# ModulatorySignal¶

## Overview¶

A ModulatorySignal is a subclas of OutputPort that belongs to a ModulatoryMechanism, and is used to modulate the value of one or more Ports by way of one or more ModulatoryProjctions. A ModulatorySignal modulates the value of a Port by modifying a parameter of that Port’s function. There are three types of ModulatorySignals, each of which is associated wth a particular type of ModulatoryMechanism and ModulatoryProjection, and modifies the value of different types of Ports, as summarized below:

These are shown in a figure below, and are descdribed in greater detail in in the sections under Structure.

See ModulatoryMechanism for conventions used for the names of Modulatory components.

## Creating a ModulatorySignal¶

ModulatorySignal is a base class, and cannot be instantiated directly. However, the three types of ModulatorySignals listed above can be created directly, by calling the constructor for the desired type. More commonly, however, ModulatorySignals are created automatically by the ModulatoryMechanism to which they belong, or by specifying them in the constructor for a ModulatoryMechanism (the details of which are described in the documentation for each type of ModulatorySignal). If a ModulatorySignal is constructed explicitly, the type of modulation it uses is specifed in the modulation argument of its constructor, using a 2-item tuple that contains the Port to be modulated as the first item, and either the name of the parameter of the Port’s function to be modulated, or a keyword specifying the type of modulation, as the second item (see Types of Modulation for additional details).

## Structure¶

A ModulatorySignal is always assigned to a ModulatoryMechanism, and must be assigned to an ModulatoryMechanism of the appropriate type (see Types of ModulatoryMechanism). The ModulatorySignal receives an allocation from the ModulatoryMechanism to which it is assigned, that it uses as the variable for its function, the result of which is the modulatory value of the ModulatorySignal. A ModulatorySignal is associated with one or more ModulatoryProjections of the corresponding type, that receive the ModulatorySignal’s value, and use this to modulate the Port(s) to which they project. All of the ModulatoryProjections from a given ModulatorySignal are assigned the same modulatory value (see ModulatoryProjections below) and use the same type of modulation specified by the the ModulatorySignal’s modulation attribute. The ModulatoryProjections received by a Port are listed in the Port’s mod_afferents attribute.

The section on Modulation below provides a comparison of ModulatorySignal subclasses and their uses (summarized in an accompanying table and figure), as well as a description of the different types of modulation and a more detailed description of how modulation is implemented.

### ModulatoryProjections¶

A ModulatorySignal can be assigned one or more ModulatoryProjections, using either the projections argument of its constructor, or in an entry of a dictionary assigned to the params argument with the key PROJECTIONS. These are assigned to its efferents attribute. See Port Projections for additional details concerning the specification of Projections when creating a Port.

Although a ModulatorySignal can be assigned more than one ModulatoryProjection, all of those Projections receive and convey the same modulatory value from the ModulatorySignal, and use the same form of modulation. This is a common use for some ModulatorySignals (e.g., the use of a single GatingSignal to gate multiple InputPort(s) or OutputPort(s)), but requires more specialized circumstances for others (e.g., the use of a single LearningSignal for more than one MappingProjection, or a single ControlSignal for the parameters of more than one Mechanism or function).

### Modulation¶

A ModulatorySignal modulates the value of a Port either by modifying a parameter of the Port’s function (which determines the Port’s value), or by assigning a value to the Port directly. The type of modulation is determined by the ModulatorySignal’s modulation attribute, which can be specified in the modulation argument of its ModulatorySignal’s constructor, or in a MODULATION entry of a Port specification dictionary used to create the ModulatorySignal (see Type of Modualtion and figure below for details). If the type of modulation is not specified when a ModulatorySignal is created, it is assigned the value of the modulation attribute for the ModulatoryMechanism to which it belongs.

#### Uses of Modulation¶

There are three broad types of modulation that serve different purposes, and differ according to the ModulatorySignals used and the type of Port modulated; these are modulation of a:

The following table summarizes the three uses of modulation, the ModulatorySignals for each, and the Ports they modulate. The mechanics of modulation are described in greater detail in Implementation of Modulation, and shown in the figure below.

