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Kuniyasu Imanaka

Publications and source records attributed to Kuniyasu Imanaka.

12 recordsLinked to original sources
PubMed2006

Interaction between space and number representations during motor preparation in manual aiming.

The existence of a spatial component in the representation of number magnitude has been repeatedly supported by the demonstration that the left hand responds faster to smaller numbers, whereas the right hand responds faster to larger numbers. These results support the view that the 'mental number line' is oriented such that smaller numbers are associated with the left side of space while larger numbers are associated with the right side. We investigated whether the link between spatial and number processing arises from a continuous or categorical mapping between space and number representations. The investigation was designed to study all aspects of the motor act, including both planning and execution phases. For this purpose we measured reaction times (RTs), movement times (MTs), spatial accuracy, and endpoint pressure of manual aiming, while subjects reached with the right hand towards the location of a visual digit target. Five different digits were equiprobably presented at five positions along the horizontal axis. A GO/NO-GO choice task paradigm was used to ensure that digit parity (i.e., odd/even) was being processed. Analyses of MT, accuracy, and pressure data showed no digit effects. However, two number-related effects were observed on RTs. First, shorter RTs were obtained for smaller digits independent of target location, despite the use of the right hand. Second, an interaction was observed between target location and number magnitude whereby relative RTs were shortest when there was a congruity between target magnitude and location. These results imply that motor preparation is contaminated both by the direct activation of number magnitude and by the congruity between the spatial location of a target number and its magnitude. We conclude that continuous mapping intervenes between mental number representation and physical space.

Computer Graphics↗
PubMed2005

The functional role of central and peripheral vision in the control of posture.

Three experiments were conducted to investigate the role of central and peripheral vision (CV and PV) in postural control. In Experiment 1, either the central or peripheral visual field were selectively stimulated using a circular random dot pattern that was either static or alternated at 5 Hz. Center of foot pressure (CoP) was used to examine postural sway during quiet standing under both CV and PV conditions. The results showed that, when the visual stimulus was presented in the periphery, the CoP area decreased and more so in the anterior-posterior (AP) than in the medio-lateral (ML) direction, indicating a characteristic directional specificity. There was no significant difference between the static and dynamic (alternating) conditions. Experiment 2 investigated the directional specificity of body sway found in Experiment 1 by having the trunk either be faced toward the stimulus display or perpendicularly to it, with the head always facing the display. The results showed that the stabilizing effect of peripheral vision was present in the direction of stimulus observation (i.e., the head/gaze direction), irrespective of trunk orientation. This suggested that head/gaze direction toward the stimulus presentation, rather than a biomechanical factor like greater mobility of the ankle joint in AP direction than in ML direction, was essential to postural stability. Experiment 3 further examined whether the stabilizing effect of peripheral vision found in Experiments 1 and 2 was caused because more dots (500) were presented as visual cues to the peripheral visual field than to the central visual field (20 dots) by presenting the same number of dots (20) in both conditions. It was found that, in spite of the equal number of dots, the postural sway amplitudes were larger for the central vision conditions than for the peripheral vision conditions. In conclusion, the present study showed that peripheral rather than central vision contributes to maintaining a stable standing posture, with postural sway being influenced more in the direction of stimulus observation, or head/gaze direction, than in the direction of trunk orientation, which suggests that peripheral vision operates primarily in a viewer-centered frame of reference characterized by the head/gaze direction rather than in a body-centered frame of reference characterized by the anatomical planes of the body.

Body Height↗
PubMed2005

Motor strategies responsible for maintaining standing posture after deafferentation of the unilateral leg.

OBJECTIVE: To identify the motor strategies responsible for maintaining standing posture after deafferentation of the unilateral leg. DESIGN: Pretest-posttest, repeated-measures design. SETTING: A Japanese university hospital rehabilitation facility. PARTICIPANTS: Nine healthy subjects aged 25 to 32 years. INTERVENTION: Two separate sessions that consisted of prolonged standing (control task) and standing until the H-reflex disappeared through the application of an inflated pneumatic cuff above the right knee. MAIN OUTCOME MEASURES: Center of pressure (COP), hip and ankle joint positions, and electromyographic activities. RESULTS: In the control task, no time-related change during prolonged standing was found in any of the measured parameters. After deafferentation, the right soleus activity decreased significantly (P<.01), so the mean velocities of the COP in the anteroposterior and mediolateral directions were greater and the average COP position under the right foot shifted backward compared with those in the previous periods (P<.01). Also, the left tibialis anterior and soleus were activated, as was the bilateral gluteus medius. CONCLUSIONS: The unilateral loss of leg and foot sensory information necessitated additional regulatory activities to stabilize the standing posture. The newly organized posture appeared to partly simulate the standing posture in patients with sensory disturbance of a unilateral leg.

