Extremely long-term memory and familiarity after 12 years

Rhesus monkeys show greater habituation to repeated computer-generated images than do orangutans

Humans and several other species of animals have demonstrated the ability to use familiarity to recognize that they have seen images before. In prior experiments, orangutans failed to show use of familiarity in memory tasks, even when other solutions were not available. We tested for evidence of habituation, a decreased response to repeated stimuli, as a behavioral indicator that repeated images were familiar to subjects. Monkeys and orangutans selected the smallest target out of four while computerized images were presented as distractors. Latency to complete the target-finding task was compared between conditions in which the distractor image was a familiar, repeating image, a novel, never-before-seen image, or no distractor was present. Rhesus macaques showed significant habituation, and significantly more habituation than orangutans, in each of four experiments. Orangutans showed statistically reliable habituation in only one of the four experiments. These results are consistent with previous research in which orangutans failed to demonstrate familiarity. Because we expect that familiarity and habituation are evolutionarily ancient memory processes, we struggle to explain these surprising, but consistent findings. Future research is needed to determine why orangutans respond to computerized images in this peculiar way.

Large-scale network dynamics underlying the first few hundred milliseconds after stimulus presentation: An investigation of visual recognition memory using iEEG

Recognition memory is the ability to recognize previously encountered objects. Even this relatively simple, yet extremely fast, ability requires the coordinated activity of large-scale brain networks. However, little is known about the sub-second dynamics of these networks. The majority of current studies into large-scale network dynamics is primarily based on imaging techniques suffering from either poor temporal or spatial resolution. We investigated the dynamics of large-scale functional brain networks underlying recognition memory at the millisecond scale. Specifically, we analyzed dynamic effective connectivity from intracranial electroencephalography while epileptic subjects (n = 18) performed a fast visual recognition memory task. Our data-driven investigation using Granger causality and the analysis of communities with the Louvain algorithm spotlighted a dynamic interplay of two large-scale networks associated with successful recognition. The first network involved the right visual ventral stream and bilateral frontal regions. It was characterized by early, predominantly bottom-up information flow peaking at 115 ms. It was followed by the involvement of another network with predominantly top-down connectivity peaking at 220 ms, mainly in the left anterior hemisphere. The transition between these two networks was associated with changes in network topology, evolving from a more segregated to a more integrated state. These results highlight that distinct large-scale brain networks involved in visual recognition memory unfold early and quickly, within the first 300 ms after stimulus onset. Our study extends the current understanding of the rapid network changes during rapid cognitive processes.

Long-term memory for movie details: selective decay for verbal information at one week

Mnemonic representations of complex events are multidimensional, incorporating information about objects and characters, their interactions and their spatial-temporal context. The present study investigated the degree to which detailed verbal information (i.e., dialogues), as well as semantic and spatiotemporal (i.e., "what", "where", and "when") elements of episodic memories for movies, are forgotten over the course of a week. Moreover, we tested whether the amount of dimension-specific forgetting differed as a function of the participant's age. In a mixed design, younger and middle-aged participants were asked to watch a ∼90 min movie and provide yes/no answers to detailed questions about different dimensions of the presented material after 1, 3 days, and 1 week. The results indicate that memory decay mainly affects the verbal dimension, both in terms of response accuracy and confidence. Instead, detailed information about objects/characters' features and spatiotemporal context seems to be relatively preserved, despite a general decrease in response confidence. Furthermore, younger adults were in general more accurate and confident than middle-aged participants, although, again, the verbal dimension exhibited a significant age-related difference. We propose that this selective forgetting depends on the progressive advantage of visual compared to auditory/verbal information in memory for complex events.