ModulatorySignals and Ports they Modulate (colors listed are those used in the figure below)

Purpose

ModulatorySignal

Default type of modulation

Recipient Port

Default Function (mod param) for Recipient Port

Modulate the parameter of a Mechanism’s function

ControlSignal (blue)

MULTIPLICATIVE

Mechanism ParameterPort (by default) but can also be an InputPort or OutputPort

Modulate the input or output of a Mechanism’s function

GatingSignal (brown)

MULTIPLICATIVE

Mechanism InputPort/OutputPort

Modulate a MappingProjection’s matrix parameter

LearningSignal (green)

MappingProjection ParameterPort

It is important to emphasize that, although the purpose of a ModulatorySignal is to modify the functioning of a Mechanism or a MappingProjection, it does this indirectly by modifying a Port that determines the input or output of a Mechanism, or the parameters of a Mechanism or Projection’s function, rather than directly modifying the function of the Mechanism or Projection itself. This is shown in the following figure, and described in greater detail under Implementation of Modulation.

Anatomy of Modulation

#### Types of Modulation¶

The modulation attribute of a ModulatorySignal determines the way in which it modulates the value of a Port, by specifying which parameter of the Port’s function that it modifies (see figure below). This is specified in a tuple containing the Port and the name of the parameter to be modified (see example). Alternatively, a keyword can be used in place of the parameter’s name. For some Functions, keywords can be used to specify function-specific forms of modulation (e.g., see TransferWithCosts Function for an example). In addition, there are four keywords that can be used to specify generic forms of modulation supported by most Functions:

Note

the MULTPLICATIVE_PARAM and ADDITIVE_PARAM keywords can be used only with Functions that specify a multiplicative_param and/or additive_param, respectively.

The default type of modulation for ControlSignals and GatingSignals is MULTIPLICATIVE. The default for LearningSignals is ADDITIVE (which additively modifies the value of the LearningSignal (i.e., the weight changes computed by the Learning Mechanism) to the Port’s variable (i.e., the current weight matrix for the MappingProjection being learned).

#### Implementation of Modulation¶

Although the purpose of a ModulatorySignal is to modify the operation of a Mechanism or MappingProjection, it does not do this directly; rather, it does it by way of a Port that modulates the input, function parameter, or output of the Mechanism or MappingProjeciton to be regulated. More specifically, a ModulatorySignal modulates the function of a Port responsible for generating those values, by modifying a parameter of that Port’s function. This is shown in the figure below:

Detailed View of Modulation

Though this implementaton of modulation is indirect, it provides a standard for all forms of modulation, as well as considerable flexibility in the modulatory regulation of Components within a Composition (see Types of Modulation below).

The types of Ports modulated by each type of ModulatorySignal are summarized in Uses of Modulation, and the accompanying table and figure.

Any modulable parameter of a Port’s function can be modulated, and different parameters of the same function of a Port can be modulated by different ModulatorySignals. The same parameter can also be modulated by more than on ModulatorySignal. If more than one ModulatorySignal modulates the same parameter of a Port’s function, then that parameter’s modulation_combine_function attribute determines how the values of the different ModulatorySignals are combined. By default, the product of their vaues is used. However, if OVERRIDE is specfied as the type of modulation for one of them, then that ModulatorySignal’s value is assigned directly as the Port’s value, and the others are all ignored. Only one ModulatorySignal specified as OVERRIDE can modulate a given parameter; if there is more than, then an error is generated.

## Execution¶

ModulatorySignals cannot be executed directly. This done when the ModulatoryMechanism to which they belong is executed. When a ModulatorySignal is executed, it calculates its value, which is then assigned as the variable of the ModulatoryProjections listed in its efferents attribute. When those Projections execute, they convey the ModulatorySignal’s value to the function of the Port to which they project. The Port’s function then uses that value in determining value of the parameter designated by the modulation attribute of the ModulatorySignal when the Port’s value is updated.

