This is just an exert. For more info, follow the link at the end.
Response: We have never found this to be the case. Bike helmets do not affect vision. If the helmet intrudes on upward vision it will be evident to the user, who can adjust the tilt of the helmet to raise the front lip. Bike helmets also do not affect hearing, since normally they do not cover the ears. That question is easily settled by riding with and without a helmet, or by standing beside a road with helmet on and off. The US DOT has conducted a study on this question using motorcycle helmets and found that even these larger helmets with additional coverage do not affect hearing, and have little effect on vision.
Response: This is a subjective judgment for each individual, and is easily tested by the user. Most riders find today's helmets light, comfortable and cool enough.
Response: Putting a helmet on takes less time than putting on bike gloves, but it does add another step every time you get on the bike, and we agree that it can be a nuisance on very short trips from one store to another. So is fastening your seat belt in a car, but you do it for safety. The helmet can be left with the bike, locked if the bike needs to be locked in that location.
Response: We have ample evidence from medical studies that helmets are indeed highly effective, and you will find references on our statistics page. Although bicycle helmets are tested in labs in impacts at 14 miles per hour, they usually do a fine job of protecting the rider in a crash where the initial forward speed is higher, because the severity of the impact is normally determined by the closing speed of the head and pavement, not by the rider's forward motion. Research on crashed helmets shows that most people hit the ground at a relative speed of about 10 MPH. If a rider is hit by a car or hits a brick wall at 30 mph and the head takes a direct blow at that speed, no helmet will prevent injury or death. But that type of crash is rare, and helmets are designed for the severity of the most frequent crash types.
As a reality check, ask any club cyclist about helmet effectiveness. They have shared experience that gives them more perspective on crashes. Club cyclists were the first to adopt helmets in the U.S., and the first to see the results. You will see helmets on all or most of the riders on virtually any club ride in the US. Among racers, the United States Cycling Federation (now USA Cycling--our road racing organization) adopted a mandatory helmet rule in 1986, because every year two or three riders were being killed in their races and more were suffering head injuries. In the years since it has been rare for a racer to die in a US race, even though their crashes occur at racing speeds. We have a page up on helmet protection limits.