## Bayesian Recognition

We don’t meet often, but every time we talk, she reminds me that I had failed to recognize her the first time we had met after graduating together from school. Yes, I could claim in my defence that I was seeing her for the first time in over six years. While that might be a valid excuse for most people, it doesn’t apply to me, since I normally claim to have superior long-term memory. If I’ve seen you somewhere before, I ought to recognize you. The only times I don’t I’m pretending, since I don’t want to embarrass you (and myself) by recognizing you while you don’t recognize me (see this incident for an example of this).

The reason for my failure that cold Bangalore evening in December 2006 was that my Bayesian system had failed me. Let me explain, in the process giving you an insight into my Bayesian system which I use to recognize you when I meet you.

About a month or two back, I was at a friend’s wedding, which is where I hit upon this term “Bayesian recognition” to explain this phenomenon  (which I’ve been practicing for ages). Now, this friend whose wedding I was attending was one year my junior at two different schools. As you might expect at an event where you and the host share more than one social network, there were a lot of familiar faces. Some people I knew fairly well, and could easily recognize. But the others had to go through a “Bayesian search”.

So when I saw someone who was one of three people I know – let’s say X, Y and Z. In order to determine which of these this person is, I would ask myself two questions – firstly, what were the prior odds that the person I saw could be each of X, Y or Z. Secondly, what were the odds of each of X, Y and Z being there at that event. Note that the latter is important. For example, if someone at the event looks like you and I know (for example) that you are currently in another country, despite the strong resemblance I can discount the possibility that that person is you, and go ahead with my search.

Note that this differs from “frequentist recognition”, where I only look at the person’s face and try and understand who he/she most resembles, without any thought to the odds that that person is there. Frequentist recognition can lead to a large number of false positives, and after a few rounds of embarrassment, you start giving up on recognizing, and many a possible reunion thus gets missed. Bayesian recognition, on the other hand, restricts your field of search (to the people who you give good odds of being there), prevents you from being distracted and increases your chances of making a good recognition.

So why did Bayesian recognition fail me when I met this former classmate back in 2006? The problem was her company. She had come for this Deep Purple concert with another friend of mine, who was my classmate in another school (and who I had been in touch with, and so easily recognized). I had no clue that these two were friends (it turned out they didn’t know each other that well – they had come there with a common friend). So when this girl (the one I didn’t recognize) popped up with “Hey SK! Do you remember me?” I assumed that she was someone I knew from the same school as the other girl I was meeting, and that wrongly restricted my search space. And so my mind was trying to map her to my friends from school 1, while she happened to be a friend from school 2. And my search returned a blank, and my legendary long-term memory skills were embarrassed.

I must mention here, though, that this is possibly the only time that my Bayesian recognition model has acted up, and refused to recognize someone I know. There have been 2-3 false positives, but this has been the only negative. And when you consider the sample size to be all the people I have recognized in different places, this is small indeed.

Oh, and after failing to recognize her then, I’ve kept in touch with this friend.

## You know, I have this condition

My memory cache (talking about my memory, not my computer’s or my laptop) seems to have suddenly diminished. My life seems to have become very Markovian. In fact, a few months back, I used to think that a Markovian existence is the best kind of existence, since in that kind of a situation, you respond to every situation on instinct, don’t make plans, are always on the lookout to optimize, etc. Now that I’ve actually reached close to that state, I don’t know if it’s desirable.

So basically my already weak short-term memory has become weaker. I’ve already talked about one paradox – I’ve traditionally had great long-term memory but awful short-term memory. I remember strange things, dates when those things happened, the colour of the shirt I was wearing when certain things happened, etc. And I typically can’t remember much of what someone told me recently, or what my mom asked me to buy at the market. The explanation I give myself for this is that I’m weak with details – and missing out on details is not as critical when you are talking about long-term stuff as it is in the short term.

Anyways what has been happening to me of late is that days seem very long. Towards the evening of most days, I really can’t remember what I did that morning. Ok, it’s not that bad – I can remember with some effort, but that effort is approximately equal to the effort required to remember what I did a year ago or some such. Once I get into doing a certain activity, I completely forget about everything I was doing prior to that particular activity – it all goes into memory, rather than staying in cache (like it used to earlier).

The most interesting (and scary) part of the deal is that my memory loss seems to be especially bad when it comes to numbers. This evening, I was out shopping for a computer table. I checked out stuff at some four shops, but as soon as I entered one shop, I completely forgot about the prices quoted in the previous shop. So I actually didn’t have a handle on comparative price. Tomorrow, I’ll mostly go buy that table which I liked best, and trust the shopkeeper to rememeber the price that I’ve bargained.

Considering that I’ve traditionally been a “numbers guy” and have a good eye for numbers, this is extremely scary. I just hope it’s some minor problem caused due to something like lack of sleep (i sleep only 8 hours a day) or hunger (i eat at least 6 times a day) and not something more serious. For example, I use a prepaid mobile phone. And each time after a call or a message I see the balance, I don’t know how much I’ve spent becasue I don’t know the previous balance. I remember that the last time I used a pre-paid phone (the same number; back wehn i was at IIMB) I would meticulously keep track of expenses.

While the condition lasts, I seem to be enjoying myself. Days seem so much longer, so I can relax so much more in the given time. I occasionally feel bored, but quickly find myself something to do, and get engrossed in it. I don’t get easily distracted like I used to. I don’t multitask (earlier I was a compulsive multitasker). I’m able to concentrate again, like I used to during the days of blindfold chess in the backbench. I don’t get worried. I don’t remember a thing from my previous jobs – though I’m sure I can pull it up from secondary memory if absolutely required.

But you know, I have this condition..