A circular diffusion model of continuous-outcome source memory retrieval: Contrasting continuous and threshold accounts.

Brain–behavior relationships in source memory: Effects of age and memory ability

A functional gradient has been proposed across the medial temporal lobes (MTL) such that the anterior MTL is thought to support processing of individual items (e.g., item memory and complex object perception), whereas the posterior MTL is thought to support item-context retrieval (e.g., source memory). Whereas functional imaging studies have provided evidence supporting this anatomical organization, results from structural analyses remain inconclusive. The current study examined the relationship between volume of MTL regions of interest (ROIs), and performance on a source memory task and a fine-grain complex object perception task, in healthy young adults (mean age = 21.5, range = 18-29). Using a semiautomated procedure, we segmented the parahippocampal and perirhinal cortices (PHC, PRC), posteromedial and anterolateral entorhinal cortices (pmERC, alERC), and posterior and anterior hippocampus (postHC, antHC) on high-resolution T2-weighted MRIs. Regional volumes were computed as proportions of intracranial volume, and as posterior-anterior volumetric ratios (PHC:PRC, pmERC:alERC, postHC:antHC). Partial-least squares regressions were applied to predict source and item memory, and perceptual discrimination accuracy, based on ROI and ratio volumes. In our ROI regressions, we found that postHC volume was positively correlated with a latent factor predicting source memory, and PRC and antHC volumes were negatively correlated to this latent factor. In our ratio regressions, we observed an effect relating the posterior-anterior distribution of gray matter across the MTL with source memory. Our results demonstrate differential associations between anterior and posterior MTL and source memory performance. Findings from this study highlight the importance of considering patterns of structure-behavior associations in the neurobiology of episodic memory.

A single trial analysis of EEG in recognition memory: Tracking the neural correlates of memory strength

Diffusion models of decision making, in which successive samples of noisy evidence are accumulated to decision criteria, provide a theoretical solution to von Neumann’s (1956) problem of how to increase the reliability of neural computation in the presence of noise. I introduce and evaluate a new neurally-inspired dual diffusion model, the linear drift, linear infinitesimal variance (LDLIV) model, which embodies three features often thought to characterize neural mechanisms of decision making. The accumulating evidence is intrinsically positively-valued, saturates at high intensities, and is accumulated for each alternative separately. I present explicit integral-equation predictions for the response time distribution and choice probabilities for the LDLIV model and compare its performance on two benchmark sets of data to three other models: the standard diffusion model and two dual diffusion model composed of racing Wiener processes, one between absorbing and reflecting boundaries and one with absorbing boundaries only. The LDLIV model and the standard diffusion model performed similarly to one another, although the standard diffusion model is more parsimonious, and both performed appreciably better than the other two dual diffusion models. I argue that accumulation of noisy evidence by a diffusion process and drift rate variability are both expressions of how the cognitive system solves von Neumann’s problem, by aggregating noisy representations over time and over elements of a neural population. I also argue that models that do not solve von Neumann’s problem do not address the main theoretical question that historically motivated research in this area.

The millisecond component of the Jovian decameter emission has been studied at high resolution, in order to examine the short‐term behavior of the S‐burst drift rates and to define the drift rate spectrum at high frequencies. By using dynamic spectra having 300‐µs and 3.3‐kHz resolution and covering discrete frequency bands in the range 26–33 MHz, large systematic changes in the magnitude of the S‐burst drift rates are observed to take place on a time scale of seconds to minutes. It is noted that the drift rate variability is of sufficient magnitude to prevent reliable evaluation of the drift rate dependence on frequency, unless simultaneous or near‐simultaneous multifrequency measurements are made. In presenting such observations we fail to observe the predicted drift rate turnover in the spectrum, in spite of measurements made at frequencies within 0.6 to 4.4 MHz of the electron gyrofrequency at the Jovian foot of the Io flux tube. This result is interpreted in terms of an ionospheric electron source, rather than within the conventional theoretical framework of trapped particles initially accelerated at Io. Low‐resolution intensity‐time tracings reveal a characteristic organization of S bursts into groups, each of several seconds duration and consisting of tens to hundreds of bursts. Abrupt changes in mean drift rates from group to group suggest that some of the group structuring may be a source‐related rather than a scintillation‐related phenomenon. Finally, some evidence exists for systematic variations in the group‐to‐group mean drift rates, which may be due to predictiable temporal changes in the magnetic field gradient on the Io flux tube. These temporal changes are due to motion of the Io‐associated magnetic flux tube in the Jovian magnetosphere.

Event-related potentials (ERPs) were recorded during recognition tasks for line drawings (items) or for both drawings and their spatial locations (sources). Recognized drawings elicited more positive ERPs than new drawings. Independent of accuracy in the spatial judgment, the old/new effect in the source recognition task was larger over the prefrontal scalp, and of longer temporal duration than in the item recognition task, suggesting that the source memory task engaged a qualitatively distinct memory process. More posterior scalp sites were sensitive to the accuracy of the source judgment, but this effect was delayed relative to the difference between studied and unstudied drawings, suggesting that source memory processes are completed after item recognition. Similarities and differences between spatial source memory and memory for conjunctions of other stimulus attributes are discussed, together with the role of prefrontal cortex in memory.

