The nature and causes of this transformation, which largely took place during late antiquity, have been a subject of scholarly debate for centuries. Giorgio Vasari attributed it to a decline in artistic skills and standards, which had in turn been revived by his contemporaries in the Italian Renaissance. Although this point of view has been occasionally revived, most notably by Bernard Berenson, modern scholars tend to take a more positive view of the Byzantine aesthetic. Alois Riegl and Josef Strzygowski, writing in the early 20th century, were above all responsible for the revaluation of late antique art. Riegl saw it as a natural development of pre-existing tendencies in Roman art, whereas Strzygowski viewed it as a product of "oriental" influences. Notable recent contributions to the debate include those of Ernst Kitzinger, who traced a "dialectic" between "abstract" and "Hellenistic" tendencies in late antiquity, and John Onians, who saw an "increase in visual response" in late antiquity, through which a viewer "could look at something which was in twentieth-century terms purely abstract and find it representational."