def filtered_response(spk_times, tau = .01):
    spk_times = spk_times.reshape((-1, 1))
    norm_factor = tau * np.sqrt(2. * np.pi)
    return lambda t: np.sum(np.exp(-(spk_times - t.reshape((1,-1))) ** 2 / (2 * tau * tau)), 0) / norm_factor