Internal noise determines external stochastic resonance in visual perception

AbstractWe provide the first experimental evidence that the internal noise level determines whether external noise can enhance the detectability of a weak signal. We conduct a visual detection experiment in the absence and presence of visual noise. We define three indices of external stochastic resonance effects, consider the spread of the psychometric function without external noise as an internal noise level index, and find that the indices of external stochastic resonance effects negatively correlate with the internal noise level index. Our results suggest that external stochastic resonance depends not only on the external but also on the internal noise level

Transient increase in systemic interferences in the superficial layer and its influence on event-related motor tasks: a functional near-infrared spectroscopy study

Abstract. Functional near-infrared spectroscopy (fNIRS) is a widely utilized neuroimaging tool in fundamental neuroscience research and clinical investigation. Previous research has revealed that task-evoked systemic artifacts mainly originating from the superficial-tissue may preclude the identification of cerebral activation during a given task. We examined the influence of such artifacts on event-related brain activity during a brisk squeezing movement. We estimated task-evoked superficial-tissue hemodynamics from short source–detector distance channels (15 mm) by applying principal component analysis. The estimated superficial-tissue hemodynamics exhibited temporal profiles similar to the canonical cerebral hemodynamic model. Importantly, this task-evoked profile was also observed in data from a block design motor experiment, suggesting a transient increase in superficial-tissue hemodynamics occurs following motor behavior, irrespective of task design. We also confirmed that estimation of event-related cerebral hemodynamics was improved by a simple superficial-tissue hemodynamic artifact removal process using 15-mm short distance channels, compared to the results when no artifact removal was applied. Thus, our results elucidate task design-independent characteristics of superficial-tissue hemodynamics and highlight the need for the application of superficial-tissue hemodynamic artifact removal methods when analyzing fNIRS data obtained during event-related motor tasks

Anodal transcranial direct current stimulation of the right anterior temporal lobe did not significantly affect verbal insight.

Humans often utilize past experience to solve difficult problems. However, if past experience is insufficient to solve a problem, solvers may reach an impasse. Insight can be valuable for breaking an impasse, enabling the reinterpretation or re-representation of a problem. Previous studies using between-subjects designs have revealed a causal relationship between the anterior temporal lobes (ATLs) and non-verbal insight, by enhancing the right ATL while inhibiting the left ATL using transcranial direct current stimulation (tDCS). In addition, neuroimaging studies have reported a correlation between right ATL activity and verbal insight. Based on these findings, we hypothesized that the right ATL is causally related to both non-verbal and verbal insight. To test this hypothesis, we conducted an experiment with 66 subjects using a within-subjects design, which typically has greater statistical power than a between-subjects design. Subjects participated in tDCS experiments across 2 days, in which they solved both non-verbal and verbal insight problems under active or sham stimulation conditions. To dissociate the effects of right ATL stimulation from those of left ATL stimulation, we used two montage types; anodal tDCS of the right ATL together with cathodal tDCS of the left ATL (stimulating both ATLs) and anodal tDCS of the right ATL with cathodal tDCS of the left cheek (stimulating only the right ATL). The montage used was counterbalanced across subjects. Statistical analyses revealed that, regardless of the montage type, there were no significant differences between the active and sham conditions for either verbal or non-verbal insight, although the finding for non-verbal insight was inconclusive because of a lack of statistical power. These results failed to support previous findings suggesting that the right ATL is the central locus of insight

An example of the non-verbal insight problems used in the matchstick arithmetic task.

<p>Column one displays the problem, and column two gives the corresponding solution. The last column indicates the problem type. The magenta lines in columns one and two indicate the sites where manipulation occurred. Type-A insight problems were used in the learning session and practice phase of the tDCS session. Type-B and Type-C problems were used in the testing phase of the tDCS sessions.</p

Results of the matchstick arithmetic task.

<p>Results of the matchstick arithmetic task.</p

Results of the RAT task.

<p>Results of the RAT task.</p

Experimental procedure and tDCS electrode montages.

<p>(A) A schematic representation of the experimental procedure. The shaded area represents the time of tDCS application. Each subject completed all three sessions on separate days; the first tDCS session was conducted 1–4 days after the learning session, and the two tDCS sessions were separated by an interval of 1 week (more than 1 week for a few subjects). The order of active and sham tDCS sessions was counterbalanced across subjects to reduce the possibility of any potential learning effects. In tDCS sessions, the testing phase started 5 min after tDCS onset to ensure that there was sufficient change in cortical excitability [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0184749#pone.0184749.ref010" target="_blank">10</a>]. (B) tDCS electrode montages. Left, the bi-cephalic electrode montage. Right, the extra-cephalic reference electrode montage. The anodal and cathodal electrodes are shown in red and blue, respectively. These figures were drawn using the COMETS toolbox.</p

Results of all tasks during the test phase of the tDCS sessions.

<p>The left and right panels show the number and proportion of correct answers, respectively. The dark and light gray columns represent the effect sizes for the “bi-cephalic” and “extra-cephalic” montages, respectively. The error bars represent 95% confidence intervals.</p

Results of the two-digit addition arithmetic task.

<p>Results of the two-digit addition arithmetic task.</p