Visual placebo-like effects on subjective assessment of room acoustics: Sound absorption in classrooms

When studying occupants' environmental perception of well-being in indoor spaces, subjective questionnaires are most often used to evaluate indoor comfort domains. When estimating parameters which can be influenced in some way by certain visual aspects, researchers may question if the obtained results could be affected by other issues. In particular, certain aesthetic aspects, such as indoor furnishing or room shape may have impact on occupants’ perceptions. For this reason, this paper focuses on determining the influence of the visual aspect on occupants’ perception of indoor acoustics. Classrooms were chosen as an example of an enclosed environment; we modified the indoor acoustics of a real classroom twice, inserting false and real sound absorbing panels featuring an identical external layout. Following this, using questionnaires, the indoor acoustics perceived by students were analyzed. Results clearly demonstrate that the sight of false absorbers is sufficient to provide the same perceived acoustics as real absorbers. Since only the visual aspect is varied, a placebo-like effect is assessed. Therefore, this issue can bias results when using surveys as a scientific approach in experimental studies.