Brain Function for Visual Processes

[jeeperrs]

I know there are many well educated people on this forum. So, I have a question that I personally find intriguing.

A condition known as "blindsight" is currently being studies in humans. The basis of the problem is that the primary visual cortex has been damaged. If you ask the patient what they see they will report not being able to see anything. However, they often can tell you the position of the object. Blindsight is most noticed when the object moves. Again, the patient doesn't know what the object is but they can tell you if it is moving up, down, left or right at great accuracy. The logic is that in humans we have a higher order process for vision which is the primary visual cortex that we all study (a much later evolutionary process). The issue we are trying to understand is the lower order process for vision; the area that primarily detects movement and orientation of objects. However, we have started to identify the region in the brain associated to the lower order process to be just above the primary visual cortex and just below the parietal lobe.

Now this brings me to my question. I have noticed that my frogs will eat a moving fly before a non moving fly (actually, sometimes they will just move to another moving fly and skip the non moving fly). The toe tapping that everyone observes appears to be a technique to make the flies move, as the moving toe may cause the fly to run away. If the flies need to be moving this would indicate that the visual process in the brain is not necessarily the primary visual cortex but some other process. Has any of our zoo people looked into this? I will have to do some searching but I have heard a neuroscientist associate blindsight to how some reptiles function while eating. I just don't know enough about the frog brain structure to take this logic any further.

[jeeperrs]

I thought I would bring this back up because of all the talk about toe twitching and feeding.

Humans have two visual systems. The most evolved is what we currently understand to be vision, we see something and we focus on that item. This visual process took longer to develop through evolution than the initial visual process, which is present in animals such as frogs. I stumbled across this at a neuroscience presentation and they made quick reference to how frogs catch food.

The logic is, primitive visual process influences aspects such as attention and orientation. Often, something will grab our attention but we will report not knowing or seeing what it was. Animals who have been surgically made blind may orient the eye to something they cannot visually see, also we can see the lens want to focus when something is moving or blink if it moves toward they eye; yet we surgically made them blind. This phenomenon is reported in cases of blindsight in humans. People with blindsight often have damage to a part of their main visual system, yet they can tell when something is moving and the direction it is moving but they will not know what the object was.

So, it may be safe to say that a frog is using this primitive visual system when hunting. If so, the frog does not have to be "seeing" the target as we see the target. The motion of the target is required for the primitive visual field to orient the attention and to then accurately strike the target. It would be my guess that toe tapping is a method to encourage movement in the target. The movement allows for activation of the primitive visual system and an accurate strike can be made. I have not found this in any article but I would speculate that the frog may not have a good visual field of the target at close ranges and the primitive visual system is essential to the hunt (again, that is speculation as I have not found that answer).

I would be interested to hear what the frog experts have to say. I have heard Psychology and Neurology people reference this a few times. However, they always go into detail of the human brain as that is what we study and not the details of the frog brain.

[Ed]

Check Amphibian Biology Volume 3, Sensory Perception, author/editor Heatwole published by Surrey Beatty and Sons

Ed