In order to explain the appearances of Jesus after His death, critics have put forth the theory that all these appearances were hallucinations or visions. This goes against the psychological understanding of what a hallucination is. Hallucinations are very individual and no two people see the same thing. To believe that five hundred people had the same hallucination of seeing the risen Jesus, strains belief. Not only did these hallucinations have to happen, they happened to different groups of people at different times over a period of forty days. Hallucination theory also does not account for the fact that Thomas touched Jesus or that Jesus ate with the disciples.
Josh McDowell covers the refutation of hallucination in greater detail in The New Evidence That Demands a Verdict. (1)
1. McDowell, The New Evidence That Demands A Verdict, 273 to 279.