Periodic Reporting for period 1 - CHROME (Cortical hierarchy of memories - deciphering the neuronal mechanisms of serial dependence in the human brain)
Periodo di rendicontazione: 2022-09-01 al 2024-08-31
What we perceive at any moment is not a direct snapshot of the external world. Rather, perception is shaped by incoming sensory input and filtered through prior experience. For example, in medical image analysis, a doctor may misidentify—or miss—a detail because earlier images biased their expectations. While it has long been recognized that perception involves inference based on memory, scientific research has often treated perception and memory as separate processes. This project set out to bridge that gap by investigating how different forms of memory shape what we perceive in the present.
The research focused on serial dependence, a phenomenon where recent visual experiences systematically bias current perception. The project aimed to identify what determines whether these biases are “attractive” (pulling perception toward the past) or “repulsive” (pushing it away), to understand the timescales of these effects, and to reveal the brain mechanisms involved.
Several important findings emerged. First, the project uncovered stable individual differences in serial dependence: some people consistently showed attractive biases, others repulsive ones. This suggests that serial dependence reflects a trait-like cognitive strategy, not just situational noise. Second, the research demonstrated that longer-term memories held in working memory can override short-term perceptual history, indicating that the brain flexibly prioritizes different sources of information depending on task demands. Third, the findings showed a temporal dissociation: recent history shapes objective discrimination, while more distant experience influences subjective visibility. Finally, the project revealed that even non-conscious experiences can support long-term learning and prediction, suggesting that perceptual continuity relies on both conscious and non-conscious memory systems.
Together, these results advance the understanding of how perception and memory interact. They show that multiple memory systems—short- and long-term, conscious and non-conscious—jointly shape perceptual experience. These insights lay the groundwork for a more integrated understanding of perception in both healthy and clinical populations.
The research focused on serial dependence, a phenomenon where recent visual experiences systematically bias current perception. The project aimed to identify what determines whether these biases are “attractive” (pulling perception toward the past) or “repulsive” (pushing it away), to understand the timescales of these effects, and to reveal the brain mechanisms involved.
Several important findings emerged. First, the project uncovered stable individual differences in serial dependence: some people consistently showed attractive biases, others repulsive ones. This suggests that serial dependence reflects a trait-like cognitive strategy, not just situational noise. Second, the research demonstrated that longer-term memories held in working memory can override short-term perceptual history, indicating that the brain flexibly prioritizes different sources of information depending on task demands. Third, the findings showed a temporal dissociation: recent history shapes objective discrimination, while more distant experience influences subjective visibility. Finally, the project revealed that even non-conscious experiences can support long-term learning and prediction, suggesting that perceptual continuity relies on both conscious and non-conscious memory systems.
Together, these results advance the understanding of how perception and memory interact. They show that multiple memory systems—short- and long-term, conscious and non-conscious—jointly shape perceptual experience. These insights lay the groundwork for a more integrated understanding of perception in both healthy and clinical populations.
Over the course of this project, I set out to investigate a fundamental question in cognitive neuroscience: how do our past experiences shape what we perceive in the present? Rather than viewing perception as a passive mirror of the external world, this research approached it as a dynamic, interpretive process—one continuously influenced by memory.
A core focus was serial dependence—the tendency for recent experiences to bias perception of new stimuli. Behavioral and eye-tracking studies revealed a consistent and surprising pattern: individuals showed stable perceptual biases that were either “attractive” (pulling perception toward the past) or “repulsive” (pushing it away). These patterns held across sessions and tasks, suggesting a stable “perceptual phenotype”—a kind of cognitive fingerprint for how memory influences perception. This finding challenges the view that perceptual biases are random or purely situational and opens up new research on individual differences in sensory processing.
The project also showed that different types of memory interact to guide perception. In one study, when participants held a task-relevant visual template in mind, the usual serial dependence effect disappeared. Instead, perception was drawn toward the memory template, indicating that working memory can override sensory history when task demands require it. These findings support the idea of a flexible memory hierarchy, in which short- and long-term memories are weighed dynamically to guide perception.
To investigate the brain mechanisms behind these effects, I collected a large-scale MEG dataset with 40 participants tested across two sessions. This dataset will allow us to track how perceptual memory evolves over time and across brain regions. While analysis is ongoing, the data already represent a valuable resource for future modeling and theory development.
