Academic journal article Perception and Psychophysics

Spatial Acuity and Summation on the Hand: The Role of Thermal Cues in Material Discrimination

Academic journal article Perception and Psychophysics

Spatial Acuity and Summation on the Hand: The Role of Thermal Cues in Material Discrimination

Article excerpt

The spatial characteristics of thermal perception were studied in two experiments that examined how thermal stimuli are processed within the hands. A thermal display that simulates cues associated with making contact with different materials was used in these studies. In the first experiment, participants indicated which of two simulated materials that were presented to the index fingertip was cooler. The results indicated that participants were unable to resolve the two areas of thermal stimulation. In the second experiment, the effects of concurrent thermal stimulation on the ability to discriminate between simulated materials were evaluated. Thermal cues were presented to the middle fingers of both hands and to two adjacent fingers on one hand. Thermal spatial summation was evident across the fingers, which enhanced the ability to discriminate between materials when the cooler stimulus was presented to three fingers. When the same stimulus was presented to the two hands, the stimulation of adjacent fingers altered the perceived thermal response.

(ProQuest: ... denotes formulae omitted.)

When an object is grasped in the hand, thermal cues provide information about the objectfs temperature and thermal properties, which can be used to assist in identifying it. Because the fingers are usually warmer than objects encountered in the environment, the perception of temperature is based on the responses of cold thermoreceptors in the skin that respond to decreases in skin temperature. The rate at which the skin changes temperature on contact depends on both the initial temperatures of the hand and object, and their thermal properties, such as conductivity and heat capacity. Several studies have shown that people can identify materials on the basis of thermal cues alone (Caldwell & Gosney, 1993; Ho & Jones, 2007; Ino et al., 1993), although their ability to do so depends on the thermal properties of the materials being identified. Materials with lower thermal effusivities (see Table 1), such as foam or plastic, are easier to identify than those with higher effusivities, such as stainless steel or copper (Ho & Jones, 2007).

A number of thermal displays have been built and tested to evaluate the role of thermal cues in object identification and discrimination (see, e.g., Caldwell, Tsagarakis, & Wardle, 1997; Ino et al., 1993; Jones & Berris, 2003). These systems typically comprise a thermal heater/cooler (Peltier device), temperature sensors, and a temperature control system that monitors and controls the surface temperature of the display (for a review, see Jones & Ho, 2008). For some of these displays, experimental data on the changes in skin temperature when the hand makes contact with a real material have been used to simulate thermal changes (Caldwell et al., 1997; Ino et al., 1993), whereas for others a thermal model has been used to characterize the heat transfer process between the skin and an object during contact (see, e.g., Benali-Khoudja, Hafez, Alexandre, & Kheddar, 2003; Ho & Jones, 2006a). The thermal responses required to simulate materials are then calculated from the model on the basis of the materialfs properties and initial conditions. In general, these thermal displays can provide thermal cues that allow participants to either identify materials or discriminate between them with a success rate that parallels their performance with real materials (Caldwell & Gosney, 1993; Ho & Jones, 2007; Ino et al., 1993).

Multifingered thermal displays have also been developed to study the spatial characteristics of thermal perception within and across the hands so that effective thermal cues can be created in virtual environments (Caldwell & Gosney, 1993; Deml, Mihalyi, & Hannig, 2006; Yang, Jones, & Kwon, 2008). The focus of this research has been on determining the contribution of thermal cues to haptic object recognition and on how discrete thermal stimuli are processed within the hand. …

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