For physical work more money as a reward frequently translates into better or more work. For complicated mental work a sense of self-worth, some autonomy to improve or develop a skill set, and having a purpose to the job beyond mere profit is frequently more important.
Having goals beyond mere money and having the creative freedom to pursue those goals autonomously to some extent can produce superior on the job performance.
This link provides some scientific evidence to support these findings in a very interesting informative format.
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