Diffusion model drift rates can be influenced by decision processes: An analysis of the strength-based mirror effect.

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.

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

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

Doubt is subjective uncertainty about one’s perceptions and recall. It can impair decision-making and is a prominent feature of obsessive-compulsive disorder (OCD). We propose that evaluation of doubt during decision-making provides a useful endophenotype with which to study the underlying pathophysiology of OCD and potentially other psychopathologies. For the current study, we developed a new instrument, the Doubt Questionnaire, to clinically assess doubt, and evaluated its psychometric properties. The random dot motion task was used to measure reaction time and subjective certainty, at varying levels of perceptual difficulty, in individuals who scored high and low on doubt, and in individuals with and without OCD. We found that doubt scores were significantly higher in OCD cases than controls. Drift diffusion modeling revealed that high doubt scores predicted slower evidence accumulation than did low doubt scores; and OCD diagnosis lower than controls. At higher levels of dot coherence, OCD participants exhibited significantly slower drift rates than did controls. In addition, at higher levels of coherence, high doubt subjects exhibited even slower drift rates and reaction times than low doubt subjects. Moreover, under high coherence conditions, individuals with high doubt scores reported lower certainty in their decisions than did those with low doubt scores. We conclude that the Doubt Questionnaire is a useful instrument for measuring doubt. Compared to those with low doubt, those with high doubt accumulate evidence more slowly and report lower certainty when making decisions under conditions of low uncertainty. High doubt may affect the decision-making process in individuals with OCD. The dimensional doubt measure is a useful endophenotype for OCD research and could enable computationally rigorous and neurally valid understanding of decision-making and its pathological expression in OCD and other disorders.

Differentiation models of recognition memory predict a strength-based mirror effect in the distributions of subjective memory strength. Subjective memory strength should increase for targets and simultaneously decrease for foils following a strongly encoded list compared with a weakly encoded list. An alternative explanation for the strength-based mirror effect is that participants adopt a stricter criterion following a strong list than a weak list. Behavioral experiments support the differentiation account. The purpose of this study was to identify the neural bases for these differences. Encoding strength was manipulated (strong, weak) in a rapid event-related fMRI paradigm. To investigate the effect of retrieval context on foils, foils were presented in test blocks containing strong or weak targets. Imaging analyses identified regions in which activity increased faster for foils tested after a strong list than a weak list. The results are interpreted in support of a differentiation account of memory and are suggestive that the angular gyrus plays a role in evaluating evidence related to the memory decision, even for new items.

A circular analogue of the diffusion model adapted for continuous response tasks is applied to a continuous-outcome source memory task. In contrast to existing models of source retrieval that attribute all of the variability in responding to memory, the circular diffusion model decomposes noise into variability arising from memory and from decision processes. We compared three models: (1) a single diffusion process with trial-to-trial variability in drift rate, (2) a mixture of two diffusion processes, one with positive drift that does not vary from trial-to-trial, and a second zero-drift process that represents discrete guessing, and (3) a hybrid model that mixed positive and zero-drift processes with trial-to-trial variability in the positive drift process. Comparison of model fits to joint response error and response-time (RT) data suggest that a memory strength threshold under which no information is retrieved appears to underlie responding in a continuous-report source memory task. Additionally, we also conditioned participants' source responding on their confidence in an old/new recognition task, ruling out the possibility that participant guessing was only due to unrecognized items. Overall, our findings support an all-or-none or some-or none view of source memory retrieval and pose a challenge to continuous models of source memory.

The influence of encoding intention on electrophysiological indices of recognition memory

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

Global semantic similarity effects in recognition memory: Insights from BEAGLE representations and the diffusion decision model

How do individuals with trait anxiety perform in an approach-avoidance (ap-av) conflict situation? To answer this question, we employed computational models to explore the effect of trait anxiety on decisions in ap-av conflict situations and uncover the computational mechanism involved in resolving such conflicts. Sixty-seven participants with high or low trait anxiety completed the ap-av conflict task, which was analysed using the hierarchical drift-diffusion model (HDDM). Anxiety levels were assessed during both baseline and six-month follow-up sessions. Results showed that, during ap-av conflict decision-making, the reaction time of the high trait anxiety group was slower than that of the low trait anxiety group. The slower reaction time in the high trait anxiety group was due to a longer non-decision time. However, the intercept of drift rate and the effect of reward and aversion on drift rate significantly increased in the high trait anxiety group compared to the low trait anxiety group. The high trait anxiety group had a starting point closer to avoidance decisions. This study provides evidence that individuals with high and low trait anxiety manifest distinct alterations in the underlying computational decision-making processes during ap-av conflict situations.

