The table reflects the results of a study by Roediger and Karpicke (2006). The authors investigated whether the test-enhanced learning effect (the demonstration that repeated testing improves memory for material) was due merely to repeated exposure to the material. They randomly assigned participants to one of two study conditions (study-study or study-test) and to one of three retention interval conditions (final test at a delay of 5 minutes, 2 days, or 1 week). The dependent variable was the proportion of idea units recalled from an encyclopedia passage.

5 Minutes 2 Days 1 Week Mean

Study-Study 0.80 0.55 0.42 0.59

Study-Test 0.75 0.70 0.55 0.67

Mean 0.78 0.63 0.49

Table: Test-Enhanced Learning

Based on the cells of the study, what effects appear to be present?

a. an interaction between study condition and retention interval

b. a main effect of study condition and an interaction between study condition and retention interval

c. a main effect of study condition and main effect of retention interval

d. a main effect of study condition, a main effect of retention interval, and an interaction between study condition and retention interval