Eye contact is a salient social cue which is assumed to influence early brain processes involved in face perception. The N170 component in the event-related potential (ERP) has frequently been reported to be larger to faces with an averted rather than direct gaze towards the observer. In most studies, however, this effect has been investigated in comparatively artificial, passive settings where participants were instructed to fixate their gaze while observing occasional gaze changes in stimulus faces. Yet, it is unclear whether similar mechanisms are in place during naturalistic gaze interactions involving the continuous interplay of directed and averted gaze between the communication partners. To fill this gap, we compared passive viewing of gaze change sequences with an active condition where participants´ own gaze continuously interacted with the gaze of a stimulus face; while recording ERPs and monitoring gaze with eye tracking. In addition, we investigated the relevance of emotional facial expressions for gaze processing. For both passive viewing and active interaction, N170 amplitudes were larger when the gaze of stimulus faces was averted rather than directed at the participants. Furthermore, eye contact decreased P300 amplitudes in both conditions. Emotional facial expression influenced N170 amplitudes but did not elicit an early posterior negativity nor did it interact with gaze direction. We conclude that comparable mechanisms of gaze perception are in place in gaze interaction as compared to passive viewing, encouraging the further study of the eye contact effect in naturalistic settings.
Ultrasound mid-air haptic (UMH) devices are a novel tool for haptic feedback, capable of providing localized vibrotactile stimuli to users at a distance. UMH applications largely rely on generating tactile shape outlines on the users’ skin. Here, we investigate how to achieve sensations of continuity or gaps within such 2D curves by studying the perception of pairs of amplitude-modulated (AM) focused ultrasound stimuli. On the one hand, we aim to investigate perceptual effects which may arise from providing simultaneous UMH stimuli. On the other, we wish to provide perception-based rendering guidelines for generating continuous or discontinuous sensations of tactile shapes. Finally, we hope to contribute towards a measure of the perceptually achievable resolution of UMH interfaces. We performed a user study to identify how far apart two focal points need to be in order to elicit a perceptual experience of two distinct stimuli separated by a gap. Mean gap detection thresholds were found at 32.3mm spacing between focal points, but a high within- and between-subject variability was observed. Pairs spaced below 15mm were consistently (>95%) perceived as a single stimulus, while pairs spaced 45mm apart were consistently (84%) perceived as two separate stimuli. To investigate the observed variability, we resort to acoustic simulations of the resulting pressure fields. These show a non-linear evolution of actual peak pressure spacing as a function of nominal focal point spacing. Beyond an initial threshold in spacing (between 15mm and 18mm), which we believe to be related to the perceived size of a focal point, the probability of detecting a gap between focal points appears to linearly increase with spacing. Our work highlights physical interactions and perceptual effects to consider when designing or investigating the perception of UMH shapes.
Attentional cueing tasks using gaze direction as spatial cues have sometimes yielded an early directing attention negativity (EDAN) component in the ERP, presumably reflecting the initial orienting toward the cued location. However, other studies have failed to identify an EDAN component for gaze cues, yielding an inconsistent picture. In the present study, we re‐examined the EDAN to gaze cueing, using a continuous task where the specific direction of the gaze changes was task irrelevant. Face stimuli changed gaze direction several times during each trial between direct, left‐, and right‐averted positions. Participants counted the number of gaze shifts during the trial. Results showed an unusually large EDAN‐like ERP asymmetry at posterior scalp sites that was of similar amplitude for large and small gaze shifts into the periphery. Shifts from an averted position toward a direct gaze elicited a qualitatively similar but smaller effect than shifts into the periphery. Together, these findings shed new light on gaze‐elicited spatial attention as they indicate a reflexive attention orienting, following the direction of gaze motion, even when the gaze direction itself is irrelevant for the task.
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