Refractory Period Effect Research Articles

Interference control theory: A new perspective on dual-task interference in memorizing and responding to visual targets

In a recent study, Nieuwenstein and Wyble (2014) showed that the consolidation of a masked visual target can be disrupted for up to one second by a trailing 2-alternative forced choice task. Aside from demonstrating that working memory consolidation involves a time-consuming process that continues after a mask, the results of Nieuwenstein and Wyble are remarkable in demonstrating retroactive interference (RI) with little to no proactive interference (RI) – the opposite of what is typically found in studies on the attentional blink and psychological refractory period effect. Here, we show that the reversal from PI to RI depends on the probability of T2 presence (p[T2]), such that a high p(T2) results in strong PI with little RI whereas a low p(T2) results in strong RI with little PI. To explain these findings, we propose that the degree of PI and RI reflects the workings of an attentional control mechanism that aims to protect T1 consolidation against interference, and that is applied in accordance with the risk of such interference. In this view, a high p(T2) entails a high risk of interference with T1 processing, and this results in the protection of T1 at the expense of a postponement of T2 processing. Converely, a low p(T2) means that the risk of interference is low and this entails that T1 is left vulnerable, while T2 can be processed unabated. Consistent with this account, we show that if the risk of interference with T1 processing is increased by embedding the targets in an RSVP stream of distractors, we find strong PI with little RI even when p(T2) is low. Aside from offering a new perspective on dual-task interference, this work makes clear that attentional control plays a central role in phenomena observed in studies using RSVP.

Uni- and crossmodal refractory period effects of event-related potentials provide insights into the development of multisensory processing.

To assess uni- and multisensory development in humans, uni- and crossmodal event-related potential (ERP) refractory period effects were investigated. Forty-one children from 4 to 12 years of age and 15 young adults performed a bimodal oddball task with frequent and rare visual and auditory stimuli presented with two different interstimulus intervals (ISIs). Amplitudes of the visual and auditory ERPs were modulated as a function of the age of the participants, the modality of the preceding stimulus (same vs. different) and the preceding ISI (1000 or 2000 ms). While unimodal refractory period effects were observed in all age groups, crossmodal refractory period effects differed among age groups. Early crossmodal interactions (<150 ms) existing in the youngest age group (4–6 years) disappeared, while later crossmodal interactions (>150 ms) emerged with a parietal topography in older children and adults. Our results are compatible with the intersensory differentiation and the multisensory perceptual narrowing approach of multisensory development. Moreover, our data suggest that uni- and multisensory development run in parallel with unimodal development leading.

Fano factor estimation

Fano factor is one of the most widely used measures of variability of spike trains. Its standard estimator is the ratio of sample variance to sample mean of spike counts observed in a time window and the quality of the estimator strongly depends on the length of the window. We investigate this dependence under the assumption that the spike train behaves as an equilibrium renewal process. It is shown what characteristics of the spike train have large effect on the estimator bias. Namely, the effect of refractory period is analytically evaluated. Next, we create an approximate asymptotic formula for the mean square error of the estimator, which can also be used to find minimum of the error in estimation from single spike trains. The accuracy of the Fano factor estimator is compared with the accuracy of the estimator based on the squared coefficient of variation. All the results are illustrated for spike trains with gamma and inverse Gaussian probability distributions of interspike intervals. Finally, we discuss possibilities of how to select a suitable observation window for the Fano factor estimation.

Intra- and cross-modal refractory period effects in healthy children and adults: An ERP study

Aims: To assess multisensory interactions in the developing human brain, intra- and cross-modal refractory period effects of event-related potential (ERP) were investigated.

N1, P2, and P3b are affected by the matching-stimulus-interval in an auditory equiprobable Go/NoGo task