Linking the diffusion model and general recognition theory: Circular diffusion with bivariate-normally distributed drift rates

The shifted-Wald model is a popular analysis tool for one-choice reaction-time tasks. In its simplest version, the shifted-Wald model assumes a constant trial-independent drift rate parameter. However, the presence of endogenous processes—fluctuation in attention and motivation, fatigue and boredom—suggest that drift rate might vary across experimental trials. Here we show how across-trial variability in drift rate can be accounted for by assuming a trial-specific drift rate parameter that is governed by a positive-valued distribution. We consider two candidate distributions: the truncated normal distribution and the gamma distribution. For the resulting distributions of first-arrival times, we derive analytical and sampling-based solutions, and implement the models in a Bayesian framework. Recovery studies and an application to a data set comprised of 1469 participants suggest that (1) both mixture distributions yield similar results; (2) all model parameters can be recovered accurately except for the drift variance parameter; (3) despite poor recovery, the presence of the drift variance parameter facilitates accurate recovery of the remaining parameters; (4) shift, threshold, and drift mean parameters are correlated.

The question of animal awareness: Evolutionary continuity of mental experience: Revised and enlarged paperback edition. By Donald R. Griffin. Los Altos, CA: William Kaufmann, Inc., 1981, 221 pp., $8.95

1591 – Different brain responses with matched performances between mild cognitive impairment and normal older adults during episodic retrieval: an erp study

Given the importance of memory to our daily functioning, humans have made use of many strategies to improve their encoding and later retrieval. Recently, drawing has emerged as a particularly effective strategy that robustly improves memory compared with traditional encoding strategies, and in the current study, we investigate the cognitive features that underlie this effect. Participants (N = 60) engaged in four distinct encoding tasks-Drawing, No Ink Drawing, Tracing, and Visualizing-each designed to engage one or more of the multisensory 'components' thought to underlie the impact of drawing on memory. We evaluated memory performance using both a classic old/new recognition task and source memory judgment, providing insights into both general recognition performance, and memory for specific encoding contexts. Consistent with prior work, we found Drawing led to the best memory performance in both recognition and source memory. Notably however, the No Ink Drawing condition, which lacked the visual component offered by Drawing, produced the second best old/new recognition performance, but the worst source memory. Unpacking this result, we found participants were frequently confusing No Ink Drawing with Drawing during source memory judgments, perhaps reflecting a hierarchy to the components that enhance memory, which seems to favor motoric engagement and elaboration over visual information. Together, our results extend our current understanding of the cognitive processes underlying successful encoding and provide new insights into how various memory tests can provide information about the specific information encoded alongside memories.

Directed forgetting (DF) assists in preventing outdated information from interfering with cognitive processing. Previous studies pointed that self-referential items alleviated DF effects due to the elaboration of encoding processes. However, the retrieval mechanism of this phenomenon remains unknown. Based on the dual-process framework of recognition, the retrieval of self-referential information was involved in familiarity and recollection. Using source memory tasks combined with event-related potential (ERP) recording, our research investigated the retrieval processes of alleviative DF effects elicited by self-referential information. The FN400 (frontal negativity at 400 ms) is a frontal potential at 300–500 ms related to familiarity and the late positive complex (LPC) is a later parietal potential at 500–800 ms related to recollection. The FN400 effects of source memory suggested that familiarity processes were promoted by self-referential effects without the modulation of to-be-forgotten (TBF) instruction. The ERP results of DF effects were involved with LPCs of source memory, which indexed retrieval processing of recollection. The other-referential source memory of TBF instruction caused the absence of LPC effects, while the self-referential source memory of TBF instruction still elicited the significant LPC effects. Therefore, our neural findings suggested that self-referential processing improved both familiarity and recollection. Furthermore, the self-referential processing advantage which was caused by the autobiographical retrieval alleviated retrieval inhibition of DF, supporting that the self-referential source memory alleviated DF effects.

We use response time decision models to determine whether visual working memory (VWM) is best described by a fixed-capacity ‘slot’ model or a continuously allocated ‘resource’ model. We used a double-decision paradigm that combined continuous-outcome recall and two-choice recognition to characterize performance in a VWM task. Participants viewed one to six colored items, recalled the color of a cued target using a color wheel, and then identified the target color from two options in a recognition task. We used continuous-outcome and two-choice EZ diffusion models to analyze the speed and accuracy of the two decisions. The models provided estimates of the latent cognitive parameters, drift rate and boundary separation, with the former providing measures of the memory strengths in the two decisions. We found significant correlations in both drift rate and boundary separation for the two decisions, indicating that continuous recall and two-choice recognition tasks engage similar memory and decision processes. Removing responses within the highly inaccurate ‘heavy tails’ of the recall distribution reduced, rather than increased, drift rate correlations – especially in the six item condition – implying that the heavy tails of the response distribution represent meaningful low-precision memory traces rather than guesses. Simulations showed that only a small fraction of the heavy tailed memory trace could be accounted for by swap errors. Our results are consistent with variable precision and resource accounts of VWM and inconsistent with slot-based accounts. Our findings underscore the value of joint modeling response time and accuracy data, and highlight the utility of double-decision tasks in clarifying theoretical accounts of memory processes.

In this experiment, event-related potentials were used to examine whether the neural correlates of encoding processes predicting subsequent successful recall differed from those predicting successful source memory retrieval. During encoding, participants studied lists of words and were instructed to memorize each word and the list in which it occurred. At test, they had to complete stems (the first four letters) with a studied word and then make a judgment of the initial temporal context (i.e. list). Event-related potentials recorded during encoding were segregated according to subsequent memory performance to examine subsequent memory effects (SMEs) reflecting successful cued recall (cued recall SME) and successful source retrieval (source memory SME). Data showed a cued recall SME on parietal electrode sites from 400 to 1200 ms and a late inversed cued recall SME on frontal sites in the 1200-1400 ms period. Moreover, a source memory SME was reported from 400 to 1400 ms on frontal areas. These findings indicate that patterns of encoding-related activity predicting successful recall and source memory are clearly dissociated.

A note on decomposition of sources of variability in perceptual decision-making