Dr. Jay Warren

Electrotactile stimuli delivered across fingertips inducing the Cutaneous Rabbit Effect.
Warren JP, Santello M, Helms Tillery SI
School of Biological and Health System Engineering, Arizona State University, ECG 334, Tempe, AZ, 85287-9709, USA, jaypwarren@gmail.com.
23 Sep 2010
 Abstract
Previous studies have been unable to induce the Cutaneous Rabbit Effect (CRE) when the most likely perceived location of the illusory stimulus is on a non-continuous skin area. To determine whether the CRE could be elicited when each of the delivered stimuli were on non-continuous skin areas, we developed a new electrotactile stimulation paradigm attempting to induce the CRE across the fingertips. Though our stimulation paradigm differed from classic reduced CRE paradigms through the use of electrotactile stimuli, focusing the subject attention to a 'likely' illusory site, and the inclusion of a fourth stimulation site (two stimuli after the illusory stimulus), these factors were not the cause of the illusory effect we observed. Experiments conducted on the forearm validated that our paradigm elicited similar results to those reported in previous CRE studies that used either 3-stimulation-point mechanical or electrotactile stimuli with subject attention focused on the 'likely' illusory site. Across the fingertips, we observed an increase in stimulus mislocalization onto the middle fingertip, the 'likely' perceived location of the illusory stimuli, under Illusory Rabbit Trains compared to the Motion Bias Trains. Because the Motion Bias Trains should not induce a perceived location shift of the illusory stimulus but stimulates the adjacent digits in a similar way to the Illusory Rabbit Trains, differences observed between their mislocalization rates between these trains indicate that the CRE can be induced across the fingertips. These results provide the first evidence that the CRE can 'jump' when the stimuli occur across non-continuous skin areas.

Receptive field characteristics under electrotactile stimulation of the fingertip.
Warren JP, Bobich LR, Santello M, Sweeney JD, Tillery SI
Harrington Department of Bioengineering, Arizona State University, Tempe, AZ85287, USA. jpwarren@asu.edu
Aug 2008
 Abstract
Skin on human fingertips has high concentrations of mechanoreceptors, which are used to provide fine resolution tactile representations of our environment. Here, we explore the ability to discriminate electrotactile stimulation at four sites on the fingertip. Electrical stimulation was delivered to arrays of electrodes centered on the index fingertip (volar aspect). Accuracy of discrimination was tested by examining electrode size, interelectrode spacing, and stimulation frequency as primary factors. Electrical stimulation was delivered at 2 mA with the pulse width modulated to be at (or above) perceptual threshold at 25 and 75 Hz and an average pulse width of 1.03 ms (+/- 0.70 ms standard deviation). Discrimination of the stimulated locations under this stimulation paradigm was significantly above chance level in all cases. Subjects' ability to discriminate stimulus location was not significantly influenced by electrode size or stimulation frequency when considered as separate factors. However, increased electrode spacing significantly increased subjects' ability to discriminate the location of the stimulated electrode. Further analysis revealed that errors were only significantly reduced along the medial-lateral direction with increasing interelectrode spacing. These results suggest that the electrotactile stimulus localization on the fingertip has some directional dependency, in addition to its dependency on interelectrode spacing. The neural mechanisms underlying this phenomenon are discussed in relation to electrical stimulus transduction characteristics of tactile mechanoreceptors.

Electrotactile Stimuli Delivered across Fingertips Inducing the Cutaneous Rabbit Effect
Warren JP, Santello M, Helms Tillery SI
(In Press 2010 - EBR)