Event Abstract Back to Event N1, P2, and P3b are affected by the matching-stimulus-interval in an auditory equiprobable Go/NoGo task Genevieve Z. Steiner1*, Robert J. Barry1 and Craig J. Gonsalvez1 1 University of Wollongong, School of Psychology, Australia Aims: It has been demonstrated that as the target-to-target interval (TTI) and the nontarget-to-nontarget interval (NNI) increase P3b amplitude augments in a linear fashion. A similar response pattern has also been demonstrated for N1, but this has been explored with TTI only. This study aimed to discern whether both TTI and NNI affect early sensory components (N1 and P2) in a fashion analogous to the P3b. Method: Thirty university students completed an auditory equiprobable Go/NoGo task with a variable SOA and manipulations of TTI and NNI whilst their EEG activity was recorded. Data were corrected for EOG artefact, epoched, baseline-corrected, filtered, and averages were computed for five separate TTIs and NNIs for each subject. An unrestricted temporal principal components analysis with VARIMAX rotation was applied, and factors identified as N1, P2, and P3b ERP components were analysed further. Results: Across stimuli, P3b showed a linear increase as interval increased. This trend did not differ significantly between targets and nontargets. N1 amplitudes became more negative as interval increased before plateauing at the longest interval (15 s); this did not differ with stimulus type. A similar linear trend was observed for P2 with amplitudes augmenting as interval increased. Again, there was no difference in this linear trend between targets and nontargets. Conclusions: Here we demonstrated that NNI effects are present for N1, and that changes in both TTI and NNI affect N1, P2, and P3b in a similar fashion. Together, these findings indicate that matching-stimulus-interval effects are present at the early sensory stages in sequential processing, for both task-relevant and background information. The mechanism of TTI and NNI effects is currently unknown, but these findings could suggest that early-perceptual processes, or a refractory period effect, are contributing to this phenomenon. Keywords: event-related potentials (ERPs), Target-to-target interval (TTI), Sequence effects, Interstimulus interval (ISI), P3(00), Principal Components Analysis (PCA), Nontarget-to-nontarget interval (NNI) Conference: ASP2013 - 23rd Annual meeting of the Australasian Society for Psychophysiology, Wollongong, Australia, 20 Nov - 22 Nov, 2013. Presentation Type: Oral Presentation Topic: Attention Citation: Steiner GZ, Barry RJ and Gonsalvez CJ (2013). N1, P2, and P3b are affected by the matching-stimulus-interval in an auditory equiprobable Go/NoGo task. Conference Abstract: ASP2013 - 23rd Annual meeting of the Australasian Society for Psychophysiology. doi: 10.3389/conf.fnhum.2013.213.00010 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Oct 2013; Published Online: 05 Nov 2013. * Correspondence: Miss. Genevieve Z Steiner, University of Wollongong, School of Psychology, Wollongong, NSW, 2522, Australia, G.Steiner@westernsydney.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Genevieve Z Steiner Robert J Barry Craig J Gonsalvez Google Genevieve Z Steiner Robert J Barry Craig J Gonsalvez Google Scholar Genevieve Z Steiner Robert J Barry Craig J Gonsalvez PubMed Genevieve Z Steiner Robert J Barry Craig J Gonsalvez Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Matching-stimulus-interval affects the N2 and the P3: a principal components analysis

Event Abstract Back to Event Matching-stimulus-interval affects the N2 and the P3: a principal components analysis Genevieve Z. Steiner1*, Robert J. Barry1 and Craig J. Gonsalvez1 1 University of Wollongong, School of Psychology, Australia Aims: Intervals between matching stimuli (target-to-target interval, TTI; nontarget-to-nontarget interval, NNI) have been shown to play a role in determining the amplitude and latency of the P3 ERP component in a variety of oddball tasks. The mechanism of matching-stimulus-interval effects is unknown, however it has been theorised that interval effects seen in the P3 are an outcome of working memory processes (update and decay of the memory trace, or “template”). To further understand this mechanism, we explored whether TTI and infrequent NNI determined the magnitude of another ERP component, the N2, in a visual three-stimulus oddball task. Method: Continuous EEG data were acquired from 24 university students whilst they completed a three-stimulus visual oddball task with a fixed SOA and seven manipulations of TTI and infrequent NNI. Offline data were corrected for artefact, filtered, epoched, baselined, and separate averages were computed for each TTI and infrequent NNI. Post-processed ERPs were then submitted to an unrestricted temporal principal components analysis (PCA) with orthogonal VARIMAX rotation. Two factors identified as the N2 and P3 in terms of their latency, topography, and sequence, were extracted for subsequent analysis. Results: As expected, P3 amplitude augmented as matching-stimulus interval increased; this linear trend differed between stimuli, with targets eliciting a steeper increase in P3 amplitude than infrequent nontargets. N2 also showed an across-stimulus increase in negativity as interval increased, but unlike the P3, this did not differ significantly between stimulus types. Conclusions: It was demonstrated that matching-stimulus-interval effects are not restricted to the P3, with interval effects evident in an earlier component, the N2. This suggests that the TTI/NNI-mechanism may be the outcome of a wider range of executive processes than originally conceptualised, or a refractory-period effect, and future theory development needs to take this into account. Keywords: Keywords: Event-related potentials (ERPs), Target-to-target interval (TTI), Sequence effects, Interstimulus interval (ISI), P3(00), Principal Components Analysis (PCA) Conference: ASP2013 - 23rd Annual meeting of the Australasian Society for Psychophysiology, Wollongong, Australia, 20 Nov - 22 Nov, 2013. Presentation Type: Oral Presentation Topic: Memory Citation: Steiner GZ, Barry RJ and Gonsalvez CJ (2013). Matching-stimulus-interval affects the N2 and the P3: a principal components analysis. Conference Abstract: ASP2013 - 23rd Annual meeting of the Australasian Society for Psychophysiology. doi: 10.3389/conf.fnhum.2013.213.00034 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Oct 2013; Published Online: 05 Nov 2013. * Correspondence: Miss. Genevieve Z Steiner, University of Wollongong, School of Psychology, Wollongong, NSW, 2522, Australia, G.Steiner@westernsydney.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Genevieve Z Steiner Robert J Barry Craig J Gonsalvez Google Genevieve Z Steiner Robert J Barry Craig J Gonsalvez Google Scholar Genevieve Z Steiner Robert J Barry Craig J Gonsalvez PubMed Genevieve Z Steiner Robert J Barry Craig J Gonsalvez Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Study on the effect of stochastic perturbations on the dynamics of spiral wave

The cardiac muscle, which is composed of many discrete cells, is a typical excitable medium. In this paper, we study the effect of refractory period with stochastic perturbations on dynamical behaviors of spiral wave using the model of discrete excitable medium. When the perturbations are random in space, the stability of spiral wave is related to the amplitude of the perturbations and the number of perturbation cells. Computer simulation results show that refractory period perturbations can result in meandering, breakup and disappearance of the spiral waves under suitable conditions, and then their mechanisms are analyzed.

Mitigating the effects of in-vehicle distractions through use of the Psychological Refractory Period paradigm

Modern driving involves frequent and potentially detrimental interactions with distracting in-vehicle tasks. Distraction has been shown to slow brake reaction time and decrease lateral and longitudinal vehicle control. It is likely that these negative effects will become more prevalent in the future as advances are made in the functionality, availability, and number of in-vehicle systems. This paper addresses this problem by considering ways to manage in-vehicle task presentation to mitigate their distracting effects. A driving simulator experiment using 48 participants was performed to investigate the existence of the Psychological Refractory Period in the driving context and its effect on braking performance. Drivers were exposed to lead vehicle braking events in isolation (single-task) and with a preceding surrogate in-vehicle task (dual-task). In dual-task scenarios, the time interval between the in-vehicle and braking tasks was manipulated. Brake reaction time increased when drivers were distracted. The in-vehicle task interfered with the performance of the braking task in a manner that was dependent on the interval between the two tasks, with slower reactions following a shorter inter-task interval. This is the Psychological Refractory Period effect. These results have implications for driver safety during in-vehicle distraction. The findings are used to develop recommendations regarding the timing of in-vehicle task presentation so as to reduce their potentially damaging effects on braking performance. In future, these guidelines could be incorporated into a driver workload management system to minimise the opportunity for a driver to be distracted from the ongoing driving task.

Importance of atrial surface area and refractory period in sustaining atrial fibrillation: Testing the critical mass hypothesis

The critical mass hypothesis for atrial fibrillation (AF) was proposed in 1914; however, there have been few studies defining the relationship between atrial surface area and AF. This study evaluated the effect of tissue area and effective refractory period (ERP) on the probability of sustaining AF in an in vivo model. Domestic pigs (n = 9) underwent median sternotomy. Epicardial activation maps were constructed from bipolar electrograms recorded from form-fitting electrode templates placed on the atria. Baseline ERPs were determined. ERP was lowered with a continuous infusion of acetylcholine (0.005-0.04 mg/Kg/min) until AF could be sustained after burst pacing. The atria were sequentially partitioned using bipolar radiofrequency ablation. ERPs were lowered using acetylcholine until AF could be sustained in each subdivision of atrial tissue. Each subdivision was further divided until AF was no longer inducible. At study completion, the heart was excised and the surface area of each section was measured. Over a range of ERPs from 75 to 250 ms, the probability of AF was correlated with increasing tissue area (range, 19.5-105 cm(2)) and decreasing ERP. Logistic regression analysis identified shorter ERP (P < .001) and larger area (P = .006) as factors predictive of an increased probability of sustained AF (area under the curve of the receiver-operator characteristic = 0.878). The probability of sustained AF was significantly associated with increasing tissue area and decreasing ERP. These data may lead to a greater understanding of the mechanism of AF and help to design better interventional procedures.

