From the PlanetXbox360 feature editorial:
"Every single time a player snags another orb in Crackdown 2, they’re rewarded by a subtle audible tone in addition to visual cues denoting advancement towards the next level in whatever skill they might be filling at the time. While the activity may seem boring and even detrimental to the overall play experience according to some, there is very little denying that there is an addictive quality to nabbing another orb easily relatable to Pavlov’s psychology of classical conditioning. Ivan Pavlov, a Russian doctor and psychologist was the first to expound on the idea of classical condition through his theoretical research, which eventually found grounding in the scientific community. The essential basis of the training involves the utilization of neutral stimulus in conjunction with outside stimulation of significance."