1 Introduction A question of central importance at the interface of the grammar and the language process- ing system is how grammatical constraints are deployed during sentence processing. Tis pa- per focuses on how the grammatical constraints of the syntactic Binding Teory (BT)—the structural constraints on refexives and pronouns—apply during online processing. Our study is presented against a background literature proposing a variety of models for the application of the BT during processing. Te Initial Filter approach (Nicol and Swinney 1989) suggests that the BT constraints constrain from the very beginning of processing which potential an- tecedents people consider during processing; the Defeasible Filter approach (Sturt 2003) posits that initially people consider only potential antecedents consistent with the BT, but may at a later stage of processing consider antecedents not sanctioned by the BT; and the Multiple Constraints approach (Badecker and Straub 2002) claims, instead, that the con- straints of the BT apply alongside other processing constraints throughout processing. Using a novel visual world eye-tracking method which manipulates the gender of potential an- tecedents visually, we fnd clear evidence that listeners consider gender-matching potential antecedent NPs for refexives and pronouns that match in gender regardless of whether they are licensed structurally by the BT, consistent with the Multiple Constraints view. We also consider how our results also bear on the formulations of the BT, favoring an approach that recognizes that the constraints of the BT apply diferently for refexives and pronouns, in particular appearing to be less robust for the later. Many thanks to editor Christopher Piñón and an anonymous reviewer for comments that helped to im- prove the paper. We also thank the research assistants who helped collect the data: Kimberly Morse, Amanda Baker, Joelle Mamon, and Seth Rosenblat. Funding was provided by NSF BCS-1150337. Empirical Issues in Syntax and Semantics 10, ed. Christopher Piñón, 269–286 htp://www.cssp.cnrs.fr/eiss10/ © 2014 Jefrey T. Runner and Kellan D. L. Head 269 What Can Visual World Eye-tracking Tell Us about the Binding Teory? Jefrey T. Runner Kellan D. L. Head Tis paper presents the results of a visual world eye-tracking experi- ment that tests two claims in the literature: that the Binding Teory (BT) is a set of “linked” constraints as in the classic BT (Chomsky 1981) and HPSG’s BT (Sag, Wasow, and Bender 2003); and that the BT applies as an initial flter on processing (Nicol and Swinney 1989, Sturt 2003). Our results instead support two diferent claims: that the constraint on pronouns and the constraint on refexives are sep- arate constraints that apply diferently and with diferent timelines, in line with “primitives of binding” theory, Reuland (2001, 2011); and that neither constraint applies as an initial flter on processing, as proposed in Badecker and Straub (2002). Keywords: visual world eye-tracking, Binding Teory, initial flter, defeasible flter, multiple constraints