[Martin Taylor 2017.11.15.13.49]
I suppose it depends on how you look at it. What makes a control
loop rather than a generic negative feedback loop is the asymmetry
between the perceptual side of the loop and the output side. The
perception passively follows changes in the CEV with as little added
energy as can be achieved, whereas the output uses an external
source of energy in order to exert influence on the CEV. In an
effective control loop constructed so that an observer could see
perception and output, reference and disturbance all at the same
time, but not much else about the loop, I suppose that observer
would have a hard time figuring out which side or end of the loop
was which. Typically, however, the observer can see only the CEV (assuming the
TCV has been used), the disturbance, and the output (or rather, the
output influence on the CEV). That looks as though the CEV is trying
to get to some reference value. In a pursuit task the CEV is the
relation between some moving target and some movable entity (say,
cursor). the movable seems to chase the target. But according to
theory it does that only because the perception “chases” the
internal reference value. I don’t think there’s a logical reason for preferring the observable
over the hidden when you talk about pursuit, other than that in
theory, every control performance is pursuit if you look at the
internal variables, whereas if you look at the external observables,
pursuit only occurs if the perception being controlled is a
relationship. At least that way of looking at it allows “pursuit” to
be used as a contrast to “compensatory” tracking. So I suppose that
is a reason, even if it isn’t logical.
As above, I guess you could legitimately say so, but I would prefer
not to. I prefer to keep the term for the situation in which it is
traditionally used – a moving target is “chased” by a movable
entity that an organisms control in order to keep a higher-level
perception near its reference value.
Martin
···
On 2017/11/15 12:50 PM, Erling
Jorgensen wrote:
[From Erling Jorgensen (2017.11.15 1212 EST)]
Erling Jorgensen (2017.11.15 0925 EST)
Martin Taylor 2017.11.15.11.29
EJ: Just a clarification.
>EJ: But in a hierarchical PCT arrangement forcontrolling Position, don’t all of these implementing layers
below that relationship level of Position become pursuit
tracking tasks in their own right, since references for
changing each of those implementing perceptions are also being
generated?
>>MT: Not pursuit tracking, which implies chasing anever-changing target. Here, only the reference values for the
perceptions are being varied.
EJ: As I am visualizing it, the ever-changing referencevalues are the target that the perceptions are chasing.
EJ: If the perception is being pushed away from an alreadyacceptable preference state, we call that compensatory
tracking. But if the reference signal is leading the way in a
changing manner, isn’t that pursuit tracking?