"This is a foreground." That was the last lyric left hovering in the mist of Grizzly Bear's breakout 2009 album, Veckatimest, and it's a pretty good image to describe what it's like to listen to one of their records. The key word there is "a," signifying one of many. Whether it's the ethereal, friendly-ghost vibes of Yellow House or Veckatimest's pristine chamber pop, Grizzly Bear create music in deep focus; what's going on in the margins of their songs is just as important and expressive as the center. Taking cues from artists like Talk Talk and Van Dyke Parks, the Brooklyn four-piece make pop music with an ear for the ambient, asking us to notice the importance in detail, the beauty of texture, and the foregrounds that exist all across our spectrum of perception.

While there's no question that Grizzly Bear's last two records have sounded gorgeous, critics of the band have wondered if that's enough. Shields, the band's fourth and most compositionally adventurous record, should put those concerns to bed. Though full of baroque, detail-rich production and latticework melodies, Shields also offers an emotionally resonant core. The album is an excavation of loneliness, melancholy, and self-reliance. It's also a demanding record, without an instantly gratifying single like "Knife" or "Two Weeks" to hook restless ears. But the rewards that come from immersing yourself in it are odd and profound. Shields feels like a summation of Grizzly Bear's strengths, drawing a line from the muddy, minor key sonic palette of Ed Droste's home-recorded Horn of Plenty and stringing it to the heels of boundless ambition.

Shields' spectacular opener, "Sleeping Ute", is the lone track retained from an aborted early session in Marfa, Tex., and it feels like a continuation down the path Daniel Rossen ambled on his 2012 solo EP, Silent Hour/Golden Mile, which sought solace from a busy life in the elements. "If I could be still as that gray hill," Rossen pines, before giving into an admission of humanness: "But I can't help myself." Chris Bear's drum rolls emulate thunder while chords crest with the rhythm of waves. "Sleeping Ute" moves so evocatively and theatrically like water that it sounds like a big-budget radio play of The Tempest. But as grandiose as it often gets, "Ute", like Shields itself, always retains a certain intimacy. These are dark and anxious waters, the choppy and tumultuous movement of the sea inside.

Grizzly Bear have acquired a reputation for politeness; maybe it was the bow ties, maybe it was the passive-aggressive inflection of their most famous lyrics ("Would you always? Maybe sometimes? Make it easy?"), maybe it was just that Michael McDonald collaboration. But Shields serves as a visceral reminder of how unsettled and uncanny Grizzly Bear's music often feels. (Remember that superbly creepy video for "Two Weeks," full of smiles pulled tight enough to induce nightmares?) The pair of lead-off singles, "Sleeping Ute" and "Yet Again", each find a way of transcending the tension of "putting on appearances," one of Grizzly Bear's favorite themes. The lyrics of the Droste-led "Yet Again" detail repression and repose ("Take it all in stride/ Speak, don't confide"), which makes the payoff-- a final minute of instrumental fury lead by the torrent of Chris Bear's percussion and the squiggling lightning strikes of Rossen's guitar-- that much more cathartic. Dynamic shifts like this give the record an air of uncertainty that contrasts with the sheer beauty of the arrangements.

Grizzly Bear is a democracy. They stand in a horizontal row on stage, and you get this sense of intra-band egalitarianism from their records, too. By now, each of the four members has cultivated his own unique and expressive vocabulary, and each feels integral to the sound of Shields. Chris Bear's drumming is lyrical and swift, moving from delicately timed details to big, booming ruckuses (check out the way his percussive rumbles in the background of the verses of "Yet Again" foreshadow its avalanche of a conclusion), while Chris Taylor's penchant for haunting effects and gently buoyant grooves adds an otherworldly weightlessness to these soundscapes. Droste's voice resounds with ache and longing, and there's a newfound and welcome gravel to his vocals that add a raw, unvarnished quality to songs like "The Hunt" and "Speaking in Rounds".

But Shields showcases Rossen's growth most of all. The songs that sounded distinctly his on Yellow House-- "Little Brother" and "On a Neck, On a Spit" in particular-- were grounded in a familiar folk sound. But from the rollicking strums that propel "Speaking in Rounds" to the creaking, rusted textures he teases out of "The Hunt", Rossen's playing on Shields is a seamless blend of folksy textures, jazzy fluidity, and proggy imagination that feels downright inimitable. Joni Mitchell has called her own idiosyncratic tunings as "chords of inquiry," and this feels like an apt term for the tones and inflections that Rossen conjures too. They're stirring precisely because they're unresolved: the progression that ends "Speaking in Rounds"' chorus, for example, chirps like a series of unanswered questions, each one a little more urgent and insoluble than the last.

And that's a great part of Shields' emotional pull: The album reverberates with a sense of irresolution. This was present before with Grizzly Bear-- Yellow House's "Colorado" concludes with a fireworks display of unanswered pleas: "What now? What now? What now?"-- but never to such a degree. And it's that tension that makes returning to Shields so rewarding. The final one-two punch is a stunner, where the poignant grace of "Half-Gate" gives way to the magnificently epic "Sun in Your Eyes". If "Sleeping Ute" was the start of a sojourn from society, "Sun" ends not with a return but a transcendent kiss-off: "So long, I'm never coming back."

This closing pair of songs speaks to the album's complexity. Despite the formalism and easy-to-love production, Shields' best moments inflict a sense of unease that wriggles under the skin and lingers after the final crescendo. But this collection of unvarnished shipwreck-spirituals is after something more challenging than a feel-good ending. With Shields, Grizzly Bear make certain demands--hold still, listen closely-- that seem downright radical in a busy and impatient world.