Retention of Spanish learned in school was tested over a 50-year period for 733 individuals. Tests of reading comprehension, recall, and recognition vocabulary and grammar were administered together with a questionnaire to determine the level of original training, the grades received, and rehearsals during the retention interval in the form of reading, writing, speaking, or listening to Spanish. Multiple regression analysis shows that retention throughout the 50-year period is predictable on the basis of the level of original training. The great majority of subjects rehearse so little that the data reveal no significant rehearsal effects. The analysis yields memory curves which decline exponentially for the first 3-6 years of the retention interval. After that retention remains unchanged for periods of up to 30 years before showing a final decline. Large portions of the originally acquired information remain accessible for over 50 years in spite of the fact the information is not used or rehearsed. This portion of the information in a "permastore" state is a function of the level of original training, the grades received in Spanish courses, and the method of testing (recall vs. recognition), but it appears to be unaffected by ordinary conditions of interference. The life-span frequency distribution of learned responses is discontinuous; one portion of the response distribution has life spans of 0-6 years, the other portion, life spans in excess of 25 years, and no responses have life spans of 6-25 years. This suggests a discrete transition into a permastore state during the extended period of original training. Analysis of successive relearning processes over extended time periods is deemed essential for an understanding of the acquisition of permanent semantic memory content.

Memory research has contributed little toward understanding acquisition, maintenance, or loss of complex knowledge systems. This is so because such systems are acquired and maintained over long time periods that cannot be accommodated by traditional research methods. Acquisition of semipermanent knowledge typically involves repeated exposure to information, with losses of information during intervals between exposures. Continued maintenance of knowledge depends on periodic access. Two methods are described to investigate these processes.The method of successive relearning is a laboratory method illustrated in a study in which English-Spanish word pairs are periodically relearned and the effect of varying the intersession interval from a few seconds to 30 days is established. It is shown that indefinite access to the acquired information remains highly probable if the retraining interval does not exceed the access interval. If the access interval is much longer than the retraining interval, much of the acquired information becomes inaccessible during the access interval.The method of cross-sectional adjustment is a nonlaboratory method designed to investigate the acquisition and maintenance of complex knowledge systems under ecologically realistic conditions. This method can be used if a large number of individuals acquired the same information, if the time of acquisition dates back from a few months to many years, and if both the original level of knowledge and the degree of rehearsal during the retention interval can be estimated with acceptable reliability. The method is illustrated in a study in which maintenance of knowledge of a city is related to the frequency, recency, duration, and distribution of visits during a 46-yr. retention interval.Subjects are assigned to time groups based on how long ago they acquired the information; average retention performance for various time groups yields an unadjusted retention curve. Such curves must be corrected for differences among the groups in the degree of original learning and in the amount of rehearsal. These adjustments are made on the basis of multiple regression equations that reflect correlations of rehearsal variables and retention performance. It is shown that the adjustment process can correct for major inequalities among groups. The multiple regression equations are used further to obtain estimates of the amount of rehearsal necessary to maintain the original level of knowledge.

Three hundred and ninety two high school graduates were tested for memory of names and portraits of classmates selected from yearbooks. The retention interval since graduation varied from 2 wk to 57 yr. Performance was adjusted by multiple regression procedure to control the effects of various conditions that influence original learning, such as class size, and other conditions that influence rehearsal of the material, such as attendance at class reunions.The cross-sectional approach illustrated in this study is discussed as an alternative to the traditional longitudinal approach to the study of memory. The cross-sectional adjustment approach sacrifices laboratory control over the conditions of original learning, but permits extension of investigations to conditions that significantly affect learning and memory but that cannot be adequately or conveniently manipulated in the confines of the laboratory. Examples are a greater range of learning material, of motivational conditions, of context effects, and most significantly of acquisition time and retention time. Since most of the vital information in the memory store is learned and retained over periods much longer than those which are investigated in the laboratory, available generalizations based on laboratory findings may be inadequate or inapplicable to these area of knowledge. The cross-sectional ap-

In a 9-year longitudinal investigation, 4 subjects learned and relearned 300 English-foreign language word pairs. Either 13 or 26 relearning sessions were administered at intervals of 14, 28, or 56 days. Retention was tested for 1.2.3. or 5 years after training terminated. The longer intersession intervals slowed down acquisition slightly, but this disadvantage during training was offset by substantially higher retention. Thirteen retraining sessions spaced at 56 days yielded retention comparable to 26 sessions spaced at 14 days. The retention benefit due to additional sessions was independent of the benefit due to spacing, and both variables facilitated retention of words regardless of difficulty level and of the consistency of retrieval during training. The benefits of spaced retrieval practice to long-term maintenance of access to academic knowledge areas are discussed.

Thirty-five individuals who had learned and relearaed 50 English-Spanish word pairs were tested for recall and recognition after an interval of 8 years. Two variables, the spacing between successive releaming sessions and the number of presentations required to encode individual word pairs, are excellent predictors of the likelihood of achieving permastore retention. Optimum recall occurs for words encoded in 1 -2 presentations and accessed at intervals of 30 days. Both variables yield monotonic retention functions that account for a range of variation from 0% to 23% recall. These variables also have very significant effects on the recognition of unrecalled words.