In the operant conditioning paradigm, extinction refers to the process of no longer providing the reinforcement that has been maintaining a behavior. Operant extinction differs from forgetting in that the latter refers to a decrease in the strength of a behavior over time when it has not been emitted.
Gel medium is an acrylic product. It comes in Heavy, Soft, and Regular and has a variety of finishes, Matte, Gloss and Semi-gloss. The basic use for these is to build texture in paintings by mixing them with acrylic paint. If you add a small bit of it to your paint it will also extend the drying time. The Soft gel is the medium that is most often used by paper artists. It can be used as a glue for collage and it is also used to make photocopy transfers.
The basic choices of gel mediums are matte, gloss and semi-gloss, each one providing a different level of sheen on a canvas. Gel mediums are further differentiated by texture and use. Clear tar gel adds sheen and is perfect for dripping and drizzling effects. Self-leveling clear gel adds a high gloss.