In Lew & Howe (2016), schema-relevancy was measured on a scale of 1 to 10 (very usual to very unusual). Low rating (below 3) were regarded as relevant and rating above 5 were regarded as irrelevant. Irrelevant objects therefore include neutral and unexpected objects.
Lew, A. R., & Howe, M. L. (2016). Out of Place, Out of Mind: Schema-Driven False Memory Effects for Object-Location Bindings. Journal of Experimental Psychology: Learning, Memory, and Cognition. https://doi.org/10.1037/xlm0000317