(Artificial Life, vol. 16, 1, Winter 2010, The MIT Press; cover by Philip Beesley´s Epithelium, an installation at the Siegel Gallery at Pratt Institute of Design in Brooklyn, N.Y., 2008).
On this month I would like to expose an interesting model of cultural transmission developed by Chris Marriott, James Parker and Jörg Denzinger at University of Calgary. It is called PANDAS and simulates the effects of an imitation mechanism on a population of animats (artificial animals) capable of individual ontogenetic learning.
Let be a world inhabited by animats and consisting of a discrete grid that contains besides the following objects: food, water, cave and tree. The world obeys several rules of evolution: (a) no object can occupy the same cell as a tree; (b) all objects are stationary except pands; (c) water, caves, and trees are static and (d) food is depleted when used, and grows over time. For the pandas, we have these rules: (1) pandas can move one cell in one of eight directions (N,NE,E,SE,S,SW,W,NW); (2) pandas obtain food energy, water energy, rest energy and have a health parameter and, in every round, lose a fixed amount of food energy, water energy and rest energy; (3) pandas die if any parameter in (2), drops below cero; (4) a dead panda is removed from the grid and replaced with food; (5) a panda can only mate with another mating panda; (6) a panda can create a new panda by mating or spawning but a panda can only mate or spawn when it has an excess of all energy types; (7) pandas can only interact with objects in the same cell; (8) a panda can fight with another panda, reducing the target panda´s health and (9) a panda´s health automatically recovers, at an energy cost.
A panda has only a one-cell perception range and has a limited internal sense allowing it to monitor its energy levels. All perception is done using input daemons. Daemons are similar to nodes in a network playing a specific role. The input daemons that form the input layer of the panda include 9 daemons for each object in the environment (see food, see water, see cave, see tree). There is one daemon for each of the cells in the perceptual range of the panda. The input layer contains the following set of daemons (food energy, water energy, rest energy, hungry, thirsty, tired). The cognitive cycle of a panda begins with taking input from the environment and activating input daemons, and ends with an action selected. When an action has been selected, it is executed in the system and the cycle begins with the new situation.
The model is very interesting because pandas can engage in three types of adaptation: the genome of a panda encodes both "physical properties" (the panda interacts with its environment) and "mental properties" (the panda maintains its internal organization). To study the effects of the imitation on the populations of pandas, it is considered a group of pandas without imitation drive and unable to perceive directly and a second group of imitating pandas. The authors use the life span of the pandas as an indicator of their success. To do this, they introduce a parameter called the elder age, that is, an arbitrarily selected age such that when a panda reaches this age before dying, is considered successful and the value is used for the measurement of frequency. According to Marriott, Parker and Denzinger, the data of the experiments using this model, show that the median frequencies for imitating pandas are hogher than the frequencies for non-imitating pandas. Obviously, the imitating pandas have the tendency to group together, being particularly strong in newborn pandas. The model supports that mechanisms of cultural transmission can increase the frequency of success in a population but the authors look for extending it to the more sophisticated mechanisms of the "true imitation" because they think that the attribution of higher-order intentionality to artificial agents is something pending nowadays.
