What is consciousness? What is it like to feel pain, or to see the colour red? Do robots and computers really think? For that matter, do plants and amoebas think? If we ever meet intelligent aliens, will we be able to understand what they say to us? Philosophers and scientists are still unable to answer questions like these. Perhaps science fiction can help. In Discognition, Steven Shaviro looks at science fiction novels and stories that explore the extreme possibilities of human and alien sentience.