Nocebo and pseudo-neglect: Paradoxical effects detected with eye-tracking.

The knowledge about effects of placebos and nocebos on specific visual attention processes is still very limited. In the present eye-tracking study, it was analyzed if a nocebo (sham transcranial magnetic stimulation) is able to elicit left-sided attentional deficits (pseudo-neglect). Fifty-two healthy participants performed a search task on the computer, once with and once without the nocebo. Indicators of left-biased search behavior (e.g. fixation count, reaction times for left vs. right-sided target detection) and affective state (e.g., valence, arousal) were assessed. The sample was divided into two groups (nocebo responder, non-responder) based on the experienced effectiveness of the nocebo. The nocebo treatment was associated with a positive and calm affective state. Contrary to the verbal suggestion, the nocebo increased the number of fixations and the dwell time on the left side of the computer screen. Moreover, the nocebo decreased the detection time for targets on the left side. These paradoxical nocebo effects were restricted to nocebo responders. Possible implications of nocebo-related compensatory behaviors for neuropsychological therapy are discussed.