While even German readers can find Adorno's work difficult to understand, an additional problem for English readers is that his German idiom is particularly difficult to translate into English. A similar difficulty of translation is true of Hegel, Heidegger, and a number of other German philosophers and poets. As a result, some early translators tended toward over-literalness. In recent years, Edmund Jephcott and Stanford University Press have published new translations of some of Adorno's lectures and books, including Introduction to Sociology, Problems of Moral Philosophy and his transcribed lectures on Kant's Critique of Pure Reason and Aristotle's "Metaphysics", and a new translation of the Dialectic of Enlightenment. Professor Henry Pickford, of the University of Colorado at Boulder, has translated many of Adorno's works such as "The Meaning of Working Through the Past." A new translation has also appeared of Aesthetic Theory and the Philosophy of New Music by Robert Hullot-Kentor, from the University of Minnesota Press. Hullot-Kentor is also currently working on a new translation of Negative Dialectics. Adorno's correspondence with Alban Berg, Towards a Theory of Musical Reproduction, and the letters to Adorno's parents, have been translated by Wieland Hoban and published by Polity Press. These fresh translations are slightly less literal in their rendering of German sentences and words, and are more accessible to English readers.^{[citation needed]} The Group Experiment, which had been unavailable to English readers, is now available in an accessible translation by Jeffrey K. Olick and Andrew J. Perrin on Harvard University Press, along with introductory material explaining its relation to the rest of Adorno's work and 20th-century public opinion research.