The purpose of this experiment was to follow up on previous findings of a gain in opinion change produced by eating-while-reading (Razran, 1940; Janis, Kaye, and Kirschner, 1965) by testing predictions from a “conditioning” theory and from an alternative explanation in terms of greater receptivity to any communication endorsed by E, the donor of the food. A factorial design was used to determine the extent to which the opinion changes induced by two persuasive communications were influenced by (1) E‘s giving food contiguously with exposure to the communications vs. giving the food beforehand, and (2) E‘s positive vs. negative endorsement of the conclusions advocated by the communication. An analysis of variance of the opinion-change scores showed that neither variable had a significant main effect but there was a significant interaction effect: Positive endorsement of the communications by E was highly influential when he gave food contiguously with the communications but not when he gave food beforehand. The following “momentary compliance” hypothesis was inferred from the findings: The consumption of proferred food induces a momentary mood of compliance toward the donor that is strongest at the time the food is being consumed and that decreases in strength rapidly after the food has been consumed.
Source: “Why does eating while reading facilitate opinion change?—An experimental inquiry” from Journal of Experimental Social Psychology, Volume 1, Issue 2, May 1965, Pages 133-144
I first read about the 1940 study by Razran in Robert Cialdini’s fantastic book, Influence. It’s one of the books I most highly recommend, especially if you’re interested in negotiation and persuasion.