Abstract

Many emerging technologies are attempting to leverage the tactile domain to convey complex spatiotemporal information translated directly from the visual domain, such as shape and motion. Despite the intuitive appeal of touch for communication, we do not know to what extent the hand can substitute for the retina in this way. Here we ask whether the tactile system can be used to perceive complex whole hand motion stimuli, and whether it exhibits the same kind of established perceptual biases as reported in the visual domain. Using ultrasound stimulation, we were able to project complex moving dot percepts onto the palm in mid-air, over 30 cm above an emitter device. We generated dot kinetogram stimuli involving motion in three different directional axes (‘Horizontal’, ‘Vertical’, and ‘Oblique’) on the ventral surface of the hand. Using Bayesian statistics, we found clear evidence that participants were able to discriminate tactile motion direction. Furthermore, there was a marked directional bias in motion perception: participants were both better and more confident at discriminating motion in the vertical and horizontal axes of the hand, compared to those stimuli moving obliquely. This pattern directly mirrors the perceptional biases that have been robustly reported in the visual field, termed the ‘Oblique Effect’. These data demonstrate the existence of biases in motion perception that transcend sensory modality. Furthermore, we extend the Oblique Effect to a whole hand scale, using motion stimuli presented on the broad and relatively low acuity surface of the palm, away from the densely innervated and much studied fingertips. These findings highlight targeted ultrasound stimulation as a versatile method to convey potentially complex spatial and temporal information without the need for a user to wear or touch a device.

Highlights

  • The human tactile system is increasingly being targeted as a means to communicate explicit information via spatial and temporal stimuli from electronic devices

  • Discrimination of complex tactile percepts exceeds chance On the group level, there was extreme evidence that performance was statistically above chance in all conditions (Fig. 3A), indicating that participants were able to distinguish the direction of complex tactile motion perceptions delivered across the palm

  • The highest evidence for performance above chance was observed in the vertical condition and the lowest was observed in the oblique condition

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Summary

Introduction

The human tactile system is increasingly being targeted as a means to communicate explicit information via spatial and temporal stimuli from electronic devices This trend has developed from a desire to avoid saturating the auditory and visual systems. The recent development of targeted ultrasound technology has made it possible to project complex tactile percepts or ‘scenes' onto the surface of the hand without any physical contact (Carter et al, 2013) (see Fig. 1). This technology can produce stimuli translated almost directly from the visual domain, including defined points, lines, and shapes; both static and moving. Just as light is projected onto the retina for vision, ultrasound technology can project tactile scenes directly onto the hand

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