Surprise response as a probe for compressed memory states

Abstract

The limited capacity of recent memory inevitably leads to partial memory of past stimuli. There is also evidence that behavioral and neural responses to novel or rare stimuli are dependent on one's memory of past stimuli. Thus, these responses may serve as a probe of different individuals' remembering and forgetting characteristics. Here, we utilize two lossy compression models of stimulus sequences that inherently involve forgetting, which in addition to being a necessity under many conditions, also has theoretical and behavioral advantages. One model is based on a simple stimulus counter and the other on the Information Bottleneck (IB) framework which suggests a more general, theoretically justifiable principle for biological and cognitive phenomena. These models are applied to analyze a novelty-detection event-related potential commonly known as the P300. The trial-by-trial variations of the P300 response, recorded in an auditory oddball paradigm, were subjected to each model to extract two stimulus-compression parameters for each subject: memory length and representation accuracy. These parameters were then utilized to estimate the subjects' recent memory capacity limit under the task conditions. The results, along with recently published findings on single neurons and the IB model, underscore how a lossy compression framework can be utilized to account for trial-by-trial variability of neural responses at different spatial scales and in different individuals, while at the same time providing estimates of individual memory characteristics at different levels of representation using a theoretically-based parsimonious model. Author summarySurprise responses reflect expectations based on preceding stimuli representations, and hence can be used to infer the characteristics of memory utilized for a task. We suggest a quantitative method for extracting an individual estimate of effective memory capacity dedicated for a task based on the correspondence between a theoretical surprise model and electrophysiological single-trial surprise responses. We demonstrate this method on EEG responses recorded while participants were performing a simple auditory task; we PLOS Computational Biology | https://doi.

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“…The subjective experience of novelty is often explored within the “oddball” paradigm (e.g., Levi-Aharoni et al, 2020 ). The oddball paradigm is an experimental procedure where items (meaningful/meaningless; sensory/verbal; pictorial/spoken; etc.)…”

Physiological and Medico-Social Research Trends of the Wave P300 and More Late Components of Visual Event-Related Potentials

“…In other works, the relief of N 400 was noted upon the initial presentation of a picture or a word, and, conversely, the amplitude dropped upon repeated presentation of the object. On the basis of a series of experiments, where the evoked responses were compared when stimulated with “new” and “old” stimuli, a number of authors put forward a hypothesis that N 400 , in response to a new semantically significant stimulus, reflects the processes of an “exhaustive search” of all stimuli in memory with the aim of subsequent identification [ 11 ].…”

“…In each case, the subject is asked to monitor the achievement of the goal by pressing a button or mentally counting followed by a report. The single-stimulus paradigm irregularly presents only one type of stimulus, or a goal with zero appearance of any other type of target [ 10 , 11 ].…”

Physiological and Medico-Social Research Trends of the Wave P300 and More Late Components of Visual Event-Related Potentials

“…In other works, the relief of N400 was noted upon the initial presentation of a picture or a word, and, conversely, the amplitude dropped upon repeated presentation of the object. On the basis of a series of experiments, where the evoked responses were compared when stimulated with "new" and "old" stimuli, a number of authors put forward a hypothesis that N400, in response to a new semantically significant stimulus, reflects the processes of an "exhaustive search" of all stimuli in memory with the aim of subsequent identification [11].…”