- There is no special magic about visual images.
- Whether verbal or visual mnemonic techniques are better for learning depends partly on the learning material, partly on the nature of the learning task, and partly on the individual.
- Older adults in general are probably better advised to use verbal mnemonics.
- There is no particular advantage to using bizarre images.
Most mnemonic strategies use visual images. But as I say in The myth of imagery, while there is no doubt that imagery can be an effective tool, there is nothing particularly special about it. The advantage of imagery is that it provides an easy way of connecting information that is not otherwise readily connected. However, providing verbal links can be equally effective.
One study that compared verbal and visual imagery methods for remembering serial items (lists of words) found that using a verbal strategy resulted in equal performance on both lists of items rated as "high imagery" and "medium imagery". The two visual imagery techniques (method of loci, and pegword) resulted in higher performance than the verbal strategy for the high-imagery list, but poorer performance for the medium-imagery list .
A more recent study found that connecting three nouns by imagery was more beneficial for immediate unexpected recall than relating them by sentence, however, after a week, recall was the same for both techniques .
It is well-established that people differ in their abilities to visualize, and clearly the usefulness of visual imagery is partly dependent on whether you are a "high-imager" or a "low-imager" (but don't be fooled by these categorical labels - people will vary along a continuum rather than fall into an either-or category).
This talent also seems to change over the course of one's life. It has been suggested that older adults in particular might be better advised to use verbal mnemonics rather than visual image techniques, as they apparently find it difficult to produce and remember visual images (; ).
Not entirely independent of these individual differences, there is also a significant difference between the effectiveness of visual images presented to you and those you must generate for yourself.
There is also some evidence that imagery techniques are more effective in particular types of memory tasks compared to others. Herrmann  suggested that interactive imagery was the most effective strategy for paired associate learning (linking two items together), but a story mnemonic was most effective for free recall (remembering various items in any order).
On a related subject, a study that looked into the usefulness of bizarre imagery as a mnemonic aid found that bizarre images were remembered better in the immediate term but not the long term, and only if the images were experienced as part of a mixed list (bizarre and non-bizarre items), and the learner could control their pace of learning . A number of studies have failed to find any particular benefit to constructing bizarre images, and indeed, have suggested that bizarre images take longer to construct and may result in poorer performance. Most recently, the bizarreness advantage in mixed lists was eliminated when alternative retrieval strategies were encouraged . These researchers suggested that the advantage of bizarreness depends on your retrieval strategy (whether or not it is based on distinctiveness).
In sum, then, I would say that use of visual imagery is an entirely personal matter, that there is no clear superiority of visual over verbal techniques, and that (as always) it comes down to individual idiosyncracy. Don't feel pressured into using imagery if you're not easy with it. And if you are comfortable with imagery, still restrict your use of the technique to situations where the images come easily - don't spend more time on constructing images than is warranted; be open to using other techniques. There's no magic to visual imagery. Meaningfulness, organization, depth of processing are the crucial elements in learning, not the precise tools you use to get there.
- Baltes, P. B., & Kliegl, R. (1992). Further testing of limits of cognitive plasticity: Negative age differences in a mnemonic skill are robust. Developmental Psychology, 28, 121-125.
- Herrmann, D.J. 1987. Task appropriateness of mnemonic techniques. Perceptual and Motor Skills, 64, 171-178.
- Hishitani, S. 1985. Coding strategies and imagery differences in memory. Japanese Psychological Research,27(3),154-162.
- Iaccino, J. F., & Sowa, S. J. 1989. Bizarre imagery in paired-associate learning: An effective mnemonic aid with mixed context, delayed testing and self-paced conditions. Perceptual and Motor Skills, 68, 307-316.
- Marston, P.T. & Young, R.K. 1974. Multiple Serial List Learning with Two Mnemonic Techniques.
- McDaniel, M.A., DeLosh, E.L. & Merritt, P.S. 2000. Order information and retrieval distinctiveness: Recall of common versus bizarre material. Journal of Experimental Psychology: Learning, Memory, and Cognition, 26(4), 1045-1056.
- Poon, L. W., Walsh-Sweeney, L., & Fozard, J. L. (1980). Memory skill training for the elderly: Salient issues on the use of imagery mnemonics. In L. W. Poon, J. L. Fozard, L. S. Cermak, D. Arenberg, & L. W. Thompson, (Eds.), New directions in memory and aging: Proceedings of the George A Talland Memorial Conference (pp. 461-484). Hillsdale, NJ: Lawrence Erlbaum Assoc.