Periodicity in wide-band time series

Summary: To test the hypotheses that (i) electroencephalograms (EEGs) are largely made up of oscillations at many frequencies and (ii) that the peaks in the power spectra represent oscillations, we applied a new method, called the Period Specific Average (PSA) to a wide sample of EEGs. Both hypotheses can be rejected

Optimal low-thrust trajectories to asteroids through an algorithm based on differential dynamic programming

In this paper an optimisation algorithm based on Differential Dynamic Programming is applied to the design of rendezvous and fly-by trajectories to near Earth objects. Differential dynamic programming is a successive approximation technique that computes a feedback control law in correspondence of a fixed number of decision times. In this way the high dimensional problem characteristic of low-thrust optimisation is reduced into a series of small dimensional problems. The proposed method exploits the stage-wise approach to incorporate an adaptive refinement of the discretisation mesh within the optimisation process. A particular interpolation technique was used to preserve the feedback nature of the control law, thus improving robustness against some approximation errors introduced during the adaptation process. The algorithm implements global variations of the control law, which ensure a further increase in robustness. The results presented show how the proposed approach is capable of fully exploiting the multi-body dynamics of the problem; in fact, in one of the study cases, a fly-by of the Earth is scheduled, which was not included in the first guess solution

On the “cyclopean eye”: Saccadic asymmetry and the reliability of perceived straight-ahead

AbstractIf two targets are both on the visual axis of one eye or the other, and binocular fixation is shifted from the farther one to the nearer, the aligned eye consistently makes an initial, seemingly pointless saccade in a temporal direction. The size of those saccades typically differs markedly, depending on whether the targets are aligned with the observer's dominant or non-dominant eye. Pickwell [(1972) Vision Research, 12, 1499–1507] proposed that this binocular asymmetry in oculomotor performance reflects a subject-specific lateral displacement of the egocenter (the “binoculus” of Hering, which has traditionally been assumed to be on the midline). An empirical test of Pickwell's widely endorsed hypothesis has now been conducted and the proposal has been found wanting. In an otherwise darkened room, subjects were required repeatedly to set a small light to a perceived straight-ahead location in the horizontal plane, first for a target at 300 cm distance and then for one at 30 cm. Extrapolation of a line that connects the two averages of those settings to the inter-ocular axis provides an estimate of the subjective egocenter to which visual directions are referred. Contrary to Pickwell's proposal, those locations of the inferred egocenter were usually quite near the midline, and were completely uncorrelated with same-subject data on the extent of saccadic asymmetry at the onset of asymmetrical convergence. The data on perceived straight-ahead underlying this result indicate the availability of extraretinal information about eye orientation that is quite precise at a given moment (median standard deviation of 47 min arc) but conspicuously non-stationary over several-minute intervals (monotonic drifts in sequential settings being very common)

Forays with the additive periodogram applied to the EEG.

The most information-rich measure of the working brain is the electrical activity, recorded as wideband, extracellular local field potentials from multiple sites, in extent and depth, with millisecond and millimeter resolution. We still lack a common view of the electrical activity in terms of simple description - which must precede explanation in terms of mechanisms. The situation is much like the diverse views on the nature and characteristics of a jungle. We have elsewhere addressed related questions. (i) How much of the wideband activity is stochastic - concluding that a significant and highly labile amount of coherence and bicoherence bespeak temporal fine structure and cooperativity. (ii) How much fine structure is spatial, concluding that differentiation increases as the volume sampled is smaller (Bullock et al. 1995a,b, 1997)