Monaural localization: An analysis of practice effects

Four listeners (experimental group) received one trial a session for 60 sessions on a monaural localization task in which six loudspeakers, positioned 15 deg apart, were placed on the side of the functioning ear. Four additional listeners (control group) received 60 massed trials first and then one trial a session for 60 sessions. The stimulus consisted of a single train of five high-frequency pulses. An ANOVA conducted on the 60 trials distributed over sessions showed that the experimental group’s performance was significantly inferior to that of the control group. Members of the former continued to displace sounds toward the open ear throughout the entire test. Those of the control group exhibited this tendency, but to a much lesser extent. The experience of locating 60 massed trials clearly had a robust effect on subsequent performance. We contend that, by virtue of presenting only one trial a session, the magnitude of the massed-trial effect was little attenuated by our tests to measure it. We interpret our substantive finding to mean that during the 60 massed trials, the control group formed a perceptual representation of the auditory space which served it well when placed on the one-trial-a-session regimen. Those in the experimental group were unable to develop an adequate representation of the auditory space, presumably because their monaural localization experience was restricted to only one trial a session.