Bollywood films are known for powerful dialogues. But once in a blue moon, the film industry delves into characters who live in a silent world, sending top stars like Amitabh Bachchan, Ranbir Kapoor and Priyanka Chopra to classes in the sign language.

Learning lessons for about a month or so, the actors get invaluable glimpses into the lives of the hearing- and speech-impaired, even if they do so only for their roles.

Upcoming projects like Anurag Basu's "Barfee" and Neeraj Ghosh's "Soundtrack" are once again delving into this quietly alive world that remains largely unexplored in Hindi films.

"People don't really touch this section on screen much in comparison to the handicapped, blind or mentally challenged people. The reason could be that deaf people don't create or add drama to the script because their appearance is similar to normal people," Charanpreet Kaur Walia, deputy director of education at the Helen Keller Institute for Deaf & Deafblind in Mumbai, told on phone.

Some estimates say there are over 50 million hearing-impaired people in India. Previously just a handful of films have dealt with this section of society.

One such was Gulzar's "Koshish" in 1972 starring Sanjeev Kumar and Jaya Bachchan. The movie depicted a deaf and mute couple and their conflicts, pain and struggle to carve a niche for themselves in an insensitive society.

Many years later came Sanjay Leela Bhansali's debut film "Khamoshi: The Musical" (1996) with Nana Patekar and Seema Biswas playing a deaf and mute couple.

The year 2005 saw two critically acclaimed films, "Black" and "Iqbal". Megastar Amitabh Bachchan and actress Rani Mukerji learnt the sign language from the Helen Keller Institute.

Big B, who won the National Award for the film, had told: "It was an extremely uplifting experience. It took me six months of training to prepare for the movie. It has turned out to be the most challenging film of my career."

Rani who played a deaf, mute and blind girl, said: "Working on 'Black' has made me realize that those who are physically or mentally challenged are actually much stronger than normal, successful human beings."

Not that the stars gain extensive knowledge of the sign language.

Walia said: "The learning procedure extends to a month mostly. We don't teach them from scratch. As they have limited time and their dialogues are already written, we teach them only those particular sentences."

But the active participation of actors helps in building a connection with hearing-impaired fans.

"The projection definitely helps in connecting the celebrities more with their hearing-impaired fans. When they see these popular actors delivering dialogues in the same manner, they feel more connected and happy, as their communication mode is only the sign language," said Walia.

"Moreover, they don't even need any interpreter then, to explain them the dialogues, so they feel even more attached," she said.

Ranbir, who plays a deaf and dumb person in "Barfee", has learnt the sign language. Co-star Priyanka, who plays a mentally challenged girl in the film, has also been attending classes as she interacts with Ranbir's character in the film.

Soha Ali Khan is gearing up to get into the skin of her character in "Soundtrack" and says: "I play a DJ who loses her hearing but decides to play music despite the handicap. I am learning the sign language."

Even stars from the West like pop star Lady Gaga and "Desperate Housewives" actress Eva Longoria have announced they are learning the sign language to communicate with hearing-impaired fans.

But Walia does wish Bollywood actors would connect more to the speech- and hearing-impaired.

"One may call it the need of the script - but the actors here learn the language and go through workshops keeping in mind their characters and not really to connect. They do their bit by donating money, but expecting that they would learn the sign language specifically for them is a little too much," she said.

"They do it for their role. But we can't blame them as they are busy and tied up with their hectic schedules," she added.

She, however, does feel that their active participation helps in changing their attitude: "The actors come, learn, interact and, after their learning period gets over, they go.

"But we have seen that they make it a point to come and spend some time with them later on. Definetly their attitude changes."