Kazuyoshi Fukuzawa

Internal representations and the conceptual operation of color in pure alexia with color naming defects

This research examined the structure of internal representation and the conceptual operation of color in two pure alexic cases (Case I and Case II) with color naming defects. Experiment I investigated the structure of the internal representation of different kinds of colors using a similarity judgment task. Experiment II examined categorical judgments of perceived colors using a two-alternative-forced choice task. Experiment III tested the classification of perceived colors using a color sorting task. The performance of Case I essentially fell within the normal range while the results of Case II showed some impairment in the conceptual operation of color. Analysis of the responses obtained from these experiments indicated that the color naming defects in Case I can be explained in terms of visual-verbal disconnection. However, the naming defects in Case II reflect disfunction in some other higher cortical processes coupled with visual-verbal disconnection.

The influence of the indicator arm on end point distribution in proprioceptive localization with multi-joint arms

The present study attempted to demonstrate that the indicator arm influences end point distribution in contralateral multi-joint proprioceptive tasks and also that intrinsic physical characteristics of multi-joint arms (arm stiffness) may predict the error pattern. For this purpose, we carried out two types of contralateral localization tasks with multi-jointed arm movements. In the concurrent localization task, the end point distribution was significantly more elongated in the direction of the lower stiffness at each target position when based on the indicator stiffness, while in the remembered localization task, there was no significant difference between the axes. The best-fit ellipse for the end point distribution also confirmed those results. These findings may support the idea that a large part of the configuration of end point distribution could be determined by the characteristics of arm stiffness of the indicator arm in the condition without memory decay of position representation. Further, error bias of proprioceptive localization may be influenced by the combined effect between movement direction and orientation of the lower stiffness. In conclusion, this study suggests that error patterns largely reflect indicator factors such as the elastic property of the arm in multi-joint proprioceptive tasks, which have been assumed to assess the proprioceptive sense of the reference arm.

An examination of a relation between hand height position and motion duration on the human sagittal plane movement based on the minimization principle

Abstract We confirmed from human arm movement measurement on the sagittal plane that the highest position in the vertical direction where the hand passes through changes according to the motion duration. The minimum commanded torque change criterion is one of the optimal criteria for a trajectory formation in a reaching movement. We examined whether the criterion can explain the highest position change on the sagittal plane movement for various motion durations. This shows the possibility that the position where the hand passes through, which changes according to the motion duration, can be estimated by using the differential coefficient of the criterion with respect to the hand height with the amount of change in the hand height of measurement trajectory.

Writing in the air: Contributions of finger movement to cognitive processing

The present study investigated the interactions between motor action and cognitive processing with particular reference to kanji-culture individuals. Kanji-culture individuals often move their finger as if they are writing when they are solving cognitive tasks, for example, when they try to recall the spelling of English words. This behavior is called kusho, meaning air-writing in Japanese. However, its functional role is still unknown. To reveal the role of kusho behavior in cognitive processing, we conducted a series of experiments, employing two different cognitive tasks, a construction task and a stroke count task. To distinguish the effects of the kinetic aspects of kusho behavior, we set three hand conditions in the tasks; participants were instructed to use either kusho, unrelated finger movements or do nothing during the response time. To isolate possible visual effects, two visual conditions in which participants saw their hand and the other in which they did not, were introduced. We used the number of correct responses and response time as measures of the task performance. The results showed that kusho behavior has different functional roles in the two types of cognitive tasks. In the construction task, the visual feedback from finger movement facilitated identifying a character, whereas the kinetic feedback or motor commands for the behavior did not help to solve the task. In the stroke count task, by contrast, the kinetic aspects of the finger movements influenced counting performance depending on the type of the finger movement. Regardless of the visual condition, kusho behavior improved task performance and unrelated finger movements degraded it. These results indicated that motor behavior contributes to cognitive processes. We discussed possible mechanisms of the modality dependent contribution. These findings might lead to better understanding of the complex interaction between action and cognition in daily life.

Hand-use and tool-use in grasping control.

The goal of this study was to elucidate the underlying mechanisms of hand and tool grasping control. We assumed that there is a single principle-governing grasping control irrespective of its effectors and that the degree of prior experience of the effector determines the smoothness of aperture control. Eight participants performed a reach-to-grasp task with four different effectors: index finger and thumb, middle finger and thumb, chopsticks, and a scissor-like tool. Although we employed different effectors with large mechanical variations and different degrees of prior use, maximum grip aperture was scaled as a function of object size and appeared at almost the same timing in all four types of grasping movements. Moreover, reaching time did not substantially differ among grasping conditions. However, plateau duration of the aperture profile differed by effector. Plateau duration was the longest in the unfamiliar scissor-like tool grasping condition. There was no difference between the unfamiliar hand-use grasp with the thumb and the middle finger and the familiar tool-grasp with chopsticks. The familiar hand-use grasp with the thumb and the index finger had the shortest plateau duration. These results supported the idea that there is an effector-independent continuity between hand-use and tool-use in motor control as a function of prior degree of use, rather than the conventionally assumed dichotomy between them.

