The possibility that language offers more to humans than the externalisation and transcription of thoughts has been at the heart of research on human cognition from millennia. In the past thirty years, the question of language-cognition interaction has received considerable attention in psycholinguistics and neuroscience, fuelling intense debate in several areas of human cognition, from basic brain organisation to social interaction. This thesis attempts to demonstrate the existence of effects of language on three levels of human cognition: perception, categorisation and conceptual associations. First, I show that distinctions brought about by grammatical gender influence object conceptualisation since gender information is retrieved spontaneously even when it is task-irrelevant. Event-related brain potentials collected in native speakers of Spanish asked to categorise triplets of pictures based on semantic category are significantly modulated by gender consistency between pictures. This effect is absent in native speakers of English, who do not have grammatical gender in their language. Second, I show that lexical distinctions in English that are not found in Spanish lead to differences in early visual discrimination. Native English speakers, who have two labels for the objects cups and mugs, perceive the two objects as more different compared to Spanish speakers who only have one word (taza).Third, language idiosyncratic lexical links brought about by word compounding result in predictable semantic associations between otherwise unrelated objects such as neck and turtle given their lexical link in compounds such as turtleneck. Overall, the work presented in this thesis offers novel evidence for linguistic relativity at an abstract grammatical level, at the interference between perception and conceptualisation and at the semantic/conceptual level