Health Communication --Elaboration Likelihood Model Motivation and processing ability determine attitude change History and Orientation Petty and Cacioppo(1979) 60% discovered,in contrast to social judgment-involvement theory,that high levels of involvement do not invariably decrease persuasion.Health Communication -- Elaboration Likelihood Model Motivation and processing ability determine attitude change  History and Orientation  Petty and Cacioppo (1979) discovered, in contrast to social judgment-involvement theory, that high levels of involvement do not invariably decrease persuasion