correlation_detector – Device for evaluating cross correlation between two spike sources¶
Description¶
The correlation_detector
is a device that receives spikes from two pools of
spike inputs and calculates the count_histogram
of interspike intervals
(raw cross correlation) binned to bins of duration \(\delta_\tau\).
The corresponding parameter delta_tau
defaults to 5 times the simulation
resolution.
The result can be obtained from the node’s status dictionary under the key
count_histogram
.
In parallel it records a weighted histogram, where the connection weights are used to weight every count. In order to minimize numerical errors, the Kahan summation algorithm is used when calculating the weighted histogram. Both are arrays of \(2\cdot\tau_{max}/\delta_{\tau}+1\) values containing the histogram counts in the following way:
Let \(t_{1,i}\) be the spike times of source 1,
\(t_{2,j}\) the spike times of source 2.
histogram[n]
then contains the sum of products of the weight
\(w_{1,i}\cdot w_{2,j}\), count_histogram[n] contains 1 summed over all events
with \(t_{2,j}t_{1,i}\) in
The bins are centered around the time difference they represent, but are leftclosed and rightopen. This means that events with time difference \(\tau_{max}\delta_\tau/2\) are counted in the leftmost bin, but event with difference \(\tau_{max}+\delta_\tau/2\) are not counted at all.
The correlation detector has two inputs, which are selected via the
receptor_port of the incoming connection: All incoming connections with
receptor_port = 0
will be pooled as the spike source 1, the ones with
receptor_port = 1
will be used as spike source 2.
Correlation detectors ignore any connection delays.
See Auto and crosscorrelation functions for spike trains to learn more about the usage of the correlation detector.
Parameters¶
Tstart 
real 
Time when to start counting events. This time 
should 
be set to at least start + tau_max in order to 

avoid 
edge effects of the correlation counts. 

Tstop 
real 
Time when to stop counting events. This time 
should 
be set to at most Tsim  tau_max, where Tsim is 

the 
duration of simulation, in order to avoid edge effects of the correlation counts. 

delta_tau 
ms 
Bin width. This has to be an odd multiple of the resolution, to allow the symmetry between positive and negative timelags. Defaults to 5 times the simulation resolution 
tau_max 
ms 
Onesided width. In the lower triangular part events with differences in [0, tau_max+delta_tau/2) are counted. On the diagonal and in the upper triangular part events with differences in (0, tau_max+delta_tau/2]. Defaults to 10 times the value of delta_tau. 
N_channels 
integer 
The number of pools. This defines the range of receptor_type. Default is 1. Setting N_channels clears count_covariance, covariance and n_events. 
histogram 
squared 
readonly  raw, weighted, crosscorrelation 
counts 
synaptic weights 
Unit depends on model 
histogram_correction 
list of integers 
readonly  Correction factors for Kahan summation algoritm 
n_events 
list of integers 
Number of events from source 0 and 1. By setting n_events to [0,0], the histogram is cleared. 
Receives¶
SpikeEvent
See also¶
Device, Detector