(A) Flies trained with sucrose, which produces robust 24 hr memory, were immediately provided either rich nutritious food or water. If sucrose’s nutritional value is assessed beyond the 2-min training, nutritious food immediately after training may interfere with the fly’s ability to attribute its nutritional status to the 2-min training, and thus interfere with memory formation. However, flies trained with 1 M sucrose and given food or no food for 3 hr post-training showed similar memory, unpaired t-test, p=0.480. (B) Flies trained with L-sorbose—a sweet but non-nutritious sugar that produces short- but not long-term memory—were immediately fed sucrose. If the nutritional evaluation occurred after the 2-min training, immediate feeding on sucrose may substitute as a nutritional cue, resulting in enhanced long-term memory. However, flies trained with 1 M L-sorbose and given sucrose immediately after training showed similar memory to flies not given sucrose, suggesting that the critical association period was confined to the 2-min training, unpaired t-test, p=0.207. (C) Matrix of flies’ preference for one sugar (top) when paired side-by-side with another sugar (side) for 5 min. Each comparison was tested with four independent trials, 50 flies per trial. Numbers are the proportion eating the sugar listed at top. (Proportions may not sum to 1.0; often several flies would not eat either sugar.) Short-term memory and long-term memory averages shown below with ± s.e.m. Memory scores labeled a are significantly different (p<0.05) from bars labeled b, analyzed by one-way ANOVA with Tukey’s multiple comparisons test.