A ModulatoryMechanism is a type of Mechanism that modifies the operation of one or more other Components. In general, a ModulatoryMechanism receives its input from an ObjectiveMechanism, however this need not be the case.
There are two primary types of ModulatoryMechanism:
- Control Mechanisms
- modulates the
valueof a States of a Mechanisms. Takes an evaluative signal (generally received from an ObjectiveMechanism) and generates a
control_allocation, each item of which is assigned to one of its ControlSignals; each of those generates a
control_signalthat is used by its ControlProjection(s) to modulate the parameter of a
function(and thereby the
value) of a States. ControlSignals have costs, and a ControlMechanism has a
net_outcomethat is computed based on the
costsof its ControlSignals. A ControlMechanism can be assigned only the ControlSignal class of Modulatory Signals, but can be also be assigned other generic OutputStates that appear after its ControlSignals in its
- Learning Mechanism
- modulates the
matrixparameter of a MappingProjection. Takes an error signal (received from an ObjectiveMechanism or another Learning Mechanism) and generates a
learning_signalthat is provided to its LearningSignal(s), and used by their LearningProjections to modulate the
matrixparameter of a MappingProjection. A LearningMechanism can be assigned only the LearningSignal class of Modulatory Signals as its OuputStates, but can be also be assigned other generic OutputStates, that appear after its LearningSignals in its
See ModulatorySignal for conventions used for the names of Modulatory components.
A single Modulatory Mechanisms can be assigned more than one ModulatorySignal of the appropriate type, each of which
can be assigned different
control_allocations (for ControlSignals) or
learning_signals (for LearningSignals). A single ModulatorySignal can also be
assigned multiple ModulatoryProjections; however, as described in ModulatoryProjections, they will all
be assigned the same
Creating a ModulatoryMechanism¶
A ModulatoryMechanism can be created by using the standard Python method of calling the constructor for the desired type.
ModulatoryMechanisms of the appropriate subtype are also created automatically when other Components are created that
require them, or a form of modulation is specified for them. For example, a ControlMechanism is
automatically created as part of a System (for use as its
controller), or when control is specified for the parameter of a
Mechanism; and one or more LearningMechanism are created when learning is
specified for a Process or a System (see the documentation for
subtypes of ModulatoryMechanisms for more specific information about how to create them).
A ModulatoryMechanism has the same basic structure as a Mechanism. In addition, every ModulatoryMechanism
modulation attribute, that determines the default method by which its
ModulatorySignals modify the value of the Components that they modulate (see the modulation for a description of how modulation operates, and the documentation for individual
subtypes of ModulatoryMechanism for more specific information about their structure and modulatory operation).
LearningMechanism and ControlMechanism are always executed at the end of a
TRIAL, after all ProcessingMechanisms in the Process or System to which they belong have been executed; all LearningMechanism
executed first, and then ControlMechanism. All modifications made are available during the next
GatingMechanism are executed in the same manner as ProcessingMechanisms; however, because they almost invariably
introduce recurrent connections, care must be given to their
initialization and/or scheduling).
ModulatoryMechanism is an abstract class and should NEVER be instantiated by a call to its constructor. They should be instantiated using the constructor for a subclass.