Proceedings of the Annual Meeting of the Cognitive Science Society

The dilution effect occurs when the introduction of non-diagnostic information lessens the impact on reasoning ofdiagnostic information despite having no relevance to thehypothesis in question. While the effect has been reproducedin several studies, the psychological basis of the effectremains unclear. Some believe it to be conversational whileothers believe it to be cognitive and social.The paper tests the conversational basis of the effect byminimising pragmatic, conversational influence. To this end,it makes use of a legal setting with witness testimonies. Thestudies replicate the dilution effect, which suggests that thebasis of the results in the original studies is notconversational. However, the credibility of the sourcestrongly influences whether or not the effect occurs. Ifreliable sources provide the non-diagnostic information, theeffect lessens. Conversely, if unreliable sources provide thenon-diagnostic information, we observe a stronger dilutioneffect.