NEW PAPER out from the lab

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Perceiving polarization with the naked eye: characterization of human polarization sensitivity

Shelby E. Temple, Juliette E. McGregor, Camilla Miles, Laura Graham, Josie Miller, Jordan Buck, Nicholas E. Scott-Samuel, Nicholas W. Roberts

Published 1 July 2015.DOI: 10.1098/rspb.2015.0338  click here for a link to the paper

Like many animals, humans are sensitive to the polarization of light. We can detect the angle of polarization using an entoptic phenomenon called Haidinger's brushes, which is mediated by dichroic carotenoids in the macula lutea. While previous studies have characterized the spectral sensitivity of Haidinger's brushes, other aspects remain unexplored. We developed a novel methodology for presenting gratings in polarization-only contrast at varying degrees of polarization in order to measure the lower limits of human polarized light detection. Participants were, on average, able to perform the task down to a threshold of 56%, with some able to go as low as 23%. This makes humans the most sensitive vertebrate tested to date. Additionally, we quantified a nonlinear relationship between presented and perceived polarization angle when an observer is presented with a rotatable polarized light field. This result confirms a previous theoretical prediction of how uniaxial corneal birefringence impacts the perception of Haidinger's brushes. The rotational dynamics of Haidinger's brushes were then used to calculate corneal retardance. We suggest that psychophysical experiments, based upon the perception of polarized light, are amenable to the production of affordable technologies for self-assessment and longitudinal monitoring of visual dysfunctions such as age-related macular degeneration.

NEW FUNDED PhD PROJECT

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How animals see their world: understanding how animals see better using polarized light

Can you imagine how ultra violet patterns on flowers appear to birds? Or how insects view the polarization patterns in the sky as a navigation compass. As humans we are often not aware of all the visual information that is in our natural environment, and especially how it is used by many different species.

The polarization of light is an important source of information from insects, fish, crustaceans and cephalopods. Whilst we know most about how insects use the polarization of light to navigate, many other aquatic animals use polarization for secret channels of communication, a way of breaking camouflage and for seeing further in scattering visual environments.

We are currently offering a fully funded PhD place starting Oct 2015 to study how and why crustaceans (crabs and stomatopods) see and use polarized light. Ultimately we would like to understand the role polarization plays for these animals and discover when polarization information provides an animal an advantage. The PhD will consist of lab based  behavioural ecology experiments, light and electron microscopy, and fieldwork both in the UK and possibly at the Lizard Island research station, Great Barrier Reef, Australia.

Funding: This PhD is funded through the Engineering and Physical Sciences Research Council (EPSRC) CASE conversion scheme. The CASE partner is DSTL and is restricted to only UK students.

The successful candidate could have a background in either sensory biology or even computer vision and image processing with a strong interest in biology. If you are a student (MSc or final year Undergraduate) with an excellent academic track record from a top-rank institution, and would like more information, please email nicholas.roberts@bristol.ac.uk or check more on our website http://www.ecologyofvision.com

To apply, please follow the instructions on

http://www.bris.ac.uk/prospectus/postgraduate/2014/apply/

We HAVE NOT SET A CLOSING DATE for this application  - applications are encouraged as soon as possible.