Leabra Implementation Reference - Computational Explorations in Cognitive Neuroscience - page 449

Variable Default Description

opt thresh Optimization thresholds for speeding up computation:

.send .1 Don't send activation when act <= send.

0 Don't learn on recv unit weights when both phase acts <= learn.

.learn

true Whether to apply learn threshold to updating weights (otherwise always update).

.updt wts

0 Don't learn when +/- phase difference ratio (- / +) < phase dif. This is off (0) by

default, but can be useful if network is failing to activate output (e.g., in a deep
network) on minus phase of some trials — learning in this case is just massive
increase in all weights, and tends to produce “hog” units for all the active units.
To use, set to .8 as a good initial value.

.phase dif

0, .95 Range of clamped (external) activation values ( min, max ) — Don't clamp to 1

because NOISY XX1 activations can't reach that value, so use .95 as max.

clamp range

0, 1 Membrane potential range ( min, max ), 0-1 for normalized, -90-50 for bio-based.

vm range

Random distribution for initializing the membrane potential (constant by default):

v m init

Select type of random distribution to use (e.g., UNIFORM (default), NORMAL
(Gaussian)).

.type

.15 Mean of the random distribution, .15 is default resting potential (a.k.a. v rest

or V rest ).

.mean

0 Variance of the distribution (range for UNIFORM), no var by default.

.var

0 2nd parameter for distributions like BINOMIAL and GAMMA that require it (not

typically used).

.par

Time constants for integrating values over time:

dt

.2 Membrane potential v m time constant: dtvm in equation 2.8: Vm ( t +1) =

.vm

net ￿ .

.7 Net input net time constant: dt net in equation 2.16: g e (t)=(1￿ dt net )g e (t ￿

.net

( t )+ dt

.

Maximal conductances for channels:

g bar

1 Excitatory (glutamatergic synaptic sodium (Na) channel).

.e

.1 Constant leak (potassium, K+) channel.

.l

1 Inhibitory GABA-ergic channel (computed by kWTA or directly).

.i

.1 Hysteresis (excitation) voltage-gated channel (Ca++).

.h

.5 Accommodation (fatigue, inhibition) voltage-gated channel (K+).

.a

Reversal potentials for each channel (see above, defaults: 1, .15, .15, 1, 0).

e rev

Hysteresis (excitation) voltage-gated channel specs, see accommodation ( acc )
for details, defaults are: false, .05, .8, .7, .1 and true).

hyst

Accommodation (fatigue, inhibition) voltage-gated channel:

acc

false Activate use of channel if true.

.on

.01 Time constant for integrating basis variable, dt b a in equation 2.41: b a (t)=b a (t￿

.b dt

.

.5 Activation threshold for basis variable, when exceeded opens the channel, ￿ a in

equation 2.39.

.a thr

1) + dt ( y ( t ) ￿ b ( t ￿ 1))

.1 Deactivation threshold for basis variable, when less than closes channel (after

having been opened), ￿ d in equation 2.39.

.d thr

.1 Time constant for changing conductance when activating or deactivating, dt g a in

equation 2.39.

.g dt