Figure 1.
(a) Typical setup of the visual acuity test. Participants indicate by key the perceived or guessed (forced choice) position of the Landolt gap. (b) Representative example of a FrACT (Bach & Kommerell 1998) visual acuity test run of one participant. Visual acuity is estimated with an adaptive algorithm (Best PEST Algorithm, Lieberman & Pentland 1982) starting with large optotypes (Landolt Cs) and decreasing step sizes depending on the correctness of participant's response. The optotype size converges on a threshold value (1.45) that is used as the participant's visual acuity. (•) correct responses; (*) incorrect responses.
Table 1.
Participants' age and gender (S1-S6: spacing conditions).
Figure 2.
(a) Vocabulary Experiment: In the study phase of each Learning Block (LB, blue-framed squares) participants viewed and had to learn 40 Japanese-German word pairs. In a subsequent cued-recall test (test phase) the Japanese words were presented and the German translations had to be recalled. A learning block was finished by a 1-s presentation of the correct word as feedback. Initially all participants performed two Learning Blocks separated by 7.2 min. The subsequent three learning blocks were spaced by a condition-specific time Si. (b) Visual Acuity Experiment: In the visual acuity experiment participants had to indicate the gap position of a size-varying Landolt-C by key-press. In this experiment, each of the four “Learning Blocks” (blue-framed squares) and each of the three final tests (red-framed squares) consisted of three consecutive visual acuity tests. As in the vocabulary experiment the 6 different experimental conditions differed in the spacing interval durations Si between Learning Blocks.
Table 2.
Average applied spacing and retention intervals.
Table 3.
Average applied spacing and retention intervals.
Figure 3.
Grand Mean of the test results from the learning period (blue traces) and test results from the final test period (red traces) ± SEM.
(a) Results from the vocabulary experiment in % of the total number of presented vocabulary word pairs ( = 40). Maximal performance decreases with spacing interval duration but best long-term retention is found with a spacing interval of 12 h. (b) Results from the visual acuity experiment as the positive logarithm of the maximal visual acuity. Visual acuity is defined as one over the minimal angle of resolution. Again a spacing interval of 12 h produces best long-term retention, although variability is larger compared to (a).
Figure 4.
Final Test performance as a function of spacing interval duration (abscissa), separately for each retention interval duration (different traces).
(a) Vocabulary experiment: The data are % values of the total number of presented vocabulary word pairs ( = 40), averaged across participants. (b) Data from the visual acuity test.
Table 4.
Polynomal contrast analysis results
Figure 5.
Overview of the spacing intervals (abscissa) and retention intervals (ordinate) used in a number of representative studies.
Dots indicate studies with specific spacing/retention interval combinations. Black dots are from an extensive review by Cepeda et al. [2]. Green and red dots are from recent studies of this group. The orange dots indicate spacing and retention intervals used in the present study. The larger orange dots indicate spacing intervals with local and global performance maxima.