NOTICE: Posting schedule is irregular. I hope to get back to a regular schedule as the day-job allows.

Sunday, March 13, 2011

*IS* the hand quicker than the eye?

We have sort of backed into a description of the Frontal Lobe via the description of motor cortex.  Frontal Lobe is largely responsible for the *output* functions of the brain: muscle movements, speech, and decision-making.  I will cover the latter, termed “executive function” in the next blog, and concentrate on …


What is it Ratley?




Oh.  Excuse me, folks, but I have to go rescue Ratface.  He’s gotten his paws caught in a mousetrap again.  The lad has *no* paw-eye coordination.  Ratley?  Want to take over for a minute?

(squeak.  Sque-eek. Squick.  Squeek.)


Hah.  Well, Ratface has no paw-eye coordination, then again, he’s participated in a few too many of those head-injury experiments. 

See, there actually *is* a place in the brain that controls eye movements, assists in tracking moving objects and provides signals for coordinating movement with respect to those ye movements.  The figure that Dr. Tedd has so thoughtfully provided at the right shows the location of the “Frontal Eye Fields” with the primary job of moving the eyes to track moving objects.  In the previous discussion of the visual system, Teddy mentioned that there are neurons in the thalamus and brainstem that detect moving objects.  However, in order to continue to follow a moving object, it is necessary to move the eyes to keep an object centered on the retina. Neurons in the Frontal Eye Fields are active in conjunction with location, direction and speed of *eye* motion and provide control of the eye muscles through Cranial Nerve III, the occulomotor nerve.  Incidentally, neurons in the surrounding areas are also associated with light sensitivity, pupil dilation and focusing the lens – the latter an ability that Teddy is severely lacking as he gets older, thus the need for bifocals.

You will note that the eye regions of the frontal lobe are quite close to the hand areas of motor cortex.  Yes, there *is* a logic to this, since a major element of muscle movement is what we LabRats like to call “goal acquisition.”  Like the cheese at the end of the maze, each muscle movement has a goal.  If muscle movement used *only* the position feedback from the joints and muscles, each movement would end with a lot of minor movements (tremors or oscillations).  Instead, visual feedback from your eyes provides information that, yes, your foot *is* on the stair, your hand *is* on the door handle, etc.  This is very important to *stopping* movement when the goal is reached.

Hand-eye coordination?  Yeah, all Frontal Lobe functions.  Feedback from motor cortex to cerebellum, to muscles – coupled with visual feedback – helps guide the hand to the appropriate place.  Rapid eye movement makes sure that all of the objects are in view.  The process is extremely fast, and simply requires practice to get used to it.


Oh, hi, Boss!

Thanks, Ratley.  Now that Ratface is out of the trap, the key question:  *Is* the hand quicker than the eye? 


Visual tracking is extremely fast, and the eye is extremely sensitive to movement.  In fact, we know that it requires over 16 times changes per second before we stop  seeing the individual images and start seeing the continuous video motion.  We can still detect discontinuities at up to 60 frames per second, which is one reason why the best high-definition and IMAX films are projected at over 70 frames per second.  In the famous “three-card monty”  card trick, the hands are certainly not moving faster than the eye can track.  Rather, the “trick’ is distraction and deception.  The con-man’s speech, and certain hand passes that block the victim’s view of the other hand are the key elements of deception that allow the operator to relieve the “mark” of his money more often than not.

Hand-eye coordination is just another example of one of the associative functions of the brain, and as has been repeatedly mentioned in other blogs, the associative functions are often more important than the simple sensory inputs.  And of course, association is the key element of memory, which are the topics for next week.

On behalf of myself and the LabRats --- Ratface, NO!  (snap) – uh, excuse me, gotta go, see you next time!

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