Unconscious odour conditioning 25 years later: Revisiting and extending ‘Kirk-Smith, Van Toller and Dodd’

The pioneering work by Kirk-Smith, Van Toller, and Dodd [Kirk-Smith, M. D., Van Toller, C., & Dodd, G. H. (1983). Unconscious odour conditioning in human subjects. Biological Psychology, 17, 221–231], established that an unnoticed odorant paired with an emotionally meaningful task can influence mood and attitudes when the odorant alone is re-encountered subsequently. This study was particularly important in highlighting unconscious odour learning processes as they may happen in everyday life. However, it was severely criticized by Black and Smith [Black, S. L., & Smith, D. G. (1994). Has odor conditioning been demonstrated? A critique of “Unconscious odour conditioning in human subjects”. Biological Psychology, 37, 265–267] on methodological grounds. In the present paper, we replicated and extended Kirk-Smith et al.’s investigation taking into account Black and Smith’s criticisms and carrying out additional controls to improve the validity of the study. The results confirm the initial findings of Kirk-Smith and colleagues by demonstrating the effectiveness of olfactory stimuli in inducing conditioned hedonic reactions even when presented below the level of awareness.