My research on implicit and explicit memory (also automatic and conscious memory) has focused on what the differences really are. One popular view of the implicit/explicit distinction is that of separable memory systems for the two forms of memory. Several authors (e.g., Dosher & Rosedale, 1991; Nadel, 1994; Schacter & Tulving, 1994) have cited forgetting differences as an important criterion for distinguishing memory systems. Along these lines, claims of differing forgetting rates have been made for implicit and explicit tasks.
My work addressing this issue (McBride & Dosher, 1997) involved several experiments that measured forgetting rates for implicit and explicit memory using stem completion as an implicit task and stem cued recall as an explicit task. Performance was measured for several study-test retention delays from 1 to about 60 min. Forgetting rate did not differ for the two types of memory in this range. The form of the forgetting function was also characterized and was found to include a rapid decline in performance from 1 to 15 min and a very slow decline from 15 to 60 min.
A second study (McBride & Dosher, 1999) addressed the possibility of overlap in memory processing for either task type by estimating conscious and automatic memory processes for the same stem completion tasks using Jacoby's (1991) process dissociation procedure and multinomial process models of the tasks. Forgetting rate did not differ for conscious and automatic memory processes over a range of delays from 1 to 60 min and the same form of decline (rapid, then slow) was seen in this study.
A third study (McBride, Dosher, & Gage, 2001) examined another common memory task used in the current literature, that of fragment completion. Different claims regarding forgetting rate had been previously made for implicit memory as measured by stem completion tasks and by fragment completion tasks (Schacter, 1987). Fragment completion tasks were given with explicit and implicit instructions in one experiment that measured forgetting for a range of delays from 1 to 45 min. No forgetting rate differences were evident for the two kinds of memory, but data were not entirely consistent with previous data found for fragment completion tasks (e.g., a levels of processing effect was found for both tasks). Therefore, the second experiment in this study compared forgetting rates for conscious and automatic memory processes using these tasks in a process dissociation procedure. Estimates of memory were obtained through multinomial modeling analyses. Again, no differences were evident. For both experiments, the form of forgetting was similar to previous studies. A rapid decline in performance was found for delays from 1 to 15 min with a period of slow decline following.
Currently, I am planning to conduct experiments to further examine the form of forgetting seen in the previous studies. One possibility is that the two portions of the forgetting function represent a difference in retention for different kinds of information. I am also exploring the possibility of forgetting differences with longer retention intervals.