Interpreters: Grandmasters of Language Processing
Research in skill based activities indicates that experts possess more skills and process information more efficiently than amateurs.
Psychologist and chess player Adrian de Groot devised and conducted experiments in the 1940s, which were improved upon and refined by William Chase and Herbert Simon of Carnegie-Mellon University in 1973. In the Chase Simon studies, chess players of different strength were given legitimate positions to study for a limited time and then told to reconstruct the positions from memory. Grandmasters performed better than experts, and the experts did better than novices. The surprising discovery was that when pieces were placed randomly, the grandmasters did no better than novices.
For example, the experts would have no difficulty in memorizing and reconstructing from memory the position on the left, but would do no better than novices when presented random positions on the right, even though the number of pieces are the same for both diagrams. Similar experiments in music notation could be conducted.

Score from: http://educ.queensu.ca/~fmc/october2001/Twinkle.htm
Researchers could gather specific subjects and assess their respective memory recall abilities. Without doubt, musicians will outperform non musicians when presented with meaningful data, but musicians and non musicians will perform similarly when confronted with meaningless information. These experiments demonstrate that experts do not necessarily have superior memory capacity, but instead they are able to process meaningful information more efficiently than novices.
Upon closer scrutiny of the above chess example, the expert should pronounce White mates in 3 involving a discovered check, queen sacrifice and smothered mate. Similarly, in the music example our musicians should announce it is the score for "Twinkle Twinkle Little Star" and might even give us an impromptu performance when prompted.
In the context of interpreting, when presented with a piece of written text or hearing a speech, the interpreter is processing and applying information in a manner that is much more sophisticated than the novice. Chunking theory as proposed by Simon and Chase might be at work here, but perhaps there is even more going on in the interpreter's mind.
For example, when interpreting the Chinese text: “己所不欲勿施于人”, the novice would offer clumsy efforts while we could go straight to: "do not unto others what you would not have them do unto you". At this point we may be satisfied and congratulate ourselves for attending Ethics 101 and remembering what was said in class. The expert without dropping a syllable would have interpreted: "Golden Rule" instead. Yes, he recalled the Chinese memory chunk and the Mahabharata chunk, but deep in his memory he also recalled the Golden Rule chunk. His preference for "Golden Rule" is due to it's relative simplicity, ease of enunciation, time savings, and target audience's cultural familiarity with the term.
As numerous studies have shown, expert ability takes a long time to develop. In chess and music it is common to spend years in practice and competition to be proficient. To become a competent interpreter would likewise take a long process, but employers are not willing to provide years of training in today's competitive environment. Employees are expected to perform professionally from day one on the job. Therefore classroom instruction under the tutelage of practicing interpreters is one way of learning the necessary skills. Ideally, interpretation programs should include apprenticeship courses, where students can observe interpreters exercising their craft.
Finally, the interpreter, like the chess grandmaster, should have a wide repertoire of responses to various situations. He should be able to recall from memory different "chunks", sifting through them for the most apt interpretation. The interpretation should be accurate, grammatically correct and in the appropriate linguistic register. All this is done instantaneously while maintaining grace under pressure.
Bibliography and Suggested Reading
W.R. Hartson, P.C. Wason, The Psychology of Chess, B.T. Batsford Ltd, p50-64
THE EXPERT MIND., By: Ross, Philip E., Scientific American, 00368733, Aug2006, Vol. 295, Issue 2
online version:http://www.hawaii.edu/geog_mr/shogi/ross.htm
Wikipedia: Golden Rule
First published on 24 May 2007. Copyright of Pierre Wong
Revised on 12 June 2008.