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Analyzing the Ordered 'And' Node

Compact notation for the ordered 'and'

When we consider the internal structure of
the ordered 'and', we see that that it must
specify sequencing. One way to explicitly
specify the ordering is by using a wait
element or delay element. It can be shown
explicitly using the narrow notation.

Narrow notation for the ordered 'and'
using 'wait' elements

In producing this sequence (B C), it won't work for C to come out at the same time as B — the delay on C needs to be long enough for B to be produced.  And in the upward direction, the activation from B has to wait for the activation for C to arrive, since B will get there first. 


The Wait Element

Now we must consider exactly what the wait element consists of. It must be able to do two important things:

1)  it must keep the activation alive during the period of delay, and
2)  it must "know" how long to wait.

Pathways of the Brain (pg. 99-102) discusses two means of fullfilling these requirements:
Fixed Interval Timing and Feedback Timing.


Feedback Timing
for the ordered 'and' 
(downward direction)


Click here to see an animation of how feedback timing works

Fixed Interval Timing
for the ordered 'and' 
(downward direction)

Click here to see an animation of how fixed interval timing works.

Mechanism for Recognizing Items in Sequence

For the upward direction, or recognition, the mechanism required is slighly different.  It is only necessary to keep alive the activation from the first element until the activation from the second arrives.  If no further input is received (i.e. at the end of a sentence or phrase when there is no second element) a centrally located reset turns off the activation kept alive in the loop.


Compact and Narrow Notation

Relational Networks

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This page was last modified on 27 June 2000.

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