Assessing the evidence for response time mixture distributions

I describe a technique for comparing two simple accounts of a distribution of response times: A mixture model and a generalized-shift model. In the mixture model, a target distribution is assumed to be a mixture of response times from two other (reference) distributions. In the generalized-shift model, the target distribution is assumed to be a quantile average of the reference distributions. In order to distinguish these two possibilities, quantiles for the target distribution are estimated from the quantiles of the reference distributions assuming either a shift or a mixture, and the predicted quantiles are used to calculate the multinomial likelihood of the obtained data. Monte Carlo simulations reported here demonstrate that the index is relatively unbiased, is effective with moderate sample sizes and modest spreads between the reference distributions, is relatively unaffected by changes in the number of bins or by data trimming, can be used with data aggregated across subjects, and is relatively insensitive to a range of subject variations in distribution shape and in mixture or shift proportion. As an illustration, the index is applied to the interpretation of three effects from distinct paradigms: residual switch costs in the task-switching paradigm, the psychological refractory period effect, and sequential effects in the Simon task. I conclude that the multinomial likelihood index provides a useful and easily applied tool for the interpretation of effects on response time distributions.

On the trade-off between single-neuron complexity and network size with respect to spike-timed computations

Certain types of neurons in the brain seem to possess richer computational ability at the single-neuron level than others due to anatomical as well as physiological factors such as elaborate dendritic arbors and a larger variety of ion channels respectively. While, clearly, such features seem to endow the neurons themselves with a richer repertoire of computations, it is less clear how this exactly affects computation at the network level. For instance, is it true that there exist computations performed by large networks of “simple” neurons that can be achieved by small networks of more “complex” neurons (possessing such richer computational ability)? If so, what is the nature of the trade-off between the complexity of single neurons and the size of network required to achieve certain computations? In other words, can we quantify the number of “complex” neurons required to achieve the computation in question, given precise constraints on the computational ability of the “complex” neurons available? In order to examine these questions, as a first step, we study here the case of feedforward networks of neurons. When a feedforward network is driven with input spike trains that start with quiescence, one can view the network as a transformation, which is to say a function that maps input spike trains to output spike trains (As a simplifying assumption, we do not treat stochastic variability in the response of neurons). In this setting, the computation performed by the network is exactly a transformation, as described above. Here, our main result, in essence, is that feedforward networks equipped with ``simple'' neurons, where the network may have an arbitrary number of neurons and arbitrary depth turn out to have small-sized equivalent networks of depth equal to two made up of more complex neurons that achieve exactly the same spike-train to spike-train transformation. Our broad approach is to consider a large class of neuron models that include “complex” neuron models as well as “simple” neuron models. Technically speaking, this class of neuron models is characterized by the fact that the models in it satisfy certain properties. Each such model has a membrane potential function that depends on input spikes received and output spikes emitted by the neuron in a bounded past time-window, with the following constraints. (a) The neuron settles to the resting potential upon receiving no input spikes in the input time-window and having no output spikes in the output time-window, (b) The neuron has an absolute refractory period, (c) Relative refractory period effects, i.e. presence of spikes in the past output time-window has a hyperpolarizing effect vis-a-vis absence of spikes in the output time-window, when spikes in the input time-window are the same in either case; and (d) The neuron emits an output spike when its membrane potential hits a certain threshold. Notably, no specific functional form of the membrane potential is assumed for this class of neuron models. This class of neuron models includes, up to arbitrary accuracy, a number of contemporary neuron models such as the Leaky Integrate-and-Fire Model and the Spike Response Model, although models significantly more powerful satisfy the aforementioned properties as well. Our main technical result then states the following. Given a feedforward network (with arbitrary number of neurons and arbitrary depth), each of whose constituent neurons obey a model that lies in the aforementioned class, with the network having n output neurons, there exists an equivalent feedforward network of depth equal to two having 2n neurons (each satisfying a model in the same class), so that the latter network effects exactly the same spike-train to spike-train transformation as the former. This, in particular, implies that arbitrarily large feedforward networks of “simple” neurons have very small equivalent networks of “complex” neurons. These results provide an impetus to explore several questions in this direction. For instance, tailoring the class of neuron models considered to reflect specific anatomical and physiological features of complex biological neurons might yield better insights on the nature of this fundamental trade-off and help us understand why evolution may have chosen large networks of simple neurons for some tasks and small networks of complex neurons for others.

