IMPLEMENTATION  AND EVALUATION OF AUDITORY MODELS FOR HUMAN ECHOLOCATION

Abstract: Blind  people use echoes to detect  objects  and  to  find their  way, the  ability  being known as human echolocation.   Previous  research  have found some of the  favorable  conditions  for the  detection  of the object,  with  many  factors  yet  to  be analyzed  and  quantified.    Studies  have  also shown  that blind people are more efficient than  the  sighted  in echolocating,  with  the  performance  varying  among  the individuals.   This  motivated the  research  in human  echolocation  to move in a new direction  to get a fuller understanding for the high detection  of the blind.  The psychoacoustic  experiments solely cannot determine  how the superior echo detection  of the blind listeners should be attributed to perceptual or physiological causes.  Along with the perceptual results it is vital to know how the sounds are processed in the  auditory system.   Hearing  research  has led to the  development of several auditory  models by combining  the  physiological  and  psychological  results  with  signal  analysis  methods.    These  models try  to describe how the auditory system  processes the signals.  Hence, to analyze how the sounds are processed for the high detection  of the blind, auditory  models available  in the literature were used in this thesis.  The results  suggest  that repetition pitch  is useful at  shorter  distances  and is determined from the peaks in the temporal  profile of the autocorrelation function computed  on the neural activity pattern. Loudness attribute also plays a role in providing information  for the listeners to echolocate at shorter  distances.  At longer distances  timbre  aspects such as sharpness  information  might be used by the listeners  to detect  the objects.  It was also found that the repetition pitch,  loudness and sharpness attributes in turn  depend on the room acoustics  and type of the stimuli  used.  These results  show the fruitfulness  of combining  results  from different  disciplines  through  a mathematical framework  given by signal analysis.