title: Dentists make larger holes in teeth than they need to if the teeth present a visual illusion of size.
abstract: BACKGROUND
  Health care depends, in part, on the ability of a practitioner to see signs of disease and to see how to treat it. Visual illusions, therefore, could affect health care. Yet there is very little prospective evidence that illusions can influence treatment. We sought such evidence.
  
  
  RESULTS
  We simulated treatment using dentistry as a model system. We supplied eight, practicing, specialist dentists, endodontists, with at least 21 isolated teeth each, randomly sampled from a much larger sample of teeth they were likely to encounter. Teeth contained holes and we asked the endodontists to cut cavities in preparation for filling. Each tooth presented a more or less potent version of a visual illusion of size, the Delboeuf illusion, that made the holes appear smaller than they were. Endodontists and the persons measuring the cavities were blind to the parameters of the illusion. We found that the size of cavity endodontists made was linearly related to the potency of the Delboeuf illusion (p<.01) with an effect size (Cohen's d) of 1.41. When the illusion made the holes appear smaller, the endodontists made cavities larger than needed.
  
  
  CONCLUSIONS
  The visual context in which treatment takes place can influence the treatment. Undesirable effects of visual illusions could be counteracted by a health practitioner's being aware of them and by using measurement.
authors.affiliation: Department of Psychology, University of Otago, Dunedin, New Zealand ; Discipline of Psychology and Cognitive Neuroscience Research Cluster, School of Health and Human Sciences, Southern Cross University, Coffs Harbour, Australia.
authors.forename: Robert P
authors.initials: RP
authors.lastname: O'Shea
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: Chandler
authors.forename: Rajneesh
authors.initials: R
authors.lastname: Roy
mesh_terms: D000328:Adult; D003731:Dental Caries / Q000628:therapy*; D003815:Dentists / Q000523:psychology*; D006801:Humans; D016014:Linear Models; D008875:Middle Aged; D009520:New Zealand; D009903:Optical Illusions / Q000502:physiology*; D012858:Size Perception / Q000502:physiology*