The effect of notched noise on fl icker detection

20 Flicker perception was investigated using two-alternative forced-choice detection and discrimination tasks with four different 21 types of external noise: (1) broadband noise, (2) 5-Hz notched-noiseVbroadband noise with a 5-Hz band centered on the 22 signal frequency removed, (3) 10-Hz notched-noise, and (4) no external noise. The signal was a burst of 10-Hz sinusoidal 23 flicker presented in one of two observation intervals. In discrimination experiments, a pedestalVsinusoidal flicker with the 24 same frequency, duration, and phase as the signalVwas added to both observation intervals. With no noise, observers’ 25 performance first improved with increasing pedestal modulation, before deteriorating in accordance with Weber’s Law, 26 producing the typical “dipper” shaped plot of signal versus pedestal modulation. Noise affects performance, but the dipper 27 effect persisted in each type of noise. The results exclude three models: the ideal-observer in which the pedestal improves 28 performance by specifying the signal exactly; off-frequency-looking models in which the dipper depends on detection by 29 channels tuned to temporal frequencies different from that of the signal; and strict energy detectors. Our data are consistent 30 with signal processing by a single mechanism with an expansive non-linearity for near-threshold signal modulations (with an 31 exponent of six) and a compressive “Weberian” non-linearity for high modulations. 32