Recent evidence suggests that a low-level "early warning system" is constantly operating in the background to protect the organism from threats in the environment (Surveillance Attention, SA). SA is more prominent in the space behind the body as compared to peripersonal space directly in front. Furthermore, SA is assumed to operate at a low, bottom-up level and should be independent of other top-down spatial attention mechanisms. To investigate this possibility, SA and sustained tactile attention (STA) were orthogonally manipulated in the present event-related potential (ERP) study. On different blocks of trials, participants covertly attended to one hand (STA+) to perform a tactile target-nontarget discrimination while ignoring non-target stimuli to the unattended hand (STA-). Because SA is more strongly engaged when stimuli are presented to the hand placed in rear than in front space, posture was manipulated across blocks with participants placing one hand in front (SA-) and the other behind them, in rear space (SA+). In line with existing literature, sensory-specific ERP components elicited by tactile stimuli were strongly modulated by STA, with enhanced positivities for STA+ compared to STA-. Crucially, the same early ERP components were also modulated by SA. However, the effect of SA on touch showed an opposite pattern, with enhanced negativities for SA+ compared to SA-. This dissociation in the pattern of the effects of SA and STA on somatosensory processing reveals that these processes can be simultaneously engaged, are mediated by independent mechanisms and have different effects on touch.
Elena et al. (Wed,) studied this question.