Flashcards in Polarisation vision Deck (34):
dont say polarized light...
polarization of light
define polarization vision
using polarization properties of light to distinguish fields of view of the same size and shape.
what is linear polarization?
when the peaks and troughs of the electric and magnetic fields are aligned/in phase.
can he horizontal or vertically polarized based on orientation of electric field.
what is circular polarization?
two electric waves oriented at a right angle, and out of phase, the resultant wave between them goes in a spiral.
define angle and degree of polarisation
AoP - average direction that each wave is
DoP - distribution of angles, given as a percentage. 0% if all random, non polarized.
what 3 requirements are needed for polarization sensitivity?
1. visual pigment sensitive to polarization
2. photoreceptors must be aligned to provide constant and tractable information
3 animal needs to process the information in a way which is relevant to beh. (even though humanscan see polarisation of light, it isnt beh relevant so we dont notice it).
describe how retinol is dichroic.
Differential absorption of polarizations. Doesn't absorb polrizations perpendicular to long axis of molecule.
It does absorb polarisations which are parallel to long axis. in this direction, electrons can oscillate with the electric field.
what is the textbook explanation of polarisation absorbance?
proteins in membrane naturally rotate, so rhodopsin will become out of orientation with polarization direction, whereas other rhodopsin molecules will become aligned. if a flash of light bleaches rhodopsin, rotational diffusion causes recovery of absorbance.
why might the textbook view not be correct?
all studies were done on rods, when actually cones are the sensitive ones to polarized light. also all studies done on Rana pipiens - frog, and there is no evidence for polarization sensitivity in this species.
what is the evidence for polarization sensitivity?
1. side on illumination of the chromophore in a rod/cone, shows two different absorption spectra when illuminated parallel to rod and perpendicular to rod. the ratio of absorbances is the dichoric ratio, DR.
what is the DR of UV cones and double cones?
what is the 2nd stage of detecting polarization of light
an ordered detector
eg regular photoreceptor mosaics in salmon and goldfish. Double cones arranged in 90 degree orientation to be able to compare angles of polarization.
what evidence is there that cones dont undergo rotational diffusion
rhodopsin forms and ordered array of dimers in photoreceptors, suggesting they aren't free to rotate.
cryo EM images show how chromophores are aligned within cones, and this alignment makes them sensitive to polarization.
How is information regarding polarization sensitivity relayed to the brain?
Seen from electrophys recordings from that the optic nerve in salmon demonstrates polarization sensitivity in particular spectral channels. UV, MWS and LWS channels give highest PS values. max when polarization is vertical, least when horizontal.
how does invert PS differ from vertebrate?
the microvilli are aligned, and are dichroic, and parallel to in coming light (in vertebrates, it is the chromphores which are aligned).
microvilli do not spin, due to different structure of opsins,which have a long tail and interact, not allowing them to spin. unsure if they form dimers. DR of 1.2
which part of the insect eye is polarisation sensitive?
Dorsal Rim area. maps out the polarization patterns in the sky. cellular orientation change to match the overhead polarization pattern.
Many species have PS across the whole eye.
what do insects use polarisation for?
orientation, to find water
why are crustacean photoreceptors different to insect and vertebrate?
How is the info transduced?
they are intrinsically polarisation sensitive, as microvilli are layered at 90 degrees. gives 2 channels (1,4,5 vs 2,3,6,7) of Pol info to be compared.
each cell projects onto layers of the lamina in the brain, either epl1 or epl2. then monpolar cells M3 and M4 relay the info to the medulla.
whats the difference betwee a cue and a signal?
cue - environmental eg colour of the sun. polarisation is a cue for navigation.
signal - under NS. eg use polarization for target discrimination.
what causes polarization of light?
caused by raleigh scattering. angle of polarization is directly perpendicular to the sun. as the position of sun changes, band of strongest polarization changes, creating a predictable pattern which insects use to navigate.
underwater, the band of max pol surrounds the observer. sky polarization pattern enters the water through Snell's window.
is light polarized by reflection
AoP is parallel to the surface.
suggested recently that glass buildings create pol pollution to insects which use pol to identify water.
examples of animals which use polarization to signal
stomatopods' maxillopods and uropods.
when was polarisation sensitivity first seen in insects?
1920s, insects can only walk straight and navigate home if some blue sky is visible.
also observed by Karl von Frisch in 40s in honeybees.
what is requires for insect polarization naviation?
only works if UV light is present as the DRA is UV sensitive.
what did Rudgier Wehner discover?
-Saharan ants use sky polarization when navigating. join together path integration and celestial cues.
- noticed that there is sometimes a 180 degree bimodial distribution of orientation data, in a choice test, which suggests they cannot absolutely tell the position of the sun.
What have more careful studies of polarisation sensitivity shown?
ants showed 180 degree bimodial distribution when trained under a restricted skylight pattern and tested under full sky.
can cope with only a restricted skylight pattern if it is experienced for the whole foraging trip.
how do dung beetles travel in a straight line?
use a variety of celestial and visual cues to roll balls in a straight line.
sun, moon, solar polarization, intensity gradient and milky way.
Moon creates polarization pattern used by nocturnal dung beetles. Use a heirarchy of cue information, which polarization dominates in crepuscular periods.
which animals use a time compensated compass and what is that?
navigate over much longer distances, so takes longer. therefore light intensity and colour ratios are changing so must incorporate this in the map in their brain.
how is polarization information mapped in the locust brain?
polarization coding network is in the locust central complex of the brain.
Protocerebral bridge encodes directions. There is unusual columnar architecture - each column is tuned to a diff polarization. v efficient. activity in the PB is correlated to the orientation of the locust
what can be used in polarisation experiments to deliver different levels of polarization?
use LCD to present different stimuli, therefore minimising interference by a human and other info changing.
present pattens on a LCD with glass removed to animal and observe colour changes if the see polarization.
can animals see all polarization?
no there if a threshold in the angle and degree of polarization above which they can detect changes.
Give an example of animals which create a polarization signal
1. Heliconus butterflies - irridescent patterns create polarisation. Exploited in mate choice.
2. haptosquillids (stomatopods)- use pol and structural colour as a visual signal. blue signals on 1st maxillipeds. 4 species have an innate preference for horizontal pol.
describe a habitat which has pol glare
mudflat, light reflecting off water gets polarized.
increases contrast of animals against bright background creating silhouettes. advantageous to fiddler crabs: early detection of preds and conspecifics. Semi transparent claws boost intensity and pol contrast.