Tag Archives: Bertrand Russell

The death of the pure percept — otoacoustic division

Rooming with 2 philosophy majors warps the mind even if it was 60 years ago.  Conundrums raised back then still hang around.  It was the heyday of Bertrand Russell before he became a crank.  One idea being bandied about back then was the ‘pure percept’ — a sensation produced by the periphery  before the brain got to mucking about with it.   My memory about the concept was a bit foggy so who better to ask than two philosophers I knew.

The first was my nephew, a Rhodes in philosophy, now an attorney with a Yale degree.  I got this back when I asked —

I would be delighted to be able to tell you that my two bachelors’ degrees in philosophy — from the leading faculties on either side of the Atlantic — leave me more than prepared to answer your question. Unfortunately, it would appear I wasn’t that diligent. I focused on moral and political philosophy, and although the idea of a “pure precept” rings a bell, I can’t claim to have a concrete grasp on what that phrase means, much less a commanding one.

 Just shows what a Yale degree does to the mind.

So I asked a classmate, now an emeritus prof. of philosophy and got this back
This pp nonsense was concocted because Empiricists [Es]–inc. Russell, in his more empiricistic moods–believed that the existence of pp was a necessary condition for empirical knowledge. /Why? –>
1. From Plato to Descartes, philosophers often held that genuine Knowledge [K] requires beliefs that are “indubitable” [=beyond any possible doubt]; that is, a belief counts as K only if it [or at least its ultimate source] is beyond doubt. If there were no such indubitable source for belief, skepticism would win: no genuine K, because no beliefs are beyond doubt. “Pure percepts” were supposed to provide the indubitable source for empirical K.
2. Empirical K must originate in sensory data [=percepts] that can’t be wrong, because they simply copy external reality w/o any cognitive “shopping” [as in Photoshop]. In order to avoid any possible ‘error’, percepts must be pure in that they involve no interpretation [= error-prone cognitive manipulation].
{Those Es who contend  that all K derives from our senses tend to ignore mathematical and other allegedly a priori K, which does not “copy” the sensible world.} In sum, pp are sensory data prior to [=unmediated by] any cognitive processing.

So it seems as though the concept is no longer taken seriously.

I’ve written about this before — as it applies to the retina — https://luysii.wordpress.com/2013/02/11/retinal-physiology-and-the-demise-of-the-pure-percept/

This time it involves the ear and eye movements.  Time for some anatomy.  Behind the eardrum are 3 tiny little bones (malleus, incus and stapes — the latter looking just like a stirrup with the foot plate pressed against an opening in the bone to communicate movement of the eardrum produced by sound waves to the delicate mechanisms of the inner ear).  There is a a tiny muscle just 1 millimeter long called the stapedius which stabilizes the stapes making it vibrate less protecting the inner ear against loud sounds.  There is another muscle called the tensor tympani which tenses the eardrum meaning that external sounds vibrate it less.  It protects us against loud sounds.

An article in PNAS (vol. 115 pp. 1309 – E1318 ’18) shows that just moving your eyes to a target causes the eardrum to oscillate.  Even more interesting, the eardrum movements occur 10 milliSeconds before you move your eye.  The oscillations last throughout the eye movement and will into subsequent periods of steady fixation.

It is well recognized in addition to the brain receiving nerve input from the inner ear, it sends nerves to the inner ear to control it.  So ‘the brain’ is controlling the sense organs proving input to it.  Of course the whole question of control in a situation with feedback is up in the air — see https://luysii.wordpress.com/2011/11/20/life-may-not-be-like-a-well-but-control-of-events-in-the-cell-is-like-a-box-spring-mattress/

As soon as feedback (or simultaneous influence) enters the picture it becomes like the three body problem in physics, where 3 objects influence each other’s motion at the same time by the gravitational force. As John Gribbin (former science writer at Natureand now prolific author) said in his book ‘Deep Simplicity’, “It’s important to appreciate, though, that the lack of solutions to the three-body problem is not caused by our human deficiencies as mathematicians; it is built into the laws of mathematics.” As John Gribbin (former science writer at Natureand now prolific author) said in his book ‘Deep Simplicity’, “It’s important to appreciate, though, that the lack of solutions to the three-body problem is not caused by our human deficiencies as mathematicians; it is built into the laws of mathematics.” The physics problem is actually much easier than the brain because we know the exact strength and form of the gravitational force. We aren’t even close to this for a single synapse.

