Group labels are what make outgroups cognitively exist for perceivers.

Evidence

One of the most straightforward aspects of Allport’s perspective is his notion that the use of antilocutions is a reflection of social categorization. This notion is illustrated in Allport’s (1954/1979) signature phrase, “nouns that cut slices” (p. 174), referring to the group labels that cluster the social world into meaningful groups for the perceiver. This is also illustrated in direct statements, such as “until we label an outgroup it does not clearly exist in our minds” (p. 49). — , Rudman, Laurie A - On the Nature of…, 1261