The Postural Substrate and Learning

The distinction which was made in the last chapter between phasic and postural reaction has significance for the problems of learning. While most learning consists in acquiring new adjustments which are mainly phasic, these are sustained and carried forward by the patterning of the postural substrate. Numerous experiments have shown that increments in muscular tension facilitate learning. Induced tension artificially by having subjects squeeze dynamometers during the learning of nonsense syllables and other tasks. The tension group learned in about of the time required by the control group. Assuming that the tension of the finger muscles would be symptomatic of the tension of the entire musculature, he constructed a stylus which recorded both downward and horizontal pressure. On mazes divided into parts of unequal difficulty, the subjects' tension seemed to vary with complexity. Mean tension for easy short mazes was, however, greater than for long difficult mazes.

The relation between tension and degree of mastery turned out to be statistically more reliable than the relation of tension to degree of complexity. Data taken on the more difficult mazes revealed that the longer the learning time, the greater was the progressive decline of tension.

Learning apparently involves a resystematization of the total action pattern, including the postural as well as the phasic influences. Not only is it possible for performance to be carried out with less cortical elaboration, but also these phasic aspects require less support from the postural substrate to maintain the level of vigilance requisite to the task.

In the development of habits, the curve of output and the curve of supporting postural activity seem to be at first inversely related. For the initial stages of learning, gross tension is necessary to accomplish a minimum of output. Later on, a period is reached where a certain minimum of tension accompanies a maximum of output. From this point on, theoretically, the two curves should be asymtotic, subject, of course, to temporary increments in tension acting to compensate for factors which either lower the irritability of the dominant neural integration or favor the dominance of stronger competing tendencies.

An interesting confirmation of the influence of the postural substrate upon learning is found in experiments. These experimenters produced muscular paralysis in animals by injections of curare. Since the effect could easily be removed by neutralization of the drug, it was possible to try to form conditioned responses during curarization and test for the effect upon recovery. Under such conditions there was little evidence of learning. Other tests showed the presence of functional activity in exteroceptors and central adjustors during curarization, indicating that the effect is due to the absence of an effective postural substrate. These curare experiments are suggestive for further work. For example, by increasing the amount of curare-free muscle tissue it should be possible to find some minimal point at which learning can occur.

The studies cited above deal mainly with the relation of amount of tension to learning. Let us now examine the changes which occur in the pattern of the postural substrate as a result of practice. At first there is much tension and writhing in practically all the muscles; this gradually reduces to the muscles which hold the pencil. The subject was placed in an apparatus which recorded simultaneously the thickening of four muscle groups. A visual object in sine wave motion provided the stimulus. The subject watched the movement of the stimulus lever and attempted to follow it with his own reaction lever. The pattern of the postural substrate for the one subject at the beginning and at the end of an extended practice in this skill. At the beginning of training pursuit was poor, and the muscular accompaniments were more or less general for the four groups under survey. With the acquisition of skill, however, the pattern tended to become localized in the muscle group specifically involved in the task. Thus, under habituation, tension becomes reduced not only quantitatively but qualitatively as well.