# FIX 5/8/20 – REWORK TO BE ALIGNED WITH ModulatoryMechanism

Note

The change in the value of a Port in response to a ModulatorySignal does not occur until the Mechanism to which the port belongs is next executed; see Lazy Evaluation for an explanation of “lazy” updating).

## Class Reference¶

class psyneulink.core.components.ports.modulatorysignals.modulatorysignal.ModulatorySignal(owner=None, size=None, reference_value=None, default_allocation=1.0, function=None, modulates=None, modulation=None, index=None, assign=None, params=None, name=None, prefs=None, **kwargs)

Subclass of OutputPort used by a ModulatoryMechanism to modulate the value of one more Ports. See OutputPort and subclasses for additional arguments and attributes.

Note

ModulatorySignal is an abstract class and should never be instantiated by a call to its constructor. It should be instantiated using the constructor for a subclass.

Parameters
• default_allocation (scalar : defaultModulatoryAllocation) – specifies the default template and value used for variable.

• modulation (str : default MULTIPLICATIVE) – specifies the type of modulation the ModulatorySignal uses to determine the value of the Port(s) it modulates; must be either a keyword defined by the Function of the parameter to be modulated, or one of the following generic keywords – MULTIPLICATIVE, ADDITIVE, OVERRIDE or DISABLE (see Types of Modulation for additional details).

variable

same as allocation.

Type

scalar, list or np.ndarray

allocation

value assigned by the ModulatorySignal’s owner, and used as the variable of its function to determine the ModulatorySignal’s ModulatorySignal.value.

Type

float

function

used to transform the ModulatorySignal’s allocation into its value; default is the Identity Function that simply assigns allocation to value.

Type

TransferFunction

value

result of function, used to determine the value of the Port(s) being modulated.

Type

number, list or np.ndarray

modulation

determines how the value of the ModulatorySignal is used to modulate the value of the port(s) being modulated (see Types of Modulation for additional details).

Type

str

efferents

a list of the ModulatoryProjections assigned to the ModulatorySignal.

Type

[List[GatingProjection]]

name

the name of the ModulatorySignal. If the ModulatorySignal’s initialization has been deferred, it is assigned a temporary name (indicating its deferred initialization status) until initialization is completed, at which time it is assigned its designated name. If that is the name of an existing ModulatorySignal, it is appended with an indexed suffix, incremented for each Port with the same base name (see Naming). If the name is not specified in the name argument of its constructor, a default name is assigned as follows; if the ModulatorySignal has:

• no projections (which are used to name it) – the name of its class is used, with an index that is incremented for each ModulatorySignal with a default named assigned to its owner;

• one ModulatoryProjection – the following template is used: “<target Mechanism name> <target Port name> <ModulatorySignal type name>” (for example, 'Decision[drift_rate] ControlSignal', or 'Input Layer[InputPort-0] GatingSignal');

• multiple ModulatoryProjections, all to Ports of the same Mechanism – the following template is used: “<target Mechanism name> (<target Port name>,…) <ModulatorySignal type name>” (for example, Decision (drift_rate, threshold) ControlSignal, or 'Input Layer[InputPort-0, InputPort-1] GatingSignal');

• multiple ModulatoryProjections to Ports of different Mechanisms – the following template is used: “<owner Mechanism’s name> divergent <ModulatorySignal type name>” (for example, 'ControlMechanism divergent ControlSignal' or 'GatingMechanism divergent GatingSignal').

Note

Unlike other PsyNeuLink components, Port names are “scoped” within a Mechanism, meaning that Ports with the same name are permitted in different Mechanisms. However, they are not permitted in the same Mechanism: Ports within a Mechanism with the same base name are appended an index in the order of their creation.

Type

str

_instantiate_projections(projections, context=None)

Instantiate Projections specified in PROJECTIONS entry of params arg of Port’s constructor

Specification should be an existing ModulatoryProjection, or a receiver Mechanism or Port Disallow any other specifications (including PathwayProjections) Call _instantiate_projection_from_port to assign ModulatoryProjections to .efferents

exception psyneulink.core.components.ports.modulatorysignals.modulatorysignal.ModulatorySignalError`(error_value)