More Stable Memory Retention of Novel Words Learned from Fast Mapping than from Explicit Encoding

There is a heated debate on a learning paradigm known as "fast mapping" for its early neocortical dependence and retained memory over time for amnesic patients with hippocampal system damage. Whether the fast mapping allows hippocampus independent learning and induces rapid integration is poorly understood. The present study aims to investigate the effect of fast mapping on very long-term retention, which to our knowledge has not been previously explored. We tested memory retention ranging from 10 min to 1.5 years, for novel word-object associations learned from fast mapping or explicit encoding procedures. The three-alternative forced choice recognition task was employed to assess memory performance. Besides the slight adjustment of the testing schedule, other settings remained the same in Experiment 2 to replicate and verify the findings of Experiment 1. Results showed that overall memory retrieval performance was higher after explicit encoding as compared to fast mapping. However, retrieval performance after explicit encoding dropped after 1.5 years, but remained stable in the fast mapping condition. Furthermore, matching the semantic category of the known and the novel items during the fast mapping paradigm might affect long-term retention. These results suggest that fast mapping creates more stable long-term memory representations as compared to the explicit encoding strategy.

Long-Lasting Verbatim Memory for the Words of Books After a Single Reading Without Any Learning Intention

The present study reveals an intriguing ability of our human memory: when reading a book once without any intention of learning, we store long-lasting verbatim memories of the words written in the book without being aware of it. Participants read a book chapter consisting of 32 pages (3,772 words) once without knowing that their memory would be tested later. In memory tests immediately after reading and 1 week after reading, they were asked to remember exactly which word was written at a specific position in the book chapter. Only memory for words was tested that were theme-unrelated and non-central. To measure memory, a two-alternative forced choice recognition test was used where a page was shown either as read before or with the replacement of one single word by a synonym. For each response, participants indicated whether the response was based on phenomenal memory experience (recollection or familiarity) or guessing. In the immediate test, participants claimed to have phenomenal memory experience for about a quarter of the tested positions, truly remembering the word in about half of cases. In the 1-week-delayed test, phenomenal memory experience was nearly entirely absent and completely uninformative. When claiming to have no phenomenal memory experience, participants still truly remembered the word for about 10% of the tested positions in both the immediate test and the 1-week-delayed test, without any forgetting. These findings demonstrate that we store more from read texts in memory than commonly believed.

A Fast Visual Recognition Memory System in Humans Identified Using Intracerebral ERP

One key item of information retrieved when surveying our visual world is whether or not objects are familiar. However, there is no consensus on the respective roles of medial temporal lobe structures, particularly the perirhinal cortex (PRC) and hippocampus. We considered whether the PRC could support a fast recognition memory system independently from the hippocampus. We recorded the intracerebral electroencephalograph activity of epileptic patients while they were performing a fast visual recognition memory task, constraining them to use their quickest strategy. We performed event-related potential (ERP) and classification analyses. The PRC was, by far, the earliest region involved in recognition memory. This activity occurred before the first behavioral responses and was found to be related to reaction times, unlike the hippocampus. Single-trial analyses showed that decoding power was equivalent in the PRC and hippocampus but occurred much earlier in the PRC. A critical finding was that recognition memory-related activity occurred in different frontal and parietal regions, including the supplementary motor area, before the hippocampus. These results, based on ERP analyses, suggest that the human brain is equipped with a fast recognition memory system, which may bypass the hippocampus and in which the PRC plays a critical role.

Extremely long-term memory and familiarity after 12 years

In 2006 Mitchell demonstrated that implicit memory was robust to decay. He showed that the ability to identify fragments of pictures seen 17 years before was significantly higher than for new stimuli. Is this true only for implicit memory? In this study, we tested whether explicit memory was still possible for drawings (n = 144) that had been presented once or three times, two seconds each time on average, approximately 12 years earlier. Surprisingly, our data reveal that our participants were able to recognize pictures above chance level. Preserved memory was mainly observed in the youngest subjects, for stimuli seen three times. Despite the fact that confidence judgments were low, reports suggest that recognition could be based on a strong sense of familiarity. These data extend Mitchell's findings and show that familiarity can also be robust to decay.