as significantly larger than cubes with a lower thermal conductivity (average bias of about 7 %). In addition, the magnitude of the bias in this condition was not changed by increasing or decreasing the temperature of the test objects, suggesting that the effect of thermal conductivity could not be attributed directly to the heat flow. Finally, a hard cube was perceived as significantly larger than a soft cube of equal physical volume, with an average bias of about 25 %. These results reveal that the studied material properties have significant and consistent influences on the haptic perception of volume. The observed biases provide an indication of the levels at which the processing of haptic information on volume and material properties occurs.

Haptic perception

Fueled by novel applications, interest in haptic perception is growing. This paper provides an overview of the state of the art of a number of important aspects of haptic perception. By means of touch we can not only perceive quite different material properties, such as roughness, compliance, friction, coldness and slipperiness, but we can also perceive spatial properties, such as shape, curvature, size and orientation. Moreover, the number of objects we have in our hand can be determined, either by counting or subitizing. All these aspects will be presented and discussed in this paper. Although our intuition tells us that touch provides us with veridical information about our environment, the existence of prominent haptic illusions will show otherwise. Knowledge about haptic perception is interesting from a fundamental viewpoint, but it also is of eminent importance in the technological development of haptic devices. At the end of this paper, a few recent applications will be presented. WIREs Cogn Sci 2013, 4:357-374. DOI: 10.1002/wcs.1238 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Haptic perception of wetness

In daily life, people interact with textiles of different degrees of wetness, but little is known about the mechanics of wetness perception. This paper describes an experiment with six conditions regarding haptic discrimination of the wetness of fabrics. Three materials were used: cotton wool, sponge-structured viscose and thin viscose. Two ways of touching were investigated: static touching, in which only thermal cues were available, and dynamic touching, in which additional mechanical cues were available. For dynamic touching, average Weber fractions for discrimination were around 0.3, whereas for static touching, they ranged from 0.34 to 0.63. The results show that people can make use of the additional mechanical cues to significantly improve their discrimination performance. There was no significant difference between Weber fractions for the three materials, showing that wetness can be judged as a separate perceptual quantity, independent of the material.

Tactile perception of thermal diffusivity

The thermal diffusivity of an object is a parameter that controls the rate at which heat is extracted from the hand when it touches that object. It is an important feature for distinguishing materials by means of touch. In order to quantitatively describe the ability of human observers to discriminate between materials on the basis of heat extraction rate, we conducted an experiment in which this heat extraction was performed in a controlled way. In different conditions, subjects were repeatedly asked to select from two stimuli the one that cooled faster. The discrimination threshold was around 43% of the extraction rate. A rate that was twice as slow also yielded twice the absolute threshold. When we halved the temperature difference between the beginning and end of the stimulus, the threshold did not change as much. In separate experiments, we investigated the different cues that were available in the stimulus: initial cooling rate and end temperature. Both cues were used for discrimination, but cooling rate seemed to be the most important.

Warm or Cool, Large or Small? The Challenge of Thermal Displays

Thermal displays have been developed to present thermal cues to the hand to facilitate object recognition in virtual environments or in teleoperated robotic systems. This review focuses on this application domain of thermal displays and considers the models developed to simulate the thermal interaction between an object and the hand as they make contact. An overview of thermal perception and the mechanisms underlying the processing of thermal information is provided to give a framework for analyzing the design of thermal displays. The models developed to simulate thermal feedback are examined together with a description of the implementation of these models in thermal displays. The domains in which thermal displays have been used are described; this includes the simulation of material properties, the recreation of large-scale thermal effects in virtual environments, the encoding of abstract concepts and the use of thermal feedback in interactive art. The review concludes by considering the advantages and challenges associated with using thermal displays in these diverse areas.