The whole premise of the survey part of this paper strikes me as very flawed. The idea was "show some professors histograms we know are normal, and see if they

The whole premise of the survey part of this paper strikes me as very flawed. The idea was "show some professors histograms we know are normal, and see if they see bimodality that isn't there". The problem is, they didn't show them 6 random histograms of the normal distribution. For one, they didn't actually show them normal distributions at all; they showed them normal distributions capped at 100. That's going to give you a point mass at 100... making it a bimodal distribution! Second, they didn't give 6 random examples of a capped normal histogram; they gave them 6 examples chosen from a random set of histograms chosen in such a way that 4 of the 6 look bimodal. The survey participants didn't see bimodality that wasn't there, they saw bimodality that was purposefully generated by the histogram selection methodology!