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J Nishii

Publications and source records attributed to J Nishii.

6 recordsLinked to original sources
PubMed2000

Legged insects select the optimal locomotor pattern based on the energetic cost.

The gait transition in legged animals has attracted many researchers, and its relation to metabolic cost and mechanical work has been discussed in recent decades. We assumed that the energetic cost during locomotion is given by the sum of positive mechanical work and the heat energy loss that is proportional to the square of joint torque and examined the optimal locomotor pattern based on the energetic cost in a simple dynamical model of a hexapod by computer simulations. The obtained results well agree with characteristics in the locomotor patterns in legged animals; for example, the leg protraction time, step length, and the metabolic cost of transport are almost constant for many velocities, the leg cycling period decreases with velocity, and the energetic cost of locomotion induced by carrying loads linearly increases with mass loaded. This correspondence of the results of calculation to experimental results suggest that the heat energy loss for torque generation is proportional to the square of the torque during locomotion, and that the locomotor pattern in legged animals is highly optimized based on the energetic cost.

Animals↗
PubMed1999

Learning model for coupled neural oscillators.

Neurophysiological experiments have shown that many motor commands in living systems are generated by coupled neural oscillators. To coordinate the oscillators and achieve a desired phase relation with desired frequency, the intrinsic frequencies of component oscillators and coupling strengths between them must be chosen appropriately. In this paper we propose learning models for coupled neural oscillators to acquire the desired intrinsic frequencies and coupling weights based on the instruction of the desired phase pattern or an evaluation function. The abilities of the learning rules were examined by computer simulations including adaptive control of the hopping height of a hopping robot. The proposed learning rule takes a simple form like a Hebbian rule. Studies on such learning models for neural oscillators will aid in the understanding of the learning mechanism of motor commands in living bodies.

Action Potentials↗
PubMed1994

Modelling of movement of the lamprey: control of oscillators.

This article discusses the control methods of the central pattern generator (CPG). First a control model of the CPG is presented using 2 oscillators, and we suggest that phasic modulation to the CPG by means of phasic information is effective for controlling the phase difference between oscillators. Next, two models for controlling the CPG of a lamprey are proposed. One model describes a control system from the brain stem, in which the reticulospinal neurons control the CPG by receiving feedback signals and sending control signals to the neck region of the CPG. The other is a model for learning an localized control system to generate a desired motor pattern. By means of these models, a role of the efference copy is suggested.

Animals↗