Adult↗
PubMed2004

Effects of practice on cardiorespiratory responses during postural control.

The present study examined the effects of practice of a balance test on cardiorespiratory changes in response to a 1-min balance test performed by standing on one leg with eyes closed (SOLEC) in 30 females (n=15, 21+/-4 years, mean+/-SD, for the experimental group; n=15, 22+/-4 years for the control group). Blood pressure (BP), heart rate (HR), minute ventilation (VE), respiratory rate (RR), tidal volume (VT), expiratory duration (Te), inspiratory duration (Ti), and oxygen uptake (VO(2)) were measured during the balance test before and after 2 wk of daily practice. The experimental group was given a daily 15-min practice session for the balance test. In contrast, the control group was instructed not to do any special practice for the balance test. In both the experimental and control groups, SOLEC induced significant increases in BP, HR, VE, RR, and VO(2), and decreases in Te and Ti. Following the practice sessions, the balance time increased significantly in the experimental group (P<0.01). In addition, 2 wk of practice reduced the increases in BP (P<0.01), VE (P<0.05), and RR (P<0.01), and prolonged Te (P<0.01) during the SOLEC test. These results suggest that practice of a postural task affects cardiorespiratory responses to the balance test in addition to postural control.

Adult↗
PubMed2004

Visual estimation of spatial requirements for locomotion in novice wheelchair users.

Locomotion using a wheelchair requires a wider space than does walking. Two experiments were conducted to test the ability of nonhandicapped adults to estimate the spatial requirements for wheelchair use. Participants judged from a distance whether doorlike apertures of various widths were passable or not passable. Experiment 1 showed that participants underestimated the spatial requirements for wheelchair use but overestimated the spatial requirements for walking. Experiment 2 showed that their underestimation improved but was not completely eliminated after 8 days of practice passing through apertures. Analyses of wheelchair performance in the practice condition showed that the underestimation may have arisen from misperception of the positions of the hands when the participants were grasping the wheelchair hand-rims. The theoretical and practical implications of these findings are discussed.

Adult↗
PubMed2004

Lateral difference and interhemispheric transfer on arm-positioning movement between right and left handers.

We investigated the transfer of an arm-positioning movement between the right and left arms of right and left handers. 30 male (15 strong right handers and 15 strong left handers) subjects were asked to perform a constrained criterion movement, 12 cm in length, with right or left arm and a test movement at estimated 6-, 12-, or 24-cm length with the contralateral arm. In the right handers, the constant error of the left arm test movement was near zero, and that of the right arm indicated overshooting. In the left handers, the constant errors of the left arm test movement were farther from zero than those of right arm test movement. Left handers as well as right handers showed manual asymmetry on positioning movement. A plausible explanation for the manual asymmetry on the arm-positioning task is related to interhemispheric transfer of spatial information on positioning movement.

Adolescent↗
PubMed2002

Reaction times and anticipatory skills of karate athletes.

Two experiments were conducted to investigate the reaction times (RTs) and anticipation of karate athletes. In Experiment 1, choice RTs and simple RTs were measured with two types of stimuli. One was videotaped scenes of opponent's offensive actions, which simulated the athletes' view in real situations, and the other was static filled circles, or dots. In the choice RT task, participants were required to indicate as soon as possible whether the offensive actions would be aimed at the upper or middle level of their body, or the dot was presented either at a higher or a lower position. In the simple RT task, they were required to respond as soon as possible when the offensive action started from a static display of the opponent's ready stance, or a dot appeared on the display. The results showed significant differences between the karate athletes and the novices in the choice RT task, the difference being more marked for the video stimuli than for the dot stimuli. There was no significant difference in simple RT between the two groups of participants, for either type of stimuli. In Experiment 2, the proportions of correct responses (PCRs) were measured for video stimuli which were cut off at the seventh frame from the onset of the opponent's offensive action. The athletes yielded significantly higher PCRs than the novices. Collectively the results of the two experiments demonstrate the superior anticipatory skills of karate athletes regarding the target area of an opponent's attack (Scott, Williams, & Davids, Studies in perception and action II: Posters presented at the VIIth International conference on Event Perception and Action, Erlbaum, Hillsdale, NJ, 1993, p. 217; Wiiliams & Elliot, Journal of Sport & Exercise Psychology 21 (1999) 362), together with their advantage over novices in non-specific sensory functions (e.g., vertical discrimination).

Adult↗
PubMed2002

The effects of different instructions for preparatory muscle tension on simple reaction time.

