The reaction time- and temporal order judgment-defined temporal window of integration.

<p>Means and standard deviations of the boundaries of the temporal window of integration (TWI) defined by the reaction time (RT) and temporal order judgment (TOJ) tasks for the participants who displayed task demand-induced TWI malleability (red, n = 5) and for those who did not (blue, n = 6). n.s. not significant, *p<0.05.</p

Recalibration of the Multisensory Temporal Window of Integration Results from Changing Task Demands

<div><p>The notion of the temporal window of integration, when applied in a multisensory context, refers to the breadth of the interval across which the brain perceives two stimuli from different sensory modalities as synchronous. It maintains a unitary perception of multisensory events despite physical and biophysical timing differences between the senses. The boundaries of the window can be influenced by attention and past sensory experience. Here we examined whether task demands could also influence the multisensory temporal window of integration. We varied the stimulus onset asynchrony between simple, short-lasting auditory and visual stimuli while participants performed two tasks in separate blocks: a temporal order judgment task that required the discrimination of subtle auditory-visual asynchronies, and a reaction time task to the first incoming stimulus irrespective of its sensory modality. We defined the temporal window of integration as the range of stimulus onset asynchronies where performance was below 75% in the temporal order judgment task, as well as the range of stimulus onset asynchronies where responses showed multisensory facilitation (race model violation) in the reaction time task. In 5 of 11 participants, we observed audio-visual stimulus onset asynchronies where reaction time was significantly accelerated (indicating successful integration in this task) while performance was accurate in the temporal order judgment task (indicating successful segregation in that task). This dissociation suggests that in some participants, the boundaries of the temporal window of integration can adaptively recalibrate in order to optimize performance according to specific task demands.</p></div

Participants’ performance on the reaction time task at the group level.

<p>The group performance on the reaction time (RT) task is plotted as the mean and standard deviation of reaction times as a function of the stimulus onset asynchrony (SOA). A-only and V-only indicate reaction times to unisensory, auditory- and visual-only trials respectively. The complete list of SOAs is provided in the Methods section.</p

Participants’ performance at the group level.

<p>The group performance on the temporal order judgment (TOJ) task is plotted as the proportion of “visual-first” responses as a function of the stimulus onset asynchrony (SOA, bold curve). The dashed lines represent the thresholds for above-chance performance on the TOJ task. The grayed area represents the SOAs where significant violation of the race model was observed on the reaction time task.</p

Race model violation in the reaction time task at the individual participant level.

<p>In this plot, each participant is represented by one line and each stimulus onset asynchrony (SOA) by one column. The p value for violation of the race model is color-coded for each participant and each SOA. Red color indicates p values closer to 0.05, yellow color indicates p values closer to 0. White color indicates that the race model could not be confidently rejected. Participant 1 (bold number) is the exemplary participant illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0071608#pone-0071608-g005" target="_blank">Figure 5</a>. None of the subjects displayed race model violation at SOAs beyond −120 ms and beyond +120 ms. Participants 1 to 5 (red numbers) displayed task-induced TWI malleability, whereas Participants 6 to 11 (blue numbers) did not.</p

Results for an exemplary individual participant.

<p>The participant’s performance on the temporal order judgment (TOJ) task is plotted as the proportion of “visual-first” responses as a function of the stimulus onset asynchrony (SOA, filled circles). The psychometric function fitted onto these data is plotted as a continuous line. Dashed lines indicate the thresholds for above-chance performance. The grayed area represents the SOAs where significant violation of the race model was observed on the reaction time task.</p

Parameters of the psychometric function and priors for the Bayesian analysis.

<p><b>A.</b> The parameters that define the logistic function are illustrated: λ_A, lapse rate when the auditory stimulus precedes the visual stimulus by a long interval (large negative values of the stimulus onset asynchrony, SOA); λ_V, lapse rate when the visual stimulus precedes the auditory one (large positive values of the SOA); μ, location parameter; σ, shape parameter. In order to illustrate how the prior distributions selected for each parameter (illustrated in the following panels) affect the shape of the logistic function, the numerical values of the parameters were set to the maximum of their prior distribution. <b>B.</b> The beta distribution used as a prior for the lapse rates λ_A and λ_V. The maximum prior probability corresponds to λ = 0.05. <b>C.</b> The normal distribution used as a prior for the location parameter μ. The maximum prior probability corresponds to μ = 0. <b>D.</b> The gamma distribution used as a prior for the shape parameter σ. The maximum prior probability corresponds to σ = 50.</p

Demographic characteristics for the control and abstinent cocaine groups.

<p>Entries are of the form: mean ± SEM (min-max). Gender was compared using the binomial proportion test; all other observations were compared by Welsh T-tests. C = control, CD = cocaine dependent. Significance code: p ≤ 0.001 ‘***’.</p

Regions in the left and right anterior cingulate showing, respectively, increases in GM with weeks of abstinence and decreases in GM with years of use.

<p>The solid line is the robust regression line for CD individuals. The dashed line is the mean GM in the same ROI for the control participants.</p

Regions identified in the regression analysis.

<p>Center-of-mass coordinates are in the MNI152 (LPI) standard and structure labels are from the Talairach & Tournoux atlas. RL: Right-Left, AP: Anterior-Posterior, IS: Inferior-Superior. STG: Superior Temporal Gyrus, IFG: Inferior Frontal Gyrus, AI: Anterior Insula. BA: Brodmann Area. Crossover point refers to the location on the x-axis (years of use or weeks of abstinence) where the regression (solid) line for the CD users intersects with the mean of the control participants (dashed line). Term refers to the term of interest in the regression model (years of use or weeks of abstinence) from which the clusters were derived. Polarity refers to the sign (positive or negative) of the regression coefficients from which the cluster was generated.</p