Predictability of sinusoidally moving stimuli does not improve the accuracy of the accommodative response

Previous research work suggests that predictable target motion such as sinusoidal movement can be anticipated by the visual system, thereby improving the accommodative response. The validity of predictable motion for studying human dynamic accommodation is sometimes put into question. The aim of this work was to assess the effect of anticipation along with learning (and motivation, etc.) and fatigue (and boredom, loss of attention, etc.) on dynamic accommodation experiments from a practical perspective. Specifically, changes in amplitude and temporal phase lag were estimated within and between trials as 9 adult observers were instructed to focus on a stimulus that oscillated sinusoidally towards and away from the eye at specific temporal frequencies. On average, amplitude decreased whereas phase increased within trials. No evidence of anticipation or learning was observed either within or between trials. Fatigue consistently dominated anticipation and learning within the course of each trial. Even if the eye is equipped by a prediction operator as it is often assumed, fatigue confounds the results from dynamic accommodation experiments more than anticipation or learning.

Predictability of Sinusoidal Stimulus Movement in Accommodative Demand Does Not Improve Accommodation

Previous research work suggests that predictable target motion such as sinusoidal movement can be anticipated by the visual system, thereby improving the accommodative response. The validity of predictable motion for studying human dynamic accommodation is sometimes put into question. The aim of this work was to assess from a practical perspective the effect of anticipation along with learning (and motivation, etc.) and fatigue (and boredom, loss of attention, etc.) on dynamic accommodation experiments. Specifically, changes in amplitude and temporal phase were estimated within and between trials as 9 adult observers were instructed to focus on a stimulus that oscillated in distance at specific temporal frequencies. On average, amplitude decreased whereas phase increased within trials. No evidence of anticipation or learning was observed either within or between trials. Fatigue consistently dominated anticipation and learning within the course of each trial. Even if the eye is equipped by a “prediction operator”, in practice, it is fatigue, and not anticipation or learning, that seems to muddle the results from dynamic accommodation experiments.

Anterior–Posterior Balance Perturbation Protocol Using Lifelike Virtual Reality Environment

Virtual reality (VR) paradigms have proved to be a valid method to challenge and perturb balance. There is little consensus in the literature on the best protocol design to perturb balance and induce postural sway. Current VR interventions still lack a well-defined standardized metric to generate a virtual environment that can perturb balance in an efficacious, lifelike, and repeatable manner. The objective of this study was to investigate different configurations of amplitude and frequency in an anterior–posterior translation VR environment, that is, lifelike and scaled. Thirteen young adults with no conditions affecting balance were recruited. Balance was challenged by anterior–posterior sinusoidal movement of the lab image within the VR headset. Four different amplitudes of the sinusoidal movement were tested: 1, 5, 10, and 20 cm, with each amplitude being presented at 2 test frequencies : 0.5 and 0.25 Hz. Mean center of pressure velocity was significantly greater than baseline at 0.5 Hz and amplitudes of 10 and 20 cm. Mean center of pressure at approximate entropy was greater than baseline at 0.5 Hz and amplitude of 20 cm. The results suggest that sinusoidal movement of a realistic VR environment produces altered balance compared with baseline quiet standing, but only under specific movement parameters.

Study of Hydrostatic Pump Created Under Liquid Sloshing in a Rectangular Tank Subjected to External Excitation

The aim of this work is to study the hydrostatic pump created under liquid sloshing in a rectangular tank partially filled with liquid. A numerical simulation was performed to predict the liquid motion in the tank. The apparition of the compression and the depression zones due to the liquid motion was presented and analyzed. An experimental setup with sinusoidal movement was developed to study the hydrostatic pump. The hydrostatic pump is created using a mixing element. The experimental results show that the compression and the depression zones can create the hydrostatic pump. The effect of the connecting chamber value was studied for different values of external excitation frequency. The pump depends considerably on the dimension of the connecting zone between the two volumes. For the different connecting chamber values, the pumped quantity increase with the increase of the frequency.

Sensing Physiological Tremor in a Hand-Held Microsurgical Instrument

Physiological tremor is an involuntary, approximately rhythmic and roughly sinusoidal movement [1]. It is inherent in all humans. The characteristics of physiological tremor are highly dependent on the body parts [2]. For instance, the frequency of tremor in the elbow ranges from 3 to 5 Hz while it ranges from 8 to 12 Hz in the wrist. Physiological tremor is benign for everyday tasks such as walking or eating. However, tasks that require fine muscle control such as microsurgery or military targeting are susceptible to physiological tremor. The imprecision in positioning the tool-tip due to the tremor makes some ophthalmological, neurological and inner ear microsurgeries difficult [3]. Therefore, real-time compensation of physiological tremor would enable surgeons to accurately perform microsurgeries.