Systematic laboratory measurements were performed to determine the steady drift of isolated, tabular ice-floe models in regular waves. A relatively simple expression for the steady wave-induced drift of two-dimensional floes of uniform thickness and density in deep water was developed. This empirical wave-drift formula indicates that the drift velocity depends primarily on the ratio of wave period to ice-floe roll period, wave steepness and length of the floe. The highest drift velocity is produced by waves with period somewhat greater than the ice-floe roll period, with fundamentally different drift behavior evident on either side of this maximum (long-wave and short-wave drift response). The dependence on wave height was found not to be linear but increased with wave length (from approximately H1/2 to H3/2). A simplified equation for the roll period of a prismatic body of uniform density and rectangular cross-section was developed and found to be of practical value. INTRODUCTION An object floating freely at the surface is generally exposed to the combined action of winds, waves and currents, and will normally undergo oscillatory motions and also experience a net drift with respect to the seafloor. When ocean currents and wind forcing can be neglected, the body will drift in the approximate direction of wave advance while simultaneously undergoing horizontal oscillations at the wave frequency. Drift rates are typically small so that the net drift is often only of interest over time periods much longer than the wave period. Horizontal motions diminish as the wave length decreases, so that the associated oscillatory velocities can often be neglected compared to the drift velocity, i.e., the steady drift velocity and maximum instantaneous velocity are practically identical for short waves. By time-averaging the horizontal motions of the floating body (over periods large compared to the wave period), the so-called steady drift velocity is obtained. Although the steady drift excludes motions at wave frequency, it is still of practical interest because (a) it permits time-of-travel estimates to be made (when will an abandoned barge or an ice floe reach a given location); (b) it provides information about the rate of dispersal to be expected for a group of floating objects of different size (wave-induced separation of ice floes); and (c) it can be used to estimate the maximum kinetic energy with which drifting objects can strike a fixed or floating structure (at least for the case of relatively short waves). We report here the results of laboratory measurements of the steady (mean) drift of ice-floe models in regular waves. This is the first part of an ongoing effort to define the wave-induced motions (both mean and instantaneous) of ice-floes nearing the point of impact with fixed structures or sand and gravel beaches. The present investigation was performed with regular progressive waves as the only driving force. In the absence of winds and large-scale ocean currents, the body is propelled by wave action alone, and a separation into a wave-induced surface current Vs and a wave-thrust velocity may be conceptually helpful.

Modulation of the word frequency effect in recognition memory after an unrelated lexical decision task

Theoretical accounts disagree on the role of dopamine in intertemporal choice and assume that dopamine either promotes delay of gratification by increasing the preference for larger rewards or that dopamine reduces patience by enhancing the sensitivity to waiting costs. Here, we reconcile these conflicting accounts by providing empirical support for a novel process model according to which dopamine contributes to two dissociable components of the decision process, evidence accumulation and starting bias. We re-analyzed a previously published data set where intertemporal decisions were made either under the D2 antagonist amisulpride or under placebo by fitting a hierarchical drift diffusion model that distinguishes between dopaminergic effects on the speed of evidence accumulation and the starting point of the accumulation process. Blocking dopaminergic neurotransmission not only strengthened the sensitivity to whether a reward is perceived as worth the delay costs during evidence accumulation (drift rate) but also attenuated the impact of waiting costs on the starting point of the evidence accumulation process (bias). In contrast, re-analyzing data from a D1 agonist study provided no evidence for a causal involvement of D1R activation in intertemporal choices. Taken together, our findings support a novel, process-based account of the role of dopamine for cost-benefit decision making, highlight the potential benefits of process-informed analyses, and advance our understanding of dopaminergic contributions to decision making.

Evidence accumulation models have enabled strong advances in our understanding of decision-making, yet their application to examining learning has not been common. Using data from participants completing a dynamic random dot-motion direction discrimination task across four days, we characterized alterations in two components of perceptual decision-making (Drift Diffusion Model drift rate and response boundary). Continuous-time learning models were applied to characterize trajectories of performance change, with different models allowing for varying dynamics. The best-fitting model included drift rate changing as a continuous, exponential function of cumulative trial number. In contrast, response boundary changed within each daily session, but in an independent manner across daily sessions. Our results highlight two different processes underlying the pattern of behavior observed across the entire learning trajectory, one involving a continuous tuning of perceptual sensitivity, and another more variable process describing participants’ threshold of when enough evidence is present to act.

Basalt core paleomagnetic data from Ocean Drilling Program Site 883 on Detroit Seamount, northern Emperor Seamount chain, and implications for the paleolatitude of the Hawaiian hotspot