Sotaro Shimada

Rubber Hand Illusion under Delayed Visual Feedback

Background Rubber hand illusion (RHI) is a subjects illusion of the self-ownership of a rubber hand that was touched synchronously with their own hand. Although previous studies have confirmed that this illusion disappears when the rubber hand was touched asynchronously with the subjects hand, the minimum temporal discrepancy of these two events for attenuation of RHI has not been examined. Methodology/Principal Findings In this study, various temporal discrepancies between visual and tactile stimulations were introduced by using a visual feedback delay experimental setup, and RHI effects in each temporal discrepancy condition were systematically tested. The results showed that subjects felt significantly greater RHI effects with temporal discrepancies of less than 300 ms compared with longer temporal discrepancies. The RHI effects on reaching performance (proprioceptive drift) showed similar conditional differences. Conclusions/Significance Our results first demonstrated that a temporal discrepancy of less than 300 ms between visual stimulation of the rubber hand and tactile stimulation to the subjects own hand is preferable to induce strong sensation of RHI. We suggest that the time window of less than 300 ms is critical for multi-sensory integration processes constituting the self-body image.

Deactivation in the sensorimotor area during observation of a human agent performing robotic actions

It is well established that several motor areas, called the mirror-neuron system (MNS), are activated when an individual observes others actions. However, whether the MNS responds similarly to robotic actions compared with human actions is still controversial. The present study investigated whether and how the motor area activity is influenced by appearance (human vs. robot) and/or kinematics (human vs. robot) of the observed action using near-infrared spectroscopy. The results showed that there was a strong interaction between these factors, revealing strong deactivations in sensorimotor areas when the subject saw a human agent performing robotic actions, which was significantly different from responses when observing the human agent acting in a human way and the robot agent performing robotic actions. These results indicate that MNS activity is sensitive to congruency between the appearance and kinematics of the agent, especially when the agent has a human appearance. We discuss the experience-dependent characteristics of MNS sensitivity to observed actions.

Frontotemporal oxyhemoglobin dynamics predict performance accuracy of dance simulation gameplay: Temporal characteristics of top-down and bottom-up cortical activities

We utilized the high temporal resolution of functional near-infrared spectroscopy to explore how sensory input (visual and rhythmic auditory cues) are processed in the cortical areas of multimodal integration to achieve coordinated motor output during unrestricted dance simulation gameplay. Using an open source clone of the dance simulation video game, Dance Dance Revolution, two cortical regions of interest were selected for study, the middle temporal gyrus (MTG) and the frontopolar cortex (FPC). We hypothesized that activity in the FPC would indicate top-down regulatory mechanisms of motor behavior; while that in the MTG would be sustained due to bottom-up integration of visual and auditory cues throughout the task. We also hypothesized that a correlation would exist between behavioral performance and the temporal patterns of the hemodynamic responses in these regions of interest. Results indicated that greater temporal accuracy of dance steps positively correlated with persistent activation of the MTG and with cumulative suppression of the FPC. When auditory cues were eliminated from the simulation, modifications in cortical responses were found depending on the gameplay performance. In the MTG, high-performance players showed an increase but low-performance players displayed a decrease in cumulative amount of the oxygenated hemoglobin response in the no music condition compared to that in the music condition. In the FPC, high-performance players showed relatively small variance in the activity regardless of the presence of auditory cues, while low-performance players showed larger differences in the activity between the no music and music conditions. These results suggest that the MTG plays an important role in the successful integration of visual and rhythmic cues and the FPC may work as top-down control to compensate for insufficient integrative ability of visual and rhythmic cues in the MTG. The relative relationships between these cortical areas indicated high- to low-performance levels when performing cued motor tasks. We propose that changes in these relationships can be monitored to gauge performance increases in motor learning and rehabilitation programs.

