Martinijn de Lange and his colleagues made their recommendation after conducting a field experiment in which they concealed seven small containers of cleaning product (spiced up with a little Capitaine perfume oil) in the luggage racks of two carriages on a train travelling between Amersfoort-Schothorst and Enkhuizen, a journey of one hour and forty-four minutes.
The amount of rubbish not in bins on these two carriages was collected at the final stop, counted and weighed and compared with the amount of rubbish left in two, scent-free control carriages. Based on measures taken over 18 journeys, the average amount of rubbish on the unscented carriages was more than three times the weight of the rubbish collected from the scented carriages (35.6 grams vs. 11.7 grams). In terms of individual rubbish items, there were an average of 5.1 in the control carriages per journey vs. 2.7 in the scented carriages.
For comparison, rubbish was also collected from these exact same carriages over several journeys a week or so earlier, prior to the use of the scent (the train company agreed to use the same train on the same route during the period of the study rather than following their usual practice of rotating train stock across different routes). In this case, there was no difference in the amount of litter left in the different carriages.
"It seems to be possible to change the littering behaviour of people in a train environment using a simple and relatively cheap intervention," the researchers said.
Why should the scent of cleaning product have had this effect on passengers' littering behaviour? de Lange and his colleagues think the effect probably occurs via the non-conscious priming of cleaning related motives and behaviours. Supporting this account, a 2005 lab study (pdf) reported that exposing participants discreetly to the smell of citrus cleaning product led them to list more cleaning-related activities in their plans for the day and to spill fewer crumbs when munching on a cookie. "The positive results of our scent manipulation in a field setting provide support for the idea that the cognitive route of scents to behaviour can be used as a tool for behavioural change," de Lange and his team said. "Merely dispersing a scent seems to trigger related goals and influence subsequent behaviour."
Alternatively, perhaps passengers grew sick of the citrus smell and simply avoided sitting in the scented carriages! That would explain a surprising finding I didn't mention earlier - that rubbish in the non-scented carriages (but not the scented ones) was higher during the intervention period than during the earlier comparison weeks. The researchers put that down to the intervention weeks being busier than the comparison weeks, leading to more rubbish in the non-scented carriages (but not in the scented carriages because of the behavioural effect of the scent).
de Lange, M., Debets, L., Ruitenburg, K., and Holland, R. (2012). Making less of a mess: Scent exposure as a tool for behavioral change. Social Influence, 7 (2), 90-97 DOI: 10.1080/15534510.2012.659509
Post written by Christian Jarrett for the BPS Research Digest.