Attention span is "the amount of concentrated time on a task without becoming distracted" and it can easily be measured under proper conditions. In a recent New York Times column Timothy Egan cites recent data: the average attention span (among Canadian subjects) has fallen to 8 seconds, down from 12 in the year 2000.
Imagine orchestra players distracted every eight seconds! Rehearsals and performances would be chaos. It’s hard to imagine a task requiring more intense and prolonged concentration than that demanded of an orchestra violinist. Developing the ability to maintain attention may underlie the benefits of learning to play an instrument in childhood. It’s almost certainly a skill ‘transferrable’ later to other endeavors, like reading.
Listening to classical music does not require quite such a high degree of attention — it’s natural for your mind to wander during a movement of a symphony (not, we hope, to Donald Trump or ISIS) — but the music is composed to travel from a beginning to an end, a narrative, so to speak. That progression, sonata-allegro form only a simple example, is one of the main distinguishing characteristics of ‘classical’ music. It takes you on a musical journey with wonderful sensations and mental images along the way, one leading to another. You aren’t supposed to get off the train whenever you want.
I suppose digital generations can’t imagine not texting or checking email every eight seconds, so there’s little chance for them to withstand Schubert’s ‘heavenly length’ without the frequent breaks they are accustomed to in pop music concerts. Those resemble sports events more than the original concert invented in the 19th century. “Why can’t we talk to friends? Get a beer?” Maybe the reason pop music concerts are so ear-shatteringly loud is to keep the attention of the fans.
As for the claim that they have evolved a new ability to ‘multitask,’ Dan Levitin in The Organized Mind says that multitasking is a very good way to sabotage productivity, efficiency and accuracy.