Ken-ichiro Ogawa

Interactive Rhythmic Cue Facilitates Gait Relearning in Patients with Parkinson's Disease

To develop a method for cooperative human gait training, we investigated whether interactive rhythmic cues could improve the gait performance of Parkinsons disease patients. The interactive rhythmic cues ware generated based on the mutual entrainment between the patients gait rhythms and the cue rhythms input to the patient while the patient walked. Previously, we found that the dynamic characteristics of stride interval fluctuation in Parkinsons disease patients were improved to a healthy 1/f fluctuation level using interactive rhythmic cues and that this effect was maintained in the short term. However, two problems remained in our previous study. First, it was not clear whether the key factor underpinning the effect was the mutual entrainment between the gait rhythms and the cue rhythms or the rhythmic cue fluctuation itself. Second, it was not clear whether or not the gait restoration was maintained longitudinally and was relearned after repeating the cue-based gait training. Thus, the present study clarified these issues using 32 patients who participated in a four-day experimental program. The patients were assigned randomly to one of four experimental groups with the following rhythmic cues: (a) interactive rhythmic cue, (b) fixed tempo cue, (c) 1/f fluctuating tempo cue, and (d) no cue. It has been reported that the 1/f fluctuation of stride interval in healthy gait is absent in Parkinsons disease patients. Therefore, we used this dynamic characteristic as an evaluation index to analyze gait relearning in the four different conditions. We observed a significant effect in condition (a) that the gait fluctuation of the patients gradually returned to a healthy 1/f fluctuation level, whereas this did not occur in the other conditions. This result suggests that the mutual entrainment can facilitate gait relearning effectively. It is expected that interactive rhythmic cues will be widely applicable in the fields of rehabilitation and assistive technology.

Relationship between Neural Rhythm Generation Disorders and Physical Disabilities in Parkinson's Disease Patients' Walking

Walking is generated by the interaction between neural rhythmic and physical activities. In fact, Parkinson’s disease (PD), which is an example of disease, causes not only neural rhythm generation disorders but also physical disabilities. However, the relationship between neural rhythm generation disorders and physical disabilities has not been determined. The aim of this study was to identify the mechanism of gait rhythm generation. In former research, neural rhythm generation disorders in PD patients’ walking were characterized by stride intervals, which are more variable and fluctuate randomly. The variability and fluctuation property were quantified using the coefficient of variation (CV) and scaling exponent α. Conversely, because walking is a dynamic process, postural reflex disorder (PRD) is considered the best way to estimate physical disabilities in walking. Therefore, we classified the severity of PRD using CV and α. Specifically, PD patients and healthy elderly were classified into three groups: no-PRD, mild-PRD, and obvious-PRD. We compared the contributions of CV and α to the accuracy of this classification. In this study, 45 PD patients and 17 healthy elderly people walked 200 m. The severity of PRD was determined using the modified Hoehn–Yahr scale (mH-Y). People with mH-Y scores of 2.5 and 3 had mild-PRD and obvious-PRD, respectively. As a result, CV differentiated no-PRD from PRD, indicating the correlation between CV and PRD. Considering that PRD is independent of neural rhythm generation, this result suggests the existence of feedback process from physical activities to neural rhythmic activities. Moreover, α differentiated obvious-PRD from mild-PRD. Considering α reflects the intensity of interaction between factors, this result suggests the change of the interaction. Therefore, the interaction between neural rhythmic and physical activities is thought to plays an important role for gait rhythm generation. These characteristics have potential to evaluate the symptoms of PD.

The Effect of Visual Apparent Motion on Audiovisual Simultaneity

Visual motion information from dynamic environments is important in multisensory temporal perception. However, it is unclear how visual motion information influences the integration of multisensory temporal perceptions. We investigated whether visual apparent motion affects audiovisual temporal perception. Visual apparent motion is a phenomenon in which two flashes presented in sequence in different positions are perceived as continuous motion. Across three experiments, participants performed temporal order judgment (TOJ) tasks. Experiment 1 was a TOJ task conducted in order to assess audiovisual simultaneity during perception of apparent motion. The results showed that the point of subjective simultaneity (PSS) was shifted toward a sound-lead stimulus, and the just noticeable difference (JND) was reduced compared with a normal TOJ task with a single flash. This indicates that visual apparent motion affects audiovisual simultaneity and improves temporal discrimination in audiovisual processing. Experiment 2 was a TOJ task conducted in order to remove the influence of the amount of flash stimulation from Experiment 1. The PSS and JND during perception of apparent motion were almost identical to those in Experiment 1, but differed from those for successive perception when long temporal intervals were included between two flashes without motion. This showed that the result obtained under the apparent motion condition was unaffected by the amount of flash stimulation. Because apparent motion was produced by a constant interval between two flashes, the results may be accounted for by specific prediction. In Experiment 3, we eliminated the influence of prediction by randomizing the intervals between the two flashes. However, the PSS and JND did not differ from those in Experiment 1. It became clear that the results obtained for the perception of visual apparent motion were not attributable to prediction. Our findings suggest that visual apparent motion changes temporal simultaneity perception and improves temporal discrimination in audiovisual processing.

