Difficult material: leeches

Learning material can be inherently difficult (e.g. numbers, sets, enumerations, etc.) or it can be wrongly formulated. Mnemonic techniques and other tools can be used in tackling inherently difficult material (see: 20 rules of formulating knowledge in learning)

Important! A small proportion of difficult items in SuperMemo can consume a large proportion of your time

The term leech is used in SuperMemo to refer to ill-formulated items. An element is called a leech when it meets user-defined leech criteria such as the number of memory lapses and the current interval. These parameters can be defined when using View : Other : Leeches (Shift+F3). An element becomes a leech when the number of memory lapses passes a defined limit. However, an element is no longer considered a leech if it is remembered beyond a certain interval (independent of the number of lapses).

Difficult items (leeches) are one of the top reason people give up SuperMemo! Hunting leeches improves your chances!

Leech Hunting Options

Although View : Other : Leeches (Shift+F3) can be used to review, delete and reformulate leeches, the best approach to tackling most leeches is to review them in detail one by one in the course of the learning process. In Tools : Options : Leeches, you can select the following leech management options:

SuperMemo: Tools : Options : Leeches tab

Include semi-leeches checkbox can be used to tighten the criteria for a leech warning. A semi-leech is an element that is one memory lapse away from becoming a leech. For example, if a leech is defined as an element with five or more lapses and an interval up to 60 days, an element with four lapses and 1000 day interval will be a semi-leech (because after a single lapse, it will reach 5 lapses combined with a short interval thus becoming a leech). If your collection is well-structured and you do not encounter many leeches, you can turn Include semi-leeches on to tighten leech supervision.

Leech Alert Wizard

If you choose Tools : Options : Leeches : Wizard, the following dialog will be displayed each time you encounter a leech during repetitions:

SuperMemo: A Leech Alert raised for an item that has already been forgotten 7 times which qualifies it as an intractable one requiring user's attention and action

Figure: A leech alert raised for an item that has already been forgotten 23 times. This makes for an intractable leech that requires rewording, or using mnemonic techniques. In this case, the user needs to either look for ways to represent proboscis in his memory, or to give up the word altogether, e.g. on the grounds of its low use frequency in English. This particular example comes from a preschooler's collection and the item can safely be deleted as too advanced, or just delayed by 1-3 years

This is the function of individual controls:

Recommended leech strategy

If you use the wizard, make the following choices upon encountering a leech:

Defining and viewing leeches

The option View : Other : Leeches (Shift+F3) can be used to locate leeches in your collection. This option uses the Element filter dialog box that can be used to find all elements meeting a specific set of criteria such as the number of repetitions, number of memory lapses, length of the current interval, status (memorized, pending, or dismissed), type (item, topic or task), etc.

The purpose of locating leeches is to reedit most intractable items with a view to applying appropriate mnemonic techniques. Alternatively, you can reset elements (e.g. to deal with them later), dismiss them (to use them only as reference, e.g. with Search : Find elements), or simply delete them.

A new powerful tool against leeches is a possibility of exporting your leeches to a handheld device (see: Revolution in the pocket). Although, it may seem that pocket repetitions are usually done in conditions of lesser focus, working in the leech-only mode sets your brain onto an emergency alertness level. You approach repetitions differently if recall failure is expected. At time, this is enough to wrap your mind around harder material and gradually reduce the leech load.

To maximize the effectiveness of the learning process, you should learn to use View : Other : Leeches and periodically remove from your collection most intractable and badly structured material.

SuperMemo: Element filter dialog box which you can use to browse all elements that meet your search criteria (e.g. in leech hunting)

The following fields can be used to select the minimum and the maximum values that fall into the range defined for difficult elements:

If you do not want to use a given criterion, uncheck the check-box associated with a given field. If you do want to use it, check the check-box and specify appropriate Minimum and Maximum values.

By definition, all leeches are memorized items. This is why Type and Status fields of Element filter are disabled.

Once you click OK, all leeches meeting the specified criteria will be found and will be displayed in a browser. You can then use Learn (Ctrl+L) in the leech browser to make repetitions in the leech subset only.

Using Tools : Random test : Leeches you can run a random test on all leeches. However, you should remember that part of the leech problem is repetition that is too frequent (i.e. causing the spacing effect). This is why Auto-postpone and Auto-forget are so efficient. This is also why leeches are much less of a problem in heavily overloaded incremental reading.

Leech parameters are stored between sessions in the file <supermemo folder>\<systems>\<collection name>\collection.ini in the section [Leech]


You can clear the Leech Alert with Esc

From: Jens Buurgaard Nielsen
Country: Denmark
Sent: Thursday, August 09, 2001 9:53 PM


Leech alert: Nice feature, but I hate that per default, the leech window becomes active. I don't want to move my mouse to another window to do the grading. I often use Space bar to activate the default button, and sometimes, it automatically moves to Postpone when I intended to grade myself Good


You can either disable leech alert entirely in Options or just clear it with Esc and continue the repetition cycle using standard keys

Semi-leeches cannot be auto-forgotten

From: Mike Condron
Country: USA
Sent: Thursday, August 09, 2001 9:53 PM


Why can I not choose Include semi-leeches in leech manager for auto-postpone or auto-forget?


Semi-leeches are not leeches. They can be scheduled for repetition at very long intervals. Removing them from or reintroducing them to the learning process would add a substantial cost to learning