My last performance (last Thursday) was a performance of a graphic score - Per San Pietro Martire (Saint Peter the Martyr).
It was interesting to play. It was written by Colin Holter and has five sections. There are notes prescribed (four lines) for any instruments and voice. Dynamics are rather like a cityscape skyline or blobs in the case of the base. Each section is timed but the note value is for each player's own interpretation.
I enjoyed the performance. It allows you to play uninhibited by the scoring or by what others might expect (if they know the music). Each musician's interpretation differs but within a overall framework. There is cohesion as we move from section to section and we all start and finish together. Its also interesting in that the score used quarter tones.
The last section is only three notes and is depicted by a large hatchet - St Peter's beheading!
Its not the first time I've played a graphic score but the last one looked quite different. I have also written a graphic score and performance notes called "Self determination" . Again is looks nothing like this one.