In parallel, I developed and piloted a new paradigm for intracranial EEG (iEEG) studies to test whether the hippocampus—a deep brain structure critical for memory—contributes to perceptual history effects. Extensive piloting with healthy participants led to a more naturalistic task design and revealed a striking result: even non-conscious experiences can support long-term learning and shape future expectations. This challenges the idea that serial dependence is limited to consciously perceived stimuli and suggests that deeper memory systems may be involved.
Project results have been shared through two peer-reviewed publications, three manuscripts in preparation, and seven invited talks at major conferences and institutions. Several high-quality datasets and validated protocols were produced and will be made openly available in line with open science practices.
In sum, the project has advanced understanding of how perception and memory interact, revealed stable individual differences, and generated tools and data that will support future research in both basic and applied neuroscience.
A core focus was serial dependence—the tendency for recent experiences to bias perception of new stimuli. Behavioral and eye-tracking studies revealed a consistent and surprising pattern: individuals showed stable perceptual biases that were either “attractive” (pulling perception toward the past) or “repulsive” (pushing it away). These patterns held across sessions and tasks, suggesting a stable “perceptual phenotype”—a kind of cognitive fingerprint for how memory influences perception. This finding challenges the view that perceptual biases are random or purely situational and opens up new research on individual differences in sensory processing.
The project also showed that different types of memory interact to guide perception. In one study, when participants held a task-relevant visual template in mind, the usual serial dependence effect disappeared. Instead, perception was drawn toward the memory template, indicating that working memory can override sensory history when task demands require it. These findings support the idea of a flexible memory hierarchy, in which short- and long-term memories are weighed dynamically to guide perception.
To investigate the brain mechanisms behind these effects, I collected a large-scale MEG dataset with 40 participants tested across two sessions. This dataset will allow us to track how perceptual memory evolves over time and across brain regions. While analysis is ongoing, the data already represent a valuable resource for future modeling and theory development.
In parallel, I developed and piloted a new paradigm for intracranial EEG (iEEG) studies to test whether the hippocampus—a deep brain structure critical for memory—contributes to perceptual history effects. Extensive piloting with healthy participants led to a more naturalistic task design and revealed a striking result: even non-conscious experiences can support long-term learning and shape future expectations. This challenges the idea that serial dependence is limited to consciously perceived stimuli and suggests that deeper memory systems may be involved.
Project results have been shared through two peer-reviewed publications, three manuscripts in preparation, and seven invited talks at major conferences and institutions. Several high-quality datasets and validated protocols were produced and will be made openly available in line with open science practices.
In sum, the project has advanced understanding of how perception and memory interact, revealed stable individual differences, and generated tools and data that will support future research in both basic and applied neuroscience.
While the idea that perception and memory interact is well established, this project has pushed the field forward by offering new insights into how these interactions unfold over time and across individuals. Most notably, it uncovered stable individual differences in serial dependence—a phenomenon where perception is biased toward or away from recent stimuli. This “perceptual phenotype” challenges the field’s focus on group-averaged results and opens new directions for personalized cognitive modeling.
The project also demonstrated that short-term perceptual history, longer-term working memory, and even implicit learning processes interact dynamically to shape current perception. This goes beyond earlier work, which typically examined these influences in isolation. In addition, pilot data suggest that non-conscious learning mechanisms and subcortical structures like the hippocampus may contribute to perceptual continuity, extending the study of serial dependence beyond its usual sensory and cortical focus.
The datasets and experimental paradigms developed through this action will continue to fuel research in this area. The project’s findings could inform future applications in education (e.g. how memory affects learning), clinical neuroscience (e.g. understanding perceptual distortions in psychiatric conditions), and the development of adaptive technologies.
Although some components of the project will continue beyond the reporting period, the work already marks a significant step toward a more integrated, mechanistic understanding of how the brain blends memory and perception to construct a coherent experience of the world.
The project also demonstrated that short-term perceptual history, longer-term working memory, and even implicit learning processes interact dynamically to shape current perception. This goes beyond earlier work, which typically examined these influences in isolation. In addition, pilot data suggest that non-conscious learning mechanisms and subcortical structures like the hippocampus may contribute to perceptual continuity, extending the study of serial dependence beyond its usual sensory and cortical focus.
The datasets and experimental paradigms developed through this action will continue to fuel research in this area. The project’s findings could inform future applications in education (e.g. how memory affects learning), clinical neuroscience (e.g. understanding perceptual distortions in psychiatric conditions), and the development of adaptive technologies.
Although some components of the project will continue beyond the reporting period, the work already marks a significant step toward a more integrated, mechanistic understanding of how the brain blends memory and perception to construct a coherent experience of the world.