Erlewine, Michael Yoshitaka, 2017. “Why the null complementizer is special in complementizer-trace effects.”
A Pesky Set: Papers for David Pesetsky, pages 371–380.

As first noted by Perlmutter (1968), long-distance subject extraction in English must proceed across a null local complementizer, rather than the pronounced ("that") variant. In this squib, I present a brief proposal for the that-trace effect which explains the direction of this asymmetry, using the Spec-to-Spec Anti-Locality constraint on A’-movement proposed in my previous work and Fox & Pesetsky’s Cyclic Linearization view of successive-cyclicity. I propose that the asymmetry is not accidental and reflects a property of unpronounced terminals in linearization.