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Figure 6.10 Counter Card
70
four bits need not be stored. This is effectively achieved by making the
pulses accumulate in a U-bit counter in the fraction multiplier and then by
accumulating the carry pulses (DOUTRPS sequence) in a second H-bit counter to
give the top four bits of the correlation value. A separate counter is
provided for each T*-element addressed. Forty-two U-bit binary counters
(forty-two SN7^193s in seven 'counter' circuit boards, with six counters per
board as shown in Figure 6.10) are provided and selected appropriately.
6. k Overall Hardware Organization
The overall hardware organization of FROG is shown in Figure 6.11. Each
box represents a circuit card in the actual set-up. The function of each of
these circuit cards is described in this section.
The four circuit cards 'set up 1' through 'set up H' have preset switches
for programming-in the visual and nonvisual input values for the six different
types of stimuli. When the stimulus number is specified, the signal DSTIMNO,
the three sensory (visual) input values get defined on the DVISIN1, DVISIN2,
DVISIN3 lines. Also the reward value (GT, BT or PAIN value) is made available
on the appropriate one of the three outputs DGTSTIN, DBTSTIN, DPAININ.
As we mentioned in the last section, reading or writing from the T*-elements
is sequential, because there is really one T*-element moudle which, in con-
junction with relevant data, is used forty-two times. So during any read
or write cycle, the bookkeeping is done by the use of a 6-bit binary counter
called C0UNTER2 in the 'register' card. The value of this 6-bit signal goes
from the 'register' card to the 'decoder' card. The four least significant
bits of DTSTARNO are used for the U-bit LMADDR for the 'T*-element part I» card.
The other three bits LME1 - LME3, going to 'T*-element part I', are generated
by decoding the top two bits of DTSTARNO in the 'decoder* card.
71
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72
The 'decoder 1 also generates twelve control signals LSEL1 - LSEL12 from
the DTSTARNO signal. These go to the 'selector' circuit, the function of
which will be explained shortly. Forty-two more control signals LDOO through
LDkl are generated in the 'decoder' card from the DTSTARNO signal. These
control signals go to enable the forty-two l+-bit binary counters in the seven
'counter' cards. When DTSTARNO value is zero, LDOO is active, i.e., goes
to "0", with all other control signals remaining at "l". When DSTARNO value
is twenty-three, LD23 is "0", the rest staying at "l" and so on. These
signals enable the input to the proper counter during a write or a clear
operation.
The fourth signal which is generated in the 'decoder' circuit is the
2-bit DN signal, which specifies the level number of the T*-element, being
selected by the value of DTSTARNO signal in the following manner:
DN2 DN1 Level #
<_ DTSTARNO £ IT 1 1
17 < DTSTARNO ± 35 1 2
35 < DTSTARNO <_ kl 3
This 2-bit signal also indirectly specify the stepping parameter n for the
selected T*-element. This signal is used both in 'T*-element part II' card
and in 'fraction multiplier' card.
The 'selector' card has as its inputs the signals coming from the 'set
up' cards. It generates as its outputs, the data inputs to the 'T*-element'
cards (DMEMIN1 through DMEMINU). Obviously, the inputs to the 'T*-element '
cards depend on the DTSTARNO value. The inputs for the various values of
the DTSTARNO values are shown in Table 6.1. Necessary selection signals
LSEL1 thorugh LSEL12, derived from DTSTARNO in 'decoder*, comes to 'selector'
card to do the proper selection.
