Science: Our working Memory can only track 4 items at a time.

According to a new US study, our working memory is surprisingly lacking in mental prowess and can only track four items at a time.

The study also reveals that our working memory for space and time can recruit our extraordinary visual and auditory processing networks when needed.

Working memory is the system that is responsible for the temporary holding and processing of information.

While it is sometimes used synonymously with short term memory two concepts are distinct.

We can hold far more information in our short-term memory, because it does not entail the manipulation or organisation of material.

Working memory is generally considered to have limited capacity, and researchers had previously believe it could only hold seven ‘chunks’ of information.

This could be digits, letters, words, or other units, but anything more, and the memory network struggles. Now that number has been reduced to four.

Prior to this work, which appears in the journal Neuron, scientists believed that visual information from the eyes and auditory information from the ears merged.

They would then reach the frontal lobes, where abstract thought occurs.

The team of BU scientists, which also included Auditory Neuroscience Laboratory Director Barbara Shinn-Cunningham, performed functional MRI experiments to test the conventional wisdom

The experiments revealed that what was thought to be one large attention network in the frontal lobe is actually two interleaved attention networks; one supporting vision and one supporting hearing. 

The scientists wondered how closely the networks cooperate, and when. 'Our visual system is terrific at processing space, but just okay at processing time,' says Somers.

'But our auditory system is amazing for processing time, but not very good for space.' 

'In other words, when a person tries to locate something in space, like a speeding ambulance, vision trumps hearing. But try to keep track of intervals in time, and hearing wins.

But what happens when you have to use the inferior system? For instance, if you had to remember the location of several noises, with no visible cues.

That's what the scientists wanted to find out. This led to another set of experiments, where they asked subjects to complete spatial tasks with their hearing, and timing tasks with their vision.

The experiments showed that the two networks work together closely, with the visual network helping us understand what's happening in space, and the auditory network helping us understand events occurring over time.

'In a sense, we see space even if the spatial information is not visual, and we hear timing and rhythms even if the timing information is not auditory,' said Somers. 

The scientists say that, in this way, vision and hearing each help boost each other's capabilities.

Fine-tuning our map of the brain may eventually lead to a deeper understanding of attention disorders and better tools for predicting the outcome of brain injuries.