Effects of Forward Masking on Sound Localization in Cats. I: Basic Findings

228 words; limited 250) 19 Forward masking is traditionally measured with a detection task in which the addition of 20 a preceding masking sound results in an increased signal-detection threshold. Little is known 21 about the influence of forward masking on localization of free-field sound for human or animal 22 subjects. Here we recorded gaze shifts of two head-unrestrained cats during localization using a 23 search-coil technique. A broadband (BB) noise masker was presented straight ahead. A brief 24 signal could come from one of the 17 speaker locations in the frontal hemi-field. The signal was 25 either a BB or a band-limited (BL) noise. For BB targets, the presence of the forward masker 26 reduced localization accuracy at almost all target levels (20 to 80 dB SPL) along both horizontal 27 and vertical dimensions. Temporal decay of masking was observed when a 10-ms inter-stimulus 28 gap was added between the end of the masker and the beginning of the target. A large effect of 29 forward masking was also observed for BL targets with low (0.2–2 kHz) and mid (2–7 kHz) 30 frequencies, indicating that the interaural timing cue is susceptible to forward masking. Except at 31 low sound levels, a small or little effect was observed for high-frequency (7–15 kHz) targets, 32 indicating that the interaural level and the spectral cues in that frequency range remained 33 relatively robust. Our findings suggest that different localization mechanisms can operate 34 independently in a complex listening environment. 35