A cognitive analysis of tagging

Understanding tagging: a simple explanation for users, designers and technologists
(or how the lower cognitive cost of tagging makes it popular)

The first thing to understand about tagging is that its not categorization. If categorization is putting an item in THE right category, then tagging is simply noting whatever comes to mind. Lets try to understand when someone tags an item, e.g., a book on del.icio.us, or a picture on Flickr.

Stage 1: Related Category Activation The first stage is the computation of similarity between the item and candidate concepts. For example, I come across the book “Snowcrash” in my library. Immediately a number of related semantic concepts get activated: “book”, “science fiction”, “Neal Stephenson”, “Zodiac”. Other concepts might be more personal; e.g., “favorite author”, “airplane trip”. Still other concepts activated might be more about the physical characteristics, e.g., “paperback”, “bad condition”.

How do we know this? Cognitive psychologists have explored this phenomenon by asking by asking people to list semantic associations with an object, and mapping the type and frequency of associations. Another method is to use implicit memory measures to probe what concepts have been activated. With the advent of fMRI, it is possible to correlate such concept activation to changes in blood flow to difference parts of the brain. The details of this are not relevant for the present discussion, what’s relevant is that there is broad agreement about such conceptual activation in cognitive psychology.

So far we have learnt how related concepts are activated. Writing down some of these concepts is easy enough. For Snowcrash, I note down some of the activated concepts, namely, "sciencefiction", "toread", Neal Stephenson". There is no filtering (or choices about which association to write down). I can simply note as many activated concepts as I want to. This is how tagging works, cognitively speaking. Yes, it’s that simple. On the other hand, the work for categorization is just beginning.

Stage 2: The decision

If I was to categorize SnowCrash, my work is not yet done. Now that I have candidate categories, I need to make the DECISION. What category is the right one? Cognitively, the process is fairly simple - you compute similarity between present item and candidate categories. A function called Shepard-Luce(ppt) describes how people make this decision. (The process sounds intimidating, but generally its not. Choosing the best category is something we do all the time. We see an animal - it could be a dog or wolf. We make a quick judgment. This is a basic cognitive process - putting things into categories. Even pigeons
can do it. There is evidence that babies
can categorize.

Cognitively, we are equipped to handle making category decisions. In fact, we categorize all the time. Recognize the table as a table, the couch as a type of chair, and the palm as a plant. So, why do we find this so difficult in the digital realm - to put our email into folders, categorize our bookmarks, sort our documents. Here are some factors that lead to what I call the “post-activation analysis paralysis”.

First, there is less cultural consensus around items we categorize in the digital domain. Categorization is often based on cultural knowledge. For example, over the years we learn the cultural consensus regarding the boundary between wolf and dog, couch and chair, fruit and vegetable. With digital objects, there is less cultural knowledge about the categories - in fact, one purpose that tagging serves is transmitting cultural knowledge about our constantly evolving digital lives. In the digital world, we don’t just categorize an object, we also optimize its future findability. We need to consider not just the most likely category, but also where we are most likely to look for the item at the time of finding. These two questions might lead to conflicting answers, and complicate the categorization process.

Also, with digital objects, it’s not just adhoc categorization - put an object into a category, any category that comes to mind. We need to consider the overall categorical scheme. Is my scheme becoming unbalanced? Do I have too many items in one category, and too few in another? If I put everything in one category, I will never be able to find anything. Do I need a new category for this item? Does it even fit into this scheme? The need to consider the overall categorical scheme is much more important in the digital realm, than in everyday categorization decisions. For example, I come across an animal; I categorize it as a dog. I don’t need to worry that my mental dog category has become too large, that I might need subcategories. Cognitively, it is sufficient to make local decisions about objects we encounter, the brain does the magic computation, and my animal taxonomy evolves. As I become an expert on dogs I evolve sub-categories for spaniels, dachshunds and terriers, without explicitly thinking about the structure. Next time, I encounter a terrier, magically, the terrier subcategory gets activated. Think of how much work it would take for something like to happen with our email folders.

Finally, there are no second chances in categorizing digital objects. Well there are - but those are fairly expensive. You need to go into the first category, retrieve the item, and put it into the second. This is where user interface for categorization comes into play - most systems assume that you are done with an item once you categorize it. It’s taken away from you. The brilliance of Gmail was to separate the tagging from the archiving. Start thinking of all this and you land into “post activation analysis paralysis”.
A state of fear that you will make the wrong decision. And the item will be lost forever - it will land in some deep well, some hard to access branch of the tree and disappear from your view and attention.

We come back to the question that we started with - why is tagging simpler. In my opinion, tagging eliminates the decision - (choosing the right category), and takes away the analysis-paralysis stage for most people. (Note that some people might still freeze up in deciding between different tags, or figuring out ways to optimize future findability. These are valid concerns that tagging systems can address better than they do now).

Another observation about tagging - it provides immediate self and social feedback. Each tag tells you a little about what you are interested
in. And you find out the social context for that bit of self-knowledge. How do others view that item? Together this piecemeal feedback creates a cycle of positive reinforcement, so that you are motivated to tag even more. This might not make tagging easier, but it does make it more fun.

To conclude, the beauty of tagging is that it taps into an existing cognitive process without adding add much cognitive cost. At the cognitive level, people already make local, conceptual observations. Tagging decouples these conceptual observations from concerns about the overall categorical scheme. The challenge for tagging systems is to then do what the brain does - intelligent computation to make sense of these local observations, and an efficient, predictable way to ensure findability.

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1. I refer to tagging as on flickr and del.icio.us - associating an item with a bunch of words, writing down those associations. In this article I have focused on the input part of the tagging process - the individual assigning the tag, not the output part - or the finding information through tags.)

2. For any cognitive scientists reading this article - yes I am well aware that the cognitive explanation is a simplified version, glossing over many of the details. I believe it captures the broad jist of how it works though.

 

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