Page:Mind (Old Series) Volume 11.djvu/551

 550 J. JASTROW : to this rule we found that with the Ann as expressing sense and the Eye as receiving sense, an exaggeration, but with the Hand as. receiving sense, an underestimation takes place. Another mode of experimentation touches upon the problem in a somewhat different manner. The subject, instead of having an impression presented to one of his senses, attempts to express his mental recollection of some absolute measure (e.g., a certain num- ber of inches), by selecting a line, a distance between thumb and forefinger, or a space moved over by the arm, that seems equal to the mental recollection. In so doing the eye 'creates ' its inches about 10 per cent, too short; the hand and arm about 20 per cent, too long in small lengths, the excess decreasing as the length increases. The smallness ' of these errors seems best accounted for by assuming that in ' creating ' inches by the Eye I use the recollection of my visual inch ; by the thumb and forefinger, of my span-inch; by the arm, of my motion-inch. The operation would closely resemble that in which the receiving and expressing senses are the same ; accordingly, when the sense used is the Eye we should have an underestimation, when the Hand or Arm an exaggeration, which is exactly the case. Our conclusions then are (1) that the memory for dbsolztte measurements /* rmt >/>-iteoiui mental recollection ; (3) that thv V!n-///r// too long. These conclusions evidently favour the point of view of law C. D. Finally, a comparison of the error in reproducing by the same and by a different sense leads to the very important conclusion that the former operation is an accurate and easy one, the latter an inaccurate and dif- ficult one. The difficulty manifests itself as a feeling of dis- comforting uncertainty and lack of confidence in one's judgments, and a great susceptibility to fatigue. The connexion between two senses seems to be a loose one. Relative Accuracy of the Senses. Three indications of the relative accuracy of the three senses have already been given. (1) When the receiving and expressing .-a mo kind of error as expressing by another, this contradiction between the two laws must take place. In this case Law C is violated and Law B maintained. 1 A further indication of the regularity of these operations was obtained by requiring the subject to judge in inches the lengths of certain lines, distances and spaces by Sight, Span and Motion. If in expressing inches there is an exaggeration (or underestimation), then in judging inches there must be an underestimation (or exaggeration) ; and this is really the < !iow the etl'eet of practice in one's knowledge of absolute lengths, some carpenters en- t.-.-led and found to give mole accurate and confident judg- ments than others. This .-upeiiority was confined entirely to Sight.