Attractor models of working memory and their modulation by reward

Abstract

This work reports an empirical examination of two key issues in theoretical neuroscience: distractibility in the context of working memory (WM) and its reward dependence. While these issues have been examined fruitfully in isolation (e.g. Macoveanu et al. in Biol Cybern 96(4): 407-19, 2007), we address them here in tandem, with a focus on how distractibility and reward interact. In particular, we parameterise an observation model that embodies the nonlinear form of such interactions, as described in a recent neuronal network model (Gruber et al. in J Comput Neurosci 20:153-166, 2006). We observe that memory for a target stimulus can be corrupted by distracters in the delay period. Interestingly, in contrast to our theoretical predictions, this corruption was only partial. Distracters do not simply overwrite target; rather, a compromise is reached between target and distracter. Finally, we observed a trend towards a reduced distractibility under conditions of high reward. We discuss the implications of these findings for theoretical formulations of basal and dopamine (DA)-modulated neural bumpattractor networks of working memory.

Ghosts in the machine: memory interference from the previous trial

“…We show that while a visually guided saccade or memory period will, on their own, bias a subsequent memory-guided saccade, neither are necessary. Furthermore, behavioral studies with distractors show that merely presenting an irrelevant visual stimulus is sufficient to produce an attractive bias (Macoveanu et al 2007;Chumbley et al 2008). These findings suggest that visual target presentation, which occurs in both saccade-only and memoryonly trials, is the most likely cause for the observed response bias in every case.…”

“…When the two peaks are far apart, intermediate nodes are not excited and the global inhibition quashes the weaker bump (usually the distractor bump) before it has a chance to distort the bump representing the correct memory location. The predicted spatial pattern of within-trial interference has been replicated in behavioral studies (Macoveanu et al 2007;Chumbley et al 2008).…”

“…If memory maintenance and saccade execution contributed independently and equally to the bias effects, then we would expect that the magnitude of effects on standard memory trials would be twice as large as the effects in the other trial types. Second, previous studies using distractors show attractive bias toward irrelevant (distractor) stimuli that subjects ignore while performing a standard spatial memory task (Chumbley et al 2008;Macoveanu et al 2007). Taken together, the evidence suggests that neither memory maintenance nor saccade execution is necessary to produce bias and that instead it is the presentation of a visual stimulus that produces interference on a subsequent memory-guided saccade trial.…”

“…Prior computational and behavioral studies on memory interference have focused on the spatial working memory system because it provides continuous measures for both stimuli and responses and is well suited to studying partial memory degradation (Compte et al 2000;Macoveanu et al 2007;Chumbley et al 2008). These studies focus on interference within a trial, asking how irrelevant information and distractor stimuli interfere with the memory information of a target stimulus when both are presented in the same trial.…”

Stochastic Processes and Neuronal Modelling: Quantum Harmonic Oscillator Dynamics in Neural Structures

“…8 Model of the biological associative memory 1. Stochastic neuron models enable the study and understanding of probabilistic decision making [44]. 2.…”