Two semi-coherent thoughts on 'sensing'

[From MK (2018.12.20.1500 CET)]

Within the context of a biophysical or biological system: what does it
from a control theoretic point of view mean "to sense' something?
Keeping in mind the biological context: what is the difference between
'sensing' something and 'controlling' something? Is there a single
instance of a biological system that 'senses' something where the
process described as 'sensing' is not just another example of
controlling? The canonical PCT view treats the sensory neurons as
iotic devices; that one appears to get away with this in certain
modelling contexts does not make the viewpoint correct.



If one considers the PCT loop as consisting of controlling systems:
one controlling 'sensory' neuron; one controlling interneuron and one
controlling motor neuron one arrives at a thought that was not at all
obvious to me: the 'sensory' neurons controlling activitity -- in the
form of 'neuronal output' -- is controlled by the loop despite not
being 'sensed'.

*The loop controls but it does not sense*.

Control requires comparison; it does not require 'sensing'. The
formation of a loop of the PCT kind is not at all obvious: when such a
loop is created 'out of neurons' the loop starts controlling the
controlling activity of a constitutive control system .

The loop controls control activity.