I recently read a paper by Fang Wu and Bernardo Huberman called “Novelty and collective attention“. This paper speak about how attention to novel items propagates and eventually fades among large populations. In particular, they analyzed the dynamics of collective attention among 1 million users of the interactive website digg.com. This website allows its users to submit news stories they find while they browse the internet. Each new submission can be read by other members. If they find it interesting, they can add a digg point to it. The number of digg a submission received is displayed next to each story’s headline and indicates how many users where interested in this news. Moreover, The more digg a news received in a given period of time, the more visible to the audience of the website it becomes and the more likely it receives additionnal digg. Most popular news eventually reach the digg.com frontpage. We have here a positive feedback that tends to highlight the news that are interesting for most of the website users.

Wu and Huberman proposed that this positive feedback is counterbalanced by a negative one driven by the decay in novelty of the news: the older a news, the less it interests people and the less potentially interested people remain uninformed. After a certain time, the news receives less and less digg and gets replaced by newer stories.

The paper of Wu and Huberman particularly interested me because of the striking similarities ants foraging behaviour. Ants communicate with each other through the use of pheromones. These pheromones are chemical substances that attract other ants. For instance, once an ant has found a food source, she quickly comes back to the nest and lays down a pheromone trail. This trail will then guide other workers from the nest toward the food source. When the recruited ants come back to the nest, they lay down their own pheromone on the trail and reinforce the pathway. The trail formation therefore results from a positive feedback: the more ants use a trail, the more attractive the trail becomes.

Interestingly when several food sources are available, workers modulate their trail-laying intensity as a function of the quality of the food source. Workers therefore preferentially select and reinforce rich food sources while pheromone evaporation little by little wipe out the paths towards poor ones. This competition between rich and poor sources eventually directs the colony activity on the most profitable option. If the selected food source run out, ants stops laying pheromone and eventually the trail vanishes allowing the exploitation of other food sources.

In these two ewamples, a transfer of information occurs thanks to stigmergic (or indirect) interactions. An individual having an information releases in the environment a suitable signal that can be used by another individual at a later time. This signal is a pheromone deposit in ants and a digg point in humans. Then a reinforcing mechanism enhances the constrast between different information and put forward the one that presents an interest for most of (if not all) the individuals. The transitional nature of the signal substrate (chemicals in ants, attention in human beings) allows the collective system to retain this information for a certain period of time and then to drop it once it becomes not profitable/interesting anymore.

For more information:

1. Novelty and collective attention. Fang Wu and Bernardo Huberman. Proceedings of the National Academy of Sciences, 2007, p. 0704916104.
2. The biological principles of swarm intelligence. Simon Garnier, Jacques Gautrais and Guy Theraulaz. Swarm Intelligence, 2007, vol. 1, pp. 3-31.
3. Bernardo Huberman conference at ECCS.
4. Guy Theraulaz conference at ECCS.