Abstract
The apparent heaviness of weights placed on the skin depends on their temperature. We studied the effects of such a temperature–weight illusion (TWI) on perception and action in 21 healthy volunteers. Cold (18 °C), thermal-neutral (32 °C, skin temperature) and warm (41 °C) test objects were placed onto the palm of the non-dominant hand. Their veridical mass was 350 g (light) or 700 g (heavy). Perception of heaviness was assessed with two psychophysical experiments (magnitude estimation, cross modal matching). Cold heavy objects felt about 20% heavier than thermal-neutral objects of the same mass, shape and material. In a subsequent grip-lift experiment, the test objects were grasped with a precision grip of the dominant hand and lifted off the palm of the non-dominant hand. The grip and lift forces exerted by the fingertips were recorded. The temperature of the objects had significant effects (ANOVA, p < 0.05) on the peak grip and lift forces and on the peak grip force rate (i.e., the initial force incline). The peak grip force was about 10% higher when cold heavy objects were grasped and lifted, compared to lifts of otherwise identical thermal-neutral objects. The TWI was less pronounced when light objects or warm objects were handled. In conclusion, cooling of an object increases its apparent heaviness (perception) and influences scaling of the fingertip forces during grasping and lifting (action).
Highlights
A cold coin placed on the forehead of a supine person feels heavier than a coin at room temperature
To a lesser extent, warm objects placed on the palm of the non-dominant hand appeared to be heavier than thermal-neutral objects
Weber noted that a cold coin placed on the forehead of a supine person feels heavier than a warmer coin
Summary
A cold coin placed on the forehead of a supine person feels heavier than a coin at room temperature This temperature–weight illusion (TWI) was originally described with a silver thaler by Ernst Heinrich Weber in 1846 (translated by Ross and Murray 1996). More than 100 years later, Stevens and colleagues explored the TWI in a series of experiments (Stevens and Green 1978; Stevens 1979). They let healthy volunteers judge the apparent heaviness of cold (0 °C), neutral (32 °C), and warm (45 °C) aluminum disks, which were placed on the skin of the hand, forearm, and other body regions.
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