Vibrotactile patterns using sensitivity prioritisation

Abstract

This paper investigates sensitivity based prioritisation in the construction of tactile patterns. Our evidence is obtained by three studies using a wearable haptic display with vibrotactile motors (tactors). Haptic displays intended to transmit symbols often suffer the tradeoff between throughput and accuracy. For a symbol encoded with more than one tactor simultaneous onsets (spatial encoding) yields the highest throughput at the expense of the accuracy. Sequential onset increases accuracy at the expense of throughput. In the desire to overcome these issues, we investigate aspects of prioritisation based on sensitivity applied to the encoding of haptics patterns. First, we investigate an encoding method using mixed intensities, where different body locations are simultaneously stimulated with different vibration intensities. We investigate whether prioritising the intensity based on sensitivity improves identification accuracy when compared to simple spatial encoding. Second, we investigate whether prioritising onset based on sensitivity affects the identification of overlapped spatiotemporal patterns. A user study shows that this method significantly increases the accuracy. Furthermore, in a third study, we identify three locations on the hand that lead to an accurate recall. Thereby, we design the layout of a haptic display equipped with eight tactors, capable of encoding 36 symbols with only one or two locations per symbol.

Investigating Interactions for Text Recognition using a Vibrotactile Wearable Display

“…This method resulted in better recognition accuracy than spatial encoding, and it is faster than spatiotemporal encoding, as vibromotors share most of the activated time. Recent research leverages spatial acuity (sensitivity of locations of actuators) for achieving a better perception of encoded information [28,27]. We employ the same method as Luzhnica [29] for encoding char-Session 5A: IUIs for Wearable, Mobile and Ubiquitious Computing IUI 2018, March 7-11, 2018, Tokyo, Japan Figure 2.…”

“…Each character is encoded with one or two vibromotors using an OST (overlapped spatiotemporal) stimulation as introduced by Luzhnica and Veas. [28]. Figure 3 illustrates the details of OST and the differences with other stimulation forms.…”

“…The activation of vibromotors is done in sequence, but they share most of the activation time. Moreover, the activation is prioritised based on the sensitivity of the finger as such prioritisation yields a higher accuracy of identification of locus [28]. Sensitivity order is assumed as reported on studies on the subject [9,51,19], suggesting that sensitivity decreases from the index finger towards the little finger: the index finger is more sensitive than the middle, ring, and pinky finger.…”

“…Similar patterns have been used to train users to recognise the entire English alphabet [29], and a wearable glove based layout capable of encoding 36 characters with only one or two vibromotors have been proposed [28], which demonstrate the capabilities of such wearable device for text reading. Nevertheless, in this study, we use only ten characters: A, E, I, O, T, N, S, H, D and Y.…”

“…Luzhnica et al refer to this as vibrotactile skin-reading. While encoding alphanumeric symbols in tactile patterns to transmit words is not new [14], recent developments in vibrotactile technology and stimulation methods overcome issues in effective training, throughput, accuracy as well as portability [28]. Vibrotactile skin reading uses a vibrotactile display to convey dynamically generated textual information similar to refreshable Braille displays [43,41].…”