73
Table 6.1 Selector Circuit: Input-Output Relationship
DTSTAPNO
DMEMIN1
DMEMIN2
DMEMIN3
DMEMINU
00
DVISIN1
0000
0000
DGTSTIN
01
DVIRIN1
0000
0000
DOTSTIN
02
DVISIN2
0000
0000
DOTSTIN
level 1
03
DVISIN2
0000
0000
DOTSTIN
OTM
Oil
DVISIN3
0000
0000
DGTSTIN
05
DVISIN3
0000
0000
DOTSTIN
06
DVISIN1
0000
0000
DBTSTIN
07
DVISIN1
0000
0000
DBTSTIN
08
DVISIN2
0000
0000
DBTSTIN
level 1
09
PVISIN2
0000
0000
DBTSTIN
BTM
10
DVISIN3
0000
0000
DBTSTIN
11
DVISIN3
0000
0000
DBTSTIN
12
DVTSIN1
0000
0000
DPAININ ■
13
DVISIN1
0000
0000
DPAININ
111
DVISIN2
0000
0000
DPAININ
level 1
15
DVISIN2
0000
0000
DPAININ
PM
16
DVISIN3
0000
0000
DPAININ
17
DVISIN3
0000
0000
DPAININ
18
DVISIN1
DVISIN2
0000
DGTSTIN
19
DVISIN1
DVISIN2
oooo
DOTSTIN
20
DVTSIN1
DVTSIN3
0000
DGTSTIN
level 2
21
DVISIN1
DVISIN3
0000
DGTSTIN
GTM
22
DVTSIN2
DVIGIN3
0000
DGTSTIN
23
DVISIN2
DVISIN3
0000
DGTSTIN
2U
DVISIN1
DVISIN2
0000
DBTSTIN
25
DVISIN1
DVTSIN2
0000
DBTSTIN
26
DVISIN1
DVISIN3
0000
DBTSTIN
level 2
27
DVISIN1
DVISIN3
0000
DBTSTIN
BTM
28
DVISIN2
DVISIN3
0000
DBTSTIN
29
DVISIN2
DVISIH3
0000
DBTSTIN
30
DVISIN1
DVISIN2
0000
DPAININ
31
DVISIN1
DVISIN2
0000
DPAININ
32
DVISIN1
DVISIN3
0000
DPAININ
level 2
33
DVISIN1
DVISIN3
0000
DPAININ
PM
3U
DVISIN2
DVISIN3
0000
DPAININ
35
DVISIN2
DVISIN3
0000
DPAININ
36
DVISIN1
DVISIN2
DVISIN3
DGTSTIN
level 3
3?
DVISIN1
DVISIN2
DVISIN3
DGTSTIN
GTM
38
DVISIN1
DVISIN2
DVISIN3
DBTSTIN
level 3
39
DVISIN1
DVISIN2
DVISIN3
DBTSTIN
BTM
ko
DVISIN1
DVISIN2
DVISIN3
DPAININ
level 3
\ kl
DVISIN1
DVISIN2
DVISIN3
DPAININ
PM
Ik
The function of, the inputs to and the outputs from the 'T*-element part
I' card, the 'T*-element part II' card and the 'fraction multiplier' card have
been explained in Section 6.3.
As has been mentioned in Section 6.3, the correlation values are stored
in the seven 'counter' cards, each having six U-bit binary counters. The
input to these counters are enabled by forty-two control signals LDOO through
LDhl coming from the 'decoder'.
During a read-out from the MEMORY, as the control sequences through the
forty-two T*-elements, everytime the stored sensory input values match the
presented sensory input values, the LREAD signal goes from a "0" to a "l".
This signifies that the corresponding T*-elements should output its stored
correlation value. The status of the LREAD signal for the forty-two T*-elements
during a read-out, is stored in a sequence in a ^2-bit shift register (actually
a U8-bit shift register of which the first forty-two bit positions are used)
in the 'shift register' card. These forty-two bits are available as forty-
two control signals, LROO throug LRUl, to enable the outputs of the proper
counters in the 'counter' cards.
The forty-two U-bit numbers from the seven 'counter' cards are compared
in M-elements in seven 'comparison' cards to generate the nine level outputs
(three from each of GTM, BTM and PM) in a manner as discussed in Section 5.1.
The circuit of a 'comparison' card is functionally equivalent to the following
arrangement shown in Figure 6.12. The input-output relationship of this
arrangement, shown in terms of the basic continuous logic elements is fairly
self-explanatory .
