The Cascade Neural Network Model and a Speed-Accuracy Trade-Off of Arm Movement

We propose a hybrid neural network model of aimed arm movements that consists of a feedforward controller and a postural controller. The cascade neural network of Kawato, Maeda, Uno, and Suzuki (1990) was employed as a computational implementation of the feedforward controller. This network computes feedforward motor commands based on a minimum torque-change criterion. If the weighting parameter of the smoothness criterion is fixed and the number of relaxation iterations is rather small, the cascade model cannot calculate the exact torque, and the hand does not reach the desired target by using the feedforward control alone. Thus, one observes an error between the final position and the desired target location. By using a fixed weighting parameter value and a limited iteration number to simulate target-directed arm movements, we found that the cascade model generated a planning time–accuracy trade-off, and a quasi–power-law type of speed–accuracy trade-off. The model provides a candidate neural mechanism to explain the stochastic variability of the time course of the feedforward motor command. Our approach also accounts for several invariant features of multijoint arm trajectories, such as roughly straight hand paths and bell-shaped speed profiles.     

A longitudinal study of the moderating effects of social capital on the relationships between changes in human capital and ikigai among Japanese older adults

Ikigai, one of the indices of well‐being, tends to decline with age because resources relating to ikigai decline. However, there are individual differences in this decline. This study tested for maintenance of ikigai among Japanese elderly, using a longitudinal study investigating the moderating role of social capital on the effects of changes in human capital on ikigai. We conducted a panel survey targeting 1,068 people (M age = 73.01 years) in 2013, and 686 people in 2017. The variables were ikigai, changes in human capital (self‐rated financial status, physical health) and social capital (social networks, trust in others), educational level, and control variables. Multiple regression analyses revealed the interaction effects of changes in physical health and changes in social networks (strong ties, weak ties) on follow‐up ikigai. Post hoc analyses indicated that declines in physical health predicted declines in ikigai among those whose social networks (strong ties and weak ties) had declined in the 4‐year study, but these relationships were not significant among those whose social networks had increased. The results suggest that older adults can weaken the adverse effect of a decline in human capital on ikigai by maintaining or increasing social networks.     

Temporal modulations of agonist and antagonist muscle activities accompanying improved performance of ballistic movements

Although many studies have examined performance improvements of ballistic movement through practice, it is still unclear how performance advances while maintaining maximum velocity, and how the accompanying triphasic electromyographic (EMG) activity is modified. The present study focused on the changes in triphasic EMG activity, i.e., the first agonist burst (AG1), the second agonist burst (AG2), and the antagonist burst (ANT), that accompanied decreases in movement time and error. Twelve healthy volunteers performed 100 ballistic wrist flexion movements in ten 10-trial sessions under the instruction to "maintain maximum velocity throughout the experiment and to stop the limb at the target as fast and accurately as possible". Kinematic parameters (position and velocity) and triphasic EMG activities from the agonist (flexor carpi radialis) and antagonist (extensor carpi radialis) muscles were recorded. Comparison of the results obtained from the first and the last 10 trials, revealed that movement time, movement error, and variability of amplitudes reduced with practice, and that maximum velocity and time to maximum velocity remained constant. EMG activities showed that AG1 and AG2 durations were reduced, whereas ANT duration did not change. Additionally, ANT and AG2 latencies were reduced. Integrated EMG of AG1 was significantly reduced as well. Analysis of the alpha angle (an index of the rate of recruitment of the motoneurons) showed that there was no change in either AG1 or AG2. Correlation analysis of alpha angles between these two bursts further revealed that the close relationship of AG1 and AG2 was kept constant through practice. These findings led to the conclusion that performance improvement in ballistic movement is mainly due to the temporal modulations of agonist and antagonist muscle activities when maximum velocity is kept constant. Presumably, a specific strategy is consistently applied during practice.     

Where Grammar and Interaction Meet: A Study of Co-Participant Completion in Japanese Conversation

This article examines the practice of "co-participant completion" in Japanese conversation, and explores what kinds of resources are mobilized to provide the opportunity to complete another participant's utterance-in-progress. It suggests the following observations as potential characteristics of Japanese co-participant completion: (i) Syntactically-defined two-part formats (e.g. [If X] + [then Y]) may not play as prominent a role as in English; (ii) The majority of cases of co-participant completion take the form of 'terminal item completion;' (iii) Locally emergent structures like 'contrast' and 'list' as well as 'unprojected' features of turn construction often play an important role in enhancing the opportunity for completing another participant's utterance-in-progress. The article then discusses the implications of these findings for the investigation of the mutual bearing of grammar and social interaction. In particular, the discussion focuses on what we can learn from the practice of co-participant completion about how projection of turn-shapes is accomplished in Japanese conversation.     

The influence of Japanese mothers' styles of emotional expression on thirteen-month-old infants' reactions to a stranger

The present study investigated the hypothesized influence of mothers' styles of emotional expression on infants' responses to the stranger in Episode 3, the Ainsworth Strange Situation. One hundred and thirty-five mothers volunteered for this experiment with their 13-month-olds. The mothers' answers on an expression style questionnaire (EESQ) were factor analysed. According to their mothers' factor scores, infants were divided into four groups, those having (a) expressive type mothers (N = 40), (b) suppressive type mothers (N = 39), (c) positive expressive type mothers (N = 31), and (d) negative expressive type mothers (N = 25). The infants' behaviours were analysed in 5-sec intervals. The infants having expressive type mothers showed a strong interest in the stranger and interacted with her willingly. The infants having suppressive type mothers exhibited less smiling and much freezing behaviour. The infants having positive expressive type mothers reacted with more smiling, much bodily contact behaviour with the mother and less crying. The infants having negative expressive type mothers showed more often crying and frequent head orientation towards the stranger.     

