Interpersonal and intrapersonal variance of exponent of power function observed in grip strength task.

For grip strength there is a power function with an exponent of 1.7 between the subjective magnitude and the actual force exerted by a subject, but large variabilities among and within individuals were found. We focused on these variabilities and investigated the relationship between them by conducting a ratio production procedure requiring trials of maximum effort and half of maximum effort. For 30 adults we conducted four measurement trials, two on the same day, and the remaining two trials on a day or two later. The mean value of the exponent, the standard deviation, and the coefficient of variation of the four trials for each subject were calculated. The mean value of the exponent of the power function for all subjects was 1.6. This value approximated the value of 1.7 reported by Stevens and Mack. The values ranged from .50 to 5.39. The correlation between subjects' mean exponent value and standard deviation was .90, and the correlation between the mean value of the exponent and the coefficient of variation was .50. There was a close relationship between interpersonal and intrapersonal variance.

Relationship between age and head movement during stepping in place by nonhandicapped children and persons with mental retardation.

We investigated developmental changes in head movement during stepping in place by nonhandicapped children and clarified the relationship between chronological or mental age and head movement of persons with mental retardation. 39 nonhandicapped children aged 3 to 6 years, 13 adults aged 19 to 22 years, and 10 persons with mental retardation (range of chronological age: 17 to 22 years, range of mental age: 3 to 8 years) participated. The total extent of head movement in the frontal plane during ordinary stepping in place for 20.48 sec. was measured to assess the magnitude of head movement. Changes in the magnitude of head movement of children are noticeable across ages, and the magnitude clearly was smaller at the age of 6 years. For subjects with mental retardation, no relationship has been found between chronological age and the magnitude of head movement but rather between mental age and the magnitude of head movement.

Comparison of postural control of children with Down syndrome and those with other forms of mental retardation.

To confirm the 1994 findings of Okuzumi, Haishi, and Kokubun, the displacement of the center of foot pressure, one-foot balance and head sway were measured in children with Down syndrome (n = 11) compared to those with other types of mental retardation (n = 17). The magnitudes of the displacement of the center of foot pressure and head sway were not significantly different between the Down group and other forms of mental retardation, whereas the performance of one-foot balance was significantly lower in the Down group. The mean frequencies of sway waves were generally higher in the Down group, and the differences between the two groups were significant except for sagittal head sway. The results generally supported the prior findings. We proposed that it was not the magnitude of the displacement of the center of foot pressure but rather the manner of the whole body's sway which might be related to postural control.

Characteristics of postural control and locomotion of patients with vascular and Alzheimer-type dementias.

The postural control and locomotion of patients with Alzheimer-type senile dementia (n = 20) or vascular dementia (n = 20) were investigated. Patients with both types of senile dementia, especially patients with vascular dementia, generally showed lower scores than healthy old people (n = 53). Moreover, deterioration of locomotion was more remarkable.

Predictive value of age of walking for later motor performance in children with mental retardation.

The purpose of the present study was to clarify the predictive value of age of walking for later motor performance in children with mental retardation. While paying due attention to other factors, our investigation focused on the relationship between a subject's age of walking, and his or her subsequent beam-walking performance. The subjects were 85 children with mental retardation with an average age of 13 years and 3 months. Beam-walking performance was measured by a procedure developed by the authors. Five low beams (5 cm) which varied in width (12.5, 10, 7.5, 5 and 2.5 cm) were employed. The performance of subjects was scored from zero to five points according to the width of the beam that they were able to walk without falling off. From the results of multiple regression analysis, three independent variables were found to be significantly related to beam-walking performance. The age of walking was the most basic variable: partial correlation coefficient (PCC) = -45; standardized partial regression coefficient (SPRC) = -0.41. The next variable in importance was walking duration (PCC = 0.38; SPRC = 0.31). The autism variable also contributed significantly (PCC = 0.28; SPRC = 0.22). Therefore, within the age range used in the present study, the age of walking in children with mental retardation was thought to have sufficient predictive value, even when the variables which might have possibly affected their subsequent performance were taken into consideration; the earlier the age of walking, the better the beam-walking performance.

Age-related changes in postural control and locomotion.

Age-related changes in both postural control and locomotion were investigated. Postural control was evaluated by magnitude of body sway for 131 healthy persons aged 21 to 84 years. Locomotion was evaluated by walking velocity for 217 healthy persons aged 21 to 88 years. Analysis showed that both abilities deteriorated for older persons and particularly age-related changes were more remarkable in locomotion.

Developmental trends in pursuit eye movements among preschool children.

The purpose of this study was to investigate the developmental differences in pursuit eye movements among preschool children. The subjects were 28 children aged 3 to 6 years old and 5 adults aged 22 to 37 years. The target was moved sinusoidally on the horizontal plane at 0.3-, 0.5-, and 0.7-Hz stimulus frequency. The power ratio which represented the smoothness of eye movements and the phase difference between eye movements and target movement was calculated. The power ratio decreased with increased stimulus frequency for all subjects, indicating that eye movements became less smooth. At all stimulus frequencies, the power ratio was higher for adults than for children. Among the three age groups of children, there was no statistically significant difference on this parameter. The phase shifted from a small amount of lead for no lag to the lag with faster stimulus frequency in adults, but the gap was not statistically significant. For children, there was a statistically significant difference across age groups on change in the phase difference. These findings may suggest that the developmental differences in pursuit eye movements of children across ages 3 to 6 years were clear in what related to the phase difference.

Effect of tone on directional orientation during stepping in place with eyes closed.

To examine the effect of a tone on directional orientation during stepping in place with eyes closed 10 healthy adults ages 20 to 27 years stepped in place for 120 seconds with eyes closed in 3 conditions: without a tone, with 1000-Hz pure tone, and with white noise. To examine how the subject rotated in stepping, both range and dispersion of the head's angular displacement were measured by a compass sensitive to terrestrial magnetism. Analysis showed that white noise was effective for directional orientation during stepping. Also, in the pure-tone condition, angular displacement of the head was similar to that in the no-tone condition. This result may have been due to the fact that the stationary wave created by the interference wave made sound normalization impossible.

Factors affecting age of walking by children with mental retardation.

The relationship between age of walking and two factors of severity of intellectual disability and clinical types (autism, Down syndrome, epilepsy, and "residual") in children with mental retardation was investigated. Subjects were 118 children whose disabilities ranged from severe to mild. Measures by clinical type were significant, and the differences of any two clinical types except between children with epilepsy and the "residual" group were significant, but severity of intellectual disability was not significant. Most children with autism (27 subjects, 93%) walked by the normal time limit of 18 months. Only 3 children (11%) with Down syndrome began to walk within that limit, and 9 of them (33%) walked after 2 years of age. In the "residual" group (including children with epilepsy), 37 children (60%) walked within the normal limit but 15 (25%) only after 2 years of age.

An illusion of velocity in motion perception.

We report a phenomenon that seems to have potential to elucidate a role of eye movement in motion perception. When tracking a target controlled by a triangular wave, the viewer perceives movement of the target like a ball bouncing in between two walls. We measured eye movement with electrooculograms (EOGs) when the subject was tracking a target controlled by a triangular wave. Eye movement after passing the turning point and rapidly returning to the target with saccadic movement and then smoothly tracking the target was recorded for all 4 adults. It was considered that extraretinal information on eye position during saccade may mainly contribute to this illusion.