fMRI Validation of fNIRS Measurements During a Naturalistic Task

We present a method to compare brain activity recorded with near-infrared spectroscopy (fNIRS) in a dance video game task to that recorded in a reduced version of the task using fMRI (functional magnetic resonance imaging). Recently, it has been shown that fNIRS can accurately record functional brain activities equivalent to those concurrently recorded with functional magnetic resonance imaging for classic psychophysical tasks and simple finger tapping paradigms. However, an often quoted benefit of fNIRS is that the technique allows for studying neural mechanisms of complex, naturalistic behaviors that are not possible using the constrained environment of fMRI. Our goal was to extend the findings of previous studies that have shown high correlation between concurrently recorded fNIRS and fMRI signals to compare neural recordings obtained in fMRI procedures to those separately obtained in naturalistic fNIRS experiments. Specifically, we developed a modified version of the dance video game Dance Dance Revolution (DDR) to be compatible with both fMRI and fNIRS imaging procedures. In this methodology we explain the modifications to the software and hardware for compatibility with each technique as well as the scanning and calibration procedures used to obtain representative results. The results of the study show a task-related increase in oxyhemoglobin in both modalities and demonstrate that it is possible to replicate the findings of fMRI using fNIRS in a naturalistic task. This technique represents a methodology to compare fMRI imaging paradigms which utilize a reduced-world environment to fNIRS in closer approximation to naturalistic, full-body activities and behaviors. Further development of this technique may apply to neurodegenerative diseases, such as Parkinson’s disease, late states of dementia, or those with magnetic susceptibility which are contraindicated for fMRI scanning.

Relationship between sensitivity to visuotactile temporal discrepancy and the rubber hand illusion

The rubber-hand illusion (RHI) is that the subject feels the visually presented tactile stimulation of an artificial (rubber) hand as their own tactile sensation and is caused by stimulating the rubber and real hands synchronously. Our previous study showed that the RHI was greatly reduced as the visual feedback delay of the tactile stimulation of the hand became longer. In the present study, we investigate the relationship between the attenuation of the RHI and the detection of the delay in two experiments: (1) an RHI experiment and (2) a visuotactile asynchrony detection experiment, in which the subjects underwent tactile stimulation of their hand and judged whether visual feedback was consistent with the touch sensation. In line with our previous study, the RHI was significantly reduced as the delay lengthened. Interestingly, proprioceptive drift declined linearly as the delay increased, while the delay detection rate was better fitted by a non-linear (logistic) function. The illusion score showed the intermittent pattern. We suggest that proprioceptive drift is relevant to the processing of the body schema, whereas the delay detection and the subjective feeling of the RHI are more related to the body image processing.

Modulation of the motor area activity during observation of a competitive game.

Watching competitive games is a pervasive entertainment in humans and likely to be facilitated by our social cognitive abilities. We investigated the brain activity during observation of a competitive game by using near-infrared spectroscopy. The result showed that activity in the motor area was significantly greater when the individuals favored player won, compared with when the same player lost. The motor area was also activated when the individuals themselves performed the same action, showing the mirror neuron system property. Our results first showed that the motor area activity during observation of competitive games was modulated by the outcome of the game. We suggest that the observers brain is more likely to share the winners internal motor representation than that of the loser.

Outcome and view of the player modulate motor area activity during observation of a competitive game

In a previous study, we demonstrated that the mirror neuron system is involved in watching competitive games performed by multiple players [Shimada, S., & Abe, R. (2009). Modulation of the motor area activity during observation of a competitive game. NeuroReport, 20, 979-983]. In the present study, we investigated whether mirror neuron system activity was modulated by the outcome of a competitive game as well as by the spatial relationship between the player and the observer. We measured the activity of motor areas using near-infrared spectroscopy when a subject watched a two-player competitive game, rock-paper-scissors (RPS). Some parts of the motor area that was activated while performing the RPS action were also activated while observing the RPS game. Interestingly, the magnitude of this activity (during observation) was modulated by the outcome and the view of the particular player whom the subject was supporting. In the dorsal anterior region of the motor area measured, the activity was significantly greater when the supported player won rather than when he lost, regardless of the view. It was also greater when the player was presented with an incongruent view than with a congruent view, regardless of the outcome. In contrast, the dorsal posterior region of the motor area was activated only when the supported player won and was observed with a congruent view. We suggest that mirror neuron system activity during observation of a competitive game reflects the subjects internal assimilation of the actions of the observed player.