Context-dependent olfactory learning monitored by activities of salivary neurons in cockroaches

Context-dependent discrimination learning, a sophisticated form of nonelemental associative learning, has been found in many animals, including insects. The major purpose of this research is to establish a method for monitoring this form of nonelemental learning in rigidly restrained insects for investigation of underlying neural mechanisms. We report context-dependent olfactory learning (occasion-setting problem solving) of salivation, which can be monitored as activity changes of salivary neurons in immobilized cockroaches, Periplaneta americana. A group of cockroaches was trained to associate peppermint odor (conditioned stimulus, CS) with sucrose solution reward (unconditioned stimulus, US) while vanilla odor was presented alone without pairing with the US under a flickering light condition (1.0 Hz) and also trained to associate vanilla odor with sucrose reward while peppermint odor was presented alone under a steady light condition. After training, the responses of salivary neurons to the rewarded peppermint odor were significantly greater than those to the unrewarded vanilla odor under steady illumination and those to the rewarded vanilla odor was significantly greater than those to the unrewarded peppermint odor in the presence of flickering light. Similar context-dependent responses were observed in another group of cockroaches trained with the opposite stimulus arrangement. This study demonstrates context-dependent olfactory learning of salivation for the first time in any vertebrate and invertebrate species, which can be monitored by activity changes of salivary neurons in restrained cockroaches.     

Reduction of the flash-lag effect in terms of active observation

In the present study, we investigated how observers’ control of stimulus change affects temporal and spatial aspects of visual perception. We compared the illusory flash-lag effects for automatic movement of the stimulus with stimulus movement that was controlled by the observers’ active manipulation of a computer mouse (Experiments 1, 2, and 5), a keyboard (Experiment 3), or a trackball (Experiment 4). We found that the flash-lag effect was significantly reduced when the observer was familiar with the directional relationship between the mouse movement and stimulus movement on a front parallel display (Experiments 1 and 2) and that, although the unfamiliar directional relationship between the mouse movement and stimulus movement increased the flash-lag effect at the beginning of the experimental session, the repetitive observation with the same unfamiliar directional relationship reduced the flash-lag effect (Experiment 5). We found no consistent reduction of the flash-lag effect with the use of a keyboard or a trackball (Experiments 3 and 4). These results suggest that the learning of a specific directional relationship between a proprioceptive signal of hand movements and a visual signal of stimulus movements is necessary for the reduction of the flash-lag effect.     

Salivary conditioning with antennal gustatory unconditioned stimulus in an insect

Classical conditioning of olfactory conditioning stimulus (CS) with gustatory unconditioned stimulus (US) in insects has been used as a pertinent model for elucidation of neural mechanisms underlying learning and memory. However, a conditioning system in which stable intracellular recordings from brain neurons are feasibly obtained while monitoring the conditioning effect has remained to be established. Recently, we found classical conditioning of salivation in cockroaches Periplaneta americana, in which an odor was associated with sucrose solution applied to the mouth, and this conditioning could be monitored by activities of salivary neurons. Application of gustatory US to the mouth, however, leads to feeding movement accompanying a movement of the brain that prevents stable recordings from brain neurons. Here we investigated whether a gustatory stimulus presented to an antenna could serve as an effective US for producing salivary conditioning. Presentation of sucrose or sodium chloride solution to an antenna induced salivation and also increased activities of salivary neurons. A single pairing trial of an odor with antennal presentation of sucrose or sodium chloride solution produced conditioning of salivation or of activities of salivary neurons. Five pairing trials led to a conditioning effect that lasted for one day. Water or tactile stimulus presented to an antenna was not effective for producing conditioning. The results demonstrate that gustatory US presented to an antenna is as effective as that presented to the mouth for producing salivary conditioning. This conditioning system provides a useful model for studying the neural basis of learning at the level of singly identifiable neurons.     

An event‐related potential study on the “check operation” in the Eriksen task1

Abstract: We examined two issues for the Eriksen task with two types of stimuli, the central target letter of which was flanked with noise (e.g., HHHHH for compatible stimuli and SSHSS for incompatible stimuli). First, we examined whether or not a response‐stop function is carried out until the check operation to detect and correct erroneous response readiness has finished (Eriksen & Eriksen, 1974). Second, reaction times for incompatible stimuli are not prolonged if only identical noise stimuli are used throughout the block. This phenomenon is called the blocking effect. We then explored whether or not the blocking effect can be caused by the selective inhibition of erroneous response readiness (Eriksen & Schultz, 1979). Sixteen participants (18–29 years old) selectively pressed one of two buttons for the target letter. The results showed that the negative potential related to the response‐stop function was enlarged for incompatible stimuli. Moreover, the blocking effect was observed, while erroneous response readiness was still observable for incompatible stimuli. These results suggest that the blocking effect is caused by something other than reciprocal inhibition.