Earlier this year, Audible recruited science fiction writer Orson Scott Card to write an elaborate, six-hour dramatization of his best-selling 1985 novel 'Ender's Game.' The story unfolds entirely in dialogue, punctuated by background music and sound effects. The project was recently recorded in Los Angeles by a cast of 28 narrators, including superstar narrator Scott Brick, songwriter Janis Ian and English actress Samantha Eggar. Audible will release 'Ender's Game Alive,' this October, a month before the premiere of a big-budget Hollywood movie based on the novel, starring Asa Butterfield, Harrison Ford, and Hailee Steinfeld.

Mr. Card says the radio play has the same premise as the novel, but consists of entirely new material. Rather than telling the story through an omniscient narrator, from the perspective of the novel's young protagonist, Ender, the plot emerges though dialogue, from multiple points of view.

'It's not a simple adaptation, it is a new telling of the same story,' Mr. Card said.

Some novelists are bypassing print and releasing novels as audio exclusives. This week, British novelist David Hewson released his new mystery, 'The Flood' straight to audio with no print edition. His audio publisher, Whole Story Audiobooks, holds exclusive rights to the material for a year. Mr. Hewson says he hasn't shopped the novel to print publishers yet.

'Until a year or two ago, audio had to come out with print, but audio is kind of its own thing now,' said Mr. Hewson, who has published 22 novels. 'It's become a hot medium.'

Mr. Hewson has already developed something of a following among avid listeners. He's co-wrote four other original audio novels, including novelizations of 'Macbeth' and 'Hamlet,' which he co-wrote with A.J. Hartley, a thriller writer and Shakespeare scholar at the UNC Charlotte. The nine-hour and 45-minute novelization of 'Macbeth,' which paints a much more sympathetic portrait of Shakespeare's power-hungry protagonist, generated more than 1,000 reviews on Audible and drew an average of four stars. Their take on 'Hamlet,' which Audible will release this fall, features a punchier Ophelia, a less gloomy Hamlet, and swaps in snappy dialogue for Hamlet's famous soliloquies.

Mr. Hewson has discovered that writing for audio requires different techniques from prose writing. Word repetition becomes glaringly obvious. So do unintentional rhymes. Location changes have to be telegraphed at the beginning of the scene, so that listeners aren't confused.

'Complex sentences, long subordinate clauses -- they don't work, people get bored and confused by them,' he says. 'You're looking for the writing to disappear so that all people hear is the story.'

The rapid rise of audio books has prompted some hand- wringing about how we consume literature. Print purists doubt that listening to a book while multitasking delivers the same experience as sitting down and silently reading. Scientific studies have repeatedly shown that for competent readers, there is virtually no difference between listening to a story and reading it. The format has little bearing on a reader's ability to understand and remember a text. Some scholars argue that listening to a text might even improve understanding, especially for difficult works like Shakespeare, where a narrator's interpretation of the text can help convey the meaning.

Less is known about how well people absorb stories when they are also driving or lifting weights or chopping vegetables. Commuters still account for half of audio book buyers, according to a report from the research firm Bowker, which tracks the book business. Daniel Willingham, a psychology professor at the University of Virginia who has studied reading and listening comprehension, said that multitasking compromises a listener's attention, unless the task is truly automatic. Jogging on a treadmill would probably be fine, but running on a trail might be too distracting to fully absorb the text, he said.

Some writers worry that the practice of silent reading could be threatened, as impatient and busy readers no longer take time to concentrate on a text.

'If we come to think reading is this secondary activity we do while doing other stuff, then we lose that deepest and most important kind of reading,' said Nicholas Carr, author of 'The Shallows: What the Internet is Doing to Our Brains.' 'The broader danger is that technology will give us the illusion that everything can be done while multitasking, including reading.'

Audible is now funding cognitive research at Rutgers University to study the brain activity of test subjects while they are reading a text, listening to it, reading and listening simultaneously, and switching between the two modes. The research is continuing and has yet to be published, but early results suggest that listening to a narrator may be more emotionally engaging than silent reading, particularly for men, says Guy Story, Audible's chief scientist.

Certain book lovers can't fathom diluting the immersive experience by switching back and forth. 'It's like going to the movies and watching the first half-hour then going home and reading the script,' says Robin Whitten, editor of Audiofile magazine, which reviews audio book narrations.

For others, the distinction between print and narrated works has already evaporated. Michele Harvey, 48, a software developer who lives in Centreville, Va., has a collection of more than 470 audio books, and close to 2,000 ebooks, mostly romances and fantasy. She often buys both an audio book and an e-book so that she can stick with the story while she's doing other things. Throughout the day, she listens to books on her Android phone. She listens in the car on her way to and from work, and while she's making dinner, folding laundry and loading the dishwasher. Then, at night, after her 9-year-old son is in bed, she picks up the story on her Kindle, right where the narration left off, and reads for two or three hours. She says she's often able to recall the parts she listened to better than the passages she read, particularly if the book has a talented narrator.

When people ask her about the best or most memorable book she's read, she often mentions Susanna Clarke's fantasy novel 'Jonathan Strange & Mr. Norrell.'

'I keep having to remind myself I have never actually read it,' she says. 'I listened to it.'