I was reading that a violinist's left hand is not as special as the part of the brain that feels what the hand feels. That can grow to much more than the corresponding part of the brain of someone who doesn't use those fingers for any particularly specialized task. In blind people, the part of the brain that the sighted use to process visual signals is repurposed for other activities: it doesn't just sit there unused.
There is a prosodic brain. For example, I can hear a hendecasyllable as such, before I even speak it aloud. The analysis happens immediately. I am not counting syllables but adjusting the line to a set of paradigms.
I guy at the Córdoba conference, an American living in Spain for many years, presented on Prufrock. When he read aloud he made sure to over-emphasize the metrical pattern as much as he could.
The 11-syllable line in Spanish combines fluently with the 7. One common patter for the 11 is
7 + 4
That means that you can take any seven syllable line, and turn it into an 11 by adding four. Conversely, the first seven-syllable phrase of an 11 is indistinguishable from a 7. This is because the 7 has its accent on 6, and the 11 (in one of its major variants) has its major accents on 6 and 10.
A 7-syllable phrase will often fall into the patter of
3 + 4
de hierbas / agostadas
anude / la corbata
los muros / de verano
4 + 3
de su sueño / de siglos
done el árbol / arraiga
los muchachos / sestean
So the 11 will often take the pattern
3 + 4 + 4
4 + 3 + 4
If we throw the major accent from 6 back to 4, then we get lines in the pattern
5 + 6
Follow that with 7, as in a silva and you find
5 + 6 + 7, where the 7 can be 3 + 4 or 4 + 3.
People think of metrics as a set of rigid constraints. Thoughtless people. I think of a process of a kind of conquest of fluidity. The fluidity of English blank-verse is a marvelous thing, and the equivalent in Spanish, as Carlos Piera has pointed out to me, is the baroque silva. Free verse in Spanish is essentially a rhymeless silva with some verses of nine thrown in from time to time.
The paradox, of course, is that the perfect model of fluidity is prose itself. Verse moves toward a prose idea as is gets looser and more fluid. Juan Ramón Jiménez wrote out all his marvelous free verse as prose poetry in his later life.
Someone once said that you couldn't tell Milton from prose unless you saw it on the page. That is at once profoundly dumb and very astute, because it all comes down to perception. If we are reading verse on the page we know to tap into the prosodic brain. If we are reading prose we tend not to. Perhaps wrongly, but there it is.