I'd suggest that you do a search under the term "echo location" as there is a fairly extensive bit of data in this area. Tom Brennan, CCC-A/SLP, RHD web page http://titan.sfasu.edu/~g_brennantg/sonicpage.html web master http://titan.sfasu.edu/~f_freemanfj/speechscience.html web master http://titan.sfasu.edu/~f_freemanfj/fluency.html