Bush also relates that, unlike digital technology, Memex would be of no significant aid to business or profitable ventures, and as a consequence its development would occur only long after the mechanization of libraries and the introduction of what he describes as the specialized "group machine", which would be useful for the sharing of ideas in fields such as medicine. Furthermore, although Bush discusses the compressional ability and rapidity so key to modern machines, he relates that speed will not be an integral part of Memex, stating that a tenth of a second would be an acceptable interval for its data retrieval, rather than the billionths of a second that modern computers are capable of. "For Memex," he writes, "the problem is not swift access, but selective access". Bush states that although the code-reading and potential linking capabilities of the rapid selector would be key to the creation of Memex, there is still an issue of enabling "moderately rapid access to really large memory storage". There is an issue concerning selection, Bush conveys, and despite the fact that improvements have been made in the speed of digital selection, according to Bush, "selection, in the broad sense, is still a stone adze in the hands of the cabinetmaker". Bush goes on to discuss the record-making process and how Memex could incorporate systems of voice-control and user-propagated learning. He proposes a machine that could respond to "simple remarks" as well as build trails based on its user's "habits of association," as Belinda Barnet described them in "The Technical Evolution of Vannevar Bush's Memex." Barnet also makes the distinction between the idea of a constructive Memex and the "permanent trails" described in "As We May Think," and attributes Bush's machine learning concepts to Claude Shannon's mechanical mouse and work with "feedback and machine learning".