Prior Knowledge Facilitates Mutual Gaze Convergence and Head Nodding Synchrony in Face-to-face Communication

As prior knowledge is claimed to be an essential key to achieve effective education, we are interested in exploring whether prior knowledge enhances communication effectiveness. To demonstrate the effects of prior knowledge, mutual gaze convergence and head nodding synchrony are observed as indicators of communication effectiveness. We conducted an experiment on lecture task between lecturer and student under 2 conditions: prior knowledge and non-prior knowledge. The students in prior knowledge condition were provided the basic information about the lecture content and were assessed their understanding by the experimenter before starting the lecture while the students in non-prior knowledge had none. The result shows that the interaction in prior knowledge condition establishes significantly higher mutual gaze convergence (t(15.03) = 6.72, p < 0.0001; α = 0.05, n = 20) and head nodding synchrony (t(16.67) = 1.83, p = 0.04; α = 0.05, n = 19) compared to non-prior knowledge condition. This study reveals that prior knowledge facilitates mutual gaze convergence and head nodding synchrony. Furthermore, the interaction with and without prior knowledge can be evaluated by measuring or observing mutual gaze convergence and head nodding synchrony.

Detection of Nonverbal Synchronization through Phase Difference in Human Communication

Nonverbal communication is an important factor in human communication, and body movement synchronization in particular is an important part of nonverbal communication. Some researchers have analyzed body movement synchronization by focusing on changes in the amplitude of body movements. However, the definition of “body movement synchronization” is still unclear. From a theoretical viewpoint, phase difference is the most important factor in synchronization analysis. Therefore, there is a need to measure the synchronization of body movements using phase difference. The purpose of this study was to provide a quantitative definition of the phase difference distribution for detecting body movement synchronization in human communication. The phase difference distribution was characterized using four statistical measurements: density, mean phase difference, standard deviation (SD) and kurtosis. To confirm the effectiveness of our definition, we applied it to human communication in which the roles of speaker and listener were defined. Specifically, we examined the difference in the phase difference distribution between two different communication situations: face-to-face communication with visual interaction and remote communication with unidirectional visual perception. Participant pairs performed a task supposing lecture in the face-to-face communication condition and in the remote communication condition via television. Throughout the lecture task, we extracted a set of phase differences from the time-series data of the acceleration norm of head nodding motions between two participants. Statistical analyses of the phase difference distribution revealed the characteristics of head nodding synchronization. Although the mean phase differences in synchronized head nods did not differ significantly between the conditions, there were significant differences in the densities, the SDs and the kurtoses of the phase difference distributions of synchronized head nods. These results show the difference in nonverbal synchronization between different communication types. Our study indicates that the phase difference distribution is useful in detecting nonverbal synchronization in various human communication situations.

Gait state transition by gait training using interactive rhythmic auditory cue in development process of gait rhythm generation disorders

We have developed Walk-Mate (WM) training using interactive rhythmic auditory cue, which is a new rehabilitation method concerning gait rhythm. Also, we have proposed the new evaluation method for gait rhythm generation disorders, which is often observed in Parkinsons disease (PD) patients. However, the recovery process by rehabilitation for gait rhythm was not yet evaluated from a viewpoint of gait rhythm generation disorders. In this paper, we aim to evaluate the recovery process by rehabilitation for gait rhythm by evaluation method for gait rhythm generation disorders in PD patients. For this purpose, we evaluated the effect of WM training compared to conventional Rhythmic Auditory Stimulation (RAS) training using fixed-tempo rhythmic auditory cue. To evaluate the rehabilitation effect, we hypothesized a transition probability model of discrete states in views of gait rhythm generation disorders. In detail, the state transition probability matrices of WM training, was compared with the probability matrices of RAS training. Thirty-one PD patients walked for approximately 2 minutes. We used the gait states constructed in previous study to evaluate the disease severity for gait rhythm generation disorders. Then we made state transition probability matrices from pre-WM training to post-WM training, and that from pre-RAS training to post-RAS training. The result showed the difference in effect between two training. Specifically, the WM training showed better gait state transition of the patients in severer states of gait rhythm generation disorders, compared to the RAS training. This suggests that this transition model is useful to identify the appropriate treatment of gait rhythm generation disorders.