75
M
M
M
J&
?*>
Figure 6.12 Comparison Card: Continuous Element Logic Diagram
The level outputs go to the three 'MIS 1 cards which realizes the MIU as
detailed in Section 5.2. The six U-bit numbers (MIS0UT1 - 3, ALARMIS1 - 3)
and the DNODECF signals coming out of these 'MIS' cards go into the 'max
elements and DU' card. In this circuit, first the DMEMOUT and the DALARMOUT
signals are generated by use of M-elements (see Figure 5-3) • These signals
along with DINNATESTIM, DHUNGER, DNODECF are processed in the circuit realiza-
tion of the decision unit (DU) to result in the decisions (DDIN signal). The
signal LPOSEQLOC entering the 'max elements and DU' circuit is a signal that
indicates if the position of FROG is the same as the location of the stimulus.
The DDIN signal is U-bit wide, one bit goes to a "l" to indicate the decision
in accordance with the Figure 5-5-
The circuits in the 'comparison', the 'MIS' and the 'max elements and DU'
cards being pruely combinational, are fairly straightforward.
The circuit cards described uptil now occupy the lower rack of the FROG
assembly (see Figure 3.1). The following paragraphs give description of the
circuit cards in the upper rack, and other variously mounted circuits.
The signals from the switches on the front panel come to the circuit
board called 'switches and RNG2'. This circuit board has a psuedo-random
76
number generator to generate, if required to do so "by selection of the panel
switches, a random sequence of stimuli at random locations. The type of the
stimulus chosen for a cycle is outputted as a 3-bit signal DSTIMIN from this
card. The location choice is indicated by a 2-bit number DLOCIN. The motion
override signal, LOVERRIDE, and the enter pulse, PENTER, from the panel are
also available as outputs of this card.
The 'register' card essentially consists of several latches for storing
various signals. The HUNGER register is in the form of a 4-bit counter, which
stores the current value of the hunger signal. Incrementation or decrementa-
tion of this value is done by making the counter either count up or count down.
The counter is protected by additional logic from overflowing or underflowing
(i.e., if it is already at 1111, an attempt to increment will not affect
the count, and if a 0000, attempt to decrement will leave the value unchanged).
There is a provision, a 4-bit preset switch, by which the hunger value can be
initialized to a desired value. The 'register' card has the counter C0UNTER2
which is used for keeping count when sequencing through the forty-two T*-elements
(refer to Section 6.3). The outputs of this counter are the six bits of
DTSTARNO. The STIMULUS register loads, at the beginning of a trial, the
value of the DSTIMNO signal. This allows the switches to be changed for the
next trial, while computation for the current trial is in progress.
The decision, as generated in the decision unit, comes to the 'register'
card as the DDIN signal bits and is stored in two separate registers. The
two registers, the DECISION register and the DECISION DISPLAY register, are
both loaded at the end of the read cycle, when the DDIN signal becomes
reliable. The reason for having two registers holding the same quantity
is that when a wrong decision (i.e., a decision to feed on a dangerous stimulus)
is made, then following the encounter with the stimulus the DECISION DISPLAY
77
register is changed to show a flee, while the initial wrong decision is
maintained in the DECISION register for reference.
The output from the DECISION DISPLAY register and that from the STIMULUS
register decoded to six lines (with one active at a time) are sent via cables
to the 'monitor' circuit for the display of the decision (l of k) and the
stimulus number (l of 6). The 'monitor' card is mounted behind the panel.
The 'lighting and motion I' card has the circuitry which decides which
lamp segments to light up on the board based on i) the position of FROG,
ii) the location of the stimulus and iii) the decision about the stimulus.
The current position of FROG is maintained in a 2-bit POSITION register in
this circuit card, and updated at appropriate times. The location of the
stimulus, as indicated by the DLOCIN signal from the 'switches and RNG2' card,
is stored for a trial in another 2-bit register. This card also generates
a command signal, PSTARTMOVE , for initiating the movement of the movable
block (MB) at appropriate times. Lastly, the card has a 3-digit BCD counter
called C0UNTER1 which keeps track of the trial number.
From the 'lighting and motion control I' card, therefore, the pulse
command signal PSTARTMOVE go to the 'motion control II' circuit. The
DPOSITION ( 2-bit s) and DLOCATION ( 2-bit s) signals out of the appropriate
registers, and the DTRIALNO signal (three U-bit groups) go on cables to the
'monitor' card for display of the position of FROG, the location of the
stimulus and the trial number. Also, two more 2-bit signals, LSTART and LFINISH,
generated in this card, go on a different cable to the 'lighting control II'
circuit to indicate the starting and the end position of FROG every time a
motion has to be initiated.
