function act = input_function(N,t,Targets,VisDelay);
% N - size of input
% t - time step
% Targets - matrix of size (T,4) where T is num of targets
%            and each defined by four numbers, onset, offset, xloc, Ic
% VisDelay - delay from retinal stim till it reachs FEF visual cells

TauV = 60.;
SigP = 4.0;
SigT = 2.0;
act = zeros(1,N);
tt = t - VisDelay;

for i = 1:size(Targets,1) 
   for j = 1:N
      if ( (tt>Targets(i,1)) & (tt<Targets(i,2)) )
        xv = abs(j-Targets(i,3));
        if (xv>(N/2)) 
          xv = abs(N-xv);
        end
        phasic = exp( -(tt-Targets(i,1))/TauV );
        tonic = (1.-phasic);
        phasic = phasic * exp( -(xv^2)/(2.*SigP^2));
        tonic = tonic * 0.2 * Targets(i,4);
        tonic = tonic * exp( -(xv^2)/(2.*SigT^2));
        act(1,j) = act(1,j) + phasic + tonic;
     end
  end
end