Relative vibrotactile spatial acuity of the torso

Abstract

While tactile acuity for pressure has been extensively investigated, far less is known about acuity for vibrotactile stimulation. Vibrotactile acuity is important however, as such stimulation is used in many applications, including sensory substitution devices. We tested discrimination of vibrotactile stimulation from eccentric rotating mass motors with in-plane vibration. In 3 experiments, we tested gradually decreasing center-to-center (c/c) distances from 30 mm (experiment 1) to 13 mm (experiment 3). Observers judged whether a second vibrating stimulator (‘tactor’) was to the left or right or in the same place as a first one that came on 250 ms before the onset of the second (with a 50-ms inter-stimulus interval). The results show that while accuracy tends to decrease the closer the tactors are, discrimination accuracy is still well above chance for the smallest distance, which places the threshold for vibrotactile stimulation well below 13 mm, which is lower than recent estimates. The results cast new light on vibrotactile sensitivity and can furthermore be of use in the design of devices that convey information through vibrotactile stimulation.

Measuring relative vibrotactile spatial acuity: effects of tactor type, anchor points and tactile anisotropy

“…When relating the current results to previous studies, our findings for the P ERMs complement the results of Jóhannesson et al (2017), who found that P ERMs (10 mm diameter), in the same rPL task could be placed as close as physically possible (13 mm c/c) leading to 64% discrimination accuracy. With smaller P ERMs in the current study (8 mm diameter), the inter-tactor distance could be decreased to 10 mm c/c, but even though participants were still able to discriminate two adjacent tactors, accuracy dropped to 45%.…”

“…Cholewiak et al (2004) found no consistent effects of tactor number on localization, concluding that the most important factor for localization accuracy is the inter-tactor distance. In line with these findings, the results of Jóhannesson et al (2017) suggest that decreasing the size of the area of vibrotactile stimulation does not significantly affect the thresholds for relative vibrotactile spatial acuity.…”

“…The experiment was therefore conducted in two sessions where the apparatus was adjusted accordingly in between. The initial distance was based on previous work (Jóhannesson et al 2017). For the second session, the distance for each tactor type was decreased to the closest distance physically possible.…”

“…Novich and Eagleman (2015) reported surprisingly low tactile acuity when testing an array of 3 × 3 eccentric rotating mass tactors (size: 25 mm) on the back, and argued that these tactors need to be at least 40 mm apart. In our previous work (Jóhannesson et al 2017), we assessed relative spatial acuity on the lower back with a 3 × 3 array of coin cell eccentric rotating mass motors (10 mm diameter). Our results suggested that these tactors can be differentiated when placed only 13 mm apart (center-to-center) and therefore can be mounted as close as physically possible.…”

Cogno-Vest: A Torso-Worn, Force Display to Experimentally Induce Specific Hallucinations and Related Bodily Sensations

“…B. Cogno-Vest 1) Electronics and Software Development: In a previous study [33], we reported that an array of 3 by 3 tactile actuators on the back is sufficient to create the sensation that the entire back is covered with actuators. This is due to the poor tactile spatial acuity of the human back [38], and explains the limited number of solenoid actuators used, in our case 9. Solenoids were placed at the center-to-center distance of 60 mm, which approximates the tactile localization threshold of the human back [39], [40].…”