Splitting of the P3 component during dual-task processing in a patient with posterior callosal section

When two concurrent sensorimotor tasks have to be performed at a short time interval, the second response is generally delayed at a central decision stage. However, in patients who have undergone full or partial transection of forebrain fibers connecting the two hemispheres (split-brain), independent structures subserving all processing stages should reside in each disconnected hemisphere, thus predicting parallel processing of dual tasks. Surprisingly, this prediction is usually not verified behaviorally. We reasoned that brain imaging with high-density recordings of event-related potentials (ERPs) could clarify the extent and limits of parallel processing in callosal patients. We studied a patient (AC) with posterior callosal section in a lateralized number-comparison task. Behaviorally, the split-brain patient showed robust dual-task interference, superficially similar to the psychological refractory period (PRP) effect in the control group of 14 healthy subjects, but significantly different in important aspects such as slowing of response times in the first task. Analysis of ERPs revealed that the parietal P3 component became split into distinct contralateral components in the patient, and was dramatically reduced for targets in his left visual field. In contrast to the control group, P3 latencies showed minimal to nonexistent postponement related to dual-task processing in the patient. In summary, our findings suggest that the left and right hemisphere networks normally involved in a single distributed “global neuronal workspace” that underlies the generation of the P3 component and serial processing, became strongly decoupled after a posterior callosal lesion.

Multiple Task Interference is Greater in Children With ADHD

There is considerable lay discussion that children with attention deficit hyperactivity disorder (ADHD) have increased difficulty with multitasking, but there are few experimental data. In the current study, we examine the simultaneous processing of two stimulus–response tasks using the Psychological Refractory Period (PRP) effect. We hypothesized that children with ADHD would show a greater PRP effect, suggesting a prolonged “bottleneck” in stimulus–response processing. A total of 19 school-aged children with ADHD showed a prolonged PRP effect compared with 25 control children, suggesting a higher cognitive cost in ADHD for multitasking.

Recovery periods of event-related potentials indicating crossmodal interactions between the visual, auditory and tactile system

In sequential unimodal stimulus designs the time it takes for an event-related potential (ERP)-amplitude to recover is often interpreted as a transient decrement in responsiveness of the generating cortical circuits. This effect has been called neural refractoriness, which is the larger the more similar the repeated stimuli are and thus indicates the degree of overlap between the neural generator systems activated by two sequential stimuli. We hypothesize that crossmodal refractoriness-effects in a crossmodal sequential design might be a good parameter to assess the ‘modality overlap’ in the involved neural generators and the degree of crossmodal interaction. In order to investigate crossmodal ERP refractory period effects we presented visual and auditory (Experiment 1) and visual and tactile stimuli (Experiment 2) with inter stimulus intervals of 1 and 2 s to adult participants. Participants had to detect rare auditory and visual stimuli. Both, intra- and crossmodal ISI effects for all modalities were found for three investigated ERP-deflections (P1, N1, P2). The topography of the crossmodal refractory period effect of the N1- and P2-deflections in Experiment 1 and of P1 and N1 in Experiment 2 of both modalities was similar to the corresponding intramodal refractory effect, yet more confined and crossmodal effects were generally weaker. The crossmodal refractory effect for the visual P1, however, had a distinct, less circumscribed topography with respect to the intramodal effect. These results suggest that ERP refractory effects might be a promising indicator of the neural correlates of crossmodal interactions.

Intra- and crossmodal refractory effects in auditory and somatosensory ERPs

Refractory period effects are defined as a temporal decrement in neural response due to a previous activation of the same system. We varied the ISI and modality of a preceding stimulus to investigate overlapping and distinct neural systems processing auditory and tactile stimuli. Auditory stimuli and tactile stimuli were presented in a sequential, random manner with a duration of 50 ms and an ISI of 1000 or 2000 ms. The P1–N1–P2 complex of event-related potentials (ERP) was analyzed separately for auditory and tactile stimuli, as a function of preceding ISI and modality. Main effects of ISI and modality were found within the time-window of the P1 and P2 (auditory) and P1, N1 and P2 (tactile). These results suggest an overlap in underlying neural systems when stimuli from different modalities are being processed.

