They may be a venue to socialise and keep in touch with people, but social networking websites like 'Facebook' and 'Twitter' are making people "less human" by isolating them from reality, a US sociologist has claimed.

According to Prof Sherry Turkle of Massachusetts Institute of Technology, the way in which people frantically communicate online via social networking sites can be seen as "a modern form of madness".

In her new book, 'Alone Together', Prof Turkle writes that a behaviour that has become typical may still express the problems "that once caused us to see it as pathological".

She explains that people are become isolated from reality due to such social networking sites because technology is dominating our lives and making us "less human", 'The Daily Telegraph' reported.

Under the illusion of allowing us to communicate better, technology is actually isolating us from real human interactions in a cyber-reality that is a poor imitation of the real world, she suggests.

"We've invented inspiring and enhancing technologies, yet we have allowed them to diminish us," she writes.

Her warnings -- and those from other cyber-sceptics -- follow the death of Simone Back, a woman in Brighton who posted a suicide note on Facebook that was seen by more than 1,000 of her "friends".

Yet none of them called for help -- instead trading insults with each other on her Facebook wall.

Turkle's book has created significant attention in the US because her previous works, The Second Self and Life on the Screen, were most positive about changing technology.