Vibrotactile spatial acuity on the back.

Vibrotactile feedback can be built into clothing such as vests. This means that often vibrotactile information is presented to the back. It is known that the back has a relatively low spatial acuity. Spatial acuity varies across different limbs and sometimes with different locations on a limb. These known anisotropies suggest that there might be systematic variations in vibrotactile spatial acuity for different areas of the back and also for different orientations (i.e. horizontal vs. vertical). Here we systematically measured spatial acuity in four areas of the back for both horizontal and vertical orientations. The results show no significant differences in spatial acuity for the back areas that were tested. Spatial acuity was, however, higher in the horizontal direction than in the vertical direction by roughly a factor of two. This means that when designing vibrotactile displays for the back the tactor density can be lower in the vertical direction than in the horizontal direction and density should be constant for different areas of the back.

Influence of Back Length on Vibrotactile Acuity in Vertical Direction.

In this study, we were interested in the question whether vibrotactile thresholds on the back, in terms of the Just Noticeable Difference (JND), scale with back length. Although there exists only indirect physiological evidence, it could be assumed that the density of mechanoreceptors is lower if back size is larger. As a consequence, the JND would increase with back length. We measured psychophysical curves for 40 male participants with back lengths in the range of 36 to 55 cm. Nine equally spaced vibration motors were placed in vertical direction on their back, 2 cm left of the spine. For each stimulus pair, participants had to decide whether the second vibration was above or below the first vibration. It was found that the slope of the fit of the JND as a function of back length was not significantly different from zero, so contrary to our expectation, we did not find an influence of back length on JND. This means that when customizing a wearable haptic device for the back, measuring back length is not the way to go.

Tactile cueing effects on performance in simulated aerial combat with high acceleration.

INTRODUCTION: Recent evidence indicates that vibrotactile displays can potentially reduce the risk of sensory and cognitive overload. Before these displays can be introduced in super agile aircraft, it must be ascertained that vibratory stimuli can be sensed and interpreted by pilots subjected to high G loads. METHODS: Each of 9 pilots intercepted 32 targets in the Swedish Dynamic Flight Simulator. Targets were indicated on simulated standard Gripen visual displays. In addition, in half of the trials target direction was also displayed on a 60-element tactile torso display. Performance measures and subjective ratings were recorded. RESULTS: Each pilot pulled G peaks above +8 Gz. With tactile cueing present, mean reaction time was reduced from 1458 ms (SE = 54) to 1245 ms (SE = 88). Mean total chase time for targets that popped up behind the pilot's aircraft was reduced from 13 s (SE = 0.45) to 12 s (SE = 0.41). Pilots rated the tactile display favorably over the visual displays at target pop-up on the easiness of detecting a threat presence and on the clarity of initial position of the threats. DISCUSSION: This study is the first to show that tactile display information is perceivable and useful in hypergravity (up to +9 Gz). The results show that the tactile display can capture attention at threat pop-up and improve threat awareness for threats in the back, even in the presence of high-end visual displays. It is expected that the added value of tactile displays may further increase after formal training and in situations of unexpected target pop-up.