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Retinal physiology and the demise of the pure percept

Rooming with 2 philosophy majors warps the mind even if it was 50 years ago.  Conundrums raised back then still hang around.  It was the heyday of Bertrand Russell before he became a crank.  One idea being bandied about back then was the ‘pure percept’ — a sensation produced by the periphery  before the brain got to mucking about with it.   My memory about the concept was a bit foggy so who better to ask than two philosophers I knew.

The first was my nephew, a Rhodes in philosophy, now an attorney with a Yale degree.  I got this back when I asked —

I would be delighted to be able to tell you that my two bachelors’ degrees in philosophy — from the leading faculties on either side of the Atlantic — leave me more than prepared to answer your question. Unfortunately, it would appear I wasn’t that diligent. I focused on moral and political philosophy, and although the idea of a “pure precept” rings a bell, I can’t claim to have a concrete grasp on what that phrase means, much less a commanding one.

 Just shows what a Yale degree does to the mind.

So I asked a classmate, now an emeritus prof. of philosophy and got this back
This pp nonsense was concocted because Empiricists [Es]–inc. Russell, in his more empiricistic moods–believed that the existence of pp was a necessary condition for empirical knowledge. /Why? –>
1. From Plato to Descartes, philosophers often held that genuine Knowledge [K] requires beliefs that are “indubitable” [=beyond any possible doubt]; that is, a belief counts as K only if it [or at least its ultimate source] is beyond doubt. If there were no such indubitable source for belief, skepticism would win: no genuine K, because no beliefs are beyond doubt. “Pure percepts” were supposed to provide the indubitable source for empirical K.
2. Empirical K must originate in sensory data [=percepts] that can’t be wrong, because they simply copy external reality w/o any cognitive “shopping” [as in Photoshop]. In order to avoid any possible ‘error’, percepts must be pure in that they involve no interpretation [= error-prone cognitive manipulation].
{Those Es who contend  that all K derives from our senses tend to ignore mathematical and other allegedly a priori K, which does not “copy” the sensible world.} In sum, pp are sensory data prior to [=unmediated by] any cognitive processing.

So it seems as though the concept is no longer taken seriously.  To drive a stake through its heart it’s time to talk about the retina.

It lies in the back of our eyes, and is organized rather counter-intuitively.  The photoreceptors (the pixels of the camera if you wish) are the last retinal elements to be hit by light, which must pass through the many other layers of the retina to get to them.

We have a lot of them — at least 100,000,000 of one type (rods).  The nerve cells sending impulses back to the brain, are called ganglion cells, and there are about 1,000,000 in each eye.  Between the them are bipolar cells and amacrine cells which organize the information falling on the photoreceptors.

All this happens in something only .2 milliMeters thick.

The organization of information results in retinal ganglion cells responding to different types of stimuli.  How do we know?  Impale the ganglion cell with an electrode while still in the retina, and try out various visual stimuli to see what it responds to.

Various authorities put the number of retinal ganglion cell types in the mouse at 11, 12, 14, 19 and 22.  Each responds to a given type of stimulus. Here are a few examples:

The X-type ganglion cell responds linearly to brightness

Y cells respond to movement in a particular direction,

Blue-ON transmits the mean spectral luminance (color distribution) along the spectrum from blue to green.

From an evolutionary point of view, it would be very useful to detect motion.  Some retinal ganglion cells being responding before they should. How do we know this?  It’s easy (but tedious) to map the area of visual space a ganglion cell responds to — this is called its receptive field.  The responses of some anticipate the incursion of a moving stimulus — clearly this must be the way they are hooked to photoreceptors via the intermediate cells.

Just think about the way photoreceptors at the back of the spherical eye are excited by something moving in a straight line in visual space.  It certainly isn’t a straight line on the retinal surfaced.  Somehow the elements of the retina are performing this calculation and predicting where something moving in a straight line will be next.  Why  couldn’t the brain bedoing this?  Because it can be seen in isolated retinas with no brain attached.

Now for something even more amazing.  Each type of ganglion cell (and I’ve just discussed a few) tiles the retina. This means that every patch of the retina has a ganglion cell responding to each type of visual stimulus.  So everything hitting every area of the retina is being analyzed 11, 12, 14, 19 or 22 different ways simultaneously.

So much for the pure percept: it works for a digital camera, but not the retina.  There is an immense amount of computation of the visual input going right there, before anything gets back to the brain.

If you wish to read more about this — an excellent review is available, but it’s quite technical and not for someone coming to neuroanatomy and neurophysiology for the first time.  [ Neuron vol. 76 pp. 266 – 280 ’12 ]