"They" as a gender-unspecified singular pronoun: eye tracking reveals a processing cost.

The plural pronouns they and them are used to refer to individuals with unknown gender and when a random allocation of gender is undesirable. Despite this apparently felicitous usage, "singular they/them" should raise processing problems under the theory that pronouns seek gender- and number-matched antecedents. Using eye-tracking, we investigated whether there was any processing cost associated with using singular they/them. There was a clear cost of number incompatibility for they/them. Thus, although singular they/them is in current usage, it does not appear that they/them is immediately tolerant of a plural antecedent, though such may be rapidly accommodated. The data are consistent with the search account of pronoun resolution and preserve the semantics of they/them as denoting plurality.