Theories about the cause of the age-related differences on the AST have largely centered around two sources of cognitive dysfunction: IC and WM. According to Hasher et al. (1999), Hasher and Zacks (1988), and Crawford et al. (2011) a reduction in IC with advancing age could affect performance on cognitive tasks in various ways: an age-related deterioration of an inhibitory filter, acting as a gateway into WM, could lead to a decline in the efficiency in which task-irrelevant information is prevented from entering WM; a reduction in the ability to suppress irrelevant information that has entered WM could prevent distracting information from being inhibited, and thus increase the interference effects of this irrelevant information on the current cognitive task. Therefore, the IC hypothesis claims that the age-related impairments in tasks involving WM are causally related to inhibitory cognitive mechanisms deteriorating with age, and not the other way round. The alternative WM-led approaches claim that this should be reversed; it is primarily a deterioration of WM that is responsible for age-related AST impairments.