Glossary

From Lettvin

This page may not be used for publication without substantial rewrite, since definitions are culled from other resources.

Sensorium 

the entire sensory apparatus of the body and the those parts of the brain that receive, process and interpret sensory stimuli. The sensorium is the place to which impressions from the external world are conveyed and perceived.

Process 

a brain, or any large collection of neurons (ganglion), consists of cell bodies with long cell processes. These processes do the work of transmitting signals.

Neuropil 

A neuropil is a dense tangle of processes. The cell bodies normally sit outside the neuropil, where they won't get in the way, and where they will have easier access to the glial (non-neuronal) support cells.

Layer 

the volume in which the cell bodies of the neurons live. Signals are injected into a layer and undergo topological transform, then come out as a new set of modified signals. These layers can be stacked quite deep.

Saccade 

abrupt, rapid, small movements of both eyes, such as when the eyes scan a line of print. Saccades can be divided into two distinct groups: major saccades (observable with the naked eye), and minor saccades (observable only with special instrumentation).

Neuron 

a nerve cell that sends and receives signals over long distances within the body. A neuron may send output signals to muscle neurons (called motor neurons or motoneurons) and to other neurons. A neuron may receive input signals from sensory cells (called sensory neurons) and from other neurons. A neuron that simply signals another neuron is called an interneuron.

Temporo-spatial signals 

are signals that carry information about the size, position and time (duration/speed) of stimuli.

Feature detection

a process in which specialized nerve cells in the brain respond to specific features of a visual stimulus, such as lines, edges, angle, or movement. The nerve cells fire selectively in response to stimuli that have specific characteristics. In psychology, feature detectors are neurons in the visual cortex that receive visual information and respond to certain features such as lines, angles, movements, etc. When the visual information changes, the feature detector neurons will quiet down, to be replaced with other more responsive neurons.

JDL: I keep using sensorium as meaning the sensible world, where you keep using it to mean the apparatus that senses. We have to break this impasse. Is there a better word for what I mean?

I had it as the sensible world initially. You asked that it be changed (or at least that was my impression). Every definition that I have found so far indicates that standard usage is that it is the sensing apparatus. I have not found a consistent term for the sensible world other than that or sensory environment. There is also extoreceptive environment.--dwl 17:17, 4 June 2009 (UTC)

JDL: Neuropil is NOT cytoplasmic. Neuropil is membrane-enclosed extensions of the nerve. Cajal got his Nobel prize for proving the "Neuron" theory as opposed to the anastamosing feltwork suggested by his contemporaries.

--dwl 18:01, 4 June 2009 (UTC)Fixed.

JDL: Layer and Neuropil are so interwoven that it is hard to draw the distinction you make. See any drawing or photomicrograph of a retina, and you will find it very hard to tell where one things starts and another ends. I consider Neuropil to be as you say, but Layer is pretty much mixed in. See the structure of any cortex and you will see the cell bodies everywhere.

JDL: Saccades seem to have a hierarchy. Major, minor, micro, and all sorts. Care has to be taken when talking about these. As I pointed out once, a strobe flash yields as much information for detail as continuous light. Saccades do not figure into the idea of necessary and sufficient. However, it is necessary to make any solution allow saccades.

JDL: I used the terminology Temporo-spatial signals to mean things that change either in time (blinking) or change in space (point, boundary, vertex). You have added to this, and the additions may invite extra questions and demands for explanation.

JDL: Feature detection is what I would call layer output signals that change in relation to either changes in simple sensory input, or changes in the models generated by Projecting and Collecting signals from earlier layers.

JDL: