Broadbent and Northrup, however, independently found that pseudo-after-effects occurred after a number of trials when an inspection-block was not interpolated.2 They suggested, therefore, that the pseudo-after-effects resulted from shifts in the scale of judgment caused by repeated experience with the tapered comparison-block. Broadbent also suggested that the interpolated experience of the inspection-block may cause the forgetting of a previous series of judgments thus resulting in a greater bias in the judgments following the period of stimulation. Costello is of the opinion that Broadbent relegates the inspection-block to a too minor role. He believes that the experience with the inspection-block has a direct effect on the frame of reference relating the test-block to the comparison-block rather than merely interfering with the frame of reference established by earlier trials.3 This proposal is supported by the finding of Charles and Duncan that the amount of the after-effect first increased and then decreased as the difference in width between the testand inspection-block increased.4 That after-effects are produced by the interpolated inspection-block through a change in the frame of reference relating the test-block to the comparison-block rather than by the production of cortical satiation has been suggested also by Northrup. She found that after-effects produced by just holding the inspectionblock were significantly greater than those produced by the standard satiation procedure of rubbing the inspection-block.6 This finding would appear to be more in