What does Learn to Ride Smart say about a full-face helmet and hearing?

1. It blocks all useful traffic sounds, so a full-face helmet is inherently unsafe for normal road riding
2. It is permitted only for high-speed highway travel and must be replaced by an open-face helmet in cities
3. It does not necessarily restrict hearing and may reduce wind and engine noise
4. It is intended for passengers only because the operator must keep both ears completely uncovered