Masahiro Hirai

The Trans-Visible Navigator: A See-Through Neuronavigation System Using Augmented Reality.

INTRODUCTION The neuronavigator has become indispensable for brain surgery and works in the manner of point-to-point navigation. Because the positional information is indicated on a personal computer (PC) monitor, surgeons are required to rotate the dimension of the magnetic resonance imaging/computed tomography scans to match the surgical field. In addition, they must frequently alternate their gaze between the surgical field and the PC monitor. OBJECTIVE To overcome these difficulties, we developed an augmented reality-based navigation system with whole-operation-room tracking. METHODS A tablet PC is used for visualization. The patients head is captured by the back-face camera of the tablet. Three-dimensional images of intracranial structures are extracted from magnetic resonance imaging/computed tomography and are superimposed on the video image of the head. When viewed from various directions around the head, intracranial structures are displayed with corresponding angles as viewed from the camera direction, thus giving the surgeon the sensation of seeing through the head. Whole-operation-room tracking is realized using a VICON tracking system with 6 cameras. RESULTS A phantom study showed a spatial resolution of about 1 mm. The present system was evaluated in 6 patients who underwent tumor resection surgery, and we showed that the system is useful for planning skin incisions as well as craniotomy and the localization of superficial tumors. CONCLUSIONS The main advantage of the present system is that it achieves volumetric navigation in contrast to conventional point-to-point navigation. It extends augmented reality images directly onto real surgical images, thus helping the surgeon to integrate these 2 dimensions intuitively.

Improved motor performance in patients with acute stroke using the optimal individual attentional strategy

It is believed that motor performance improves when individuals direct attention to movement outcome (external focus, EF) rather than to body movement itself (internal focus, IF). However, our previous study found that an optimal individual attentional strategy depended on motor imagery ability. We explored whether the individual motor imagery ability in stroke patients also affected the optimal attentional strategy for motor control. Individual motor imagery ability was determined as either kinesthetic- or visual-dominant by a questionnaire in 28 patients and 28 healthy-controls. Participants then performed a visuomotor task that required tracing a trajectory under three attentional conditions: no instruction (NI), attention to hand movement (IF), or attention to cursor movement (EF). Movement error in the stroke group strongly depended on individual modality dominance of motor imagery. Patients with kinesthetic dominance showed higher motor accuracy under the IF condition but with concomitantly lower velocity. Alternatively, patients with visual dominance showed improvements in both speed and accuracy under the EF condition. These results suggest that the optimal attentional strategy for improving motor accuracy in stroke rehabilitation differs according to the individual dominance of motor imagery. Our findings may contribute to the development of tailor-made pre-assessment and rehabilitation programs optimized for individual cognitive abilities.

Developmental changes in mental rotation ability and visual perspective-taking in children and adults with Williams syndrome

Williams syndrome (WS) is a genetic disorder caused by the partial deletion of chromosome 7. Individuals with WS have atypical cognitive abilities, such as hypersociability and compromised visuospatial cognition, although the mechanisms underlying these deficits, as well as the relationship between them, remain unclear. Here, we assessed performance in mental rotation (MR) and level 2 visual perspective taking (VPT2) tasks in individuals with and without WS. Individuals with WS obtained lower scores in the VPT2 task than in the MR task. These individuals also performed poorly on both the MR and VPT2 tasks compared with members of a control group. For the individuals in the control group, performance scores improved during development for both tasks, while the scores of those in the WS group improved only in the MR task, and not the VPT2 task. Therefore, we conducted a second experiment to explore the specific cognitive challenges faced by people with WS in the VPT2 task. In addition to asking participants to change their physical location (self-motion), we also asked them to adopt a third-person perspective by imagining that they had moved to a specified location (self-motion imagery). This enabled us to assess their ability to simulate the movement of their own bodies. The performance in the control group improved in both the self-motion and self-motion imagery tasks and both performances were correlated with verbal mental age. However, we did not find any developmental changes in performance for either task in the WS group. Performance scores for the self-motion imagery task in the WS group were low, similar to the scores observed for the VPT2 in this population. These results suggest that MR and VPT2 tasks involve different processes, and that these processes develop differently in people with WS. Moreover, difficulty completing VPT2 tasks may be partly because of an inability of people with WS to accurately simulate mental body motion.

