is questionable what such tests measure; too much variation; the difference between attriters and bilinguals is complex; activating two languages at once may cause interference. Yoshitomi attempted to define a model of language attrition that was related to neurological and psychological aspects of language learning and unlearning. She discussed four possible hypotheses and five key aspects related to acquisition and attrition. The hypotheses are: 1. Reverse order: last learned, first forgotten. Studies by Russell and Hayashi both looked at the Japanese negation system and both found that attrition was the reverse order of acquisition. Yoshitomi and others, including Yukawa, argue that attrition can occur so rapidly, it is impossible to determine the order of loss. 2. Inverse relation: better learned, better retained. Language items that are acquired first also happen to be those that are most reinforced. As a result, hypotheses 1 and 2 capture the main linguistic characteristics of language attrition 3. Critical period: at or around age 9. As a child grows, he becomes less able to master native-like abilities. Furthermore, various linguistic features (for example phonology or syntax) may have different stages or age limits for mastering. Hyltenstam & Abrahamsson argue that after childhood, in general, it becomes more and more difficult to acquire "native-like-ness", but that there is no cut-off point in particular. Furthermore, they discuss a number of cases where a native-like L2 was acquired during adulthood. 4. Affect: motivation and attitude. According to Yoshitomi, the five key aspects related to attrition are neuroplasticity, consolidation, permastore/savings, decreased accessibility, and receptive versus productive abilities. The regression hypothesis The regression hypothesis, first formulated by Roman Jakobson in 1941 and originally formulated on the phonology of only Slavic languages, goes back to the beginnings of psychology and psychoanalysis. It states that which was learned first will be retained last, both in 'normal' processes of forgetting and in pathological conditions such as aphasia or dementia. As a template for language attrition, the regression hypothesis has long seemed an attractive paradigm. However, regression is not in itself a theoretical or explanatory framework. Both order of acquisition and order of attrition need to be put into the larger context of linguistic theory in order to gain explanatory adequacy. Keijzer (2007) conducted a study on the attrition of Dutch in Anglophone Canada. She finds some evidence that later-learned rules, such as diminutive and plural formation, indeed erode before earlier learned grammatical rules.