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Human recollections can be distorted within seconds of events.

Recent research indicates that individuals have the potential to inaccurately recall events within fractions of a second.

A recent study has discovered that humans can create false memories of events shortly after they occur. Termed “short-term memory illusions” by researchers, this phenomenon highlights how swiftly and effortlessly individuals reshape their recollections to align with preconceived notions instead of accurately reflecting what transpired. The findings of this research were published in the journal PLOS One.

“It seems that short-term memory is not always an accurate representation of what was just perceived,” the researchers wrote in the study. “Instead, memory is shaped by what we expected to see, right from the formation of the first memory trace.”

To evaluate the accuracy of short-term memories, the researchers recruited 534 volunteers who participated in a series of four experiments. Each experiment revolved around memorizing a sequence of letters from the Latin alphabet.

During each round, participants were presented with a circular arrangement of letters. These letters would disappear, and a box would appear at a specific position within the circle, indicating which letter they needed to remember. Participants had to recall both the identity of the letter and its orientation, as some were mirrored and faced backwards.

At times, participants were exposed to an unrelated set of letters before their memory was assessed. After providing their response, they were then requested to rate their confidence level, ranging from very low to very high, regarding the accuracy of their guess.

When participants were asked to recall what they had observed just half a second later, they provided incorrect responses in slightly less than 20% of the cases. This error rate increased to 30% when they were asked to recall after a three-second delay.

Moreover, when participants were asked to determine whether a letter was facing forwards or backwards, those who expressed high confidence in their answers had actually mentally flipped the letter to its regular position 37% of the time. It is worth noting that they had been explicitly cautioned about the presence of mirrored letters in the tests and were instructed not to mistakenly report them as real letters.

To validate their findings, the researchers conducted three additional experiments with a separate group of 348 individuals who were not part of the initial analysis. These participants demonstrated a similar inclination to mentally flip the mirrored letters. Across all the experiments, the most prevalent high-confidence error observed was the mental flipping of letters. This finding indicates that the human brain records experiences based on preconceived notions (such as the expected appearance of a letter), allowing us to make more accurate predictions about the world while disregarding idiosyncrasies that do not align with those preconceptions.

“These memory illusions seem to be the result of world knowledge and not of visual similarities,” the researchers wrote in the study. “Taken together, the results thus show that world knowledge can shape memory even when memories have only just been formed.”

The researchers plan to proceed by developing experiments that can illustrate comparable adjustments in short-term memory within real-world scenarios. Additionally, they aim to explore memory adaptations beyond visual and language-related stimuli, encompassing various types of memory.


Perception can be shaped by our expectations, which can lead to perceptual illusions. Similarly, long-term memories can be shaped to fit our expectations, which can generate false memories. However, it is generally assumed that short-term memory for percepts formed just 1 or 2 seconds ago accurately represents the percepts as they were at the time of perception. Here 4 experiments consistently show that within this timeframe, participants go from reliably reporting what was there (perceptual inference accurately reflecting the bottom-up input), to erroneously but with high confidence reporting what they expected to be there (memory report strongly influenced by top-down expectations). Together, these experiments show that expectations can reshape perceptual representations over short time scales, leading to what we refer to as short-term memory (STM) illusions. These illusions appeared when participants saw a memory display which contained real and pseudo-letters (i.e. mirrored letters). Within seconds after the memory display disappeared, high confidence memory errors increased substantially. This increase in errors over time indicates that the high confidence errors do not (purely) result from incorrect perceptual encoding of the memory display. Moreover, high confidence errors occurred mainly for pseudo-to-real letter memories, and much less often for real-to-pseudo-letter memories, indicating that visual similarity is not the primary cause of this memory-bias. Instead ‘world knowledge’ (e.g., which orientation letters usually have) appear to drive these STM illusions. Our findings support a predictive processing view of the formation and maintenance of memory in which all memory stages, including STM, involve integration of bottom-up memory input with top-down predictions, such that prior expectations can shape memory traces.