The model tends to delete because the null elements are very frequent "sounds": that is, there are many connections to them. When activated, they send activation to many other nodes, which, in turn, send activation back again. Hence, over time they become more highly activated than do their less frequent competitors. The result is an asymmetry - the null element substitutes for a consonant creating a deletion, more often than a consonant substitutes for the null element creating an addition.
- Dell (2004), Pag. 159