Pinnae assist in sound localization, and changes in auricle shape, position, or projection can theoretically alter the perceived position of a sound. The minimal displacement required to affect perceived sound location is undefined. This study quantified the error in horizontal sound localization when auricle projection is slightly decreased. The study was conducted at two sites by different experimenters, using different (though similar) systems, over a year apart. There were 21 normal-hearing participants: 11 at the University of Virginia (UVA) and 10 at James Madison University (JMU). Both UVA and JMU protocols involved a normal listening condition and a second condition with a headband that slightly altered pinnae projection by pushing the helixes medially against the temporal bones. Participants identified the location of a short, moderate-intensity noise burst from one of 8 speakers distributed in a horizontal array. Root mean squared error was calculated from tests of 48 trials. Localization errors in the UVA data were greater with the headband than without (t10=2.6; p=.023; Cohen’s d=.8 or ‘large’ effect size). The experiment was repeated at JMU and results replicated; localization errors were greater with than without the headband (t9=2.4; p=.034; Cohen’s d=.8). There was no effect of testing order and no consistent direction of error in either protocol. None of six anatomical measurements of pinnae correlated with the decrease in azimuth accuracy. Combined data from both experiments show a highly significant effect of the slightly medialized helix (t20=3.6, p=.002; d=.9). These data indicate the minimum pinna change required to alter sound localization is at least as small as the 15 mm average movement of the helix or 29 degree reduction in auricle projection. These data on psychoacoustic effect of altering auricle projection may be of relevance after otoplastic operations
