Intra-serial effects with lifted weights.

An incomplete community of subject-matter of a number of studies concerned with retentive changes in visual material and of others disclosing partially anomalous errors in various forms of the psychophysical judgment has led to the present experiment. Certain errors disclosed by psychophysical studies have in general implied that a change in the value of a past standard stimulus (one which has just been presented) occurs always in the single direction of some still earlier stimulus value or 'average' of stimulus values. On the other hand, numerous forms of changes in retained visual material have been reported. One may ask then: (x) whether there is more than one type of shift of standard stimulus value demonstrable in a modified psychophysical method involving the successive comparison of lifted weights; (2) whether, if several shifts or changes are so demonstrable, to what retentive changes do they correspond; and (3) whether, in seeking to account for any such new psychophysical errors, fruitful reference can be made to configurational principles such as the "Law of Pragnanz."