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A Java based Neuron Modeling framework
package model.MARK_II;
import java.awt.*;
import java.util.*;
import java.util.List;
/**
* Provides implementation for running the spatial learning algorithm on a
* Region. This class provides methods that simulate brain activity within
* Regions of the Neocortex.
*
* @author Quinn Liu ([email protected])
* @version July 29, 2013
*/
public class SpatialPooler extends Pooler {
private Set activeColumns;
private Set activeColumnPositions;
public static float MINIMUM_COLUMN_FIRING_RATE = 0.01f;
public SpatialPooler(Region region) {
if (region == null) {
throw new IllegalArgumentException(
"region in SpatialPooler class constructor cannot be null");
}
super.region = region;
this.activeColumns = new HashSet();
this.activeColumnPositions = new HashSet();
}
/**
* This method recomputes all Column states within this functional Region.
* Through local inhibition, only a sparse set of Columns become active to
* represent the current 2D array of sensory data or a lower Region's
* output.
*
* @return A sparse set of active Columns within this Region.
*/
public Set performPooling() {
/// for c in columns
Column[][] columns = this.region.getColumns();
for (int row = 0; row < columns.length; row++) {
for (int column = 0; column < columns[0].length; column++) {
this.computeColumnOverlapScore(columns[row][column]);
}
}
// a sparse set of Columns become active after local inhibition
this.computeActiveColumnsOfRegion();
// simulate learning by boosting specific Synapses
this.regionLearnOneTimeStep();
return this.activeColumns;
}
/**
* If only the column positions computed by spatial pooling are needed use
* this method to return a set of just the column positions that were active
* in the most recent iteration of spatial pooling. For example instead of
* using:
*
* Set Column columnActivity =
* spatialPooler.performPooling();
*
* Now use:
*
* spatialPooler.performPooling();
* Set ColumnPosition columnActivity = this.spatialPooler.getActiveColumnPositions();
*/
public Set getActiveColumnPositions() {
return this.activeColumnPositions;
}
public Set getActiveColumns() {
return this.activeColumns;
}
/**
* The overlapScore for each Column is the number of Synapses connected to
* Cells with active inputs multiplied by that Columns's boostValue. If a
* Column's overlapScore is below minOverlap, that Column's overlapScore is
* set to 0.
*/
void computeColumnOverlapScore(Column column) {
if (column == null) {
throw new IllegalArgumentException(
"the Column in SpatialPooler method computeColumnOverlapScore cannot be null");
}
/// overlap(c) = 0
int newOverlapScore = column.getProximalSegment()
/// for s in connectedSynapses(c)
/// overlap(c) = overlap(c) + input(t, s.sourceInput)
.getNumberOfActiveSynapses();
// compute minimumOverlapScore assuming all proximalSegments are
// connected to the same number of synapses
Column[][] columns = this.region.getColumns();
int regionMinimumOverlapScore = this.region.getMinimumOverlapScore();
/// if overlap(c) < minOverlap then
if (newOverlapScore < regionMinimumOverlapScore) {
/// overlap(c) = 0
newOverlapScore = 0;
} else {
/// overlap(c) = overlap(c) * boost(c)
newOverlapScore = (int) (newOverlapScore * column.getBoostValue());
}
column.setOverlapScore(newOverlapScore);
}
/**
* This method is called by performPooling and computes the
* activeColumns(t) = the list of Columns that win due to the bottom-up input
* at time t.
*/
void computeActiveColumnsOfRegion() {
// remove old active columns from last time spatial pooling was called
this.activeColumns.clear();
this.activeColumnPositions.clear();
Column[][] columns = this.region.getColumns();
/// for c in columns
for (int row = 0; row < columns.length; row++) {
for (int column = 0; column < columns[0].length; column++) {
columns[row][column].setActiveState(false);
this.updateNeighborColumns(row, column);
// necessary for calculating kthScoreOfColumns
List neighborColumnPositions = new ArrayList();
neighborColumnPositions = columns[row][column].getNeighborColumns();
List neighborColumns = new ArrayList();
for (ColumnPosition columnPosition : neighborColumnPositions) {
neighborColumns
.add(columns[columnPosition.getRow()][columnPosition
.getColumn()]);
}
/// minLocalActivity = kthScore(neighbors(c), desiredLocalActivity)
int minimumLocalOverlapScore = this.kthScoreOfColumns(
neighborColumns, this.region.getDesiredLocalActivity());
// more than (this.region.desiredLocalActivity) number of
// columns can become active since it is applied to each
// Column object's neighborColumns
/// if overlap(c) > 0 and overlap(c) >= minLocalActivity then
if (columns[row][column].getOverlapScore() > 0
&& columns[row][column].getOverlapScore() >= minimumLocalOverlapScore) {
/// activeColumns(t).append(c)
columns[row][column].setActiveState(true);
this.addActiveColumn(columns[row][column]);
this.activeColumnPositions.add(new ColumnPosition(row, column));
}
}
}
}
/**
* This method models spike-timing dependent plasticity. This is also known
* as Hebb's Rule. The inhibitionRadius for the Region is also computed and
* updated here.
