Yutaka Sakaguchi

The University of Electro-Communications | UEC · Graduate School of Informatics and Engineering

Human’s ability of optimal motor-timing decision remains debated. The optimality seems context-dependent as the sub-optimality was often observed for tasks with different gain/loss configurations: people achieved optimality with symmetric gain configuration but not with asymmetric configuration. In the current study, we designed a temporal decision...

Bayesian decision-making theory presumes that humans can maximize the expected gains by trading off risk-returns in a predefined gain function. Recent findings from spatial reaching and coincident timing tasks have challenged this theory by revealing that humans exhibited risk-seeking or risk-aversive rather than risk-neutral tendency (i.e., failed...

The present study probed into the human’s ability to achieve optimal performance by trading off risk and return in a spatial reaching task. The experimental task was to click on the mid-line of an arc-shaped region as accurately as possible within a limited time window. Participants were asked to maximize the reward determined by the accuracy of th...

To examine how individuals perceive synchrony between music and body motion, we investigated the characteristics of synchrony perception during observation of a Japanese Radio Calisthenics routine. We used the constant stimuli method to present video clips of an individual performing an exercise routine. We generated stimuli with a range of tempora...

When sight-reading music, pianists have to decode a large number of notes and immediately transform them into finger actions. How do they achieve such fast decoding? Pianists may use geometrical features contained in the musical score, such as the distance between notes, to improve their efficiency in reading them. The aim of this study is to inves...

The authors investigated the question whether humans are capable of achieving optimality in controlling the risk-return tradeoff with perceptual/motor variability. We ran a behavioral experiment where participants were asked to find a click position to maximize the expected reward received in a coincident timing task whose utility function depended...

Although there is growing evidence that breathing is modulated by various motor and cognitive activities, the nature of breathing in musical performance has been little explored. The present study examined the temporal breath pattern in piano performance, aiming to elucidate how breath timing is related to musical organization/events and performanc...

Back-and-forth motion induces perceptual shrinkage of the motion path, but such shrinkage is hardly perceived for one-way motion. If the shrinkage is caused by temporal averaging of stimulus position around the endpoints, it should also be induced for one-way motion at higher motion speeds. In psychophysical experiments with a high-speed projector,...

In visual psychophysics, a CRT monitor has been widely used to present visual stimuli, while its temporal resolution was limited by its frame length of about 5 ms (i.e., refresh rate of 200 Hz). Recently, however, a high speed DLP projector was introduced to the market, which realizes much shorter frame length (~ 0.2 ms) for binary images. For such...

The purpose of this research is to realize a dynamic information space harmonizing human perception system, recognition system, and motor system. Toward this purpose, our key technology is high-speed sensor technology and display technology focusing on vision and haptic sense which performs at the order of kHz. Based on these technologies, our info...

We found that a novel phenomenon on the high-speed (400 Hz) flickering stimuli that if the counterphase-flickering pattern (e.g. square-wave grating) is immediately switched to another flickering pattern, a luminance-averaged pattern around the time of transition can be stably perceived. The purpose of this study is to investigate the temporal prop...

The critical fusion frequency (CFF) is a threshold that represents the temporal limits of the human visual system. If two flickering stimuli with equal subjective luminances are presented simultaneously at different locations, the CFF is the temporal frequency above which they cannot be distinguished. However, when the stimuli are presented sequent...

It is a fundamental question how our brain performs a given motor task in a real-time fashion with the slow sensorimotor system. Computational theory proposed an influential idea of feed-forward control, but it has mainly treated the case that the movement is ballistic (such as reaching) because the motor commands should be calculated in advance of...

Revealing the type of information encoded by neurons activity in the motor cortex is essential not only for understanding the mechanism of motion control but also for developing a brain-machine interface. Thus far, the concept of preferred direction (PD) vector has dominated the discussion regarding how neural activity encodes information; however,...

Although the phase shifts in ongoing oscillations seen in electroencephalograms (EEGs) and magnetoencephalograms are an important factor in discussions of phase dynamics, such as synchrony and reset, few studies have focused specifically on the phase shift. Here we investigate the relationship between phase shifts in alpha-frequency rhythms and rea...

Human motor behavior often shows intermittent discontinuities even when people try to follow a continuously moving target. Although most previous studies revealed common characteristics of this “motor intermittency” using frequency analysis, this technique is not always appropriate because the nature of the intermittency is not stationary, i.e., th...

To test an idea that neurons in the motor cortex encodes a future state of the arm, we constructed a plausible model using arm state-related variables to explain neuronal activity, and applied a multiple linear regression analysis. We found that the model fit was fairly good with a mean determination coefficient of 0. 57 for analyzed 231 neurons an...

An important issue in motor learning/adaptation research is how the brain accepts the error information necessary for maintaining and improving task performance in a changing environment. The present study focuses on the effect of timing of error feedback. Previous research has demonstrated that adaptation to displacement of the visual field by pri...

