Human Echolocation in Static Situations: Auditory Models of Detection Thresholds for Distance, Pitch, Loudness and Timbre

We investigated, by using auditory models, how three perceptual parameters, loudness, pitch and sharpness, determine human echolocation. We used acoustic recordings from two previous studies, both from stationary situations, and their resulting perceptual data as input to our analysis. An initial analysis was on the room acoustics of the recordings. The parameters of interest were sound pressure level, autocorrelation and spectral centroid. The auditory models were used to analyze echolocation resulting from the perceptual variables, i.e. loudness, pitch and sharpness. Relevant auditory models were chosen to simulate each variable. Based on these results, we calculated psychophysical thresholds for detecting a reflecting object with constant physical size. A non-parametric method was used to determine thresholds for distance, loudness, pitch and sharpness. Difference thresholds were calculated for the psychophysical variables, since a 2-Alternative-Forced-Choice Paradigm had originally been used. We found that (1) blind persons could detect objects at lower loudness values, lower pitch strength, different sharpness values and at further distances than sighted persons, (2) detection thresholds based on repetition pitch, loudness and sharpness varied and depended on room acoustics and type of sound stimuli, (3) repetition pitch was useful for detection at shorter distances and was determined from the peaks in the temporal profile of the autocorrelation function, (4) loudness at shorter distances provides echolocation information, (5) at longer distances, timbre aspects, such as sharpness, might be used to detect objects. We also discuss binaural information, movements and the auditory model approach. Autocorrelation was assumed as a proper measure for pitch, but the question is raised whether a mechanism based on strobe integration is a viable possibility.