The 'motion control II' circuit controls the movement of MB. The
PSTARTMOVE command sets a flipflop in the circuit. The output LMOVE of the
flipflop is delayed by one second to allow for the lamps on the board, when
78
lit up or changed, to settle to a stable pattern. This delayed signal LM goes
via a flexible cable to the circuits in MB to start the motors. The stop
signal LP4 (active low), which is generated as soon as the end of the track
is detected (see Section 3-7), is relayed back on this cable to reset the
flipflop. This immediately deactivates LMOVE and LM signals to stop MB. The dc
power to the two motors are also provided from this card to MB through the
cable. Two potentiometers can be adjusted for partial control of the currents
in the individual motors. This helps in balancing the speeds of the two
motors .
The 'lighting control II' card is a 17 inch wide card which is mounted
below the lower card rack (see Figure 3.l). It has twenty six circuits for
driving lamps. Eighteen of these are for driving segments of under-the-
track lights, four for stop lights indicating end of track, and four lights
for indicating the four locations on the board. The signals received by
'lighting control II' circuit through the cable from 'lighting and motion
control I' are DLOCATION (2-bits), DPOSITION (2-bits), DSTART (2-bits) and
DFINISH (2-bits). These signals are decoded to light up the appropriate
lights and light segments.
The 'monitor' card is mounted at the back of the panel. The DTRIALNO
signal (three BCD digits) is displayed on three BCD 7-segment LED displays
as the TRIAL NUMBER. The hunger value is displayed on a linear display
with fifteen LEDs. The DPOSITION signal is displayed on a 7-segment LED
display to indicate the current position of FROG. The DLOCATION signal is
similarly displayed on another 7-segment LED display. The stimulus number,
given by the 6-line DSTIMULUS signal, and the decision, given by the set
of four signals (DREST, DALARM, DFLEE, DFEED) come to the 'monitor' card
79
from the 'register' card. These are displayed by LED lamps. The circuit in
the 'monitor' card is purely combinational.
The remaining four cards, 'system clock and busy flip-flops', 'control I',
'control II', and 'control III ', generates the necessary control signals for the
proper sequencing of all operations.
80
7. RESULTS AND CONCLUSION
7-1 Discussion of a Typical Sequence of Trials
In order to investigate the behavior of FROG, the machine was run through
a sequence of 50 trials, in which all the stimuli were presented in a fairly-
arbitrary fashion. A trial by trial summary of the run is given in Appendix A.
This section gives a discussion of the results.
The run started with three consecutive presentations of stimuli of type
5, which are dangerous for FROG. In the very first presentation (trial #l),
FROG ignored this stimulus because it knew nothing about the stimulus, and it
was not hungry enough (hunger = 7/15 < 1/2). In the next trial, since hunger
value was greater then 0.5 (hunger = 8/15), FROG was tempted to feed on the
stimulus. The encounter was obviously painful, and so, FROG had to flee from the
stimulus. The single encounter provided some learning in level 3, which made FROG
correctly recognize a stimulus of type 5 to be. a dangerous one in trial #3. Inspite
of the fact that the hunger value was high, FROG avoided the stimulus in this trial,
For the next three trials, FROG was presented with stimuli of type 1, which
are good tasting. The presented stimulus was fed upon each time. The first
time (trial #M, the decision was hunger-forced. But the next two times,
the decisions were memory assisted, with the cognitive mechanism making
correct inferences.
Following this, a stimulus of type 5 was presented. FROG decided to
feed on it. This obviously was a wrong decision. This happened because of
the shared feature (the color, black) between a type 1 stimulus and a type 5
stimulus. The encounters with type 1 stimulus in trial #s U,5 and 6 had
biased it into generally associating the color black with good taste. So, in
81
trial #5, on seeing a black stimulus FROG concluded that it must be good
tasting (a level 1 decision) without paying much attention to the particular
combination in which this feature appears. A previous encounter with a
stimulus of type 5 (trial #2) was not of help, because it did not provide
sufficient counteracting evidence in level 1 (the most general level). This
trend continued in the next trial (#8), when a wrong attempt to feed on a type
5 stimulus was once again made in confusion with a type 1 stimulus. This
trend got corrected in the next trial. The stimulus was correctly recognized
and avoided.
