AFFECT PROBABILITY JUDGMENT ? THE DISCRIMINATION BIAS Amber Sprenger

Title of thesis: CAN IRRELEVANT ALTERNATIVES AFFECT PROBABILITY JUDGMENT? THE DISCRIMINATION BIAS Amber Sprenger, Master of Science, 2005 Thesis directed by: Professor Michael Dougherty Department of Psychology In this paper we used a proactive interference (PI) paradigm to examine the effect of generating irrelevant alternative hypotheses on probability judgments. Two possible effects of generating irrelevant alternative hypotheses on probability judgment were tested: discrimination failure and inhibition failure. The discrimination failure account predicted that participants would fail to identify irrelevant alternatives as irrelevant, causing them to include irrelevant alternatives in their judgments. Then, the magnitude and relative accuracy of participants’ probability judgments would decrease as PI increases. The inhibition failure account predicted that participants would identify irrelevant alternatives as irrelevant, but would fail to inhibit them from working memory. Then, the magnitude of participants’ probability judgments would increase as PI increases, but that the relative accuracy of the probability judgments would be unaffected by the build-up of PI. Three experiments support the discrimination failure account of the effect of PI on probability judgment. CAN IRRELEVANT ALTERNATIVES AFFECT PROBABILITY JUDGMENT? THE DISCRIMINATION BIAS