Long-Term Memory Neural Circuits, Fast and Precise - Brain Theory from a Circuits and Systems Perspective - page 133

Fig. 8.5 Circuit for reading attributes in an example of a word of long-term memory
Either Rout or Lout may serve as a Hit signal, indicating to the cue editor, and
the recall referee, that a match was found and that returns are available. If no
matches are found after a given time limit, provisions are made to generate a NoHit
signal for the cue editor (not done at this time).
Cues must be selected before an enable is issued, given that a memory search
with no cues might lead to an excessive number of returns. The possibility of
multiple matches in response to a search, should they occur, is handled in part by a
multiple match system described below, and ultimately by a recall referee.
Multiread Circuit
When an inadequate number of cues are presented to an associative memory, one
normally expects multiple matches to the cues and thus multiple returns. This
requires special handling mainly because two images cannot simultaneously
occupy a return bus.
Intuitively a person cannot picture two images exactly at once. As an experiment
in multiple recalls, try to think of two things at once, such as your car and your
kitchen sink. It might be noticed that fuzzy images seem to alternate with each
other, although in rapid succession.
Neural logic prevents totally separate images from being recalled at exactly the
same instant. In the above figure with four standard cells, the y inputs are coming up
from other parts of memory. They were assumed to be false and will be false as long
as there are no other matches to the given cues. If there are other matches to the
given cues in the circuits below, it is necessary to delay them.
Figure 8.6 shows how. A match between cues and stored memory words means
that Rout is true. A complement of Rout is sent to the inputs of AND gates on each y
signal coming up from below. This will lock out all other matches to memories
below the top most return, at least until the Rout and Lout signals clear.
Figure 8.7 shows how a word is disabled once it produces a return. A simulated
qubit toggle is initialized to true via a multi-match initialization signal or MMINIT,
but should Rout indicate a match, the toggle gets set to false as the word is read.