*/
void regionLearnOneTimeStep() {
this.modelLongTermPotentiationAndDepression();
this.boostSynapsesBasedOnActiveAndOverlapDutyCycle();
/// inhibitionRadius = averageReceptiveFieldSize()
this.region
.setInhibitionRadius((int) averageReceptiveFieldSizeOfRegion());
}
void modelLongTermPotentiationAndDepression() {
Column[][] columns = this.region.getColumns();
if (super.getLearningState()) {
/// for c in activeColumns(t)
for (int x = 0; x < columns.length; x++) {
for (int y = 0; y < columns[0].length; y++) {
if (columns[x][y].getActiveState()) {
// increase and decrease of proximal segment synapses
// based on each Synapses's activeState
Set> synapses = columns[x][y]
.getProximalSegment().getSynapses();
/// for s in potentialSynapses(c)
for (Synapse synapse : synapses) {
/// if active(s) then
if (synapse.getConnectedCell() != null
&& synapse.getConnectedCell()
.getActiveState()) {
// model long term potentiation
/// s.permanence += permanenceInc
/// s.permanence = min(1.0, s.permanence)
synapse.increasePermanence();
} else {
// model long term depression
/// s.permanence -= permanenceDec
/// s.permanence = max(0.0, s.permanence)
synapse.decreasePermanence();
}
}
}
}
}
}
}
void boostSynapsesBasedOnActiveAndOverlapDutyCycle() {
Column[][] columns = this.region.getColumns();
/// for c in columns
for (int row = 0; row < columns.length; row++) {
for (int column = 0; column < columns[0].length; column++) {
if (columns[row][column].getActiveState()) {
// increase and decrease of proximal Segment Synapses based
// on each Synapses's activeState
// columns[row][column].performBoosting();
// 2 methods to help a Column's proximal Segment
// Synapses learn connections:
//
// 1) If activeDutyCycle(measures winning rate) is too low.
// The overall boost value of the Columns is increased.
//
// 2) If overlapDutyCycle(measures connected Synapses with
// inputs) is too low, the permanence values of the
// Column's Synapses are boosted.
// neighborColumns are already up to date.
List neighborColumnPositions = columns[row][column]
.getNeighborColumns();
List neighborColumns = new ArrayList();
for (ColumnPosition columnPosition : neighborColumnPositions) {
// add the Column object to neighborColumns
neighborColumns
.add(columns[columnPosition.getRow()][columnPosition
.getColumn()]);
}
float maximumActiveDutyCycle = this.region
.maximumActiveDutyCycle(neighborColumns);
if (maximumActiveDutyCycle == 0) {
maximumActiveDutyCycle = 0.1f;
}
// neighborColumns are no longer necessary for calculations
// in this time step
columns[row][column].clearNeighborColumns();
// minDutyCycle represents the minimum desired firing rate
// for a Column(number of times it becomes active over some
// number of iterations).
// If a Column's firing rate falls below this value, it will
// be boosted.
