Shift of attention to the body location of distracters is mediated by perceptual load in sustained somatosensory attention

We investigated the impact of task difficulty on neuronal facilitation of to-be-attended somatosensory vibrotactile stimuli and transient tactile distracters during sustained attention. In Experiment 1, we employed an easy detection task and in Experiment 2 a challenging discrimination task. Sustained attention was manipulated by presenting vibrotactile stimuli simultaneously to the index fingers of both hands for a period of 3 s. These stimuli elicited the steady-state somatosensory evoked potential (SSSEP). Subjects attended to one body side and had to detect target-stimuli that were embedded in the ongoing vibratory streams. When subjects discriminated target-stimuli we found increased SSSEP amplitudes of the to-be-attended vibrotactile stream and greater N140 amplitudes of the somatosensory evoked potential (SEP). During stimulus detection no such facilitation of the SSSEP was found. Greater N140 amplitudes elicited by to-be-ignored distracters indicated that they pull attention to that body location under conditions of low load.