Disable connection after a certain amount of time

Getting Started
1

Is there any direct way to disable the connection between a node and an ensemble without actually inhibiting the ensemble?

In the setup I’m imagining, I’d have a pre and post ensemble both receiving input from a sine node and some learning happening on the connection between pre and post.
I would then like to turn off the input from sine to post to see if the connection between pre and post has learned to properly represent pre (which is still receiving input from sine).

Would setting the weights of the connection between sine and post achieve the desired effect?

2

The easiest way to do this would probably just be to have your sine node function go to 0 after some length of time, like

nengo.Node(lambda t: np.sin(t) if t < 1.0 else 0)

(which will output sine for the first second and then 0 afterwards).

3

But I would like to maintain the sine input to pre unchanged and also outputting zero could change the representation of post.

4

You would create two input Nodes, one that cuts off after some length of time and one that doesn’t, like

input0 = nengo.Node(lambda t: np.sin(t))
input1 = nengo.Node(lambda t: np.sin(t) if t < 1.0 else 0)

And then connect input0 to pre and input1 to post.

If you just wanted to have one source of the sine wave, you could do something like.

input0 = nengo.Node(lambda t: np.sin(t))
input1 = nengo.Node(lambda t, x: x if t < 1.0 else 0)
nengo.Connection(input0, input1, synapse=None)

And then connect input0 to pre and input1 to post, same as above.

Setting the input of a Connection to zero is the same as setting the connection weights to zero (either way the output of the Connection will be zero).

5

Thanks! So, if I understand, there is now way of “removing” a connection at runtime? The best I can hope for is to set it to always transmit zero?
This in theory should not change the output of the post synaptic ensemble as it would be simply summing this zero to anything else it receives on other connections, correct?

6

That’s correct, you can’t modify a network after it has been constructed (when it is passed to the Simulator). However, setting the Connection to output zero is the same as removing it, from a functional perspective.

7

Awesome, thanks again! :slight_smile:

8 
input0 = nengo.Node(lambda t: np.sin(t))
input1 = nengo.Node(lambda t, x: x if t < 1.0 else 0)
nengo.Connection(input0, input1, synapse=None)

This does not seem to work as I’m getting:
nengo.exceptions.ValidationError: Node.output: output function '<function <lambda> at 0x111113400>' is expected to accept exactly 1 argument (time, as a float)

9

Sorry, missed one part, you need to specify nengo.Node((lambda t, x: x if t < 1.0 else 0), size_in=1)

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