David Starr Jordan, the renowned ichthyologist and founding President of Stanford in 1891, was famous for his encyclopedic knowledge of fish. Names, classifications, habitats—everything was impeccably memorized and available for recall from the expert’s exquisite memory.

Sadly, President Jordan proved unable to get to know the students at Stanford by name, as had been his initial intention. After considerable effort, he gave up on the idea, lamenting that “…every time I learned the name of a student, I forgot the name of a fish.”

This retroactive interference, whereby the acquisition of new information interferes with existing knowledge, is an academic’s constant nightmare (which I combat with named photos of my tutees in the top drawer). The reverse problem, that existing knowledge might interfere with the acquisition of new memories, is known as proactive interference. Although detrimental to learning, it likely constitutes the lesser evil for ichthyologists.

But what if remembering new students’ names is more important than knowing Aeneus corydoras or Bombay duck? One solution to proactive interference is known as directed forgetting: When people are presented with two lists to remember, and are instructed to forget the first one after they have studied it, memory for the second list is better than in a condition in which both must be remembered.

So, forget about the fish and the students will be more than an amorphous conglomerate that is threatening your memory.

A recent article in the Psychonomic Society’s journal Memory & Cognition examined the benefits of such directed forgetting on the acquisition of new motor memories; that is, memories for physical movements. We all rely on motor memory in our daily lives, for example when shifting gears in our car, although not all of our motor memories are quite as detailed as a ballerina’s motor memory for the Dance of the Sugar Plum Fairy:

[youtube https://www.youtube.com/watch?v=Wz_f9B4pPtg]

Researchers Tempel and Frings presented participants with two “lists” of sequential finger movements (SFMs) for memorization. Each SFM involved three fingers of the right hand that had to perform 4 movements. The table below shows the sequences that had to be memorized, with one sequence per row:

On each trial, the computer would first signal which fingers had to be moved, by briefly coloring the corresponding fingers in an outline drawing of a hand on the screen, and participants then had to press 3 keys (one for each finger) in the correct order from memory.

For example, for the first sequence above, the index, ring, middle, and index finger of the hand on the screen would be briefly colored in (each for 1/5th of a second). The participant would then press the response keys with their own fingers in that order. Feedback was provided after each trial, and across many such trials, participants acquired the 5 SFMs that comprised each list. Those sets are identified as A and B in the table above.

In one condition, known as the forget group, participants were told after learning of the first list (L1 from here on) that the learning up to now had been for practice only, and that the real experiment was about to begin with the second list (L2). In the remember group, by contrast, participants were told that they had to remember both lists for a final recall test.

The final recall test was identical for both groups and involved the recall of the studied sequences from both lists in response to a cue. Recall was grouped by list, and participants first had to recall L1 before recalling L2. For the forget group, the requirement to recall L1 came as a surprise whereas it was expected for the remember group.

The main results from two nearly identical experiments are shown in the figure below:

For present purposes we can ignore the differences between experiments. The comparison of greatest interest is for L2. In both experiments, L2 performance was better in the forget group—that is, when relieved of the burden to remember the first list, participants were much better at learning and then recalling L2. This difference occurred despite the fact that at recall, both lists had to be retrieved: the superior L2 recall for the forget group therefore could not reflect a reduction in retrieval demands.

In one of the experiments, L1 was also recalled less well by the forget group than by the remember group, which is the expected result in response to directed forgetting. We need not concern us with why that effect was absent in the other experiment, because the most interesting finding is that learning and recall of motor sequences benefits from the intentional forgetting of earlier information.

Forget the fish, and you can type your student’s name: “B.O.B.”

In a further analysis, Tempel and Frings were able to pinpoint the source of the L2 advantage after directed forgetting. Unlike most other memory experiments in which people simply watch or listen to the stimulus material, the present studies also included a measure of accuracy at encoding—that is, during the acquisition phase of each list, when participants had to repeat the sequence of animated fingers on the screen, it was possible to examine the accuracy with which those study trials were performed.

Tempel and Frings found that accuracy at encoding of L2 was greater for the forget group than the remember group, suggesting that it was the new learning that benefited from directed forgetting, rather than L2 retention or retrieval. In other words, people did not simply get confused between L1 and L2 items at test when they had to remember both, but they found it easier to acquire L2 in the first place when they were instructed that they could forget about L1.

So if a ballerina is building up to a once-in-a-lifetime performance of Swan Lake, then perhaps she ought to forget about the Nutcracker, Giselle, Cinderella and Sleeping Beauty.