Wednesday, 14 March 2012

Evolutionary neurology: depth perception

Level 3+

Jumping spiders jump long distances to catch their prey. This require accurate depth perception. Nagata and colleagues show that jumping spiders use a process called image defocus, which allows depth perception through the comparison of a unfocused image to a focused image within the same eye. A single layer within the spider's eye that could not focus green light nevertheless contained a green sensitive pigment; therefore this layer always receives an unfocused image, while other layers receive images in focus. Spiders are accurate jumpers in green light, but jump short of their target in red light.  

Please see original article and perspective:

Nagata et al. Depth Perception from Image Defocus in a Jumping Spider. Science 27 January 2012: 469-471.

Herberstein & Kemp. A Clearer View from Fuzzy Images. Science 27 January 2012: Vol. 335 no. 6067 pp. 409-410 

"Why is this relevant to neurology? It is an example of convergent evolution; i.e. nature has invented the means of assessing depth several times; it is obviously an important trait. Man mainly uses binocular vision to judge depth; the physical phenomenon is parallax.

Some questions to make you think:
  1. How does someone with uniocular vision or an amblyopic eye judge depth? 
  2. What symptoms would someone with a lack of depth perception complain of?
  3. Is it an important sensory attribute? 
  4. What are the DVLA rules in relation to driving regulations concerning impaired depth perception? 
All these questions should be relevant to someone studying neurology."

1 comment:

  1. I was wondering what the other eyes did if the anterior median eyes were so handy, particularly given that the experimenters deliberately occluded the anterior lateral eyes. Wikipedia has a nice diagram of the other eyes providing nearly 360 degree vision around the spider for threat detection, while the anterior medial eyes have an extremely narrow FOV (consistent with this articles comments about the spiders not having binocular vision).