/// minDutyCycle(c) = 0.01 * maxDutyCycle(neighbors(c))
float minimumActiveDutyCycle = this.MINIMUM_COLUMN_FIRING_RATE
* maximumActiveDutyCycle;
// 1) boost if activeDutyCycle is too low
/// activeDutyCycle(c) = updateActiveDutyCycle(c)
columns[row][column].updateActiveDutyCycle();
/// boost(c) = boostFunction(activeDutyCycle(c), minDutyCycle(c))
columns[row][column].setBoostValue(columns[row][column]
.boostFunction(minimumActiveDutyCycle));
// 2) boost if overlapDutyCycle is too low
/// overlapDutyCycle(c) = updateOverlapDutyCycle(c)
this.updateOverlapDutyCycle(row, column);
/// if overlapDutyCycle(c) < minDutyCycle(c) then
if (columns[row][column].getOverlapDutyCycle() < minimumActiveDutyCycle
&& this.getLearningState()) {
/// increasePermanences(c, 0.1*connectedPerm)
columns[row][column]
.increaseProximalSegmentSynapsePermanences(1);
}
}
}
}
}
/**
* Adds all Columns within inhitionRadius of the parameter Column to the
* neighborColumns field within the parameter Column.
*
* @param columnRowPosition position of Column within Region along y-axis
* @param columnColumnPosition position of Column within Region along x-axis
*/
void updateNeighborColumns(int columnRowPosition, int columnColumnPosition) {
if (columnRowPosition < 0 || columnRowPosition > this.region.getNumberOfRowsAlongRegionYAxis()
|| columnColumnPosition < 0
|| columnColumnPosition > this.region.getNumberOfColumnsAlongRegionXAxis()) {
throw new IllegalArgumentException(
"the Column being updated by the updateNeighborColumns method"
+ "in SpatialPooler class does not exist within the Region");
}
int localInhibitionRadius = this.region.getInhibitionRadius();
assert (localInhibitionRadius >= 0);
// forced inhibition of adjacent Columns
int xInitial = Math.max(0, columnRowPosition - localInhibitionRadius);
int yInitial = Math.max(0, columnColumnPosition - localInhibitionRadius);
// System.out.println("xInitial, yInitial: " + xInitial + ", " +
// yInitial);
int xFinal = Math.min(this.region.getNumberOfRowsAlongRegionYAxis(), columnRowPosition
+ localInhibitionRadius);
int yFinal = Math.min(this.region.getNumberOfColumnsAlongRegionXAxis(), columnColumnPosition
+ localInhibitionRadius);
// to allow double for loop to reach end portion of this.allColumns
xFinal = Math.min(this.region.getNumberOfRowsAlongRegionYAxis(), xFinal + 1);
yFinal = Math.min(this.region.getNumberOfColumnsAlongRegionXAxis(), yFinal + 1);
// System.out.println("xFinal, yFinal: " + xFinal + ", " + yFinal);
Column[][] columns = this.region.getColumns();
if (columns[columnRowPosition][columnColumnPosition].getNeighborColumns().size() != 0) {
// remove neighbors of Column computed with old inhibitionRadius
columns[columnRowPosition][columnColumnPosition].clearNeighborColumns();
}
for (int columnIndex = xInitial; columnIndex < xFinal; columnIndex++) {
for (int rowIndex = yInitial; rowIndex < yFinal; rowIndex++) {
if (columnIndex == columnRowPosition && rowIndex == columnColumnPosition) {
} else {
Column newColumn = columns[columnIndex][rowIndex];
if (newColumn != null) {
columns[columnRowPosition][columnColumnPosition].addNeighborColumns(new ColumnPosition(columnIndex, rowIndex));
}
}
}
}
}
/**
* @param neighborColumns
* @param desiredLocalActivity
* @return the kth highest overlapScore value of a Column object within the
* neighborColumns list.
*/
int kthScoreOfColumns(List neighborColumns,
int desiredLocalActivity) {
if (neighborColumns == null) {
throw new IllegalArgumentException(
"neighborColumns in SpatialPooler method kthScoreOfColumns cannot be null");
}
// TreeSet data structures' elements are automatically sorted.
Set overlapScores = new TreeSet();
for (Column column : neighborColumns) {
overlapScores.add(column.getOverlapScore());
}
// if invalid or no local activity is desired, it is changed so that the
// highest overlapScore is returned.
if (desiredLocalActivity <= 0) {
throw new IllegalStateException(
"desiredLocalActivity cannot be <= 0");
}
// k is the index of the overlapScore to be returned. The overlapScore
// is the score at position k(counting from the top) of all
// overlapScores when arranged from smallest to greatest.
int k = Math.max(0, overlapScores.size() - desiredLocalActivity);
if (overlapScores.size() > k) {
return (Integer) overlapScores.toArray()[k];
} else {
return 0;
}
}
/**
* Returns the radius of the average connected receptive field size of all
* the Columns. The connected receptive field size of a Column includes only
* the Column's connected Synapses.
