 Some philosophers of mind have argued that the mind is composed of fairly independent modules. Each module has its own “input” from other modules and sends “output” to other modules. For example, an “auditory analysis system” module might take as input a heard word and send a phonetic analysis to an “auditory input lexicon”. The idea of modular organization raises the empirical question of what mental modules there are and how they are linked to each other. A prominent tradition of research in cognitive neuroscience has attempted to develop a model of mental architecture along these lines by studying the responses of normal and abnormal subjects to various stimuli. The idea is to compare normal reactions with abnormal ones—often caused by brain damage—so as to draw inferences about which mental capacities depend on each other and how.