-- KarlinBark - 5 Aug 2004

Well after further thinking...some more questions have risen...

The vibration vs. skin stretch issue is a bit more complex and harder to prove than I initially thought it would be. For instance, how do you compare vibration to skin stretch in an effective and equal manner? How can we say that the vibration sensation we provide is 'equal' in strength/perceived intensity to the skin stretch in an experiment to compare the two. Initial ideas were to use the same amount of power/energy for both experiments (i.e. use 3V to power a vibrating motor, and the same 3V to power whatever skin stretch device is made). Another idea Will suggested is to find the thresholds of both skin stretch and vibration and test subjects at the thresholds.

Also, are we trying to prove that skin stretch is 'better' than vibration or can we think of a whole new application for skin stretch, where vibration cannot be used? What are the disadvantages of vibration?

Summarizing things about skin stretch that we've discovered...humans can distinguish varying magnitudes of skin stretch (varying at least 2 N) well, however, memory is an issue, and it is questionable if humans can remember the different magnitudes after time passes (a few minutes). This was because there was a medium force applied, if there were only 2 forces, a low one and a high one, then I think people could tell the difference easily, and memory loss would not be an issue. Also, at higher forces, skin stretch sensitivity decreases, but that was expected. Twisting motion is probably the more intense application of skin stretch, whereas single directional skin stretch is less so. Problems that will probably occur with skin stretch are getting the probe/tactor to 'stick' to the skin and stretch; having to accommodate different skin types (hairy skin/non hairy skin...muscular people vs. less fit people...what part of the body to apply the skin stretch?determining the size of the stimulus...)

Body motion/acceleration affects the ability to sense vibration. Li tested a bigger vibrating motor (still a pager motor) with a guessed estimate of about 10,000 (166.66 hz) rpm on his arm. The one we tested earlier had an rpm of about 4500 (75 hz), so this one was much stronger than the previous one. Li said that if he ran hard (sprinted) he couldn't feel the pager motor, but it was definitely stronger than the one used before. I brought up the point that if vibration was to be used in a virtual environment, it would be unlikely that the human would have to run at high speeds, nor would there be the need for a large, spatial environment?theoretically.