The more meaningful are the materials, the easier the learning and retention. It has been consistently shown that words are better remembered than nonsense syllables, and that the concepts and interpretations of scientific principles are retained better than the factual and separate pieces of information.
How do we know if the materials are meaningful or not? The meaningfulness of the materials depends on (a) familiarity and frequency of usage, (b) number of associations elicited within a fixed amount of time, and (c) relations among the words in the list. Since meaningful materials evoke links with information stored in the LTM, their recall becomes easier than the meaningless materials (nonsense syllables). Ebbinghaus was the first person to have conducted memory experiments on himself using nonsense syllables. A nonsense syllable is a meaningless set of three-letters with one vowel in between two consonants, which can be pronounced in a single articulation.
However, familiarity or associational value is not the only factor related to meaningfulness. There is also a factor of patterning of memorization. Meaningful materials are more likely to be organized into different groups if subjects are allowed to recall the materials freely. Bousfield demonstrated the phenomenon of category clustering, which suggests that when participants are allowed to recall freely, they recall words not in their order of presentation, but category wise. For example, if subjects are presented nine words belonging to three categories (animals, vegetables, vehicles) in the following order: potato, car, bean, dog, bus, cat, pumpkin, truck, monkey, they tend to recall potato, bean, pumpkin, car, bus, truck, dog, cat, monkey. They learn the list by placing the items into different categories. At the time of recall, the items are organized into groups, which mean that category clustering occurs with meaningful, not meaningless materials. The nature and the degree of category clustering differ from person to person depending upon how meaningfully the materials are related to subject's LTM.