Excerpt: "A form of aversion therapy in which a covert response such as a thought or an image is followed by an imagined aversive event. An individual may imagine himself relaxing in front of the television and eating a large bowl of hot buttered popcorn, enjoying the smell and taste; he then imagines the rolls of fat accumulating around his waist, having to buy new clothes, and being rejected by his girlfriend because of his weight. In covert sensitization the cognitive elements of the stimulus-response sequence rather than overt responses and external stimuli are dealt with. The goal is to block the thoughts and fantasies that precede undesired overt behaviors and increase their probability."
Bufford, Rodger K., "Covert Sensitization" (1999). Faculty Publications - Grad School of Clinical Psychology. 301.