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Visualization of hidden node activity in a feed forward neural network Adam Arvay.

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Presentation on theme: "Visualization of hidden node activity in a feed forward neural network Adam Arvay."— Presentation transcript:

1 Visualization of hidden node activity in a feed forward neural network Adam Arvay

2 Feed forward neural networks Function finding device Learns a function to transform a set of inputs into the desired output Uses supervised learning

3 Network building software PyBrain v0.3 Modular machine learning library for Python PyBrain is short for Python-Based Reinforcement Learning, Artificial Intelligence and Neural Network Library

4 Visualization tools NetworkX – Used for keeping track of node names and edges matplotlib/pyplot/pylab – Drawing everything

5 Data set Iris data set 150 total data points 4 inputs 3 outputs (classifications) 50 of each classification type CSV file

6 Networks analyzed 3 networks were constructed with different numbers of hidden layers – 4 input nodes (linear) – 4, 7, 10 hidden nodes (sigmoid) – 3 output nodes (softmax) Trained with back-propigation Training/validation data selected randomly 250 epochs

7 Visualizations Mean squared errors during training Network state Average activation levels Absolute hidden node sensitivity Weighted hidden node sensitivity Activation scatter

8 Mean squared error Quick way to evaluate training efficacy Plot the error vs. training time (epochs) Expect error to go down with increased training Greatly depends on quality of training data

9 Mean squared error

10 Network state visualization Displays abstract logical connections between nodes in a spatial layout Size to represent activation level Colored and line style used to depict connection type. Black for positive, red dashed for negative

11 Network state visualization A snapshot of what the network is currently doing Interactivity: – Shows the state of the network under a particular activation – Visible edge threshold magnitude can be set – Edges can be labeled

12 Network state



15 Network state all connections

16 Network state all connections with all labels

17 Network state 7 nodes no labels

18 Network state 7 nodes


20 Network state 10 nodes


22 Network state 10 all connections

23 Network state Gives information about current state of network Interactive Can get cluttered with many nodes and connections Difficult to see trends

24 Average activation levels Gives an idea of the network behavior over time for a particular classification type Can detect pattern differences in hidden layer between classification types Shows the average activation level of a hidden node across a classification type No interactivity

25 4 nodes, setosa

26 4 nodes, versacolor

27 4 nodes, virginica

28 7 nodes setosa

29 7 nodes versacolor

30 7 nodes virginica

31 10 nodes setosa

32 10 nodes versacolor

33 10 nodes virginica

34 Average activation Can see some patterns between classificaitons Easy to spot changes and non-changes Doesn’t depict the variance in the activations

35 Absolute hidden node sensitivity A quick way to determine the sensitivity of a hidden node to its inputs Can detect nodes which are insensitive to all inputs Can detect which inputs are ignored by all nodes Can detect patterns of connections across nodes

36 Hidden node sensitivity



39 Weighted sensitivity Accounts for differences in magnitude of the input parameters In the iris data set, the first input has a much larger average value than the last input. Normalizes the weights to the inputs

40 Weighted sensitivity



43 Comparison non-weighted vs weighted

44 Activation scatter Used along with average activation to get more information about the activation activity of hidden nodes across a classification type Can get a sense of the variance of a particular node Color used to represent a node along with data labels.

45 Activation scatter setosa

46 Activation scatter versacolor

47 Activation scatter virginica

48 Conclusion 4 main visualization tools – Training data – Network state – Average activation – Hidden node sensitivity Designed to be used with 3 layer networks with arbitrary number of nodes per layer

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