A Direct Comparison of Placebo and Nocebo Effects on Visuospatial Attention: An Eye-Tracking Experiment.

Carina Höfler,Anne Schienle,Jonas Potthoff

doi:10.3389/fpsyt.2019.00446

Abstract

Background: Placebo and nocebo effects on visual attention are still poorly understood. This eye-tracking study directly compared effects of sham transcranial magnetic stimulation (sTMS) that was administered along with the verbal suggestion that the treatment would either increase (placebo) or decrease (nocebo) left-sided visual attention. Method: Twenty women who had reported decreased attention (nocebo responders) and 20 women who had reported increased attention (placebo responders) following sTMS completed a visual search task with three visual load levels. The task was conducted once with and once without the placebo or the nocebo (sTMS). Left-sided fixations and reaction times for left-sided targets (in comparison with right-sided targets) were analyzed. Results: Contrary to the verbal suggestion, the nocebo responders showed more left-sided fixations in the nocebo condition (compared with the control condition) and responded faster to left-sided targets in the high-load condition. The placebo had no effect on fixations and reaction times. Conclusion: These results indicate a more beneficial effect of a nocebo compared with a placebo for the first time. Limits and possibilities of placebo and nocebo interventions are discussed.

Highlights

Placebos and nocebos are physically or pharmacologically inert drugs, devices, or other types of sham interventions that are able to influence various clinical and physiological outcomes related to health [1]
A few studies have shown that placebos and nocebos are able to alter visual attention [e.g., Refs. [2,3,4,5,6,7]]
To identify changes in directed attention due to the placebo/ nocebo treatment, the percentage of left-sided fixations was calculated

Summary

Introduction

Placebos and nocebos are physically or pharmacologically inert drugs, devices, or other types of sham interventions that are able to influence various clinical and physiological outcomes related to health [1]. Whereas placebos have beneficial effects on specific conditions, nocebos are associated with the occurrence of negative symptoms, the worsening of symptoms, or the prevention of improvement. Both effects are considered to be ‘context effects’ because they are mediated by diverse mechanisms, such as learning, expectations, and social cognition [1]. A few studies have shown that placebos and nocebos are able to alter visual attention [e.g., Refs. Placebo and nocebo effects on visual attention are still poorly understood. This eye-tracking study directly compared effects of sham transcranial magnetic stimulation (sTMS) that was administered along with the verbal suggestion that the treatment would either increase (placebo) or decrease (nocebo) left-sided visual attention

Methods

Results

Conclusion