How reliable is our memory for our own previous intentions

Why did I buy this?

The fallibility of eye-witness memory is well documented. But what about people's memories of their own past intentions? This is an unexplored issue in memory research with real-life implications.

Consider the copyright infringement case in 2002, in which French composer Jacques Loussier sued Eminem, claiming that the track Kill You sampled beats from Loussier's work. Loussier further claimed that the success of the album was due in large part to the popularity of that specific track. Eminem's team responded by conducting a survey of people who'd bought the album in the last three years, only one per cent of whom stated they'd bought the album for the specific song Kill You.

The survey appeared to undermine Loussier's claim, but the trouble is that without any research on the topic, we don't know whether those survey responses can be trusted. Now a team led by Suzanne Kaasa and including Elizabeth Loftus has made a start on plugging this gap in the literature.

Nearly six hundred undergrads answered open-ended questions about why they'd purchased, downloaded or copied their most recently acquired album (the vast majority had acquired one within the last two weeks), and then they provided the same information again six months to a year later. The participants' answers fell into five main categories: because they liked the artist, liked the music, liked a specific song or songs, someone had recommended the album, or they needed the album for a specific purpose.

The key finding was that only one in five participants gave a consistent reason or reasons at both time points. The researchers had anticipated that memory for some reasons might prove more durable over time than others, but this wasn't the case. Overall, the most common form of change was simply to invent new reasons at the later time point. Sometimes participants also forgot reasons they'd mentioned earlier. Unsurprisingly perhaps, participants who recalled more reasons at the first time point tended to be more prone to forgetting reasons when quizzed again later. This was also true of participants who reported liking their CD more, perhaps because they'd felt less need to dwell on their motives at the time they acquired the album.

A subset of 82 of the participants also gave their reasons at a third time point, approximately six months to a year after the second time of questioning. Although still evident, changes in memory between the second and third time points were far reduced compared with between the first and second time points. This is important for real-life legal situations because consistency of answers across later interviews could be interpreted as a sign of memory reliability. 'It appears critical to have an accurate and complete record of the very first interview given by a witness,' the researchers said.

The study had some limitations, including the fact that the precise time between album acquisition and the first questioning session was unknown. However, the researchers observed that 'although individuals may not be able to accurately recall the reasons for their behaviours ... the real world continues to rely on self-reported motivations in a variety of circumstances, including police investigations and court proceedings.'
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Kaasa, S., Morris, E., and Loftus, E. (2011). Remembering why: Can people consistently recall reasons for their behaviour? Applied Cognitive Psychology, 25 (1), 35-42 DOI: 10.1002/acp.1639