The use of translation tests to study language loss is inappropriate for a number of reasons: it 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: