[ACT-R-users] puzzled by act-r 5.0.6 behavior

[Bruno Emond]

I am puzzled by a retrieval behavior in ACT-R 5.
It seems that there is a range of activation values for which
neither a chunk nor the failure chunked are retrieved.

I have included an annotated trace as well as
the sample code that generates the behavior.
The code is meaningless as a model. It s intention is
to reproduce the behavior.

Bruno

-  TRACE
/*
This first section shows what I am anticipating: the failure chunk is 
retrieved because
the activation is below the threshold (10).
*/
  Sources of activation are: nil
     Computing a base level of  4.999 from 1 references from creation 
time  0.000
     Computing a base level of  4.999 from 1 references from creation 
time  0.000
  CHUNK failure Activation 10.000 Latency  0.000
  Time  0.050: Ret Fired
  Time  0.050: Ret Selected
  Time  0.050: Failure Retrieved
==> Failure
  Sources of activation are: nil
     Computing a base level of  4.375 from 1 references from creation 
time  0.000
     Computing a base level of  4.375 from 1 references from creation 
time  0.000
  CHUNK failure Activation 10.000 Latency  0.000
  Time  0.100: Ret Fired
  Time  0.100: Ret Selected
  Time  0.100: Failure Retrieved
==> Failure
  Sources of activation are: nil
     Computing a base level of  4.010 from 1 references from creation 
time  0.000
     Computing a base level of  4.010 from 1 references from creation 
time  0.000
  CHUNK failure Activation 10.000 Latency  0.000
  Time  0.150: Ret Fired
  Time  0.150: Ret Selected
  Time  0.150: Failure Retrieved
==> Failure
  Sources of activation are: nil
     Computing a base level of  3.751 from 1 references from creation 
time  0.000
     Computing a base level of  3.751 from 1 references from creation 
time  0.000
  CHUNK failure Activation 10.000 Latency  0.000
  Time  0.200: Ret Fired
  Time  0.200: Ret Selected
  Time  0.200: Failure Retrieved
==> Failure

/*
This first section shows what I am anticipating: a chunk is retrieved 
because the
activation level is grater than the threshold (2). It goes from 4.999 
to 3.021
without any problems.
*/
  Sources of activation are: nil
     Computing a base level of  4.999 from 1 references from creation 
time  0.000
     Computing a base level of  4.999 from 1 references from creation 
time  0.000
  CHUNK X2 Activation  4.999 Latency  0.007
  Time  0.050: Ret Fired
  Time  0.050: Ret Selected
  Time  0.057: X2 Retrieved
==> X2
  Sources of activation are: nil
     Computing a base level of  4.375 from 1 references from creation 
time  0.000
     Computing a base level of  4.375 from 1 references from creation 
time  0.000
  CHUNK X2 Activation  4.375 Latency  0.013
  Time  0.100: Ret Fired
  Time  0.100: Ret Selected
  Time  0.113: X2 Retrieved
==> X2
...

  Sources of activation are: nil
     Computing a base level of  3.021 from 1 references from creation 
time  0.000
     Computing a base level of  3.021 from 1 references from creation 
time  0.000
  CHUNK X2 Activation  3.021 Latency  0.049
  Time  0.450: Ret Fired
  Time  0.450: Ret Selected
  Time  0.499: X2 Retrieved
==> X2

/*
Then there is the problematic section. Between an activation of 2.926 
and 2.000
nil is returned, not chunk x2 or failure. Even below and activation of 
2.000 nil
is returned, contrary to the previous example.
*/

  Sources of activation are: nil
     Computing a base level of  2.926 from 1 references from creation 
time  0.000
     Computing a base level of  2.926 from 1 references from creation 
time  0.000
  CHUNK X2 Activation  2.926 Latency  0.054
  Time  0.500: Ret Fired
  Time  0.500: Ret Selected
==> NIL
  Sources of activation are: nil
     Computing a base level of  2.841 from 1 references from creation 
time  0.000
     Computing a base level of  2.841 from 1 references from creation 
time  0.000
  CHUNK X2 Activation  2.841 Latency  0.058
  Time  0.550: Ret Fired
  Time  0.550: Ret Selected
==> NIL
  Sources of activation are: nil
     Computing a base level of  2.762 from 1 references from creation 
time  0.000
     Computing a base level of  2.762 from 1 references from creation 
time  0.000
  CHUNK X2 Activation  2.762 Latency  0.063
  Time  0.600: Ret Fired
  Time  0.600: Ret Selected
==> NIL

...

  Sources of activation are: nil
     Computing a base level of  2.032 from 1 references from creation 
time  0.000
     Computing a base level of  2.032 from 1 references from creation 
time  0.000
  CHUNK X2 Activation  2.032 Latency  0.131
  Time  1.350: Ret Fired
  Time  1.350: Ret Selected
==> NIL
  Sources of activation are: nil
     Computing a base level of  2.000 from 1 references from creation 
time  0.000
     Computing a base level of  2.000 from 1 references from creation 
time  0.000
  CHUNK failure Activation  2.000 Latency  0.135
  Time  1.400: Ret Fired
  Time  1.400: Ret Selected
==> NIL
  Sources of activation are: nil
     Computing a base level of  1.968 from 1 references from creation 
time  0.000
     Computing a base level of  1.968 from 1 references from creation 
time  0.000
  CHUNK failure Activation  2.000 Latency  0.135
  Time  1.450: Ret Fired
  Time  1.450: Ret Selected
==> NIL
  Sources of activation are: nil
     Computing a base level of  1.938 from 1 references from creation 
time  0.000
     Computing a base level of  1.938 from 1 references from creation 
time  0.000
  CHUNK failure Activation  2.000 Latency  0.135
  Time  1.500: Ret Fired
  Time  1.500: Ret Selected
==> NIL
  Sources of activation are: nil
     Computing a base level of  1.908 from 1 references from creation 
time  0.000
     Computing a base level of  1.908 from 1 references from creation 
time  0.000
  CHUNK failure Activation  2.000 Latency  0.135
  Time  1.550: Ret Fired
  Time  1.550: Ret Selected
==> NIL


- Code
(clearall)
(sgp :esc t :bll .9 :act t :rt 2)
(chunk-type c val1 val2)
(chunk-type goal)
(add-dm
  (x1 isa c val1 v1 val2 v2)
  (x2 isa c val1 v3 val2 v4)
  (g1 isa goal))
(p ret
    =goal>
    isa goal

    ==>

    +retrieval>
    isa c
    )
(goal-focus g1)
(run)