The properties of V in newborns across repeated measures.

It has been argued that a recently developed measure, vagal tone (V), is a significant advancement over other existing methods of assessing the periodic variation in heart rate associated with respiration (respiratory sinus arrhythmia). It has been further suggested that, as a noninvasive measure of vagal nerve efferent activity, V may facilitate the early identification of infants at risk for developmental disabilities. This study addressed the relationship between V and other measures of cardiac activity and behavioral state and the stability of V across repeated measures. Twelve samples of cardiac activity were collected from each of 20 full term infants, 6 samples on each of two consecutive days. V values were derived using a spectral analysis program comparable to Porges' patented MXedit process. Measures of behavioral states were collected by continuous observation. Heart period and heart period variability were highly correlated with V. Variation in V between behavioral states was also detected. Repeated assessments revealed that average V values collected in the same state were not significantly correlated across successive days. This short-term variability both between and within individuals does not support the notion that a single assessment of V can, by itself, be used to identify at-risk infants or predict developmental outcome.

The influence of rotary vestibular stimulation upon motor development of nonhandicapped and Down syndrome infants.

The vestibular system plays a major role in the expression of early motor behavior. Previous research has cited extensive neural connections between the vestibular apparatus and the motor system. Accordingly, some therapists have implemented programs of supplemental vestibular stimulation to improve motor and cognitive abilities in children with delayed motor development. In the present study a quantifiable regimen of supplemental rotary vestibular stimulation was administered in a cross-over longitudinal design to nonhandicapped and Down syndrome infants. Time constants, considered a measure of habituation in the vestibular system, were derived from postrotary nystagmus. Results indicated that supplemental rotary vestibular stimulation produced no measurable gain in motor ability beyond that evident in control periods. In addition, it was determined that children exhibited greater gains in motor skills in the early phase of the study, regardless of experimental condition. A positive correlation was found between changes in time constant and motor development.

Visual perception and the guidance of locomotion without vision to previously seen targets.

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.