Presentation of a stimulus of type 1 in the 10th trial was followed by
a feeding action. Since it was the fourth time a stimulus of this type was
eaten, even the level 1 T*-element outputs were brought up to their full
potential. So a full learning of stimuli of type 1 was achieved at the end
of this trial.
A type 3 stimulus was presented for the first time in trial #11. It is
red, round and small. FROG did not have an encounter with anything red
and/or small before, but did have some unpleasant experience with something
round (stimulus of type 5). So FROG's reaction to a type 3 stimulus was one
of avoidance. Obviously no learning took place.
A stimulus of type k was introduced for the first time in trial #12. Except
for its color, which is yellow, it looks very similar to a stimulus of type 1.
A type k stimulus is a bad tasting stimulus. Because of the similarity of stimuli
of types 1 and k and because of the pleasantly rewarding experience with type 1
stimuli, FROG decided that the new stimulus must be good tasting too and fed
on it. The same behavior was witnessed in the next two trials as well. Be-
cause of these feedings, the situation was corrected in trial #15 , when a type
4 stimulus was ignored, being recognized as a bad tasting stimulus.
82
Trial #16 saw the first introduction of a type 2 stimulus. Because of
its yellow color, it was initially thought to be of type h, which FROG had
just learned to be a bad tasting stimulus. So the presented stimulus was
ignored by FROG.
FROG was again tested with some type 5 stimuli in trial #s IT and 18.
In trial #17, FROG attempted (wrongly) to feed on it, in confusion with a
stimulus of type 1, which has the same color. Although, FROG had apparently
learned to distinguish a stimulus of type 5 from a stimulus of type 1
(witness trial #9)> the encounter with a stimulus of type 1 in trial #10 led
FROG to believe, once again, that the color black is associated with good
taste. FROG's attempt to feed on a type 5 stimulus in trial #17 resulted in
full learning of a type 5 stimulus.
The second presentation of a type 2 stimulus was in trial #19 > when FROG
recognized it to be a dangerous one. This is because a type 2 stimulus is of the
same size as a t^ pe 5 stimulus, and a large number of unpleasant encounters with
type 5 stimuli had already taken place by that time. But inspite of this warn-
ing from the memory, FROG decided to go ahead and eat the stimulus because
the hunger condition was at its maximum (starvation point). In the next
eight trials (#20 through 27), FROG was presented with type 2 stimuli only.
During the trials 20 through 25, FROG consistently reocgnized type 2 stimuli
to be dangerous ones (being biased by #5) s but fed on it in trials 21, 23
and 25, being starvation forced. These four feeding attempts caused full learn-
ing of stimuli of type 2 5 and helped reverse the trend. This is evidenced by
FROG's decision to feed on stimuli of type 2 in trials 26, 27, and later in
trials 1+7, hQ as well.
A type 6 stimulus appeared for the first time in trial #28. Based solely
on color, a type 6 stimulus is similar to a type 3 (a bad tasting) stimulus.
Based on size, a type 6 stimulus is similar to both a type 2 (good tasting)
83
stimulus and a type 5 (dangerous) stimulus. Because of these shared features,
more than one submemory (GTM, BTM and PM) outputted equal values resulting in
no generated response at these levels. Since nothing was known about a stimulus
of type 6, no response came from level 3 either. So, the MIU generated no
output and NODECF signal was 1.0. Under this condition, FROG decided to feed
on the stimulus based solely on the hunger value (hunger = 1100). This feeding
attempt was obviously followed by a fleeing reaction. This encounter produced
enough learning for FROG to stay away from a stimulus of type 6 in the very
next trial (#29). This decision, of course, was primarily guided by the
level 3 output from PM, with no response generated in levels 1 and 2 as in the
last trial.
In the next eight trials (#30 through 37) » stimuli of type 3 were pre-
sented seven times. In each of the first six presentations (trial #s 30, 31,
32, 33, 35 and 36), the reaction of FROG was similar to what it had been
towards a type 3 stimulus in trial #11, i.e., one of recognizing it to be a
dangerous one (confusing it with a type 5 stimulus, which has the same shape).
Starvation forced attempts to feed, however, were made in trials 30, 32 and
36. These three feedings caused FROG to recognize a stimulus of type 3
correctly in trials 37 and 39 • Although the stimulus avoided in trial #37*
it was fed upon in trial #39 > because the hunger value was 1.0. This feeding
resulted in full learning of type 3 stimuli.
In the middle of this long spell with type 3 stimuli, a stimulus of
type h was slipped-in in trial #3^. It was correctly recognized as a bad
tasting stimulus. A starvation condition, however, caused forced feeding,
also resulting in a full learning of stimuli of type h.
FROG's reactions to stimuli of type 6 were tested in trial #s 38, *+0,
hl t and k2. In trial #38, a type 6 stimulus was correctly recognized by
8U
FROG as a dangerous stimulus, but, once again, a starvation condition existing
caused FROG to attempt to feed on the stimulus anyway. The next time a type 6
stimulus was presented (trial #1+0), FROG decided to ignore it thinking it to
be of the kind of a type 3 stimulus (both being red). The reaction was the
same in the next trial (#1+1), although hunger = 1.0 forced FROG to make a
feeding attempt with unpleasant outcome. The same behavior was repeated the
next time as well. These attempts to feed on a type 6 stimulus, in sheer
desperation, resulted in a full learning of stimuli of type 6.
The remaining trials (# 1+3 through 50) are significant. By trial # 1+2
each of the six different types of stimuli had been fed upon (or attempts had
been made to do so) at least four times. All the stimuli were fully learned.
In other words, the T*-elements were not going to be incremented or adjusted
any further. Therefore, it is important for FROG to have recognized all the
different stimuli correctly. An examination of the responses will show that
this is definitely the case.
7.2 Results in Summary and Concluding Remarks
At birth the tendencies of the device are guided by the hunger value and/or
the innate sensory input value of the presented stimulus. The reactions of
FROG toward the various types of stimuli depend, among other factors, on the
sequence in which the stimuli are encountered and the extent to which features
are shared. For example, in the given run, whereas the good tasting stimuli
of type 1 were fully learned in four appearances, the stimuli of type 2, which
are good tasting too, had to be presented eight times before they were fully
learned.
In general the good tasting stimuli have a better chance of being adapted
faster, because they are more readily fed upon. Avoidance of the bad tasting
or dangerous ones slows down the learning of those types.
85
Given a sufficient number of presentations (usually k to 10 appearances)
each type of stimulus is learned correctly. However, because of the shared
features between the different types and because of FROG's inherent tendency
to make gross decisions, errors result in the learning phase.
There are three distinct types of errors made by FROG. The first is
to decide to feed on a stimulus of the bad tasting or dangerous type. Errors
of this type are easily corrected, for the feeding encounters result in
additional learning which alleviates the problem.
The second type of error occurs when a good tasting stimulus is avoided.
This response is not self-corrective; with feeding inhibited, additional
learning is not possible. Only starvation forced feeding helped reverse
the situation in this case.
A third type of error is made when a dangerous stimulus is avoided, being
mistaken as a bad tasting stimulus or vice-versa. Although this behavior
inhibits proper learning, its effect is not altogether undesirable. However,
since this type of error means avoidance, the stimulus types are not learned
properly and might subsequently lead to type 1 error.
Admittedly the device is not always perfect; it makes mistakes. It is
these mistakes which make the simulation more realistic, showing that "pro-
cessing from the general to the specific" is a very plausible mode of operation
of the nervous systems in the biological world.
In this simulation, for the particular choice of the stimulus types, an
examination of trials k3 through 50 show that except for stimulus of type 2
and k t which were resolved only by examining the level 3 outputs, all others were
resolved at level 2. If the mechanism makes a sequential search through the data
in its world model (i.e., memory) during a read cycle (as would be the case when
86
the mechanism has only one processing element), we can argue that there will
be an improvement in the response time, when attempts are always made to make
decisions on a gross context. The response time is the time between the
presentation of the stimulus and the making of a decision about it. It
is not possible to exactly calculate the improvement in response time by
organizing data in various extra levels (of generalization), because the
improvement is data dependent. But, in most cases, where some general trends
and natural clusters exist in the stimulus range, an improvement of the
response time is to be expected. This point is further elaborated in Appendix B.
Note must be taken of the fact that generalization from the observed
data gives the ability to respond to new stimuli. In this simulation, similar
stimuli, however, were purposely made to be of absolutely different nature.
Therefore, memory assisted approach to a new sitmulus usually meant incorrect
prediction (cf,, trial #s 11, 12, l6). This facility can, of course be
conceivably exploited more for the good of the mechanism in a different situation.
In order to respond to new situations, the scheme uses extra memory over
a scheme in which the observed data is retained in a simple ordered list.
Although the extra memory requirement is not of an alarming proportion (see
Appendix B\ it is probably possible to reduce the requirement by employing
a few simple tricks. One method that seems to be of promise, is to release
the memory elements (and the related data) which are not used during read-outs
over an extended period of time. Thus, for those stimuli which are recognized
by considering the level 1 or level 2 outputs, data relevant to such stimuli
in the lower levels may be discarded. Alternatively, all memory elements may,
periodically (e.g., every trial), have their contents reduced by a small
amount, unless they are read out or written into in that period. Also, the
elements may then be released if their contents become too small. This
87
can well simulate the decay or loss of memory observed in living beings. No
attempt has been made to incorporate this in FROG.
The operation of FROG is sensitive to the assignment of values to the fea-
tures. A proper discrimination of the various classes of stimuli is dependent
on the adjustment of these values. So, the learning process in FROG is a
supervised learning. Although it is possible to propose methods of statistically
adapting to the proper values, schemes using unsupervised learning have
generally been found to have unsatisfactory results. Incorporation of built-in
premises and biases, or taking a heuristic approach, seems to provide better
results in most machine cognition activity. It might be added that even in
living organisms, a lot of knowledge and innate tendencies are handed down
from generation to generation. This may be thought to belong to the group
intelligence of the species, which an individual specimen of the species
does not totally adaptively acquire from its own experience.
Other situations, where this type of modelling (using generalizations
and using quick decision making based on the principle of "processing
from the general to the specific") will probably be quite suited, are
as follows :
(a) A complex system which is required to respond quickly to some
critical modes of failure, where an exhaustive list of failure patterns' is
either too long to search, or cannot be completely specified. Such systems
probably have to take some quick precautionary measures based on inexact
judgements, and then go into further details to resolve the cause of failures.
Since all modes of failure cannot be predicted and simulated ahead of time,
an adaptive system becomes necessary. This might find use in automatic
maintenance of a complex network or system, such as a large electornic
switching systems in telephone networks.
88
(b) An interactive advisory system where machines are employed to
advise and guide human beings in locating problems based on a pattern of
symptoms. It is conceivable that the machine, at all stages, will probably
need to make inexact decisions about probable causes, and ask the human
subject meaningful questions to get to the final interpretation. A medical
diagnostic program can probably be thought in these lines.
89
APPENDIX A
SUMMARY OF A SEQUENCE OF TRIALS
The sequence consisted of 50 trials. A summary of the run is given in
the following pages. A guide to the various columns is given below:
Trial# - serial number of the trial.
Stimulus - the number of the stimulus presented in the current trial.
HUNGER - current value of FROG's hunger.
FEED - value of the FEED signal.
ALARMOUT - value of the ALARMOUT signal.
Decision - mode of action decided upon by FROG for the stimulus pre-
sented. Abbreviations used are:
F = FROG decided to feed on the stimulus.
R = FROG decided to rest and ignore the stimulus.
A = FROG is alarmed by the presence of the stimulus.
FF = FROG decided to feed on a dangerous stimulus , and
flee to its safe resting place on encounter.
Primary Reason - Entries to this column are the signals which were primarily
responsible for the decision. The following abbreviations
are used:
h = HUNGER.
i = INNATESTIM.
GTMr = level r GTM output.
BTMr = level r BTM output.
PMr = level r PM output.
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