The effect of aborting ongoing movements on end point position estimation

Abstract The present study investigated the impact of motor commands to abort ongoing movement on position estimation. Participants carried out visually guided reaching movements on a horizontal plane with their eyes open. By setting a mirror above their arm, however, they could not see the arm, only the start and target points. They estimated the position of their fingertip based solely on proprioception after their reaching movement was stopped before reaching the target. The participants stopped reaching as soon as they heard an auditory cue or were mechanically prevented from moving any further by an obstacle in their path. These reaching movements were carried out at two different speeds (fast or slow). It was assumed that additional motor commands to abort ongoing movement were required and that their magnitude was high, low, and zero, in the auditory-fast condition, the auditory-slow condition, and both the obstacle conditions, respectively. There were two main results. (1) When the participants voluntarily stopped a fast movement in response to the auditory cue (the auditory-fast condition), they showed more underestimates than in the other three conditions. This underestimate effect was positively related to movement velocity. (2) An inverted-U-shaped bias pattern as a function of movement distance was observed consistently, except in the auditory-fast condition. These findings indicate that voluntarily stopping fast ongoing movement created a negative bias in the position estimate, supporting the idea that additional motor commands or efforts to abort planned movement are involved with the position estimation system. In addition, spatially probabilistic inference and signal-dependent noise may explain the underestimate effect of aborting ongoing movement.

A computational trajectory formation model for the human sagittal plane movement at various motion durations

Abstract We have confirmed from human arm movement measurement on the sagittal plane that the highest position in the vertical direction where the hand passes through changes according to the motion duration. In this paper, we propose an estimation algorithm of the position where the hand passes through according to the variation in the motion duration. We add the algorithm into the hardware of the trajectory formation model, i.e., the forward inverse relaxation model, which is the trajectory formation model based on the minimum commanded torque change criterion. Finally, we show that the model can reproduce the same trajectories as the human trajectories at various motion durations on the sagittal plane.

Recovery process of colour naming defects in pure alexia - A five year longitudinal experimental study

Abstract The present study investigated the recovery process of colour naming defects and the ability for matching seen colour to colour name given verbally (colour pointing) in a patient with pure alexia (M.S.). The recovery process of the patients ability to process the physical parameters involved in colour information processing was also examined. To look at how M.S. processed the physical parameters, the similarity judgment tasks of internal representation of colour generated by verbal and visual stimuli were employed. While colour pointing ability became practically normal 22 months postonset, colour naming defects took longer to recover. The analysis of the results of similarity judgment using multidimensional scaling revealed that : (1) verbal stimuli generated consistently more stable internal representation of colour than visual stimuli; and (2) colour information processing of M.S. altered ???hue with lightness??? dependent to more ???hue??? dependent in the 5 years since the onset of illness. The und...

Schizotypal traits and forearm motor control against self-other produced action in a bimanual unloading task

ABSTRACT The present study investigated the relation between schizotypy and motor control against self‐ or other‐produced action. We used an unloading task to focus on the timing component of anticipatory motor control. In the task, a weight was removed from a participants’ hand by the participants themselves or by an experimenter (voluntary versus imposed unloading). Postural disturbance at the removal timing was measured as an index of predictive function in motor control. We hypothesized that the postural disturbance in the voluntary unloading would be positively related to schizotypal traits; however, the results did not support this theory. The results showed almost zero correlation between the schizotypy scores and the postural disturbance in the voluntary unloading condition. In contrast, the schizotypy scores positively correlated with the postural disturbance in the imposed unloading condition. These findings were replicated across two participant groups and two schizotypy scales. Further analyses on subscales of the schizotypy questionnaire found moderate levels of positive correlation between each subscale for Cognitive‐Perceptual and Disorganization factors and the disturbance. Accordingly, the present study did not support the idea that non‐pathological individuals with high schizotypal traits have deficits in prediction of self‐produced actions, at least for a temporal domain. Instead, the results suggested that individuals with high schizotypal traits, particularly for the positive and disorganization symptoms, are not good at responding to others‐produced actions. The schizophrenic symptoms were discussed in terms of the failure in the processes executed after calculating prediction of sensory consequences and dysfunction in internal models for “other people”. HIGHLIGHTSThe relation between schizotypy and motor control was investigated.Almost zero correlation was found in the voluntary unloading condition.Positively correlation was found in the imposed unloading condition.The results were replicated in another participant group with another questionnaire.

Adaptive changes in automatic motor responses based on acquired visuomotor correspondence

The present study tested whether remapping of visuomotor correspondence alters automatic motor responses induced by visual stimuli. We hypothesized that the congruency effect, an automatic modulation of motor responses based on stimulus–response congruency, changes in accordance with a new visuomotor correspondence acquired through an adaptation task. To induce visuomotor adaptation, participants performed a tracking task with 30° or 150° rotation of the visual feedback. The congruency effect was evaluated multiple times by a visual response task where participants moved their finger left or right. We predicted that the congruency effect, as a measure of automatic responses, would be almost reversed after adaptation to the 150° rotation, because a visual stimulus spatially opposite to the participant’s own action would become a “congruent” stimulus in a 150°-rotated environment but not in a 30°-rotation environment. The results show that visuomotor adaptation to the 150° rotation did modulate the congruency effect in accordance with the acquired visuomotor correspondence, but did not completely reverse the effect. When the effect was assessed after the manipulation, which was assumed to switch an internal model back to its normal state, there was no change in automatic motor responses. Furthermore, we found that after effects developed as the training proceeded but decreased over time. These findings suggest that the visuomotor system subserving automatic modulation in motor responses is based on the currently active internal model and, therefore, highly adaptive. In addition, the mechanism underlying after effects in a visuomotor task is discussed in terms of a switching function of internal models.