Detection of transient generalized and mutual phase synchronization by clustering and application by single brain signals

The present work introduces an analysis framework for the detection of metastable signal segments in multivariate time series. It is shown that in case of linear data these segments represent transient generalized synchronization, while metastable segments in circular data reflect transient mutual phase synchronization. We propose a single segmentation approach for both types of data considering the space-time structure of the data. Applications to both event-related potentials and single evoked potentials obtained from an auditory oddball experiment reveal the lack of the component P300 in an experimental condition, indicates attention effects in component N100 and shows dramatic latency jitters in single trials. A comparison of the proposed method to a conventional index of mutual phase synchronization demonstrates the superiority of considering space-time data structures

Brain activation during dichoptic presentation of optic flow stimuli

The processing of optic flow fields in motion-sensitive areas in human visual cortex was studied with BOLD (blood oxygen level dependent) contrast in functional magnetic resonance imaging (fMRI). Subjects binocularly viewed optic flow fields in plane (monoptic) or in stereo depth (dichoptic) with various degrees of disparity and increasing radial speed. By varying the directional properties of the stimuli (expansion, spiral motion, random), we explored whether the BOLD effect reflected neuronal responses to these different forms of optic flow. The results suggest that BOLD contrast as assessed by fMRI methods reflects the neural processing of optic flow information in motion-sensitive cortical areas. Furthermore, small but replicable disparity-selective responses were found in parts of Brodmann's area 19

EEG Alpha Spindles as Indicators for Prolonged Brake Reaction Time During Auditory Secondary Tasks in a Real Road Driving Study

Driver distraction accounts for a substantial number of traffic accidents. Therefore, the impact of auditory secondary tasks on driving performance was examined. In addition to performance measures, i.e. reaction time on emergency brakings of a leading vehicle, mental driver states were described by electroencephalographic (EEG: alpha spindles, alpha band power) as well as cardiac activity (ECG: heart rate variability). Results show that brake reaction time (RT) increased with time-on-task during all conditions (p<.001), and was significantly higher while performing the secondary task (p<.001). Physiological measures showed similar effects. Alpha spindle rate, alpha band power as well as heart rate variability (HRV) increased with time-on-task and were significantly different during the secondary task, indicating inhibited visual information processing and reduced concentration ability. This study shows that reduced driving performance measured by means of prolonged brake reactions during increased cognitive load elicited by auditory secondary tasks is indicated by EEG measures as well as cardiac activity, enabling the direct quantification of driver distraction in experiments during real road driving

Assessing Drivers’ Fatigue State Under Real Traffic Conditions Using EEG Alpha Spindles

The effectiveness of EEG alpha spindles, defined by short narrowband bursts in the alpha band, as an objective measure for assessing driver fatigue under real driving conditions was examined using an algorithm for the identification of alpha spindles. The method is applied to data recorded under real traffic conditions and compared with the performance of the traditional EEG fatigue measure alpha band power. Statistical analysis revealed significant increases from the first to the last driving section of alpha band power; with larger effect sizes for the alpha spindle based measures. An increased level of fatigue for drop-outs, as compared to participants who did not abort the drive, was observed only by means of alpha spindle parameters. EEG alpha spindle parameters increase both fatigue detection sensitivity and specificity as compared to EEG alpha band power. It is demonstrated that alpha spindles are superior to EEG band power measures for assessing driver fatigue under real traffic conditions

The scintillating grid illusion in stereo-depth

AbstractThe dark scintillating dots occurring on a gray-on-black, modified Hermann grid [Schrauf, M., Lingelbach, B., & Wist, E. R. (1997). The scintillating grid illusion. Vision Research, 37, 1033–1038] were studied in stereo-depth by assigning various degrees of disparity to the white inducing disks. Dependent on the sign of disparity, the disks and the dark illusory spots within them appeared to lie either in the same plane, in front of, or behind the grid. At zero disparity, illusory strength was maximum and was the same for stereo, binocular and monocular viewing. With increasing disparity, the illusion became progressively weaker; however, the decrease for stereo-patterns was significantly less than for control patterns presented binocularly or monocularly. These results suggest a central contribution to the scintillation effect

Neurocognitive Approach to Research on the Effects of Workload

The concept of workload describes the relationship between a human operator and the momentary task demands. Conventionally workload is defined as a subjective state of the operator that can be reported with use of psychometric scales. The effects of workload on performance and reaction times yield important “objective” sources of information. Signal detection theory provides us with a useful framework within which we can interpret the effects of workload on discriminability (d’) and measures of response bias (β, corresponding to the likelihood ratios of the noise and noise plus signal functions at the criterion). Modern brain imaging techniques can be employed to determine the effects of workload on task-related neural responses in specific regions of the human brain. We describe a neurocognitive approach to research on the effects of workload in simulated (laboratory) and real (field) experiments. The findings suggest that functional brain imaging can provide important new insights into the way operators perform in challenging tasks

EEG alpha spindles and prolonged brake reaction times during auditory distraction in an on-road driving study

Driver distraction is responsible for a substantial number of traffic accidents. This paper describes the impact of an auditory secondary task on drivers’ mental states during a primary driving task. N = 20 participants performed the test procedure in a car following task with repeated forced braking on a non-public test track. Performance measures (provoked reaction time to brake lights) and brain activity (EEG alpha spindles) were analyzed to describe distracted drivers. Further, a classification approach was used to investigate whether alpha spindles can predict drivers’ mental states. Results show that reaction times and alpha spindle rate increased with time-on-task. Moreover, brake reaction times and alpha spindle rate were significantly higher while driving with auditory secondary task opposed to driving only. In single-trial classification, a combination of spindle parameters yielded a median classification error of about 8% in discriminating the distracted from the alert driving. Reduced driving performance (i.e., prolonged brake reaction times) during increased cognitive load is assumed to be indicated by EEG alpha spindles, enabling the quantification of driver distraction in experiments on public roads without verbally assessing the drivers’ mental states