Typical visual search performance and atypical gaze behaviors in response to faces in Williams syndrome

BackgroundEvidence indicates that individuals with Williams syndrome (WS) exhibit atypical attentional characteristics when viewing faces. However, the dynamics of visual attention captured by faces remain unclear, especially when explicit attentional forces are present. To clarify this, we introduced a visual search paradigm and assessed how the relative strength of visual attention captured by a face and explicit attentional control changes as search progresses.MethodsParticipants (WS and controls) searched for a target (butterfly) within an array of distractors, which sometimes contained an upright face. We analyzed reaction time and location of the first fixation—which reflect the attentional profile at the initial stage—and fixation durations. These features represent aspects of attention at later stages of visual search. The strength of visual attention captured by faces and explicit attentional control (toward the butterfly) was characterized by the frequency of first fixations on a face or butterfly and on the duration of face or butterfly fixations.ResultsAlthough reaction time was longer in all groups when faces were present, and visual attention was not dominated by faces in any group during the initial stages of the search, when faces were present, attention to faces dominated in the WS group during the later search stages. Furthermore, for the WS group, reaction time correlated with eye-movement measures at different stages of searching such that longer reaction times were associated with longer face-fixations, specifically at the initial stage of searching. Moreover, longer reaction times were associated with longer face-fixations at the later stages of searching, while shorter reaction times were associated with longer butterfly fixations.ConclusionsThe relative strength of attention captured by faces in people with WS is not observed at the initial stage of searching but becomes dominant as the search progresses. Furthermore, although behavioral responses are associated with some aspects of eye movements, they are not as sensitive as eye-movement measurements themselves at detecting atypical attentional characteristics in people with WS.

Electrophysiological study of face inversion effects in Williams syndrome

OBJECTIVE In order to evaluate whether face perception is intact or not in Williams syndrome (WS), the face inversion effects (FIE) in the event-related potential (ERP) or magnetoencephalography (MEG) were investigated in three teenaged patients with WS. METHODS Responses to the inverted faces and upright faces were compared using MEG for one 13year old girl with WS (subject A) and ERP for boys with WS at 16 and 14years of age (subjects B and C, respectively). RESULTS Although age-matched control children showed FIE in both MEG and ERP studies, two subjects (A and B) with WS showed no FIE at all. The neurophysiological data of ERP in subject B was significantly different from those of the age-matched controls. On the other hand, a boy with WS (subject C) showed typical FIE in the same manner as the age-matched controls. CONCLUSIONS The difference between those with or without FIE was not explained merely by the chronological age, a simple delay in mental age or in the ability to discriminate among upright faces. The absence of FIE may be related to the severity of a deficit in the dorsal pathway function that is characteristic to the syndrome.

Developmental changes in point-light walker processing during childhood: A two-year follow-up ERP study

Event-related potentials were measured in twenty-four children aged 6-15 years, at one-year intervals for two years, to investigate developmental changes in each subjects neural response to a point-light walker (PLW) and a scrambled PLW (sPLW) stimulus. One positive peak (P1) and two negative peaks (N1 and N2) were observed in both occipitotemporal regions at approximately 130, 200, and 300-400ms. The amplitude and latency of the P1 component measured by the occipital electrode decreased during development over the first one-year period. Negative amplitudes of both N1 and N2, induced by the PLW stimulus, were significantly larger than those induced by the sPLW stimulus. Moreover, for the P1-N1 amplitude, the values for the eight-year-old children were significantly larger than those for the twelve-year-old children. N1 and N2 latency at certain electrodes decreased with age, but no consistent changes were observed. These results suggest that enhanced electrophysiological responses to PLW can be observed in all age groups, and that the early components were changed even over the course of a single year at the age of twelve.

Intact attentional orienting towards inverted faces revealed by both manual responses and eye-movement measurement in individuals with Williams syndrome.

