Summary: A new study finds that people can recognize images they briefly saw years earlier—even up to a decade after the initial exposure.
Source: CNRS
Human memory sometimes surprises us. We can recall the names of classmates from five decades ago or remember a childhood television show with remarkable clarity. While strong emotions and repeated exposures are known to strengthen long-term memories, scientists asked why some everyday, non‑emotional experiences can also remain accessible for years, even after only brief encounters. Researchers from the Centre de recherche cerveau & cognition (CNRS / Université Toulouse III—Paul Sabatier) revisited participants they had tested in the laboratory about ten years earlier and found that many could still recognize images they had seen for only a few seconds a decade prior. These results were published online on November 5, 2017, in the journal Cognition.
In laboratory studies it is difficult to recreate all the real‑world factors that affect memory. We know repeated sensory exposure tends to create long-lasting traces, and that intense emotions can make a single event unforgettable. But what about neutral images viewed only once or a few times, with no instruction to memorize them? To explore this question, the research team controlled for two major influences—emotional content and frequency of exposure—and tested a different aspect of memory persistence.
The follow-up study involved 24 adults who had no memory disorders and who had participated in experiments a decade earlier. In the original sessions, each participant had been shown a sequence of simple clip‑art images, each displayed for only a few seconds, and with no explicit task to remember them. In 2016 the same individuals returned to the lab and were presented with pairs of images: one image from the earlier session and one new image. They were asked to indicate which image they had seen before.
On average, participants identified the previously seen images correctly 55% of the time. Performance rose slightly to 57% for images that had been presented at least three times during the original session. For some participants the effect was substantially stronger: roughly one third of the group scored between 60% and 70% correct, and the highest scores reached about 70% correct. Under these experimental conditions, it appears that as few as three brief exposures can leave a memory trace that remains recognizable after ten years.
These findings build on earlier research showing that implicit memory—memory that affects behavior without conscious awareness—can resist decay over long intervals. What is notable here is that retained traces of these brief, neutral images were able not only to influence choices but also to evoke a clear sense of familiarity, even when participants reported low confidence in their judgments. In other words, memories that are not consciously retrievable can nevertheless bias recognition decisions and produce a subjective feeling that an image is familiar.
The research team is now investigating the neural mechanisms that could support this form of long‑lasting recognition. One hypothesis is that extremely long‑term familiarity for simple images may depend on a small population of highly specialized neurons that retain selective representations, rather than on a widely distributed, diffuse network. Determining the biological basis of such durable traces will require targeted neurophysiological and imaging studies.
The study team included a member from the Institut de neurosciences des systèmes (AMU / INSERM).
Source: CNRS
Publisher: NeuroscienceNews.com (organized coverage)
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Original Research: Article titled “Extremely long-term memory and familiarity after 12 years” by Christelle Larzabal, Eve Tramoni, Sophie Muratot, Simon J. Thorpe, and Emmanuel J. Barbeau, published in Cognition (online November 5, 2017). DOI: 10.1016/j.cognition.2017.10.009
CNRS (2017). Our Amazing Ability to Recognize Images Seen Briefly 10 Years Later. NeuroscienceNews, 13 November 2017.
Abstract
Extremely long-term memory and familiarity after 12 years
Previous work demonstrated that implicit memory for visual fragments can remain robust over many years. This study tested whether explicit recognition remains possible for simple drawings that had been presented either once or three times for about two seconds each, on average, roughly 12 years earlier. The data revealed that participants could recognize pictures at rates above chance, particularly among younger participants and primarily for stimuli presented three times. Although confidence in these judgments was low, participants frequently reported a notable feeling of familiarity. These findings extend prior results and indicate that familiarity for briefly viewed images can be remarkably resistant to decay.
Study authors: Christelle Larzabal, Eve Tramoni, Sophie Muratot, Simon J. Thorpe, and Emmanuel J. Barbeau. Published in Cognition (online November 5, 2017). DOI: 10.1016/j.cognition.2017.10.009