Biomedical subjects

Ryoko Futami

Publications and source records attributed to Ryoko Futami.

4 recordsLinked to original sources

PubMed2006

Characteristics of human luminance discrimination and modeling a neural network based on the response properties of the visual cortex.

Reaction time (RT) and error rate that depend on stimulus duration were measured in a luminance-discrimination reaction time task. Two patches of light with different luminance were presented to participants for 'short' (150 ms) or 'long' (1 s) period on each trial. When the stimulus duration was 'short', the participants responded more rapidly with poorer discrimination performance than they did in the longer duration. The results suggested that different sensory responses in the visual cortices were responsible for the dependence of response speed and accuracy on the stimulus duration during the luminance-discrimination reaction time task. It was shown that the simple winner-take-all-type neural network model receiving transient and sustained stimulus information from the primary visual cortex successfully reproduced RT distributions for correct responses and error rates. Moreover, temporal spike sequences obtained from the model network closely resembled to the neural activity in the monkey prefrontal or parietal area during other visual decision tasks such as motion discrimination and oddball detection tasks.

Adult↗

PubMed2005

Joint angle control by FES using a feedback error learning controller.

The feedback error learning (FEL) scheme was studied for a functional electrical stimulation (FES) controller. This FEL controller was a hybrid regulator with a feedforward and a feedback controller. The feedforward controller learned the inverse dynamics of a controlled object from feedback controller outputs while control. A four-layered neural network and the proportional-integral-derivative (PID) controller were used for each controller. The palmar/dorsi-flexion angle of the wrist was controlled in both computer simulation and FES experiments. Some controller parameters, such as the learning speed coefficient and the number of neurons, were determined in simulation using an artificial forward model of the wrist. The forward model was prepared by using a neural network that can imitate responses of subject's wrist to electrical stimulation. Then, six able-bodied subjects' wrist was controlled with the FEL controller by delivering stimuli to one antagonistic muscle pair. Results showed that the FEL controller functioned as expected and performed better than the conventional PID controller adjusted by the Chien, Hrones and Reswick method for a fast movement with the cycle period of 2 s, resulting in decrease of the average tracking error and shortened delay in the response. Furthermore, learning iteration was shortened if the feedforward controller had been trained in advance with the artificial forward model.

Artificial Intelligence↗

PubMed2005

Sensory supported FES control in gait training of incomplete spinal cord injury persons.

Sensory supported electrical stimulation of the peroneal nerve during treadmill walking is proposed as a gait-training modality in incomplete spinal cord injury (SCI) patients. A multisensor device provides information on the tilt of the shank during gait. The information provided significantly improves the triggering instant of the electrical stimulation. Simultaneously, swing-phase estimation serves as a reference to determine the required motor augmentation support. Both approaches, as well as triggering using intensity control of the functional electrical stimulation were applied on a healthy person and on an incomplete C4-5 SCI patient.

Biofeedback, Psychology↗

PubMed2004

Sequential grouping of tone sequence as reflected by the mismatch negativity.

The human sequential grouping that organizes parts of tones into a group was examined by the mismatch negativity (MMN), a component of event-related potentials that reveals the sensory memory process. The sequential grouping is accomplished by the combinations of some factors, e.g., temporal and frequency proximity principles. In this study, auditory oddball stimuli in which each of the stimuli consisted of series of tone bursts, were applied to the subjects, and the MMN elicited by the deviation of the frequency of the last tone in the stimulus was investigated. The relationship between the expected phenomena of sequential grouping of tones and observed magnitudes of MMN was evaluated. It was shown that the magnitudes of MMN changed according to the configuration (number of tones, frequency) of tone sequence to be stored. This result suggested that the sequential grouping of presented tones was achieved on the preattentive auditory sensory memory process. It was also shown that the relative change of MMN magnitudes corresponded to the conditions of sequential grouping, which had been proposed by the auditory psychophysical studies. The investigation of MMN properties could reveal the nature of auditory sequential grouping.

Acoustic Stimulation↗