Most walking assist systems reported are not available for real-world environment, where frequent perturbations are caused by slips, uneven terrain, slopes and obstacles. On the other hand, it is evident that human beings cope with those perturbations, especially when the perturbations cannot be predicted or perceived in advance, with reflexes, which cause relatively fixed muscular responsive patterns to perturbations unconsciously within a short period of time ranging from several 10 to 200 ms. Our ultimate goal is to realize artificial reflexes in real-world walking support systems for those paralyzed people, whose afferent and efferent neural pathways are usually weakened, so that the reflexive system is also impaired to a certain degree. This goal needs both qualitative and quantitative understanding of human reflexive mechanism during walking. However, except for some hypotheses about the underlying neural mechanisms of the reflexes during walking, there is no widely accepted unified theory, nor are there clear experimental results that could be directly quoted in the disciplines of physiology and motor control. Our approach includes (1) acquiring muscle activity profiles during normal walking and slip-perturbed walking by recording and processing Electromyographic (EMG) signals of several walking-related muscles, in human gait experiments; (2) developing a central-pattern-generator (CPG) based neuro-musculo-skeletal simulation model; (3) comparing joint trajectories of the simulation model with those of a human subject during normal walking to verify the simulation model's conformity with human walking; (4) using muscle activity profiles of reflexive responses to slip-perturbation during walking to construct a rapid responding pathway. The results showed that, (1) The simulation model could show behavior resembling that of normal human walking; (2) in the case of occurrence of slip-perturbation, the rapid responding pathway could improve the perturbation-resistance and maintain the balance for the walking; (3) using the simulation model, several hypotheses on underlying neuro-mechanism were investigated. These reveal the possibility to realize the artificial reflex for the paralyzed people.
People usually develop different kinds of compensated gait in response to local function deficits, such as muscle weakness, spasticity in specific muscle groups, or joint stiffness, in order to overcome the falling risk factors. Compensated walking has been analysed empirically in the impaired gait analysis area. However, the compensation could be identified spatially and temporally. The stability and perturbation resistance of compensated walking have not been analysed quantitatively. In this research, a biomimetic human walking simulator was employed to model one individual paraplegic subject with plantarflexor spasticity. The pes equinus was expressed by biasing the outputs of plantarflexor neurons corresponding to the spastic muscles. Then, the compensatory mechanism was explored by adjusting the outputs of the other muscles. It was shown that this approach can be used for quantitative analysis of the spastic gait and compensated walking. Thus, this research can improve the understanding of the behaviour of compensated walking, bringing insights not only for building useful walking assist systems with high safety but also for designing effective rehabilitation interventions.
The current study investigates to what extent masked morphological priming is modulated by language-particular properties, specifically by its writing system. We present results from two masked priming experiments investigating the processing of complex Japanese words written in less common (moraic) scripts. In Experiment 1, participants performed lexical decisions on target verbs; these were preceded by primes which were either (i) a past-tense form of the same verb, (ii) a stem-related form with the epenthetic vowel -i, (iii) a semantically-related form, and (iv) a phonologically-related form. Significant priming effects were obtained for prime types (i), (ii), and (iii), but not for (iv). This pattern of results differs from previous findings on languages with alphabetic scripts, which found reliable masked priming effects for morphologically related prime/target pairs of type (i), but not for non-affixal and semantically-related primes of types (ii), and (iii). In Experiment 2, we measured priming effects for prime/target pairs which are neither morphologically, semantically, phonologically nor - as presented in their moraic scripts—orthographically related, but which—in their commonly written form—share the same kanji, which are logograms adopted from Chinese. The results showed a significant priming effect, with faster lexical-decision times for kanji-related prime/target pairs relative to unrelated ones. We conclude that affix-stripping is insufficient to account for masked morphological priming effects across languages, but that language-particular properties (in the case of Japanese, the writing system) affect the processing of (morphologically) complex words.
Functional Electrical Stimulation (FES) is a technology to generate neural activity in an artificial way to activate muscles. However, as reported by some researchers, the human responses to FES are likely to be affected by several factors, such as spasticity, muscle fatigue, nerve habituation and so forth. Consequently, the function restoration by FES is neither durable, nor stable. In order to realize long-term and stable FES assistance, this study investigated whether and why an Auxiliary Stimulation (AS) to the Gastrocnemius, with current frequency ranged from 2000 to 6000 Hz, could alleviate the symptom of spasticity and muscle fatigue caused by the stimulation to the Tibialis Anterior. We have developed a portable auxiliary stimulator, and performed experiments to verify its effectiveness. The results showed that our approach enabled comparatively stable and durable function restoration assistance. Moreover, for understanding underlying neuromuscular processes elicited by the AS and its qualitative nature, this study also measured the Hoffmann-reflex (H-reflex) in soleus muscle before and after the AS, to interpret the effect of the Auxiliary Stimulation.
Deadjectival nominals with -sa and -mi in Japanese are both phonologically transparent and morphologically decomposable. However, whilst -sa essentially serves to form nouns out of adjectives, -mi forms function as semantic labels with specific meanings. We examined -sa and -mi nominals in three experiments, an eye-movement experiment presenting -sa and -mi forms in sentence contexts and in two word recognition experiments using (primed and unprimed) lexical decision, to investigate the nature of their form-level representations. Whilst the word recognition experiments produced the same pattern of results for -sa and -mi forms, the eye-movement experiment demonstrated clear differences: -mi forms elicited longer reading times compared to -sa forms, except when the particular meanings of -mi forms were contextually licensed. These results show how different semantic properties affect the performance of derived words that have the same type of word level representation.Derived words have linguistic properties of both lexical entries and combinatorial grammatical processes. On the one hand, the products of derivational processes take on a linguistic life of their own in that they typically have their own grammatical properties and meanings, much like morphologically simplex words which have particular meanings and forms stored in lexical entries. On the other hand, derived words have internal morphological structure, which is arguably a result of rule-like grammatical operations. Consider, for example, deadjectival nouns such as agility, reality, curiosity. Although -ity formations are largely unproductive, lexically restricted to adjectives of Latin or Greek origin, and convey 148 Harald Clahsen and Yu Ikemoto abstract meanings that are not always predictable from their component parts, -ity derivation yields a morphologically structured word form consisting of an adjectival stem with a shortened penultimate vowel (compare agile -agility) and a segmentable suffix.The present study investigates the precise interplay of whole-word level and morphologically structured representations during the processing of derived words. It also contributes to experimental research on derivational morphology across typologically different languages, by providing new experimental findings from Japanese, a non-Indo-European language with purely agglutinating morphology. The specific case we examined, -sa and -mi nominalizations in Japanese, is particularly advantageous for the purpose of this study, as these two derivational processes have identical form-level but different semantic/functional properties. On the basis of results from different experiments which test the recognition of derived words both as single word forms and in sentential contexts, we show how meaning-related properties of derived words affect their online processing and how these can be dissociated from effects of their form-level representations.
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