The effects of preparatory weak muscular contraction (pre-tension) have been investigated in a number of previous studies using tasks with either simple or choice responses to measure the reaction time (RT). These studies suggested that optimal pre-tension performed prior to a motor response tends to shorten the RTs. Using a simple RT task in which participants performed a grip response to a visual stimulus, the present study compared the RTs between two pre-tension conditions (self-selection and constraint) to investigate the effects of different instructions for pre-tension. Under the self-selection condition, participants were asked to determine their optimal pre-tension levels while attempting to give responses as fast as possible. Under the constraint condition, the participants developed a pre-tension at a target force determined by the experimenter. The target force was set at the same level as the pre-tension level maintained under the self-selection. Despite the fact that the pre-tension level manipulated was the same for both conditions, the RTs were significantly shorter under self-selection than under constraint. Moreover, the present study showed a positive correlation coefficient between the proportion of shortening in RT and the variation of pre-tension level. This indicated a performance trade-off between the stability of pre-tension and RTs. The result suggests that shorter RTs that occur under self-selection are primarily mediated by mental factors, such as attention allocation, rather than by the effects of peripheral muscular preparation.

Adolescent↗
PubMed2002

Lateralized effects of target location on reaction times when preparing for manual aiming at a visual target.

To elucidate the temporal characteristics of information processing for motor action differing in complexity in relation to both perceptual and cognitive information processing, we investigated whether the reaction times (RTs) to a visual target would be affected by task complexity (finger lifting or manual aiming), pre-cueing (with a pre-cue or without a pre-cue), or target location (five horizontal positions). Using the right hand, seven right-handed subjects performed two tasks, finger lifting and manual aiming at a target, with or without a pre-cue. The pre-cue announced the location of the target to be presented. An ANOVA showed significant interactions between task and location and between pre-cue and location with no significant interaction between task and pre-cue, indicating that the task-location interaction does not depend on whether or not a pre-cue is given. The manual-aiming RTs were longer than the finger-lifting RTs, and the effects of the target location on the RTs differed for finger lifting and manual aiming. It can be assumed that the longer RTs of manual aiming reflect the time for information processing that is needed when preparing for the aiming action per se, which is an extra movement performed in addition to the simple initiation of finger lifting. Differential RTs (DRTs) calculated by subtracting the finger-lifting RTs from the aiming RTs were therefore examined. The DRTs significantly differed for target locations (i.e., a lateralized effect), with the DRTs for an ipsilateral target appearing to be significantly shorter than those for contralateral and central targets. The lateralized effect appearing on the DRTs may be mediated by the processing of visual-spatial information about visual targets as motor preparations are made for manual aiming.

Adult↗
PubMed2002

Freezing degrees of freedom under stress: kinematic evidence of constrained movement strategies.

The present study investigated the effect of psychological stress imposed on movement kinematics in a computer-simulated batting task involving a backward and forward swing of the forearm. The psychological stress was imposed by a mild electric stimulus following poor performance. Fourteen participants hit a moving ball with a horizontal lever and aimed at a distant target with as much accuracy as possible. The kinematic characteristics appearing under stress were delay of movement initiation, small amplitude of movement and low variability of spatial kinematic events between trials. These features were also found in previous studies in which the experimental task required high accuracy. The characteristic kinematics evident in the present study suggested that the movement strategies adopted by the stressed participants were similar to those that appear under high accuracy demand. Moreover, a correlation analysis between the onset times of kinematic events revealed that temporally consistent movements were reproduced under stress. Taken together, the present findings demonstrated that, under psychological stress, movement strategies tend to shift toward the production of more constrained trajectories, as is seen under conditions of high accuracy demand, even though the difficulty of the task itself does not change.

Adult↗
PubMed2002

Effects of nonconscious perception on motor response.

The present study reviews the literature on the empirical evidence for the dissociation between perception and action. We first review several key studies on brain-damaged patients, such as those suffering from blindsight and visual/tactile agnosia, and on experimental findings examining pointing movements in normal people in response to a nonconsciously perceived stimulus. We then describe three experiments we conducted using simple reaction time (RT) tasks with backward masking, in which the first (weak) and second (strong) electric stimuli were consecutively presented with a 40-ms interstimulus interval (ISI). First, we compared simple RTs for three stimulus conditions: weak alone, strong alone, and double, i.e., weak plus strong (Experiment 1); then, we manipulated the intensity of the first stimulus from the threshold (T) to 1.2T and 2T, with the second stimulus at 4T (Experiment 2); finally, we tested three different ISIs (20, 40, and 60 ms) with the stimulus intensities at 1.2T and 4T for the first and second stimuli (Experiment 3). These experiments showed that simple RTs were shorter for the double condition than for the strong-alone condition, indicating that motor processes under the double condition may be triggered by sensory inputs arising from the first stimulus. Our results also showed that the first stimulus was perceived without conscious awareness. These findings suggested that motor processes may be dissociated from conscious perceptual processes and that these two processes may not take place in a series but, rather, in parallel. We discussed the likely mechanisms underlying nonconscious perception and motor response to a nonconsciously perceived stimulus.

Agnosia↗