REMARKS ON THE CALCULATION OF AMPLITUDES OF THE LINEAR WAVE PRODUCED BY A WAVE MACHINE

We are indebted to Havelock and to Biesel for their theoretical explanation of the mechanics of generation of the Stokes plane wave produced by a wave machine operating with a simple sinusoidal movement. The calculation of the wave amplitude, produced in this way, is the most salient feature of this theory. We add nothing new to this research. But in view of its importance it seems fitting to pay special attention to a few mathematical difficulties that remain in the exposition of the above-mentioned authors, to indicate ways in which they may be solved in part, to simplify a few theoretical demonstrations and to make some comments on the physical significance of a theory which depends on very simplifying hypotheses. More accurately speaking, we investigate a series of functions of one variable, introduced by Havelock and Biesel to present the solution of the problem. A gap in the theory is closed by showing that the series is complete; in fact, to establish this point, it is sufficient to employ a few results of the spectrum theory of certain differential operators. We complement then the indications of Biesel on the legitimacy of the term by term derivation of the series developments he has formed. Finally an elementary re-examination is made of the nature of singularities found in this solution and whose study has been made in a less direct manner in the works mentioned above. It would appear that all the above remarks can be of assistance to technicians in the study of many analogous questions.

Forced vibration of a ball attached to a cable

This work describes an analytic solution to predict the forced oscillation of a suspended cable and an attached ball. The oscillations are driven by a sinusoidal movement at the fixed end of the cable. This problem may be used in the verification of numerical software which is commonly used to design systems with suspended cables.

Predicting force generation by lamprey muscle during applied sinusoidal movement using a simple dynamic model.

Experiments were performed on single-myotome preparations of lamprey muscle, to discover whether force developed by intermittent tetanic stimulation during imposed sinusoidal movement could be predicted by data collected from isometric and constant-velocity experiments. We developed a simple dynamic model consisting of a set of simultaneous ordinary differential equations with unknown parameters. Appropriate values of the parameters were found by fitting numerical solutions of the differential equations to data from the isometric and constant-velocity experiments. Predictions were made of the time course of force developed during imposed sinusoidal movement in which the phase between muscle shortening and tetanic stimulation was varied to cover the whole phase spectrum. The match between the predicted and recorded time courses was very good for all phases, and particularly for those phases that are seen during swimming in the intact animal.

The influence of neuroactive pesticides on the behaviour of entomopathogenic nematodes

The behaviour and infectivity of the infective juveniles (IJs) of two species of entomopathogenic nematodes, Steinernema carpocapsae Weiser and Steinernema feltiae Filipjev (Rhabditida: Steinernematidae), were determined after exposure to two neuroactive pesticides, oxamyl and fenamiphos, widely used against plant parasitic nematodes. Oxamyl (50 μg ml−1) initially stimulated non-sinusoidal movement in S. feltiae but had no appreciable effect on IJs of S. carpocapsae, while fenamiphos (10 and 50 μg ml−1) increased and sustained non-sinusoidal movement in both species over an observation period of 48 h. The two pesticides reduced the infectivity of both nematode species against late instar larvae of the wax moth, Galleria mellonella L. in a sand-tube bioassay when compared with controls. Infective juveniles of S. feltiae showed limited body waving behaviour on the sand surface whereas S. carpocapsae showed the full range of nictation movements, including body waving, stationary straight postures and leaping. Oxamyl had no significant (P>0.05) effect on the number of IJs of S. carpocapsae which nictated except when the IJs were pre-incubated with this compound for 24 h (P<0.05). In contrast, fenamiphos completely suppressed all nictation and body waving behaviour in both species. Nictating IJs of S. carpocapsae exposed to late instar G. mellonella for 12 h in a filter-paper bioassay were found to be more infective compared with non-nictating IJs. Treating IJs of S. carpocapsae with oxamyl (50 μg ml−1) increased the infectivity of non-nictating IJs compared with controls but reduced infectivity of nictating IJs when exposed to G. mellonella for 12 h. The work is discussed in relation to proposals to use these or other pesticides to enhance the activity and infectivity of IJs of entomopathogenic nematodes.