Some Like it Hot?Thermal Feedback for Mobile De-

vices

Graham Wilson, et al.Scholl of Computing Science, University of Glasgow

CHI 2011

Keywords

• Thermal feedback▫A rich, emotive and salient feedback▫ Yet to be fully investigated

• Two studies into how well users could detect hot and cold stimuli and analysis

Potential Examples

• Jo is travelling to a meeting on the train• She is carrying a mobile device with personalised travel apps• After some time, her device begins to slowly warm up in-

dicating that her train is nearing the station• As she boards the train, the device gets warmer as she

moves towards the seat and colder as she moves away

Potential Examples

• Ted is in the library• As one particular message is received, his phones cools in-

dicating that an important message has been received• He leaves the library to check his message• In the case that the phone vibrates, the rumbling of the

phone off the seat disturbs people close by

Potential Uses for Thermal Feedback

• Can act as an alternative non-visual notification channel▫ In situations that are too bumpy or noisy for vibrotac-

tile and audio feedback• Can augment both visual and non-visual feedback▫ To add an extra richness to the interaction experience

• Entirely private▫Vibrotactile feedback can sometimes still be heard or

felt by others

Background

• Just noticeable differences (JNDs)▫ The minimum amount of change (warming or cooling)

from current skin temperature that is required for that change to be detected

▫ In general, the smaller the JND, the more salient the stimulus

• Thermal sense is more sensitive to changes in temperature, rather than absolute temperature it-self

• Thermal sensitivity is not uniform across the body▫Variation between different locations as well as be-

tween different skin types Hairless skin vs. hairy skin

▫ In general, thermal sensitivity is best on the head and trunk but worse towards the extremities

Evaluation

• A custom microcontroller

• Situation▫ Static indoor evaluation▫ Mobile indoor evaluation

• Stimuli▫ A neutral starting temperature of 32oC was chosen▫ Three different intensity and two different rates of stimulus

change (ROC) were used Intensity: 1oC, 3oC, and 6oC ROC: 1oC/sec and 3oC/sec

Static Indoor Evaluation

• Location▫ Fingers and palm of the hand, thenar eminence, dorsal surface of the forearm, upper

arm

• Participants▫ Fourteen participants (9 male, 5 female) aged to 21 to 57▫ All were right-handed and paid £6 for participation

• Variables▫ Independent variables

Rate of change Stimulus intensity Direction of change (warm or cool) Body location

▫ Dependent variables Stimulus detection (if one was perceived) Detection time (how long after the initiation of a stimulus that it was detected) JND size (distance in oC from neutral when the stimulus was felt) Subjective intensity of stimulus (hot to cold) Subjective comfort of stimulus (comfortable to uncomfortable)

• Procedure▫ Participants were instructed to click the mouse button as soon as they felt a change in

thermal stimulation, in any direction and at any intensity

thenal forearm

Results

Overall result

• The results of static indoor evaluation show that▫ The thenar is the most sensitive area with the arm lo-

cations▫ Increasing the rate of change or stimulus in-

tensity makes the stimulus more salient, as it is more quickly detectable and more likely to be de-tected, but this comes at the expense of subjec-tive comfort

Mobile Indoor Evaluation

• Participants▫ 10 male and 4 female aged 23 and 41▫ All were right-handed and were paid £10

• Procedure▫ The same stimuli and variables were used as in the static

indoor evaluation

Results

Design Recommendation

• The thenar eminence is the optimal location for feedback, but non-glabrous arm locations are also suitable

• 1oC/sec and 3oC/sec changes are suitable, even necessary, and each has its own advantages▫ 1oC/sec: slower but less intense and more comfort-

able▫ 3oC/sec: faster but more intense and less comfortable

• Warm and cold stimuli are both suitable for use• Intensity or ‘end-point’ can be used as a parameter

for feedback design

Thank You