Priming effect as related to difficulty in selection for overlapping stimuli manipulated by the relative line thickness of attended and unattended figures.

The present study examined how difficulty of ignoring unattended stimulus affected the negative printing. To establish an experimental situation with intentional ignoring, subjects were presented overlapping stimuli consisting of two figures of different colors and were required to attend to one of the figures while ignoring the other. Moreover, the difficulty in selection was manipulated by their line thickness. The assumption was that the magnitude of that difficulty should increase with the ratio of line thickness of the unattended figure to that of the attended one. Reaction time was measured in both ignored repetition and control conditions. In the former, both the unattended figure in the prime and the attended one in the probe were of the same form, while in the latter, they were different. Priming effect was indicated by the differences between the two reaction times. Two experiments showed that the priming effect changed with the ratio of line thickness, depicted as a V-shaped curve. The effect was facilitate at the ratio of line thickness of 1, which was inconsistent with the previous studies reporting an inhibitive effect. The following two experiments, however, confirmed that the effect at the ratio of 1 was facilitative when the ratio of line thickness was varied, but it was inhibitive when the ratio of line thickness was fixed within a session. The inconsistency could then be attributed to the difference in the manipulation of the ratio of line thickness.