Prior to being cut back the plant was quite large at approximately 5' x 5' and produced a very strong spring 2012 harvest of 50 lbs of artichokes (recorded from first week of April to first week of June 2012). After the prolific harvest we noticed the plant started to go into decline. Originally we thought the reason for the yellowing might be water related, but further reading confirmed the need for extreme pruning on a yearly basis.
(see Perennial Planting section, page 1, in above link for pruning info)
(More info, including notes on withholding water after the spring pruning to assist summer dormancy. Apparently high heat can have an adverse effect on artichoke quality.)