Rational positive real approximations for LQG optimal compensators arising in active stabilization of flexible structures

In this paper the approximation problem for a class of optimal compensators for flexible structures is considered. The particular case of a simply supported truss with an offset antenna is dealt with. The nonrational positive real optimal compensator transfer function is determined, and it is proposed that an approximation scheme based on a continued fraction expansion method be used. Comparison with the more popular modal expansion technique is performed in terms of stability margin and parameters sensitivity of the relative approximated closed loop transfer functions

How actions shape perception: learning action-outcome relations and predicting sensory outcomes promote audio-visual temporal binding

To maintain a temporally-unified representation of audio and visual features of objects in our environment, the brain recalibrates audio-visual simultaneity. This process allows adjustment for both differences in time of transmission and time for processing of audio and visual signals. In four experiments, we show that the cognitive processes for controlling instrumental actions also have strong influence on audio-visual recalibration. Participants learned that right and left hand button-presses each produced a specific audio-visual stimulus. Following one action the audio preceded the visual stimulus, while for the other action audio lagged vision. In a subsequent test phase, left and right button-press generated either the same audio-visual stimulus as learned initially, or the pair associated with the other action. We observed recalibration of simultaneity only for previously-learned audio-visual outcomes. Thus, learning an action-outcome relation promotes temporal grouping of the audio and visual events within the outcome pair, contributing to the creation of a temporally unified multisensory object. This suggests that learning action-outcome relations and the prediction of perceptual outcomes can provide an integrative temporal structure for our experiences of external events

A constrained matrix factorization problem

AbstractThe present paper considers a constrained matrix factorization problem which is a natural generalization of the classical triangular factorization

How action structures time: About the perceived temporal order of action and predicted outcomes

Few ideas are as inexorable as the arrow of causation: causes must precede their effects. Explicit or implicit knowledge about this causal order permits humans and other animals to predict and control events in order to produce desired outcomes. The sense of agency is deeply linked with representation of causation, since it involves the experience of a self-capable of acting on the world. Since causes must precede effects, the perceived temporal order of our actions and subsequent events should be relevant to the sense of agency. The present study investigated whether the ability to predict the outcome of an action would impose the classical cause-precedes-outcome pattern on temporal order judgements. Participants indicated whether a visual stimulus (dots moving upward or downward) was presented either before or after voluntary actions of the left or right hand. Crucially, the dot motion could be either congruent or incongruent with an operant association between hand and motion direction learned in a previous learning phase. When the visual outcome of voluntary action was congruent with previous learning, the motion onset was more often perceived as occurring after the action, compared to when the outcome was incongruent. This suggests that the prediction of specific sensory outcomes restructures our perception of timing of action and sensory events, inducing the experience that congruent effects occur after participants' actions. Interestingly, this bias to perceive events according to the temporal order of cause and outcome disappeared when participants knew that motion directions were automatically generated by the computer. This suggests that the reorganisation of time perception imposed by associative learning depends on participants' causal beliefs

Precursor processes of human self-initiated action

A gradual buildup of electrical potential over motor areas precedes self-initiated movements. Recently, such "readiness potentials" (RPs) were attributed to stochastic fluctuations in neural activity. We developed a new experimental paradigm that operationalised self-initiated actions as endogenous 'skip' responses while waiting for target stimuli in a perceptual decision task. We compared these to a block of trials where participants could not choose when to skip, but were instead instructed to skip. Frequency and timing of motor action were therefore balanced across blocks, so that conditions differed only in how the timing of skip decisions was generated. We reasoned that across-trial variability of EEG could carry as much information about the source of skip decisions as the mean RP. EEG variability decreased more markedly prior to self-initiated compared to externally-triggered skip actions. This convergence suggests a consistent preparatory process prior to self-initiated action. A leaky stochastic accumulator model could reproduce this convergence given the additional assumption of a systematic decrease in input noise prior to self-initiated actions. Our results may provide a novel neurophysiological perspective on the topical debate regarding whether self-initiated actions arise from a deterministic neurocognitive process, or from neural stochasticity. We suggest that the key precursor of self-initiated action may manifest as a reduction in neural noise

The Sense of Agency as Tracking Control

Does sense of agency (SoA) arise merely from action-outcome associations, or does an additional real-time process track each step along the chain? Tracking control predicts that deviant intermediate steps between action and outcome should reduce SoA. In two experiments, participants learned mappings between two finger actions and two tones. In later test blocks, actions triggered a robot hand moving either the same or a different finger, and also triggered tones, which were congruent or incongruent with the mapping. The perceived delay between actions and tones gave a proxy measure for SoA. Action-tone binding was stronger for congruent than incongruent tones, but only when the robot movement was also congruent. Congruent tones also had reduced N1 amplitudes, but again only when the robot movement was congruent. We suggest that SoA partly depends on a real-time tracking control mechanism, since deviant intermediate action of the robot reduced SoA over the tone

Age-related changes in the primary motor cortex of newborn to adult domestic pig sus scrofa domesticus

The pig has been increasingly used as a suitable animal model in translational neuroscience. However, several features of the fast-growing, immediately motor-competent cerebral cortex of this species have been adequately described. This study analyzes the cytoarchitecture of the primary motor cortex (M1) of newborn, young and adult pigs (Sus scrofa domesticus). Moreover, we investigated the distribution of the neural cells expressing the calcium-binding proteins (CaBPs) (calretinin, CR; parvalbumin, PV) throughout M1. The primary motor cortex of newborn piglets was characterized by a dense neuronal arrangement that made the discrimination of the cell layers difficult, except for layer one. The absence of a clearly recognizable layer four, typical of the agranular cortex, was noted in young and adult pigs. The morphometric and immunohistochemical analy-ses revealed age-associated changes characterized by (1) thickness increase and neuronal density (number of cells/mm2 of M1) reduction during the first year of life; (2) morphological changes of CR-immunoreactive neurons in the first months of life; (3) higher density of CR-and PV-immunopositive neurons in newborns when compared to young and adult pigs. Since most of the present findings match with those of the human M1, this study strengthens the growing evidence that the brain of the pig can be used as a potentially valuable translational animal model during growth and development