In this paper, we examine the presentation order effect in the light of the neutralization hypothesis, according to which the first vowel in a pair decays, during its storing in memory, toward [er]. 12 French listeners participated in three AB discrimination sessions. For each phonetic category, a prototype and four satellite tokens were synthesized, each paired with the prototype. Results revealed minor or major order effects in the interior of every phonetic category. Nonetheless, the neutralization hypothesis could not account for at least half of these asymmetries. An explanation justifying nearly all order effects is proposed, sustaining that the periphery of the vowel space serves as a reference area triggering a contrast effect.