Exhaustive additivity suggests a new stage not an alternative model: A commentary on Fowler, Hofer and Lipitkas (2000).

Fowler et al. (Fowler, B., Hofer, K., Lipitkas, J., 2000. The exhaustive additivity displayed by nitrous oxide has implications for cognitive-energetical theory. Biol. Psychol. 52, 161-180) observed that nitrous oxide (N(2)O, an inhalation anaesthetic) does not interact with experimental manipulations derived from the additive factors literature. They proposed a two-tiered cognitive-energetical model to account for the apparent "exhaustive additivity". This model assumes that N(2)O affects a lower tier resulting in a non-selective effect on an upper tier, which is comprised of energetical mechanisms that are selectively linked to processing stages. In this commentary, it is argued that the "exhaustive additivity" can easily be accomodated by linear stage models. The findings of Fowler et al. suggest a new stage rather than a new model. Moreover, their new model seems to predict "exhaustive interaction" rather than "exhaustive additivity". It is concluded that Fowler et al. may have a highly interesting finding, but not for the reasons they submitted when accounting for the "exhaustive additivity" displayed by N(2)O.