Evaluating Affective Touch Generated via a Shape-Memory-Alloy Arm-Sleeve by Subjective Report and Facial Muscle Activity

Realistic actuation of social touch remains a pressing challenge. This study evaluated a shape-memory alloy (SMA) based arm-sleeve, which actuated touch patterns in the range of C-tactile optimal velocity (3 to 4.5 cm/s) that is known to evoke pleasant affect. We manipulated the intensity (238, 289 & 340 mA) and overlap (0, 187 & 375 ms) of the actuation. Twenty-one participants rated the perceived continuity and intensity of the resulting stroking and tapping patterns. Their psychophysiological reactions of pleasantness derived from activities of the zygomaticus major muscle were also measured by facial electromyography (EMG). At the highest actuation intensity (340 mA), greater differences in perceived continuity between conditions of actuation overlaps were observed (p . 001), with the highest continuity rating for an overlap of 375 ms. Relative to other conditions, this parameter combination elicited higher facial muscle activities of positive affect (p . 001). Crucially, individual differences in perceived continuity and psychophysiological reactions of positive affect correlated positively. These findings i) extend evidence of pleasant responses elicited by human touch and touch by haptic actuators and ii) establish a psychophysiologically based perceptual benchmark for designing haptic devices to render affective touch.