BACKGROUND Individuals with Williams syndrome (WS) exhibit atypical attentional characteristics when viewing faces. Although atypical configural processing of faces has been reported in WS, the relative strengths of configural and local feature information to capture visual attention in WS remains unclear. We previously demonstrated that attentional capture by target-unrelated upright faces differs depending on what response is measured. Whereas eye movements reflected subtle atypical attentional properties at the late stage of visual search, manual responses could not capture the atypical attentional profiles towards target-unrelated upright faces in individuals with WS. Here we used the same experimental paradigm to assess whether sensitivity to configural facial information is necessary for capturing attention in WS. METHODS We measured both eye movements and manual responses from 17 individuals with WS and 34 typically developing children and adults while they were actively involved in a visual search task with an inverted face distractor. Task measures (reaction time and performance accuracy) and gaze behaviour (initial direction of attention and fixation duration) were analysed for each stimulus. RESULTS When the target and the inverted face were displayed in the same search array, reaction times and accuracies in individuals with WS showed similar tendencies as typical controls. Analysis of task and gaze measures revealed that attentional orienting towards inverted faces was not atypical. CONCLUSION Although individuals with WS exhibited atypical gaze behaviour towards upright faces in our previous study, this unusual behaviour disappears if the faces are upside down. These findings suggest that local feature information alone (e.g. eyes) does not contribute to the heightened attention to faces, but configural information appears necessary for drawing attention to faces in individuals with WS, at least in the current experimental paradigm.

Preserved search asymmetry in the detection of fearful faces among neutral faces in individuals with Williams syndrome revealed by measurement of both manual responses and eye tracking

BackgroundIndividuals with Williams syndrome (WS) exhibit an atypical social phenotype termed hypersociability. One theory accounting for hypersociability presumes an atypical function of the amygdala, which processes fear-related information. However, evidence is lacking regarding the detection mechanisms of fearful faces for individuals with WS. Here, we introduce a visual search paradigm to elucidate the mechanisms for detecting fearful faces by evaluating the search asymmetry; the reaction time when both the target and distractors were swapped was asymmetrical.MethodsEye movements reflect subtle atypical attentional properties, whereas, manual responses are unable to capture atypical attentional profiles toward faces in individuals with WS. Therefore, we measured both eye movements and manual responses of individuals with WS and typically developed children and adults in visual searching for a fearful face among neutral faces or a neutral face among fearful faces. Two task measures, namely reaction time and performance accuracy, were analyzed for each stimulus as well as gaze behavior and the initial fixation onset latency.ResultsOverall, reaction times in the WS group and the mentally age-matched control group were significantly longer than those in the chronologically age-matched group. We observed a search asymmetry effect in all groups: when a neutral target facial expression was presented among fearful faces, the reaction times were significantly prolonged in comparison with when a fearful target facial expression was displayed among neutral distractor faces. Furthermore, the first fixation onset latency of eye movement toward a target facial expression showed a similar tendency for manual responses.ConclusionsAlthough overall responses in detecting fearful faces for individuals with WS are slower than those for control groups, search asymmetry was observed. Therefore, cognitive mechanisms underlying the detection of fearful faces seem to be typical in individuals with WS. This finding is discussed with reference to the amygdala account explaining hypersociability in individuals with WS.

The developmental change in the perception of dynamic facial emotion using ERPs

Cerebellum is involved in the motor control system to generate smooth and accurate motor command. The acquisition of the cerebellar circuit is achieved by repetitive non-declarative learning. We would like to expand the cerebellar function to thinking process, especially intuitive thinking. To verify our hypothesis, we employed Japanese-chess, “SHOGI”, and its players from trained amateur to professional player. Psychophysical experiments revealed optimal time to answer given checkmate task intuitively. Furthermore, changing rule of the SHOGI affects correct answer ratio depending to their original SHOGI experience. Then we measured cerebellar BOLD using 4T-MRI system during previously obtained condition. Their both lateral hemisphere cerebellar BOLD was selectively increased during checkmate task, not control conditions.These results imply that intuitive thinking, the answer is given within short time and semi-automatically, may use cerebellar circuitry which is acquired repetitive training. We will further investigate the analogy between cerebellar motor control and the intuition.