Informational masking increases the costs of monitoring multiple channels

This study examined the costs of simultaneously monitoring two frequency regions. Listeners detected low- and high-frequency tones in a 2I4AFC procedure. On every trial, each signal was presented in either the first or second interval independently. Comparison of thresholds in single- and dual-signal conditions provided an estimate of the costs. Thresholds were obtained in quiet, in notched-filtered noise, and in randomized multitone maskers. No cost was found in quiet, whereas large costs were found for the masked conditions, especially for the multitone masker. These results suggest that costs of dividing attention in frequency depend on both signal and nonsignal channels.