Boris are a beguiling contradiction of a band, and one it's tough to form a coherent opinion on. On the one hand they play their roles with deadpan seriousness, collaborating with Sunn0))) for the fantastic Altar and writing surprisingly affecting records like the longform beatific drift of 2003's Feedbacker. Then they repeatedly subvert any ounce of sensitivity with balls-to-the-wall blasts of rock & roll, double-necked guitars and a knowing sense of high-strung drama – often seesawing several times within the same album.

But then that forms the basis for a great deal of the group's appeal. One of Boris' defining features is their subtly self-referential, self-mythologising nature, and the resulting ability to riff on the tension between seriousness and theatre. When, as a band, your entire raison d'etre can be neatly encapsulated by any number of your own album titles (Feedbacker; Amplifier Worship; even Pink, with its oversexualised, guitar-as-organ connotations), it would be foolish to operate without a knowing nod to the grandiose, almost Spinal Tap-esque drama of it all. As if to emphasise that point, the group's latest statement is a pair of albums released on the same day, a pretty rock & roll move at the best of times. And adding an exclamation mark for extra weight, they've elected to name Heavy Rocks after one of their earlier albums, furthering that circular internal logic.

As its title suggests, Heavy Rocks largely finds the group in straight-up rock mode, with a few exceptions, but largely lacking the heady sense of lysergic wonder that marks out many of their heavier records. Instead it's fast-paced and with a delicious saccharine twist – 'Window Shopping' pairs female guitarist Wata's power-pop melodies with a thick dose of fuzz, and both 'Tu, La La' and 'Leak – Truth, Yesnoyesnoyes' are both driven by Dinosaur Jr-esque pyromaniac fretwork and dreamily sung vocals. Only ninth track 'Aileron' heads fully outward into scorched stoner territory, a startling shift after an album consisting mostly of thrashy pop songs. And it's quite brilliant, the group's sludgy guitar work in line with one of the album's contributors, Isis' Aaron Turner, gradually ascending to a choral climax worthy of that band's career-defining Oceanic album.

That said, its companion Attention Please proves the better of the two – perhaps offering proof that there's nothing wrong with breaking from the established mode to head off in (somewhat) new directions. An unusually soothing listen, it finds female guitarist Wata's vocals occupying centre stage for a full ten tracks of subtly psychedelic, shoegaze-tinted fuzz-rock. First impressions are solid, if not apparently groundbreaking: the opening title track moves with all the poise of Murray Street/Sonic Nurse-era Sonic Youth, its sparing and metronomic beat neatly countering distinctive Moore-esque guitar flourishes, and 'Hope' finds the group in Kevin Shields mode, Wata's vocals half drowned in a stormy sea of effected guitar. It's a great deal of fun hearing Boris being someone else so effectively: both tracks are infectious and hook-driven, a far cry from much of their back catalogue. They also offer proof, if the group's shapeshifting nature hadn't already provided ample of it, that they're as capable of writing fantastic slices of almost-pop as they are heaving walls of distortion. It's here that both Attention Please and Heavy Rocks display a great deal of common ground. Despite being billed as two distinct sides of a band given to veering between styles, both share the same tendency to wander away from their own allotted territory and bleed into the other.

But for all its stylistic variation, Attention Please is at its best when Boris sound most like themselves – or at the very least pass its more obvious influences through their own lens. 'See You Next Week' and 'Tokyo Wonder Land' are both excellent, slow-burning mood pieces, all static crackle, muted guitar and breathy vocal, allowing the group's natural flair for atmosphere to drift to the fore. The former is particularly affecting, its sweetly sung central melody bringing to mind Yo La Tengo at their most vulnerable, even as the quasi-industrial thrum in the background lends it a hollow and haunted feel. Then, of course, it would be impossible to get through the album without the requisite reference back to the power of rock – in this case, the neatly titled 'Les Paul Custom '86'.

It's difficult to describe Boris' career trajectory as fitting into any sort of overarching narrative. Rather than making conscious directional shifts, each record appears to approach the process of being Boris from a slightly different angle. As a result their back catalogue isn't what you might expect of a long-running rock band – rather than becoming ever more expansive in scope, or tightening their original guise into a finely honed, microcosmic point and remaining there, churning out album after album, it sprawls outward with pleasing asymmetry. That, in 2011, it's as possible to hear a contemporary Boris in (fairly) straightforward pop mode as it to hear them in fire and brimstone mode is pleasing and confounding in equal measure. However, if this pair of albums does offer any clues as to possible future incarnations – a difficult thing to determine, as ever – it would be exciting to hear the group travel further down the route they've started to explore with Attention Please.