In the present study, the author analyzed the hand movement in one-dimensional visuo-manual tracking task. When the target moved slowly or unpredictably, the hand velocity contained many bell-shaped components lasting several-hundred milliseconds. When the target moved fast and sinusoidally, on the other hand, subjects seemed to adjust the movement...

Intermittent velocity peaks of movement trajectory are commonly observed when subjects perform manual tracking task. However, the underlying mechanism of such intermittency has not been revealed yet. Focusing on the process of updating the internal target of movement, we proposed a computational model of “motor intermittency” in which a choice betw...

Humans can easily adapt to a visually distorted environment: We can make correct movements after a few dozens of actions with visual guidance in the new environment. However, it is unclear what visual information our brain uses for this visuo-motor adaptation. To answer this question, we conducted a behavioral experiment of prism adaption of a ball...

We propose a concept of "audiolization of body movement," which transforms the posture/movement of the human body or human-controlled-tools into acoustic signals and feeds them back to the users in a real-time manner. It aims at helping people being aware of their body/tool states, and resultantly assisting their motor skill learning. The present p...

Purpose. To reveal the mechanism of perceptual filling-in, the author examined the time for filling-in when two targets were presented on a background. The previous study showed that filling-in at two separated targets could interact with each other in the case that targets and background differed in luminance (ARVO-2000, #2340). The present study...

Purpose and Background. The author examined the time required for perceptual filling-in when the target and surround were differently-oriented gratings. The previous study (Vision Research, 41, 2065-77) revealed that the time significantly varied dependent on the relation between their orientations. The present study asked how the relation between...

We used mutual information analysis of neuronal activity in the macaque anterior intraparietal area (AIP) to examine information processing during a hand manipulation task. The task was to reach-to-grasp a three-dimensional (3D) object after presentation of a go signal. Mutual information was calculated between the spike counts of individual neuron...

A fundamental problem in the field of motor neuroscience is to understand how our brain generates appropriate motor commands for precise movements effortlessly. The problem seems difficult since there are infinitely many possible trajectories and our musculo-skeltal system is generally redundant. We focus on the motor command representation and sho...

We investigated the characteristics of the human action–selection in performing a Markov decision process (MDP) task, and compared them to those of reinforcement-learning (RL) agents. The behavior of human participants was roughly classified into two qualitatively different types. On the other hand, surprisingly, the variety of human behavior could...

People usually make use of visual and somatosensory feedback to perform and learn motor skills. Here, we discuss the possibility that auditory feedback can be also utilized for motor execution and learning by ldquoaudializingrdquo onepsilas body movement. To this end, we built a wearable transducer device which modulates sounds according to the use...

We propose a computational model of perceptual grouping for explaining the 3D shape representation of an illusory percept called "mime effect." This effect is associated with the generation of an illusory, volumetric perception that can be induced by particular distributions of inducing stimuli such as cones, whose orientations affect the stability...

The present paper addresses a general diagram to investigate the real-time parallel computation mechanism in the brain, using an idea of “Gantt chart.” This diagram explicitly represents the temporal relationship between the computations running in various functional modules in the brain, and helps us to understand how the brain computation proceed...

The concept of “muscle synergies” has been proposed as a working hypothesis to explain how the central nervous system coordinates the numerous degrees of freedom of the musculoskeletal system. In this study, to examine this hypothesis, we extracted muscle synergies from human electromyography (EMG) patterns during grasping movements. The EMG patter...

The present article proposes a novel computational approach to the motor planning. In this approach, each motor command is represented as a linear combination of prefixed basis patterns, and the command for a given task is designed by minimizing a two-termed criterion consisting of a task optimization term and a parameter preference (i.e., sparsene...

Two experiments were conducted to investigate how stimulus contrast affected the time required for perceptual filling-in. The stimuli consisted of a Gabor patch (target) and a circular grating region (surround). In Experiment 1, the target contrast was manipulated, and the surround contrast was fixed. Filling-in was significantly delayed with highe...

“Dynamics matching” is a design concept in sensory-motor fusion systems, where the performance is maximized by adjustment of the dynamics of the system under the physical and computational constraints. This paper models dynamics matching as an optimization problem and constructs an adaptive acquisition algorithm. A numerical experiment on the targe...

It has been proposed that the central nervous system determines reaching movement trajectories so as to minimize the positional variance of the endpoint in the presence of signal-dependent noise. The hypothesis well reproduces the empirical movement trajectories for noise to the control signal whose variance is proportional to the second power of t...

This article proposes an adaptive action-selection method for a model-free reinforcement learning system, based on the concept of the 'reliability of internal prediction/estimation'. This concept is realized using an internal variable, called the Reliability Index (RI), which estimates the accuracy of the internal estimator. We define this index fo...

