Pairs of digits or two-syllable words were presented visually for subjects to study as long as necessary in order to construct a single string reflecting the ordering inherent in the pairs. For example, given 75, 27, 58, the subject was to produce 2758. The time spent studying individual pairs was shown to reflect a set of five constructive processes identified in a theory proposed by Foos, Smith, Sabol, and Mynatt (1976) to account for errors in constructing the correct order. In addition, the results indicate that the time required to determine that a pair contains no elements in common with previously presented pairs is greater for two-syllable words than for digits, suggesting that an exhaustive search through short-term storage is occurring.One of the simplest versions of the linear order task consists of presenting a subject with a set of digit pairs and requesting that he respond with a single string of digits reflecting the order inherent in the presented pairs. For example, the subject might receive, one at a time, the pairs 72,28,83, and his task would be to write down 7283. A recent study by Foos, Smith, Sabol, and Mynatt (1976) found that the order of presentation of the pairs was a major determinant of success in this task. Subjects were successful 91 % of the time with the presentation order given above, but succeeded only 46% of the time with an order such as 62,34,46. Foos et a1. (1976) explained their results in terms of what they called constructive processes, consisting of sets of mental operations that subjects are assumed to perform on the input strings. A detailed discussion of the various mental operations may also be found in the section by Smith in Potts, Banks, Kosslyn, Moyer, Riley, and Smith (in press). Briefly, the theory asserts that the first pair is stored in a short-term memory buffer and that subsequent pairs are entered following a marker element at the end of the string in the buffer. So, for example, after hearing 91,15, the buffer contains 91-15, where the hyphen (" -") represents the marker. The buffer is continually searched for duplicate, or matching, elements and new strings are constructed in the buffer by bringing duplicate elements together around a marker and deleting both the marker and one of the duplicate elements. Thus, 91-15 would become 915 in the buffer.Five constructive processes varying in difficulty were identified. In increasing order of difficulty, they are, as This research was supported by National Science Foundation Grant BMS75-19313. The second author is also on the faculty of the University of Toledo. Requests for reprints should be sent to Kirk H. Smith, Department of Psychology, Bowling Green State University, Bowling Green, Ohio 43403. follows: (1) Process Ml: One matching element is found already arrayed on either side of the marker. Simple deletion operations produce a constructed order. (This process was illustrated above with the pairs 91, 15.) (2) Process M2: One matching element-is found, but a rearrangement is required to bring the ma...