Lecturers in America who once embraced the portable computer as an invaluable learning aide are increasingly banning them from class, The Times of London reported Thursday.

The move came about to prevent students from updating their Facebook profiles or playing World of Warcraft when they should be listening.

Allan Rubin, a professor of geosciences at Princeton University, banned laptops in his 120-strong class on natural disasters after discovering that some of the students were playing online poker during his lectures.

"What I found, and it was getting worse over the years, was that a larger and larger fraction of the students just had their heads buried in their laptops as I lectured," he said.

"I know from teaching assistants who were wandering around when the laptops were open that they were surfing the web. They were playing poker with each other.

"When I lecture now, there is a sea of faces that are looking at me."

Kieran Mullen, a science lecturer at the University of Oklahoma, went even further by destroying a student’s laptop with liquid nitrogen, in a videotaped scene later broadcast on YouTube.

Mullen admitted that the destroyed laptop was already broken and was provided by a willing student - but he proved his point.

"Students in a large lecture class can be distracted by others watching movies, reading news websites and playing games on their laptops. I had warned students many times about not using their laptops during lecture," he said.

"I am perfectly happy with students actually taking notes on their laptops in class. The demonstration did have the desired effect of improving student attention."

Studies found that "multitasking" actually impedes learning and that laptops distract not only the user but also those sitting nearby.

Diane Sieber, who teaches humanities for engineers at the University of Colorado, says it is now clear that people who think they are multitasking are actually just being distracted from one task to another.

"They have shown this in studies of cell phones or texting in cars. We do not seem to know how distracted we are," she said. "We are not multitasking. We are serialized interrupting. We are simply being interrupted."

Click here to read more on this story from the Times of London.