title: Similarity and number of alternatives in the random-dot motion paradigm.
abstract: The popular random-dot motion (RDM) task has recently been applied to multiple-choice perceptual decision-making. However, changes in the number of alternatives on an RDM display lead to changes in the similarity between the alternatives, complicating the study of multiple-choice effects. To disentangle the effects of similarity and number of alternatives, we analyzed behavior in the RDM task using an optimal-observer model. The model applies Bayesian principles to give an account of how changes in the stimulus influence the decision-making process. A possible neural implementation of the optimal-observer model is discussed, and we provide behavioral data that support the model. We verify the predictions from the optimal-observer model by fitting a descriptive model of choice behavior (the linear ballistic accumulator model) to the behavioral data. The results show that (a) there is a natural interaction in the RDM task between similarity and the number of alternatives; (b) the number of alternatives influences “response caution”, whereas the similarity between the alternatives influences “drift rate”; and (c) decisions in the RDM task are near optimal when participants are presented with multiple alternatives.
authors.affiliation: Cognitive Science Center Amsterdam, Plantage Muidergracht 24, 1018 TV Amsterdam, The Netherlands. l.vanmaanen@uva.nl
authors.forename: Leendert
authors.initials: L
authors.lastname: van Maanen
authors.forename: Raoul P P P
authors.initials: RP
authors.lastname: Grasman
authors.forename: Birte U
authors.initials: BU
authors.lastname: Forstmann
authors.forename: Max C
authors.initials: MC
authors.lastname: Keuken
authors.forename: Scott D
authors.initials: SD
authors.lastname: Brown
authors.forename: Eric-Jan
authors.initials: EJ
authors.lastname: Wagenmakers
mesh_terms: D000293:Adolescent; D000328:Adult; D001288:Attention; D001499:Bayes Theorem; D002755:Choice Behavior; D003657:Decision Making; D004192:Discrimination, Psychological; D005260:Female; D005793:Generalization, Psychological; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D008960:Models, Psychological; D009039:Motion Perception; D010364:Pattern Recognition, Visual; D011930:Reaction Time; D055815:Young Adult