Human frequency response functions of harmonic 2, 4, 8 and 16 cycle angular frequency filters

We measured narrow-band human frequency response functions for four harmonic angular frequency filters whose test frequencies were centered at either 2, 4, 8 or 16 cycles using a supra-threshold summation method. The four filter response functions of 17 experimental conditions (each) were measured eight to nine times among five observers (NAS, MMM, ERB, MC and TPL). The results show that, for the arbitrarily selected filter phases, maximum summation effect occurred at test frequency for filters centered at 2 and 4 cycles. For both 8 and 16 cycles test frequencies, maximum summation occurred at the lower harmonics. While at 8 cycles, for F₈(θ), a relative strong summation effect was observed, at 16 cycles, for F₁₆(θ), almost maximum inhibition occurred. These results allow us to conclude that there are narrow-hand angular frequency filters operating in human visual system either through summation or inhibition of specific frequency ranges. Furthermore, as a general result, it appears that addition of higher angular frequencies to low ones disturbs lower angular frequency perception (i.e. 2 and 4 cycles) whereas addition of lower harmonics to higher ones seems to improve detection of higher angular frequency harmonics (i.e. 8 and 16 cycles)