Applying the semantically motivated grammars may have been beneficial in recognizing the semantic referents correctly because the system can explicitly learn them and their appearances in certain patterns in contrast to the trigram model.
if an utterance "pink nine passes the ball to pink seven" appears during recognition and "pink seven" has not been observed in the context of the preceding words during training, then the n-gram model would assign a low probability, likely leading to a recognition error such as "pink eleven".