The testing effect for visual materials depends on pre-existing knowledge

Remembering facilitates future remembering. This benefit of practicing by active retrieval, as compared to more passive re-learning, is known as the testing effect, and is one of the most robust findings in the memory literature. However, it has typically been assessed using verbal materials such as word-pairs, sentences, or educational texts. We here investigate if memory for visual materials equally benefits from retrieval-mediated learning. Based on cognitive and neuroscientific theories, we hypothesise that testing effects will be limited to meaningful visual images that can be related to pre-existing knowledge. In a series of four experiments, we systematically varied the type of material (meaningful object images vs non-meaningful “squiggle” shapes), the format of the test used to probe memory (a more visually driven alternative forced-choice test vs a remember/know recognition test), and the delay of the final test (immediate vs 1 week delay). We found that abstract shapes never showed a significant testing benefit, irrespective of test format, and even benefitted more from restudy than retrieval at longer delays, where testing effects are typically most prominent. Meaningful object images did benefit from testing, particularly at long delays, and with a test format probing the recollective component of recognition memory. Together, our results indicate that retrieval enhances memory for visual materials only when they have a unique, distinct meaning. This pattern of results is predicted by cognitive and neurobiologically motivated theories proposing that retrieval’s benefits emerge through spreading activation in pre-existing semantic networks, producing better integrated and more easily accessible memory traces.