The P600 for singular “they”: How the brain reacts when John decides to treat themselves to sushi.

There has been increased awareness that individuals need not have a binary gender identity (i.e., male or female), but rather, gender identities exist on a spectrum. With this increased awareness, there has also been an increase in the use of they as a singular pronoun when referring to individuals with a non-binary gender identity. Has the processing of singular they changed along with a change in its usage? Previous studies have demonstrated that sentences in which they is co-indexed with singular antecedents, are judged acceptable and are easy to process, but only if the antecedents are non-referential and/or have ambiguous gender; co-indexing they with referential antecedents with unambiguous gender (e.g., Mary) results in lower acceptability ratings and greater processing effort. We investigated whether participants who frequently interacted with individuals with a non-binary gender identity and/or identified as having a non-binary gender themselves would process sentences in which themselves was co-indexed with singular antecedents similarly. We found a significant P600 effect for sentences in which themselves was co-indexed with singular referential antecedents with unambiguous gender, but failed to find a P600 effect when the antecedents were non-referential and/or had an ambiguous gender. This pattern of results is consistent with behavioural results from previous studies, suggesting that the change in the usage of singular they has not resulted in a corresponding change in the way in which this pronoun is processed.