Wednesday, December 21, 2011

An Analogy for Top-Down to Bottom-Up Communication: Cake Baking and Tasting

The creation of mental imagery by bottom-up sensory areas, and the subsequent analysis of this by top-down association areas are like a cycle of interactions between a cake baker and a cake taster. The cake baker is the sensory area, the mental imagery that is built is analogous to the finished cake. We have more than one sensory area in the brain so we have multiple cake bakers but for now, let’s just take vision for example. The visual area takes the specifications (ingredients) handed down to it from higher-order, top-down, association areas such as the PFC (the cake taster).
The visual sensory area has tons of baking experience, it is a genius of a baker, but it can only use a certain proportion of the specifications handed down to it to bake the cake. The visual area baker says: “ok, I see the ingredients that the PFC has given me, I know how to combine some of them to make a suitable cake that obeys the laws held in my networks, but some of the ingredients are just not going to work with the others.” The baker might be able to bake a cake with ¾ of the requested ingredients, combining them in certain ways that are consistent with its past baking experiences. 25% of the ingredients the top-down areas are recommending, have to be left aside though. Another caveat, the baker cannot bake the cake using only the ingredients handed down to it by the top-down areas. It has to use other ingredients as it sees fit. This is almost like a baker that says, “ok I can use these ingredients, but to make it work, I have to throw in a few of my own.” So the finished recipe for the cake (the visual imagery that is created) might be made up by 75% of the ingredients recommended to the baker but perhaps 25% of the ingredients used were improvised, not mentioned by the top-down taster (PFC).
So the top-down cake taster takes the cake once the bottom-up areas finish it and takes a bite. In the brain, this happens when higher order brain areas begin to perceive the mental imagery that has been mapped topologically across the early sensory area. The cake taster can appreciate the mix of different elements together and is able to integrate all of these different ingredients into one overall, wholistic taste. To the baker, they are just ingredients. To the taster, the ingredients come together to be more than the sum of their parts. Then the cake baker decides, from the taste of the cake, what ingredients need to be changed. It will say: “I like this aroma, I liked this taste, these ingredients go well together, do it all over baker, but this time use the following ingredients…” The baker takes these ingredients and makes a new cake. The fact that they each pay attention to what the other is doing, but selectively ignore certain aspects keeps their reciprocating conversation going.
 If the visual area is a cake maker, perhaps the auditory area is a soup maker. Importantly soup ingredients can affect cake ingredients, just like processes in the visual areas can affect those in the auditory areas. The taster eats the two, the cake and the soup together, and considers it as an overall meal, and then lets its assessment of the meal affect the ingredients that it hands back down to both the baker and the soup maker. The more intelligent the animal is, the more similar each set of ingredients handed down is to the last. The more scattered and impulsive the animal, the less similarity there is between subsequent cakes.

Read the full article that I wrote on this topic here: