Thread: Are there 'spot detector' neurons in the brain?

I've heard the term 'spot detector' thrown around in some of the brainscience literature, but I vaguely remember learning in university that there are no spot detector neurons in the brain, only on the retina.

So my first question is: are there or are there not spot detector neurons in the brain?

My second question is: if not, then how are we actually able to see spots or know about them? Doesn't being conscious of something require some kind of brain processing of that information? Doesn't the brain have to have some kind of 'detector' mechanism in place in order for us to perceive whatever's being detected? When I look at the stars I surely feel like I'm seeing spots (or points). Same with pencil marks on paper. What brain area is responsible for my perception of these things if not spot detectors?

I've been out of the research world for a while, but there is a fovea on the retina which is like an area of maximal clarity for vision. As for the brain, to my knowledge there are not special neurons nor regions to detect spots. It's just another item which gets interpreted upon receiving the signal like anything else.

Basically, some of the receptor cells in the eye fire. Those cells send a signal to the brain. The cells beside them if not triggered by light do not fire, and so do not send a signal to the brain. When the brain receives the neural impulse, it recognizes that some cells fired and others beside it did not, and this is seen as a spot.

I could be mistaken, but that's my sense on this.

http://en.wikipedia.org/wiki/Fovea_centralis
http://en.wikipedia.org/wiki/Visual_system

So you're saying that if the retina picks up information about the presence of a spot/point, there are neurons in the visual cortex which will fire in response. Correct?

Sort of. The retina contains many receptors. The response is a the level of the individual receptors, not the whole retina. If a receptor receives light, it will fire. The receptor next to it, however, may not receive light and so will not fire. The pattern of "which receptors fired" and "which receptors did not fire" is what the brain interprets.

What might be considered as "spot detection" in the retina might amount to the simple "lateral inhibition" among bipolar cells (ie, the sombrero or Mexican hat function) that occurs there.

IIRC, most of the high-level "detection" occurs in the brain, so the brain contains edge-detecting neurons in part of its visual cortex, and then the brain combines edges and other data (color, movement, distance, etc) from other parts of the visual cortex to detect objects. If such an object is a "spot," then yes, the brain has spot-detecting neurons.

Normally, light from anywhere in the room can hit any part of your body, but your retina is different. The lens in your eye acts as a sorter. Each cell receptor in your retina perceives light coming from exactly one direction and is totally blind to light coming from anywhere else.

So, if there is a red dot on a green background, then some receptors are going to see nothing but just red (no green), and other receptors are going to see nothing but just green (no red). Your brain determines the shape of the object on the basis of which receptors saw red and which ones didn't.