Where lies the boundary between musical performance and performance art? With more and more musicians choosing to incorporate digital or multimedia elements into their performances, concerts are increasingly defying easy categorisation. "Cage and Time" was a case in point: works by a number of composers were stitched into an uninterrupted 90-minute whole, with complex projections and a highly theatricalised manner of performance added to the mix. This ambitious performance was a fascinating collage of sight and sound, yet fell somewhat flat towards its end.

The performance officially marked the start of the Latvian Presidency of the Council of the European Union, which in itself celebrates a number of landmarks in Latvian history: 25 years since the country reasserted its independence, ten since it joined the EU, and one since it adopted the Euro. Bringing together music by some of Latvia's most highly-regarded composers with that by John Cage, Anders Hillborg and Jonathan Harvey, the event drew attention to some oft-overlooked names. This is where the format of the concert fell down: while we are familiar with the bell-like sonorities of Jonathan Harvey's music and Cage's infamous Waterwalk (1959) speaks for itself, the voices of Latvian composers are less well known. Although distinct episodes were identifiable within the unbroken musical flow, the lack of attribution meant that the Latvian composers were somewhat at a disadvantage.

The piece was a melting pot of different styles, incorporating earthy, folk-style ideas, buzzing electronics and ethereal, mysterious passages. Different musical layers jostled against one another, patterns overlapping and textures metamorphosing into something unrecognisable. Contemplative piano interludes (performed by Rihards Plesanovs) bound the piece together, although the frequency of these in the final third erased the sense of vitality and became somewhat repetitive.

Surprisingly, the Latvian Radio Choir assumed a relatively marginal role: spaced around the balcony, the ensemble was mostly used to create an otherworldly halo of sound. Its impeccable blend and warm but pure sound was never as effective as in the chorale as the piece approached its end. The dominant vocal roles were taken by the group of singers on stage, whose contributions ranged from earnest ballads to nonsensical utterances, squeaking and laughing.

The performance was bound together by two elements: sonority and rhythm. The spatialised electronics were used to create a sonic envelope, encapsulating the audience within a beguiling aural world. Barely audible rustlings and unobtrusive drones were deployed to hypnotic effect, while on stage the sonority was of an entirely different type. The use of prepared piano added a quirky groove to sustained, lyrical passages, with extended effects (slapping the instrument and plucking its strings) added further variety. While John Cage's Waterwalk introduced a whole new world of sounds, it stood apart from the rest of the performance as a 'set piece'; while performed with conviction, it felt out of place.

The use of rhythm was the most successful aspect of the piece. Different temporal levels drifted together and then apart again, with the pulse driving the music forwards; it was this component which bound together the disparate styles and ideas. As the piece drew towards its end, the increasingly contemplative mood meant that the rhythmic dimension was side-lined, and the structure sagged as a result.

The accompanying projections were most successful when they were abstract, with the play of black and white creating fascinating counterpoint with the sonic dimension. While pre-recorded videos of the musicians also worked well, expanding on the idea of disembodiment present in the electronically reproduced voices, the animations of a plane and buildings were overly literal and lacked the mesmerising poetry of the former ideas. Just like the music, the visuals lost their way: a more taut structure would have made a world of difference, allowing this stimulating multimedia piece to attain its full effect.