• The Thermal Grill Illusion was first described by Thunberg (1894) and later replicated by others (Craig & Bushnell, 1994) as the sensation of paradoxical strong or painful heat elicited by touching interlaced mildly warm and cool stimuli of 20°C and 40°C respectively. Green (2002) has introduced the sensation of non-painful heat elicited by similar grill apparatus of smaller temperature range (warm 35°C-40°C and cold ≥27°C).

• Our aim is to generate thermal grill illusion (TGI) stimuli for a tactile display. The majority of tactile interfaces used today are based on vibration and pressure. No previous references shows the use of thermal displays as a stand-alone signal source, nor is there evidence of the use of the thermal grill illusion for that purpose.

• This is the first use of Thermoelectric Coolers (TEC) technology for generating a thermal grill stimuli based display. We have developed a prototype which consists of three thermal actuating units (TAU)  in contact with the glabrous skin of the arm. Direct and separate computer control allows for defining the temperature and the signal duration of each of the TAUs. This architecture enables us to define the optimal characteristic for TGI signals and to explore the possibilities of tactile stimuli within the sub-modality of thermal perception.

The TAU is composed of several components yet its core is the TEC (as shown in the two images below). The TTD consists of three TAUs. In the first prototype of the TTD, each TAU was mounted on a velcro belt. In the New prototype all three TAUs are mounted on a Silicon based casing and thus wearing the display is easier. Various TGI stimuli configurations. Interlacing Hot (H) and Cold (C) Stimuli can generate various combinations.

TAU components

An assembled TAU

TTD – schematic presentation of the P/T

TTD – old configuration

TTD New Mounting

TTD New P/T

TGI stimuli configurations

The TTD was developed with my graduate student Yael Salzer. The second P/T was improved by the work of two wonderful students Or Ben-David and Yossi Falkovitch.

To read more see:

Thermoelectric Tactile Display Based on the Thermal Grill Illusion  EuroHaptics 2008: 343-348

Thermoelectric tactile display based on the thermal grill illusion ECCE 2007: 303-304