The placebo effect in reading performance: A cross-over experimental study

Converging evidence suggests that clinically-relevant benefits from placebo treatment - such as words and rituals of the therapeutic act - may change the chemistry and circuitry of the brain underlying perceptual and sensorimotor enhancements. The present study aimed to test whether placebo and nocebo effects can also modulate high-level processing, such as single word reading and pseudoword decoding. In a within-subject experiment, 102 young adults were asked to wear a sham pair of glasses purported to modify reading performance, and were informed that the purpose of the study was to evaluate the effects of these special glasses on pupil size. Positive and negative expectations were induced both explicitly, through verbal instructions provided by the experimenter, and implicitly, through feedback-based learning via manipulation of computerized performance feedback. Subjective effects and Big Five personality, as well as pupil size and heart rate, were also measured. Participants reported the lenses had influenced their performance. Explicit placebo expectations enhanced word and pseudoword reading speed. In contrast, negative expectations did not significantly impair performance, although nocebo might exert an effect in longer tasks. Expectations were not affected by the conditioning phase. Big Five factors did not modulate the effect of expectations. No significant differences were observed between the placebo and nocebo conditions in heart rate and pupil size. These findings highlight the need to consciously harness such effects in clinical practice and to rigorously control for such effects during reading training programs.