MadSci Network: Neuroscience

Re: How does the brain detect moving objects?

Date: Mon Oct 18 09:51:21 1999
Posted By: Terry Hebert, Faculty, Universite de Montreal, Biochemistry, Montréal Heart Institute
Area of science: Neuroscience
ID: 939730938.Ns

Dear Mr. Wagner,
	You ask an interesting question and for some reason they sent it to me, 
a biochemist when they should have sent it to a neurobiologist. Ah well, 
the world isn't perfect so I'll take a shot. Incidentally, I spent many a 
happy hour in Fergus when I was in university! 
	Basically, the retina in your eye is an extension of the brain, i.e. it 
is a part of the central nervous system. The neurons that make up the 
different cell layers in the retina are responsible for the perception of 
either stationary light (i.e. picking out the salient features of objects 
we look at) or motion. One group of cells, called retinal ganglia, contains 
two basic types of cells which can be distinguished on the basis of their 
responses to stationary and moving patterns of light. One class, called X 
cells responds to stationary spots or gratings in a particular manner. The 
other main class, Y cells, responds strongly to changes in illumination or 
to moving stimuli without clear spatial summation. X cells can distinguish 
the fine grain of stationary patterns and Y cells detect objects moving 
across the visual field or changes in intensity. Signals are then sent from 
these neurons to structures located in the brain including the lateral 
geniculate nucleus, the superior colliculus and ultimately the primary 
visual cortex. These signals are processed at each of these locations and 
the information is also disseminated to other sensorimotor areas. Thus, an 
initially simple analysis of edge detection by cells in the retina is 
converted into a sophisticated and integrated response which allows you to 
estimate the speed and direction of moving objects and make the necessary 
motor responses (such as jumping out of the way of a moving car!). I hope 
this helps.

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