In this study, we examined whether luminance processing in the human visual system would exhibit any history effect (i.e., inter-trial modulation) in psychophysical and magnetoencephalographic experiments. A disk was presented against a black background at various luminance levels in a randomized order. During the MEG recording, participants were instructed to rate the brightness of the disk (magnitude estimation) and to report it aloud during inter-stimulus interval. The MEG results showed that the neuromagnetic activation around 200-220 ms after the stimulus onset in the left occipito-temporal regions at a given trial was weaker when the disk luminance in the immediately prior trial was higher. An inverse inter-trial effect was also observed in the psychophysical experiment. These findings suggest that the neuromagnetic activity reflects the inter-trial modulation of luminance processing that correlates with the subjective perception of brightness.

Future standardized system for distinguishing actual and artifactual magnetoencephalogram (MEG) data is an essential tool. In this paper, we proposed the quantitative parameters based on fractal dimension (FD) analyses in which the FD may convey different features before and after artifact removal. The six FD algorithms based on time-series computation, namely, box-counting method (BCM), variance fractal dimension (VFD), Higuchi's method (HM), Kazt's method (KM), detrended fluctuation analysis (DFA), and modified zero-crossing rate (MZCR) were compared. These approaches measure nonlinear-behavioral responses in the resting-state MEG data. Experimental results showed that the FD value of actual MEG was increased statistically in comparison with the artifactual MEG. The DFA and the HM present a best performance for analyzing simulated data and resting-state MEG data, respectively. © Springer-Verlag Berlin Heidelberg 2013.

The current study examined selective encoding in visual working memory by systematically investigating interference from task-irrelevant features. The stimuli were objects defined by three features (color, shape, and location), and during a delay period, any of the features could switch between two objects. Additionally, single- and whole-probe trials were randomized within experimental blocks to investigate effects of memory retrieval. A series of relevant-feature switch detection tasks, where one feature was task-irrelevant, showed that interference from the task-irrelevant feature was only observed in the color-shape task, suggesting that color and shape information could be successfully filtered out, but location information could not, even when location was a task-irrelevant feature. Therefore, although location information is added to object representations independent of task demands in a relatively automatic manner, other features (e.g., color, shape) can be flexibly added to object representations.

A number of studies have shown that current-trial responses are biased toward the response of the preceding trial in perceptual decisionmaking tasks (the sequential effect Holland and Lockhead, 1968 Perception & Psychophysics 3 409-414). The sequential effect has been widely observed in evaluation of the physical properties of stimuli as well as more complex properties. However, it is unclear whether subjective decisions (eg attractiveness judgments) are also susceptible to the sequential effect. Here, we examined whether the sequential effect would occur in face-attractiveness judgments. Forty-eight pictures of male and female faces were presented successively. Participants rated the attractiveness of each face on a 7-point scale. The results showed that the attractiveness rating of a given face assimilated toward the rating of the preceding trial. In a separate experiment, we provided the average attractiveness rating by others for each trial as feedback. The feedback weakened the sequential effect. These findings suggest that attractiveness judgment is also biased toward the preceding judgment, and hence the sequential effect can be extended into the domain of subjective decisionmaking.

This paper presents an automatic method to remove physiological artifacts from magnetoencephalogram (MEG) data based on independent component analysis (ICA). The proposed features including kurtosis (K), probability density (PD), central moment of frequency (CMoF), spectral entropy (SpecEn), and fractal dimension (FD) were used to identify the artifactual components such as cardiac, ocular, muscular, and sudden high-amplitude changes. For an ocular artifact, the frontal head region (FHR) thresholding was proposed. In this paper, ICA method was on the basis of FastICA algorithm to decompose the underlying sources in MEG data. Then, the corresponding ICs responsible for artifacts were identified by means of appropriate parameters. Comparison between MEG and artifactual components showed the statistical significant results at p < 0.001 for all features. The output artifact-free MEG waveforms showed the applicability of the proposed method in removing artifactual components.

Recently, an independent component analysis (ICA) has been proven to be an effective method for removing artifacts and noise in multi-channel physiological measures. ICA can extract independent component (IC) which was directly regarded as artifacts. In this paper, we propose an automatic method for classifying physiological artifacts from magnetoencephalogram (MEG) data. The artifactual ICs were classified based on support vector machine (SVM) algorithm. The following parameters: kurtosis (K), probability density (PD), central moment of frequency (CMoF), spectral entropy (SpecEn), and fractal dimension (FD) were used as input vector of SVM. The proposed method showed the average classification rates of 99.18%, 92.33%, and 98.15% for cardiac (EKG), ocular (EOG), and high-amplitude changes (HAM), respectively.

Resting-state study is a useful tool to investigate the brain activity related to cognitive abilities in children because it may be difficult for children to perform some experimental tasks. In the present study, we report a preliminary examination to associate the resting-state neuromagnetic signals from magnetoencephalogram (MEG) with cognitive abilities in children. We applied a non-linear time-series analysis for 90-s resting-state neuromagnetic signals and estimated interdependency of two channels of MEG signals. Then we examined the relation between the magnitudes of interdependency and the cognitive abilities and ages. Although we found some indications of age differences in the lateralization of interdependency, the results highlighted several limiting factors in measuring cognitive abilities and resting-state neuromegnetic signals in children and suggested that further elaboration of devices, procedures, and analysis would be warranted.

In psychophysical scaling, a subjective rating in the current trial is tend to be biased by preceding trials (sequential effect). Here, we investigated the factor determining the sequential effect: physical stimulus, evaluation process, or response in the preceding trials. Participants observed disks with different luminance values and rated the perceived brightness of the disk on a 9-point scale. When participants were required to evaluate and response to the 1-back trials, the current rating was assimilated toward 1-back trials. On the other hand, when participants were not required to evaluate the 1-back stimulus, the current rating was not affected by 1-back trials, independent of whether the response to the 1-back stimulus was required or not. These results suggest that the sequential effect was due to evaluation process but not to stimulus or response in the preceding trials. © 2011 IEEE.

We used magnetoencephalography (MEG) to investigate the timing and location of cortical activity related to perceived brightness. Participants passively observed 1 of 5 disks of different luminance (1, 3.2, 10, 32, and 100 cd/m(2)) during MEG recording, and rated the perceived brightness of the disk before and after the MEG recording. The perceived brightness showed an almost perfect log-linear dependence on luminance intensity. The MEG results showed that the stimulus presentation evoked neuromagnetic responses in the occipital region approximately 150 ms after stimulus onset. The average magnitude of the response was positively correlated with the subjective ratings of perceived brightness as well as the log-scaled stimulus luminance. These findings suggest that the neuromagnetic responses in the occipital cortex reflect subjective brightness perception and that the visual cortex completes the brightness assignment as early as 150 ms after stimulus onset. The possible clinical application of these results is discussed.