Martin and Jones have shown that, although their student participants knew that old and new crescent moons have different orientations, they performed at chance levels when asked to say whether the old or the new moon faces left or right. The authors argue that this memory failure arises primarily because the information about orientation has no functional significance for this population.
Their conclusion seems intuitively plausible but the evidence from this study is less than compelling. One possibility that should not be overlooked is that the students are displaying a lack of knowledge rather than a failure of memory. They may never have known the orientation of new and old moons. Moon orientation is not like the orientation of a head on a coin because it is dynamic and changes over time. Thus the only way to learn the orientation by observation is to study the moon over a period of time and note that the right-facing crescent wanes and the left-facing crescent waxes. Many individuals may not have had the opportunity or motivation to make the successive observations that are required. Of course, they may have acquired the information from secondary sources but this cannot necessarily be assumed and it would have been interesting to ask the subjects whether they had once known the orientation of the crescent moons and then forgotten it or whether they had never known it.
In addition to the difficulty caused by the way it shifts over time, the orientation of the crescent moon may be hard to learn for a number of other reasons. It is worth noting that some of the mnemonics take the form of a confusing contradiction. The authors cite the one whereby When it is Coming (facing right) it is really Departing. When it is Departing (facing left) it is really Coming'. Another mnemonic The close brackets sign is the opening (new) phase of the moon and the open brackets sign is the closing phase' requires a similar kind of reverse mapping. Another factor may be that it is inherently difficult to learn object identity when this depends solely on orientation so that remembering the orientation of the moon is posing essentially the same problem as learning to tell bs from ds and ps from qs.
The role of functionality would receive more support if it could be shown that groups for whom the phase of the moon does have functional significance have better recall of its orientation. Farmers, gardeners and others whose activities are dependent on the weather often subscribe to the view that the new moon heralds a change in the weather and are accustomed to study the night sky and identify phases of the moon. For the students who participated in these experiments it is reasonable to assume that lack of functional significance is probably a major cause underlying their poor performance, but there are other possible factors as well that have not been addressed in this study.