*
* @return The average connected receptive field size.
*/
double averageReceptiveFieldSizeOfRegion() {
double regionAverageReceptiveField = 0.0;
// for each column
Column[][] columns = this.region.getColumns();
for (int x = 0; x < columns.length; x++) {
for (int y = 0; y < columns[0].length; y++) {
// get the set of connected synapses
Set> connectedSynapes = columns[x][y]
.getProximalSegment().getConnectedSynapses();
Dimension bottomLayerDimensions = this.region
.getBottomLayerXYAxisLength();
// get the column position relative to the input layer
double rowRatio = bottomLayerDimensions.width
/ this.region.getNumberOfRowsAlongRegionYAxis();
double columnX = rowRatio / 2 + x * rowRatio;
double columnRatio = bottomLayerDimensions.height
/ this.region.getNumberOfColumnsAlongRegionXAxis();
double columnY = columnRatio / 2 + y * columnRatio;
double totalSynapseDistanceFromOriginColumn = 0.0;
// iterates over every connected Synapses and sums the
// distances from it's origin Column to determine the
// average receptive field for this Column
for (Synapse connectedSynapse : connectedSynapes) {
double dx = Math.abs(columnX
- connectedSynapse.getCellColumn());
double dy = Math.abs(columnY
- connectedSynapse.getCellRow());
double connectedSynapseDistance = Math.sqrt(dx * dx + dy
* dy);
totalSynapseDistanceFromOriginColumn += connectedSynapseDistance;
}
double columnAverageReceptiveField = totalSynapseDistanceFromOriginColumn
/ connectedSynapes.size();
regionAverageReceptiveField += columnAverageReceptiveField;
}
}
regionAverageReceptiveField /= this.region.getNumberOfColumns();
return regionAverageReceptiveField;
}
void addActiveColumn(Column activeColumn) {
if (activeColumn == null) {
throw new IllegalArgumentException(
"activeColumn in SpatialPooler class method addActiveColumn cannot be null");
}
this.activeColumns.add(activeColumn);
}
/**
* Compute a moving average of how often this Column has overlap greater
* than minimumDutyOverlap. Exponential Moving Average(EMA): St = a * Yt +
* (1 - a) * St - 1.
*/
void updateOverlapDutyCycle(int columnRowPosition, int columnColumnPosition) {
if (columnRowPosition < 0 || columnRowPosition > this.region.getNumberOfRowsAlongRegionYAxis()
|| columnColumnPosition < 0
|| columnColumnPosition > this.region.getNumberOfColumnsAlongRegionXAxis()) {
throw new IllegalArgumentException(
"the Column being updated by the updateOverlapDutyCycle method"
+ "in SpatialPooler does not exist within the Region");
}
// Note whenever updateOverlapDutyCycle() is called, the
// overlapDutyCycle
// is always decremented less and less but only incremented if the
// Column's
// overlapScore was greater than the Region's minimumOverlapScore.
// Furthermore, the increment applied to overlapDutyCycle is a constant
// representing the maximum decrement of overlapDutyCycle from initial
// value 1. Because of this a Column's overlapDutyCycle has a upper
// bound of 1.
Column[][] columns = this.region.getColumns();
float newOverlapDutyCycle = (1.0f - Column.EXPONENTIAL_MOVING_AVERAGE_AlPHA)
* columns[columnRowPosition][columnColumnPosition].getOverlapDutyCycle();
if (columns[columnRowPosition][columnColumnPosition].getOverlapScore() > this.region
.getMinimumOverlapScore()) {
newOverlapDutyCycle += Column.EXPONENTIAL_MOVING_AVERAGE_AlPHA;
}
columns[columnRowPosition][columnColumnPosition]
.setOverlapDutyCycle(newOverlapDutyCycle);
}
public Region getRegion() {
return this.region;
}
@Override
public String toString() {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("\n===============================");
stringBuilder.append("\n---SpatialPooler Information---");
stringBuilder.append("\n biological region name: ");
stringBuilder.append(this.region.getBiologicalName());
stringBuilder.append("\n# of activeColumns produced: ");
stringBuilder.append(this.activeColumnPositions.size());
stringBuilder.append("\n===============================");
String spatialPoolerInformation = stringBuilder.toString();
return spatialPoolerInformation;
}
} |