Example of Random Token Replacement in a BERT Input Sequence

In a language model's pre-training, a portion of input tokens selected for prediction are substituted with a completely random token from the vocabulary, rather than always using a special placeholder like [MASK]. What is the primary analytical justification for this specific strategy?

Predicting from Corrupted Input

A language model's pre-training process involves selecting a subset of tokens in an input sequence for prediction. One modification technique applied to these selected tokens is to substitute them with a completely random token from the model's vocabulary. Given the original sequence: The cat sat on the mat. If the token sat is chosen for this specific random replacement technique, which of the following is a valid resulting sequence?