Paired associate tasks rely heavily on working memory. Although the bonds are stored in long term memory, you must hold one item in memory while simultaneously retrieving its pair. This requires working memory.

Working memory provides both temporary storage and processing. It is not a passive store, hence the name “working.” But it is more than storage. It is where we do our mental work.

Working memory is needed for categorization, reasoning, weighing options, and giving self-direction. It helps animals remember which arm of radial maze has already been visited that day. It is used by children to remember the rules of a game while playing it. It is used in video games to remember where you are and who to zap next. It is used to keep track of a novel’s plot.

Working memory is composed of four parts: one major unit and three sub-processes. The major unit is call the Executive Process or the Central Executive. This unit monitors and coordinates the activities of all the other processes. It coordinates current and long-term memories, decides which information to use and which activity is currently most important.

The idea of an executive process comes from working with people who are mentally retarded. My little brother, Jimmy, was profoundly retarded and was not trainable. He couldn’t sit up without support. But individuals who have less brain damage than Jimmy are often capable of employment in sheltered workshops.

At one point in time, all retarded people were considered untrainable. Then some dedicated people showed that they could be taught to do a specific task. The theory was that they could not learn other tasks.

Along come some more dedicated people who showed that many people with retardation can be taught to learn a different simple task. They can learn several simple tasks. But what they found was an inability to easily switch back and forth between tasks. Their executive function wasn’t working well or, in some cases, at all.

Because of folk like Jimmy, we know that the brain has a mechanism for assessing inputs and switching tasks on the fly. This is the central executive.

The central executive decides what needs attention and which subunit should be activated. You are probably familiar with how your executive process switches back and forth between driving the car and talking to your passenger.

But the executive doesn’t always get things right. I was standing beside the trash can, unwrapping a snack, intending to drop the wrapped in the trash and put the food in my mouth. My executive process failed me. I didn’t eat the wrapper but I watched helplessly as the food dropped in the can.

Your central executive doesn’t do the work. It assigns it to one of subunits. Work can be assigned to the phonological loop, the visuo-spatial sketch pad, or the episodic buffer.

Phonological Loop

One of the subunits of working memory specializes in processing sounds. It intakes spoken and written inputs, and holds them for 2-4 seconds so they can be processed. The memory store, sometimes called echoic memory, is only a few seconds long but it is unclear how many seconds it is. Some say 1-2 seconds, others settle on 4 seconds, and others suggest it can be as long as 20 seconds.

It is difficult to establish the capacity because as we begin to fall off our mental conveyor belt (forget them), we move them to the front of the line again (loop). The loop portion of the phonological loop is an articulatory control process. It loops the sounds over and over so the echoic memory gets extended for as long we need it.

The amount of processing needed varies with the content. Spoken word is processed quickly and easily. Written words, however, must be converted into speech, which takes longer.

Music is thought to be processed by the phonological loop. But it might also have its own loop. Musicians are better at forward digit span than non-musicians. This is true for sounds, digits and nonsense syllables. It appears that musical training and experience cause the brain to develop a dedicated storage system for tones. The tonal loop does not seem to be present in non-musicians.

Visuo-Spatial Sketchpad

This subroutine of working memory involves several parts of the brain, including the prefrontal cortex, the parietal lobe and temporal lobe. It tracks where you are in relation to your environment. As you shift your focus to look at something else, the parietal lobe remaps its representation of where you are and where everything else is. It sends this information to the visuo-spatial sketchpad. You use the sketch pad to picture your house and remember where all the doors and windows are.

On evidence that there are at least two subsystems is that we can process visual and verbal information at the same time. In fact, we love doing so (TV, videos and movies). But it is much harder to do two visual tasks at the same time. Doing two things with one system slows things down.

Like the phonological loop, the visuo-spatial sketchpad has both a store and a processor. Visual images are stored for a much shorter time than audio is, probably about ½ second. The actual length of storage varies greatly between people. Some can maintain a visual mental image for longer than others. Artists, architects and fashion designers are able to visualize finished projects early in the creative process.

It is unclear if the ½ second images are looped like phonological inputs are. Given the refresh rate it seems unlikely. If you’ve done a video chat with someone on a bad connection, frame rates of 10 per second look like still shots. It looks like the person is jumping from shot to shot.

The more samples per second, the smoother the action looks. It only takes 20-30 frames per second to fool us into thinking that the sequence of still images is live action. Films have a sample rate of 22 frames per second. TV has a sample rate of 30 frames per second.

The processing portion of the visuo-spatial sketchpad is an after-seeing process. The retina sends signals to the occipital lobe for breaking down a visual scene into components. The information is then sent in two directions. One stream of information goes to the parietal lobe. The parietal lobe makes a 3-D representation of your environment. It tells the rest of the brain where you are.

In contrast to the “where” pathway, the other stream of visual information from the occipital lobe heads to the temporal lobe. This “what” pathway identifies faces and objects.

Both streams end up in the visuo-spatial sketchpad. The spatial short-term memory indicates where you are and how far you are from a tall object. The object memory tells you that it is a tree, what kind of tree and that you fell out of it last week. All of this is coordinated by the visuo-sketchpad

Episodic Buffer

The third subunit of working memory acts as backup for the other parts. The episodic buffer communicates with both long-term memory and other portions of working memory. This buffer integrates the other functions and adds a sense of time. It helps turn individual items into a cohesive sequence. It’s the timing chain of working memory.

Episodic buffer is not the same as episodic memory, which is a long-term memory system The buffer only stores things long enough to perform a specific task. When attention shifts to another task, all the buffers are reset.

All of the components of working memory function together as a single entity. Although brain trauma can disable one or more subparts, working memory performs seamlessly in a normally functioning brain. Working memory has a limited capacity that is directed to whatever task is receiving our current attention.