Immunization Against the Observational Conditioning of Snake Fear in Rhesus Monkeys

The effects of extensive prior exposure to snakes on subsequent observational conditioning of snake fear in rhesus monkeys were examined. Three groups of monkeys (n = 8 per group) were given one of three kinds of pretreatment: (a) An immunization group spent six sessions watching a nonfearful monkey behave nonfearfully with snakes; (b) a latent inhibition group spent six sessions by themselves behaving nonfearfully with snakes with total exposure time to snakes equal to that for the immunization group; and (c) a pseudoimmunization group spent six sessions watching a monkey behave nonfearfully with neutral objects. All groups were then given six sessions of observational conditioning in which they watched fearful monkeys behave fearfully with snakes. When subsequently tested for acquisition of snake fear, the pseudoimmunization and latent inhibition groups showed significant acquisition, but 6 out of 8 subjects in the immunization group did not. Thus, it seems that for a majority of subjects, prior exposure to a nonfearful model behaving nonfearfully with snakes can effectively immunize against the subsequent effects of exposure to fearful models behaving fearfully with snakes. The implications of these results for possible modes of preventing the acquisition of human fears and phobias are discussed.