Last season, the mental homework necessary to understand each episode frustrated fans.,Polar bears in the past (well, not anymore), ABC’s mysterious island-based drama “Lost” dives into its fourth season, still brazenly expecting its viewers to do more than tread water.

Last season, the mental homework necessary to understand each episode frustrated fans. Despite the media endlessly praising its premiere season and obsessive viewers storming the Internet, “Lost” struggled in the ratings last year. The growing mountain of questions, infrequent direct answers and the random appearance of polar bears in the setting’s tropical climate created skepticism that the writers would ever reveal what was really going on with the survivors of Oceanic Flight 815.

After the show averaged 18 million viewers per episode in its first season, a sparse 13 million tuned in for the third season finale, leaving “Lost” eighth in the ratings when it once held the number two spot.

Currently, the show is doggy-paddling toward its former glory. According to the Nielsen ratings, 16 million people watched the premiere two weeks ago. The show won ABC the top spot of the night and took the ever-important 18-49 demographic in its time slot.

If the vast amount of reality programming is an accurate indication of people’s attention spans, it is strange that “Lost,” which relies heavily on its complicated concept and plot, still manages to captivate a large audience in its fourth year. “Lost” fans are willing to wait, albeit impatiently, eight months between seasons, while “America’s Next Top Model” fans need a new season’s episodes after only a few weeks.

This is because “Lost,” with all its cranial run-around, still provides the kind of attention to detail rarely seen on television. Every name, object, reference and action is full of cryptic, well-thought-out foreshadowing. A viewer could watch a single scene over and over again and still not take away every clue the writers subtly provide.

For example, characters are often named after famous philosophers whose writings and views match the character’s role in the greater story. Philosopher John Locke’s idea of the mind as a blank slate corresponds with “Lost”-ie John Locke’s increasingly open-minded take on living out his life on the island. The philosopher Locke was closely associated with fellow thinkers Jean-Jacques Rousseau and David Hume. The two characters Locke interacts with most on the island are appropriately named Desmond Hume and Danielle Rousseau.

“Lost” is television that makes fans think. It makes them search for answers in ancient texts, Greek mythology and colonial-era legend. Not only do fans obsessively watch the show, but to get the full story, they follow its online Web-isodes, theorize with friends and hunt for clues on the ABC-constructed Oceanic Airlines Web site. Bringing up “Lost” at a party or into a casual conversation, for better or worse, instantly divides the room into those who watch the show and those who don’t. The shows producers have created a whole alternative Internet world surrounding the fictional airline and those who boarded its ill-fated flight. “Lost” exists in a universe fans can tangibly immerse themselves in and those who drifted are once again toeing the shoreline, prepared to jump in.

Oddly enough, the show’s rise in ratings coincides with the death of beloved castaway Charlie Pace, the heroin-addicted English ex-rock star. Actor Dominic Monaghan’s performance of the likable, Pete Doherty-esque Charlie’s sacrifice to save the rest of the survivors, including his love interest’s newborn baby, was absolutely heartbreaking to watch.

After the third season finale, the news flooded the Internet: not only had the writers killed off one of the show’s most adored characters, but in the last scene, they introduced flash-forwards to replace the typical flashbacks to the survivors’ lives before the crash.

Thankfully, Charlie’s efforts were not in vain; the survivors were able to make contact with the outside world and call for help. Season three ended with some of them excitedly preparing to leave the island and others grappling with Charlie’s final message: to beware their would-be rescuers.

This constant ambiguity keeps the series’ viewers unsure of the fate of all of the survivors. The writers assume their audience is intelligent and they refuse to pander to the average couch potato.

While the ratings have started to rise, it hasn’t sacrificed its propensity for titillating twists and mind-melting madness. The brilliance of the fourth season will depend on the writers providing answers that still splinter into questions and the audience’s willingness to see the jungle for the trees.