Behavioral conditioning and experimental motion-induced sickness.

Adult male squirrel monkeys were the subjects of experiments conducted to determine whether or not repeated exposures to sickness-inducing horizontal rotation would result in behavioral conditioning of emetic responses. The development of conditioned food aversion and feeding suppression as a consequence of pre- and postrotation eating was quantified. It was concluded that neither instrumental conditioning nor classical conditioning were valid alternative hypotheses for the occurrence of repeated vomiting episodes over a period of ten daily exposures to motion. Conditioned aversion to fresh banana and feeding suppression developed gradually if rotation, which induced multiple bouts of vomiting, was sustained for 1- or 2-hour sessions. If spinning was terminated immediately after the first emetic response, no aversion or suppression emerged. The occurrence of food aversion, by itself, is questioned as a valid index of the presence of subjective concomitants of motion sickness in animals.