Four experiments were performed to investigate how the time required for perceptual filling-in varies with the position of the target in the visual field. Conventional studies have revealed that filling-in is facilitated by a target with greater eccentricity, while no systematic studies have examined the effect of polar angle. Experiment 1 examined...

In an attempt to clarify the dynamical process in human visual perception, we propose a neural network model explaining the figure-ground reversal phenomenon of a three-dimensional ambiguous figure, and examine its behavior in numerical experiments. In contrast to conventional models that explain perceptual reversal at a “symbolic representation le...

Four experiments examined how differences in the properties of the target and surround affect the time required for perceptual filling-in. They examined differences in luminance, orientation, spatial frequency, and color. A larger target/surround difference delayed filling-in ('feature difference effect'). Interestingly, exchanging the target and s...

Three experiments on ball-juggling were carried out in order to clarify how our brain utilizes visual information in motor control. In Experiment 1, the temporal relation between ball and eye movements were examined. The results suggested that visual information around the top of the trajectory seemed important, and that eye movements were controll...

Transparency and volume perception are important issues in 3-D object perception. We report here a new visual effect in 3-D illusory object perception with binocular viewing, named `pantomime effect', and introduce a new framework of the effect based on three types of `sustaining cues'. We also compare sustaining cues with occlusion cues. In additi...

We reported earlier that the binocularly unpaired region plays an essential role in the perception of the volume of a solid object (Idesawa, 1991 Japanese Journal of Applied Physics30-4B L751 - L754). We have investigated this volume perception using both illusory and physical objects. The illusory objects used in the tests were of two types, eithe...

Three experiments were performed to examine the effects of masked colour stimuli on the response to masking stimuli. In experiment 1, two coloured squares were presented successively at the same position so that the first one could not be perceived owing to backward masking. The task was to respond to the colour of the second square as quickly as p...

When adequate visual stimuli are suitably arranged, for example, partially along the surface boundary or beyond the covering illusory surface, an opaque or transparent illusory surface can be seen (Idesawa, 1991 Japanese Journal of Applied Physics30-4B L751 – 754; 30-7B L1289). By moving the visual stimuli of the occluding objects which were not ph...

Purpose. Clarify the mechanism of visual information acquisition during a motor task from a viewpoint of attentional function in motor control. Methods. The graphic output of PC was projected to a translucent screen laid horizontally in front of a subject, whose eye and arm positions were monitored with EOG and a manipulandum, respectively. Subject...

When perceiving an object by touch, human beings integrate various sensory information with observing the object's surface in appropriate manners, such as rubbing, pushing and picking, according to the proceeding of the recognition. This fact suggests that sensory integration and active perception play essential roles in the haptic recognition proc...

The authors constructed a haptic recognition system which discriminates feel of touch based on the principles of sensory integration and attentional perception. The system is equipped with several sensors and can push and rub the object's surface with several values of force and speed. It integrates the sensory information iteratively by selecting...

The authors propose a motor planning algorithm which reflects reliability of the internal model. The algorithm is to calculate the destination and its expected error for every motor command using the internal model, and to select the most effective command whose expected error would not exceed a given limit. Utilizing this algorithm, the system beh...

Human haptic perception is not caused by simple mechanical stimulation to the skin; it is achieved by integrating sensory information from various receptors (such as mechano-receptors and thermo-receptors) and by observing objects in various ways. The author constructed sensing systems which simulate human haptic processes in order to clarify the m...

When perceiving an object humans do not receive stimuli passively, but observe the object actively to obtain useful information for recognizing it. A neural network model which realizes such active perception by utilizing neural dynamics is proposed. The model consists of a sensory unit, a representation field, and recognition units. The model sequ...

For studying the mechanism of the brain, the synthetic approach is effective. The synthetic approach is to conjecture the mechanism of the target through constructing its model. Some 20 models of the brain were constructed for this study. One of them is described. The model includes the faculties of perception, memory, and action. Having these thre...

When perceiving an object, human beings can construct its internal image from its fragmental features and recognize it based on the image, without observing it all over. In this article, the authors propose a neural network model which constructs internal representation of a given figure and recognizes it based on the representation.The model consi...

Describes a method of compressor valve diagnosis in which a neural network was applied to analyze valve plate sound. A neural network approach to pattern recognition was considered. The system reduces the load of neural networks in function representation and function learning by using appropriate preprocessing methods, for instance the Mahalanobis...

A number of neurons which respond selectively to specific stimuli are observed in many parts of the vertebrate nervous system. These neurons are developed by self-organization through sensory experiences. This is regarded as a mechanism for representing the external world structure. However, it is insufficient to think only of this learning mechani...

As one of the synthetic approaches to brain functions, the possibility is discussed that two intellectual robots could make "words" for themselves and come to communicate with each other. Associatron, a model for associative memory with a neural network structure, is used as the memory in the brain, and information from the outer world is accumulat...