If the RNN LMs were keeping track of whether or not a sentence contained a gap, we would expect sentences with different types of RCs to be more similar to each other in the RNN LMs' representation space than lexically matched sentences without a gap.
if RC X and RC Y are two different types of RCs and Coord Y is a sentence with verb coordination lexically matched with RC Y , then we would ex- Consistent with this prediction, the adaptation effect for models adapted to RCs was greater when they were tested on sentences with other types of RCs than when they were tested on sentences with coordination (bottom panel of Figure 2b).