Effect of spectral content and learning on auditory distance perception

We studied the importance of the stimulus spectrum and of the listener’s experience on the human ability to judge distance of auditory objects. The study was performed in a virtual auditory environment (VAE), created by convolution of the stimuli with non-individual Head-Related Transfer Functions (HRTFs) measured in a regular classroom. The listeners’ task was to judge the distance of sounds originating at distances of 0.15 to 2 meters directly ahead or to the right of the listener’s head. Three types of stimuli were presented: lowpass-filtered, highpass-filtered, and broadband stimuli. Each listener performed four blocks of measurements, two on one day and two on a later day, with separation of at least 12 hours. No significant effect of spectrum was found, presumably because the non-individual HRTFs do not provide accurate cues to the listeners, making the task very difficult even with broadband stimuli. However, a systematic learning effect was observed in all listeners: while their performance did not change across the blocks performed on the same day, it improved between the blocks performed on different days. Thus, it can be hypothesized that a process similar to memory consolidation is observed that leads to improved performance and that requires a long break between the measurement sessions.