Considerable discussion and debate have been devoted to the extent and nature of structural or functional correspondence between internal representations and their external visual counterparts. An analogue representation or process is one in which the relational structure of external events is preserved in the corresponding internal representations. A great deal of experimental evidence purporting to demonstrate the existence of analogue internal representations and processes has accumulated during the past decade. These experimental efforts have the use of a powerful psychophysical technique--mental chronometry--in common, thus permitting inferences about internal mental events and processes from purely observable data. However, analogue models for visual/spatial representations and transformations have recently been challenged on both empirical and theoretical grounds. The empirical challenges can be shown to be inconclusive, and further experimental work is needed to resolve inconsistencies. The theoretical challenges have taken the form of proposing nonanalogue models that may account for at least some of the findings generally regarded as supporting the need for positing analogue representations and transformations. An internal process can qualify as analogue if it can be shown that the intermediate stage in the processing has a one-to-one relation to the intermediate stage of the corresponding external process. Conceived in this fashion, the nature of analogue representations can be assessed in behavioral experiments that have the potential of elucidating the way in which mental processes simulate or model external operations and events. (HTH)