The present invention provides reagents and methods for modulating cone photoreceptor activity, and devices for assessment of cone photoreceptor activity. The spring steel is characterized in that the wire contains oxide inclusions with a sulfur concentration no more than 10 mass % such that no less than 70% of such inclusions, which exist in the outer layer outside one quarter of the diameter of the wire and have a width no smaller than 3 \u03bcm, satisfies the formula below,CaO+Al2O3+SiO2+MnO+MgO>80. An uplink subjective signal quality for each such handheld subscriber unit is determined based on a comparison of the stored test signal and the received test signal from the handheld subscriber unit. Therefore, the shift register circuit constructed of the latch circuit LAT functions as a low-voltage interface, and the input of the clock signal ck is stopped when the latch circuit LAT is inactive, so that the load and the consumption of power of the clock signal line are reduced.