We carried out three measurements on 12 healthy men to investigate the positional perception in forward or backward flexions of the trunk while standing. In measurement (I), the subjects reproduced the target angle perceived by forward flexion (FF) or backward flexion (BF) of the trunk with their eyes blindfolded. In measurement (II), the subjects first visually perceived the angle shown by an angular, indicator, and then reproduced it by manually by operating the indicator with their eyes open. In measurement (III), the subjects first visually perceived the angle shown by an angular indicator, and then expressed the target angle by FF or BF with their eyes blindfolded. In measurements (I) and (III), indication of the target angle was set at in 5° increments from 5° to 60° in FF, and from 5° to 30° in BF, and in measurement (II) from 5° to 60°. The ability of positional perception was evaluated using the constant error (CE) and the absolute error (AE) of the reproduced or expressed angle.
In measurement (I), CE was small for all target angles, ranging from -0.2°to 2.6°in FF and from 0.3°to 1.6°in BF. However, CE from 5° to 25°in FF was significantly positive. In BF, significant CE was not recognized for any target angles, and AE at each target angle was smaller than that in FF. These results suggest that the sensitivity of positional perception of the trunk in FF is relatively low for small target angles which are close to the quiet standing position.
In measurement (II), CE was very small for all target angles, ranging from -1.2° to 0.9°. Significant CE was recognized only at 10°, 20°and 55°. AE was also small for all target angles, ranging from 0.5° to 1.8°, and no significant difference in AE was recognized among the target angles. These results suggest that visual perception, memorization and recall of the target angle is well retained.
In measurement (III), a relationship between the target angle and the CE was shown on a negative regression line in both FF and BF. As viewed from the regression line, the angle at which the CE became zero was 36°in FF and 18° in BF. AE in target angles close to these angles was also small. This indicates that angles smaller than these are perceived as smaller than they actually are, while angles larger than these are perceived as larger than the actual ones.