Motor learning and modulation of prefrontal cortex: an fNIRS assessment.

OBJECTIVE Prefrontal hemodynamic responses are observed during performance of motor tasks. Using a dance video game (DVG), a complex motor task that requires temporally accurate footsteps with given visual and auditory cues, we investigated whether 20 h of DVG training modified hemodynamic responses of the prefrontal cortex in six healthy young adults. APPROACH Fronto-temporal activity during actual DVG play was measured using functional near-infrared spectroscopy (fNIRS) pre- and post-training. To evaluate the training-induced changes in the time-courses of fNIRS signals, we employed a regression analysis using the task-specific template fNIRS signals that were generated from alternate well-trained and/or novice DVG players. The HRF was also separately incorporated as a template to construct an alternate regression model. Change in coefficients for template functions at pre- and post- training were determined and compared among different models. MAIN RESULTS Training significantly increased the motor performance using the number of temporally accurate steps in the DVG as criteria. The mean oxygenated hemoglobin (ΔoxyHb) waveform changed from an activation above baseline pattern to that of a below baseline pattern. Participants showed significantly decreased coefficients for regressors of the ΔoxyHb response of novice players and HRF. The model using ΔoxyHb responses from both well-trained and novice players of DVG as templates showed the best fit for the ΔoxyHb responses of the participants at both pre- and post-training when analyzed with Akaike information criteria. SIGNIFICANCE These results suggest that the coefficients for the template ΔoxyHb responses of the novice players are sensitive indicators of motor learning during the initial stage of training and thus clinically useful to determine the improvement in motor performance when patients are engaged in a specific rehabilitation program.

Modulation of motor area activity during observation of unnatural body movements

The mirror neuron system (MNS) is activated when observing the actions of others. However, it remains unclear whether the MNS responds more strongly to natural bodily actions in the observers motor repertoire than to unnatural actions. We investigated whether MNS activity is modulated by the unnaturalness of an observed action by inserting short pauses in the middle of the action (0, 2, and 6 pauses; no-pause, pause-1, and pause-2 conditions, respectively). The results indicated that the number of pauses significantly affected motor area activity. Subsequent analyses revealed significant differences between the pause-1 and pause-2 conditions (P<0.01), as well as the no-pause and pause-2 conditions (P<0.05). There was significant activation in the pause-1 condition (P<0.001), while significant deactivation was observed in the pause-2 condition (P<0.05). These results indicate that MNS activity is modulated by the kinematic characteristics of the observed action. We suggest the possibility that a slightly deviated action may enhance the MNS activity during action observation, while a highly unnatural action would lead to a strong attenuation (deactivation) of activity in the MNS.

Modulation of motor area activity by the outcome for a player during observation of a baseball game.

Background Observing competitive games such as sports is a pervasive entertainment among humans. The inclination to watch others play may be based on our social-cognitive ability to understand the internal states of others. The mirror neuron system, which is activated when a subject observes the actions of others, as well as when they perform the same action themselves, seems to play a crucial role in this process. Our previous study showed that activity of the mirror neuron system was modulated by the outcome of the subjects favored player during observation of a simple competitive game (rock-paper-scissors). However, whether the mirror neuron system responds similarly in a more complex and naturalistic sports game has not yet been fully investigated. Methodology/Principal Findings In the present study, we measured the activity of motor areas when the subjects, who were amateur baseball field players (non-pitchers), watched short movie clips of scenes in professional baseball games. The subjects were instructed to support either a batter or a pitcher when observing the movie clip. The results showed that activity in the motor area exhibited a strong interaction between the subjects supported side (batter or pitcher) and the outcome (a hit or an out). When the subject supported the batter, motor area activity was significantly higher when the batter made an out than when he made a hit. However, such modulation was not apparent when the subject supported the pitcher. Conclusions/Significance This result indicates that mirror neuron system activity is modulated by the outcome for a particular player in a competitive game even when observing a complex and naturalistic sports game. We suggest that our inclination to watch competitive games is facilitated by this characteristic of the mirror neuron system.