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AGE AND BEHAVIOR: PROCESSING SENSE INFORMATION - SEQUENTIAL INTEGRATION - STIMULI REFLECTING COMMON EXPERIENCE - JUDGING WEIGHTS

A different type of study, one involving comparisons between weights rather than fusion thresholds of successive stimulation, was reported by Landahl and Birren (1959). In the fusion experiment, the performances of the young, more than the old, were seen as keeping the inputs relatively discrete perceptually. In the masking experiment, the performances of the young were seen as reflecting relative escape from masking at shorter intervals between stimulation. In the word-half study, more readily fused word halves on the part of the old made for better identifications. In all these instances, the performances of the young were thought superior to the old in that they reflected more nearly the objective physical reality. In the weight judgment experiment of Landahl and Birren, good performance was seen as the ability to perceive which of two lifted weights was the heavier. Stimulus persistence theory could explain the results of this weight comparison study but not as well or as easily as the results of the fusion studies. Subjects of two age groups, 18-32 and 58-85 years, were presented with a standard weight of 100 grams and a comparison weight of either 100, 105, 110, or 115 grams. There were a variety of comparisons, but the important ones here were: (1) the standard weight was placed in one hand and a comparison weight in the other simultaneously; and (2) the standard placed in one hand and a comparison placed in the same hand after the standard weight was removed. With the stimulus persistence model, the prediction might be that the successive comparisons would be better for the older subjects than the younger, relative to the simultaneous comparisons. It could be speculated that the older subjects should be aided in making successive weight comparisons by having the trace of the standard (first) stimulus persist in the nervous system so that either its presence or more recent "clearance" would provide an adequate standard of comparison when the second weight is being judged. On the other hand, for the young, the course of neural transmission having further progressed makes for a trace less available for adequate comparison. The outcome of the Landahl-Bir-ren experiment could be interpreted in this way but, again, it must be emphasized that the experiment was not carried out for the purpose of testing the model, and this interpretation may be less direct or good than other interpretations. Moreover, as already indicated, the correct test of the model must be made of predictions that the model generates (as in the masking and corresponding stimulus halves studies), not post hoc interpretations of existing data. The model is used here mainly to suggest an organizing scheme to integrate a great variety of diverse studies. *189\220\8*