Abstract
Holcombe, Kanwisher, & Treisman (in press) reported that apprehending the relative order of a four-letter sequence is easier in a single presentation than in a repeated presentation, in which a four-letter sequence is presented many times. This phenomenon is termed the midstream order deficit (MOD). However, in their experiments the effects of repetition of the four letters and of repetition at the same location were mixed, since they presented all of the four letters at a single location. The MOD at a different location might be different from that at the same location. In the present study, we examined whether the MOD occurred when the location of each letter was maintained discretely from the others. Under a fixed-location condition, the location of each letter was fixed during a trial. On the other hand, under a random-location condition, the locations of four letters changed at every presentation. The two conditions differed in the respect whether the location of each letter was fixed during one trial. In both fixed-location and random-location conditions, relative order accuracy was lower in repeated presentation trials than in single presentation trials, although letter accuracy was significantly higher in the repeated trials than in the single trials. This result suggests that MOD occurred significantly even when the location of each letter was kept separate from the others. The larger MOD occurred under the random-location condition a compared with the fixed-location condition. This indicates that the fixedness of the locations raised the relative order accuracy.