  Standard   formulations[17]  of the ‘Unlearning Problem’, assume that they cannot: the view seems to be that learning can only take place under idealized  conditions where the world supplies unambiguous evidence pro or con  the language learner's grammatical theories. Given such a conception  of the learner, none of the examples of feedback just discussed will  seem relevant to the problem. For only a learner employing fairly  sophisticated data-analysis techniques and a confirmation measure  that is sensitive to small changes in probabilities would be able to  exploit the sorts of regularities in the linguistic environment that  we have just discussed. However, there is increasing evidence that  children are in fact remarkably sensitive to subtle feedback, in both linguistic and non-linguistic domains. For instance: