**Poster Session B** - Join me on Zoom chat during the Friday Poster Session! https://northwestern.zoom.us/j/5140702808 Please leave comments on this page or reach out over email! Contact Email: worth@u.northwestern.edu Negative polarity items (NPIs) are lexical items which are grammatically licensed by a c-commanding negative element in a sentence. The grammaticality illusion for some sentences containing unlicensed NPI has been tied to general accounts of grammaticality illusions. NPIs have a grammatical mirror, positive polarity items (PPIs), which instead have an anti-licensing constraint. In other words, PPI are lexical items which are ungrammatical in environments that can host NPI. We find that PPI are susceptible to an illusion of *ungrammaticality *in the same environments where NPI are susceptible to an illusion of grammaticality, in both offline and online measures. This suggests current processing approaches to illusion may need revised in order to correctly predict illusions of ungrammaticality.