working-memory-threshold-effect

Why did I come up here?

It happened again last night. I went upstairs during a TV commercial to get something from my bedroom, but when I reached my bedroom door, I couldn’t remember what I’d come all the way up there for. I scanned the room. Maybe I would see the thing I meant to retrieve. Once, twice I combed the contents of the room with my eyes.  Nothing.  I gave up. Why does this keep happening? Was this a glimpse into the future I pray I do not inherit from my father?

Why does this keep happening?

No! It’s actually quite normal for this to happen – especially as we age. So if you, too, can’t remember why you stopped what you were doing to go get something or do something in another room – and you only remember what you wanted when you return to the place where you decided you wanted it – you are completely normal. Here’s why.

Visual data is the most important sensory data to our survival. We rely a great deal on our hearing, but we most prefer to process the world around us, and respond to it, based on what we see.

It’s not really true to sa that we see with our eyes. We receive visual data through our eyes, but it is in the occipital lobe that we process that data. It is way back in the back of our skull where we see that round, red object as a kickball, or that open, black circle as a tire. It is in the occipital lobe that we detect form, color, depth, motion, light, and shadow. And it is the occipital lobe that heavily embeds code into our new memories.

Near the center of the skull lies the hippocampus. This is where new memories are formed. This is where I created the new memory that there was a chill in the October air, and a fleece would be nice – better than turning the furnace on. When I formed the memory that I would get my fleece jacket from my bedroom during the next TV break.

Encoded in that memory were the images of the television in front of me, the wood paneling behind it, and the black and white photo hanging above the screen. But when I left the room to climb the stairs, the imagery changed.

The threshold effect.

Because I am not young, my working memory is past its peak. For most people, many aspects of working memory peaks in our 20s or 30s.[i] But for me and most my age, we can’t hold as much information in working memory as we used to hold. So our brain arbitrates which information stays and which is determined to be no longer necessary. The hierarchy is based in part on time[ii], so recency is highly tied to relevance. This creates a sort of threshold effect; when we leave a room, we discard certain bits of data.

So as I was navigating through my house, thinking about what I’d just watched on TV, remembering to move the clothes from the washer to the dryer, recent bits of data were getting shuffled around. Coupled with the fact that my fleece memory was missing bits of visual data, I could not recall the purpose of my trip to the bedroom.

Did scanning the room help?

No! What would have been really helpful would have been the missing data. This is why I could only remember the purpose of my trip upstairs when I sat back down on the sofa and in front of the TV.

Perhaps I could have recovered if I instead had closed my eyes, imagined myself sitting on the sofa, looking at the TV screen, seeing what I was seeing when I decided to get the fleece in the first place. I will try this next time. These days, my stairs are more like a StairMaster® than I would like…

Try this instead.

I bet this happens to you, too, if you are beyond a certain age. While you are standing at the bedroom door, don’t scan the room. Try rewinding to the moment you had the thought to go get something from somewhere else. Visualize what you were looking at when you had the thought. What visual imagery surrounded that? Scan that room. You just might remember why you left and save yourself an extra trip.


[i] Hartshorne, J. K., & Germine, L.T. (2015, April). When does cognitive functioning peak? The asynchronous rise and fall of different cognitive abilities across the life span. Psychological Science. 26(4), 433-443. http://cognitivehealth.tech/wp-content/uploads/2017/01/psychsci2015.pdf

[ii] D’Esposito, M. (2007). From cognitive to neural models of working memory. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 362(1481), 761–772. doi:10.1098/rstb.2007.2086