Order Effect in Recognition Latency for Multiple-Item Probes

A strong order effect in response latency has been found in recognition experiments with varied memory sets and multiple item probes, in which all items must be positive for a positive response. In this article, three experiments are reported that support the idea that incidental order information may be stored in the form of combination items derived from subjective grouping of memory set items. Thus, the memory set of six items, ABCDEF, may be subjectively grouped into two combination items ABC and DEF. The key evidence supporting the combination item hypothesis and subjective item grouping was that prominent order effects exist if probe items are all within a subjective group but that such effects are small if the probe is "between-groups." Experiment 1 used visually degraded probes and found serial position effects but no decrease of the order effect with degradation. Experiment 2 tested whether combination items are likely to be encoded in auditory-articulatory form and thus persist for several seconds, by using interpolated intervals of up to 30 s. The order effect was found to persist at the end positions of the memory set but to decrease considerably at intermediate positions. Experiment 3 provided a test of subjective item grouping and demonstrated the dominance of three-item subjective groups. A model based on item matching strength as a function of position within a group is briefly outlined