How two share two tasks: evidence of a social psychological refractory period effect

A strong assumption shared by major theoretical approaches to cognition posits that the human cognitive system has a limited capacity for information processing. Evidence supporting this claim comes from the dual-task paradigm in which one cognitive system has to process two tasks simultaneously. In this study, we examined whether bottleneck-like processing can also be elicited when a dual task is shared between two individuals. Under dual-task instructions giving priority to Task 1, we found evidence of a psychological refractory period effect in dual-task and joint-task conditions. Under equal priority instructions, we replicated the finding of a psychological refractory period effect in the dual-task, but not in the joint-task condition. These findings are in line with the assumption that a social psychological refractory period effect can be induced across two individuals. We suggest that this effect is due to task-specific monitoring requirements. We discuss our findings with respect to both dual-task and joint action theories.

Collective oscillations of excitable elements: order parameters, bistability and the role ofstochasticity

We study the effects of a probabilistic refractory period in the collective behavior ofcoupled discrete-time excitable cells (SIRS-like cellular automata). Using mean-fieldanalysis and simulations, we show that a synchronized phase with stable collectiveoscillations exists even with non-deterministic refractory periods. Moreover, furtherincreasing the coupling strength leads to a reentrant transition where the synchronizedphase loses stability. In an intermediate regime, we also observe bistability (andconsequently hysteresis) between a synchronized phase and an active but incoherent phasewithout oscillations. The onset of the oscillations appears in the mean-field equations asa Neimark–Sacker bifurcation, the nature of which (i.e. super- or subcritical) isdetermined by the first Lyapunov coefficient. This allows us to determine theborders of the oscillating and of the bistable regions. The mean-field predictionthus obtained agrees quantitatively with simulations of complete graphs and, forrandom graphs, qualitatively predicts the overall structure of the phase diagram.The latter can be obtained from simulations by defining an order parameterq suited for detecting collective oscillations of excitable elements. We briefly reviewother commonly used order parameters and show (via data collapse) thatq satisfies the expected finite-size scaling relations.

Does dorsal processing require central capacity? More evidence from the PRP paradigm

The human vision system appears to divide into two streams: a ventral stream from V1 to the inferior temporal cortex processing 'vision for perception', and a dorsal stream from V1 to the posterior parietal cortex processing 'vision for action'. Among other characteristics, it has been suggested that dorsal processing is effortless, unconscious, and not bearing on central cognitive resources implicated in ventral processing. The present study shows that a typical dorsal task (i.e., grasping an object) is subject to a classical indicator of capacity limitations in dual-task situations, the psychological refractory period (PRP) effect. In particular, response times to task 2 (the grasping task) increased the more the two tasks overlapped in time, i.e., the shorter the time interval between the stimuli of the two tasks was. As is also common in PRP experiments, response times to task 1 were largely unaffected by this variation. The PRP effect was obtained despite careful control of strategic response deferment, and peripheral overlap of response modalities that may have artificially created performance costs in previous studies. Altogether, the present results show that dorsal processing is subject to the same capacity limitations that can almost universally be found with simple cognitive tasks.

Mapping introspection’s blind spot: Reconstruction of dual-task phenomenology using quantified introspection

Psychologists often dismiss introspection as an inappropriate measure, yet subjects readily volunteer detailed descriptions of the time and effort that they spent on a task. Are such reports really so inaccurate? We asked subjects to perform a psychological refractory period experiment followed by extensive quantified introspection. On each trial, just after their objective responses, subjects provided no less than four subjective estimates of the timing of sensory, decision and response events. Based on these subjective variables, we reconstructed the phenomenology of an average trial and compared it to objective times and to predictions derived from the central interference model. Introspections of decision time were highly correlated with objective measures, but there was one point of drastic distortion: subjects were largely unaware that the second target was waiting while the first task was being completed, the psychological refractory period effect. Thus, conscious perception is systematically delayed and distorted while central processing resources are monopolized by another task.

Firing rate of noisy integrate-and-fire neurons with synaptic current dynamics

We derive analytical formulas for the firing rate of integrate-and-fire neurons endowed with realistic synaptic dynamics. In particular, we include the possibility of multiple synaptic inputs as well as the effect of an absolute refractory period into the description. The latter affects the firing rate through its interaction with the synaptic dynamics.