In a nutshell: New research shows that we create detailed memories of faces in a single glance without trying. Surprisingly, trying to recall them doesn’t improve our memory very much.

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When you’re ordering coffee at your favourite cafe, do you sometimes get a strange sense that you’ve seen other customers before? Research suggests that your intuition is probably correct, but how is that possible if you never tried to remember their faces?

Our ability to remember things without trying is called incidental memory. For a long time, incidental memory was thought to have a very limited capacity, storing just a few items. However, it’s difficult to study because it requires convincing participants to focus their memory elsewhere and accounting for tricky things like context (for example, the cafe in the case above). Understanding the limits of incidental memory and how it works has important real-world implications – think of eyewitness testimony, for instance.

Julian Matthews, a PhD student with Brain Function CoE Associate Investigator Naotsugu Tsuchiya, and his colleagues at Monash University have been examining just how powerful incidental memory might be.

The researchers used a method called rapid serial visual presentation to display sequences of different faces very quickly in the centre of a screen. Participants were asked to search for specific faces in these sequences and to respond as quickly as possible when a target face appeared. If a participant responded correctly, the researchers tested their incidental memory by presenting two more faces – one that the participant had never seen before, and one that had appeared in the sequence much earlier than the target face. Participants were asked to differentiate between the two faces and to rate their confidence in the response, to show that they were conscious of incidental memory and weren’t just making a series of lucky guesses.

The researchers found that the participants were very good at identifying faces that they’d glanced at before. This was true even when the researchers used photos with different background images or presented the faces upside-down. Even more unexpected was the discovery that participants did not perform the task much better if the researchers removed the target search completely and asked them instead to watch the sequence and try to remember all the faces.

These results demonstrate that incidental memory, even from just a single glance, is surprisingly powerful and, in some instances, explicit memorisation isn’t that helpful – which helps to explain why all those customers seem familiar.

Next steps:
The researchers found that face memories were affected by the race, gender and age of the individual pictured. They plan to examine if an individual’s own gender, race or age affects their incidental memory and whether they are conscious of these kinds of bias.

Matthews, J., Wu, J., Corneille, V., Hohwy, J., van Boxtel, J., & Tsuchiya, N. (2018). Sustained conscious access to incidental memories in RSVP. Attention, Perception, & Psychophysics. doi: 10.3758/s13414-018-1600-1

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