http://web.qbi.uq.edu.au/ecovis/justin.htm
When you go to a journal on the Internet to read an article you often find that access is blocked unless you (or your institution) have a subscription or are willing to pay a hefty fee for each article. That is true for Science, however they do allow free access if the article is at least 6 months old. Some journals never give free access. What to do?
One strategy is to go to the web site of the senior (last) author of the paper. All universities and institutes now set up a website with a page for for each of the senior staff. You can Goggle the full name, or use the email address of the last author to get the URL of the institution (it's the segment after the "@"). Once you get to the institution you should be able to find the author.
Sometimes you can find the article you want on the author's web page. Science allows authors to post a link to a free version of the paper.
Even if you don't find a link to the article you want, you may find information on the author's web page that you didn't know existed, and may be far more interesting than the article you were looking for.
Essay- April 2014: Color vision
There was no essay for March 2014.
In the October 2012 essay I described an article in Science magazine about the Mantis shrimp. The front legs of this shrimp (which resemble a praying mantis) have very hard joints which it uses to club and break the shells of prey to expose the soft body which it then eats. The Science article was about the layered structure of the shrimp's shell which gave it the extreme strength to break its prey.
This essay is about the color vision of the same Mantis shrimp. First some background.
To see colors you need several types of photoreceptors in your eyes. Each type contains a dye that adsorbs light of a different color. Humans have three types of color receptors that adsorb red, blue, and green light respectively (we also have receptors that respond to all colors of light, which give us a grey scale image). However, we can discriminate between more than three colors by processing the ratio of intensities from the three color receptors.
The eyes of the mantis shrimp have not 3, but 12 different color receptors [1,2]. Their eyes are much smaller than ours, so the total number of receptors is much smaller, and since there are more types of receptors the number of each type is even smaller. The color receptors are confined to a narrow band across the meddle of the eyes. The eyes of the shrimp rapidly scan the environment, so the reduced number of receptors see most of the visual space. It is proposed that the shrimp uses the raw signals from its 12 types of receptors, and does not take rations. This method is fast and does not require an additional layer of neurons to take ratios to get the "real" colors.
References
[1] Extraordinary color vision. Michael F. Land and Daniel Osorio, Science 343: 381 (2014).
[2] A different form of color visionin Mantis Shrimp. Thoen, Hanne H. et al. Science 343: 411 (2014).