Perception of Weight and the Phenomenal Regression to the “Real” Weight (Thing Constancy Phenomenon). Experiments on Arm‐Amputated Subjects

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The purpose of this paper was to investigate whether the weight of the subject's own arm influences the perception of an external weight to be lifted, when the receptive mechanism is proprioceptive (as is almost the case e. g. when lifting heavy weights). The receptive mechanism of weight perception was briefly discussed. The experiments were performed on 54 war invalids amputated on the upper limb. The experimental arrangement was as follows: The subject had to compare two weights, the one of which (a standard of 3,000 g) was lifted by the arm (the intact arm, or the stump) in an abduced position, the subject standing erect and the armweight acting against gravity, the other one (variable weight) lifted with the subject in a tilting posture, the arm hanging vertically down and the tissues thus passively supporting the arm weight. The weight to be added to the variable weight in order to make the two weights phenomenally equal, showed great individual differences. In experiments with the intact arm, in 19 cases, the additional weight was at the most 300–400 g greater than a weight that corresponds to the difference threshold determined the standard weight and the variable weight both lifted in the erect posture and the arm-weight acting against gravity. The difference is not statistically significant. In 11 cases it was 500–600 g greater, i. e. on the limit of significance, and finally in 24 cases 700–2,800 g greater, which difference is surely significant. In experiments with forearm stumps the corresponding figures were 16: 4: 8, and in experiments with arm stumps 19: 1: 2. It is obvious, that when experimenting with the whole arm, the arm-weight influences the perception of an external weight in most subjects, in experiments on forearm stumps the influence is much less and in experiments on arm stumps hardly observable, quite in accordance with the fact, that the weight of the forearm stump is of course a little less, that of the arm stump considerably less than the weight of the intact arm. Those cases in which (in experiments with the intact arm) the perception of a lifted weight was not affected by the arm weight (19 cases) proved, that the proprioceptive weight perception shows phenomenal regression to a conceptual thing character analogous to the well-known constancy phenomena in the visual field. In a few cases, however, there was reason to believe, that the receptive mechanism was tactual (pressure exerted upon the skin). In these cases the weight perception is of course independent of the arm weight. Financial aid for this research has been granted by the KORDELIN foundation. I hereby wish to express my gratitude to the Head of the Red Cross Invalid Hospital, Dr. REHNBERG for his permission to carry out the investigation on patients at the Hospital. It is a pleasure to record my indeptedness to the nurses and social case workers for their kind assistance in selecting and sending the patients over to the Physiology Institute. I am also grateful to Miss LIISA LAINE, for her valuable help and thoroughness in carrying out a part of the experiments.