Look at you, look at me: Detection and analysis of mutual gaze convergence in face-to-face interaction

In human communication, mutual attentiveness between individuals is essential for social interaction. The most significant and reliable indicator of mutual attentiveness is gaze. Despite the availability of diverse exorbitant eye-tracking devices, all claim highly accurate gaze positioning, which exceeds the necessity for average researches and applications. We propose an alternative model for mutual gaze convergence detection using economical video capturing devices and straightforward techniques that can investigate natural gaze behaviors in human-human interaction. We conducted a task supposing lecture in face-to-face interaction and applied our model to investigate (1) average percentage of total mutual gaze convergence, (2) duration of mutual gaze convergence, (3) the domination relationship between lectures and students during short lectures, including (4) the effects of attention span, which claimed to last for 10-20 minutes, toward short lecture task (5 minutes). Our results showed that the average total mutual gaze convergence between the lecturer and the student is 52.83%. It reveals the fact that in both long and short lecture, humans have momentary gaze fixation at a particular direction. We also found out that attention span has effect on different durations of lecture task, resulting in different dominance between lecturer and student, be it student for long lecture and lecturer for short lecture. We believe that our developed model implementation and findings exhibit practical applicability and worthy of contribution to the communities of related research areas.

The simultaneous perception of auditory–tactile stimuli in voluntary movement

The simultaneous perception of multimodal information in the environment during voluntary movement is very important for effective reactions to the environment. Previous studies have found that voluntary movement affects the simultaneous perception of auditory and tactile stimuli. However, the results of these experiments are not completely consistent, and the differences may be attributable to methodological differences in the previous studies. In this study, we investigated the effect of voluntary movement on the simultaneous perception of auditory and tactile stimuli using a temporal order judgment task with voluntary movement, involuntary movement, and no movement. To eliminate the potential effect of stimulus predictability and the effect of spatial information associated with large-scale movement in the previous studies, we randomized the interval between the start of movement and the first stimulus, and used small-scale movement. As a result, the point of subjective simultaneity (PSS) during voluntary movement shifted from the tactile stimulus being first during involuntary movement or no movement to the auditory stimulus being first. The just noticeable difference (JND), an indicator of temporal resolution, did not differ across the three conditions. These results indicate that voluntary movement itself affects the PSS in auditory–tactile simultaneous perception, but it does not influence the JND. In the discussion of these results, we suggest that simultaneous perception may be affected by the efference copy.

Voluntary movement affects simultaneous perception of auditory and tactile stimuli presented to a non-moving body part.

The simultaneous perception of multimodal sensory information has a crucial role for effective reactions to the external environment. Voluntary movements are known to occasionally affect simultaneous perception of auditory and tactile stimuli presented to the moving body part. However, little is known about spatial limits on the effect of voluntary movements on simultaneous perception, especially when tactile stimuli are presented to a non-moving body part. We examined the effect of voluntary movement on the simultaneous perception of auditory and tactile stimuli presented to the non-moving body part. We considered the possible mechanism using a temporal order judgement task under three experimental conditions: voluntary movement, where participants voluntarily moved their right index finger and judged the temporal order of auditory and tactile stimuli presented to their non-moving left index finger; passive movement; and no movement. During voluntary movement, the auditory stimulus needed to be presented before the tactile stimulus so that they were perceived as occurring simultaneously. This subjective simultaneity differed significantly from the passive movement and no movement conditions. This finding indicates that the effect of voluntary movement on simultaneous perception of auditory and tactile stimuli extends to the non-moving body part.

Body and psychological state synchrony and change by the grant of prior knowledge

According to recent studies, the existence of previous knowledge has been found to be involved in more advanced knowledge acquisition in the human study. Further, when the body motion synchronized, empathy for others has also been found to be important key of interaction. In this study, we focus on those points, by looking at whether the psychological state and body motion are affected by the prior knowledge, and of evaluating the internal understanding and consent of knowledge understanding from the body synchrony will consider the possibility. Specifically, we conducted the experiment lecturer task on teacher-student interaction. There are two group conditions. One is given prior knowledge, the other is not given prior knowledge. The students of the two groups are given same lecture. psychological state is measured using a questionnaire, physical motion is measured using an acceleration sensors. The results reveal that in prior knowledge group, the psychological synchrony is likely to occur more than no prior knowledge group and the body synchrony is found to occur at an early stage with closer to 0 time lag. These differences are occurred due to the involvement of the lecture. The students with prior knowledge is more likely to be involved in the lecture more than the students with no prior knowledge.