 In addition to these approaches, in a number of prominent psychological accounts emerged over the last two decades, the study of word meaning is essentially considered a chapter of theories of the mental realization of concepts (see the entry on  concepts).  Lexical units are seen either as ingredients of conceptual networks or as (auditory or visual) stimuli providing access to conceptual networks. A flow of neuroscientific results has shown that understanding of (certain categories of) words correlates with neural activations corresponding to the semantic content of the processed words. For example, it has been shown that listening to sentences that describe actions performed with the mouth, hand, or leg activates the visuomotor circuits which subserve execution and observation of such actions (Tettamanti et al. 2005); that reading words denoting specific actions of the tongue (‘lick’), fingers (‘pick’), and leg (‘kick’) differentially activate areas of the premotor cortex that are active when the corresponding movements are actually performed (Hauk et al. 2004); that reading odor-related words (‘jasmine’, ‘garlic’, ‘cinnamon’) differentially activates the primary olfactory cortex (Gonzales et al. 2006); and that color words (such as ‘red’) activate areas in the fusiform gyrus that have been associated with color perception (Chao et al. 1999, Simmons et al. 2007; for a survey of results on visual activations in language processing, see Martin 2007).