23. A method of identifying a source of data input to a computing system comprising: a) associating a first challenge item with a first set of individual text descriptors; wherein said first set of text descriptors are based on feedback provided by a group of human reviewers; b) associating a second challenge item with a second set of individual text descriptors; wherein said second set of individual text descriptors are also based on feedback provided by a group of human reviewers; c) identifying at least a first reference correlation between at least a first reference text descriptor for said first challenge item and a second reference text descriptor for said second challenge item, including a probability that a human reviewer identifying said first reference text descriptor when presented with said first challenge item also provides said second reference text descriptor when presented with said second challenge item, or vice-versa; d) presenting the first challenge item to an entity as part of an automated access challenge adapted to distinguish humans from computing machines; e) receiving speech utterance from said entity related to said first challenge item to determine a first input text descriptor; f) presenting the second challenge item to said entity as part of said automated access challenge adapted to distinguish humans from computing machines; g) receiving speech utterance from said entity related to said second challenge item to determine a second input text descriptor; h) comparing said first and second input text descriptors to identify said reference correlation between them as measured during step (c); i) generating a determination of whether said speech utterance originated from a machine or a human based on a value of said reference correlation.
25. The method of claim 23 wherein said challenge items include a question.