Bilateral implantation can offer CI listeners the ability to track dynamic auditory spatial difference cues and compare these changes to changes in their own head position, resulting in a reduced rate of front-back confusions. This suggests that, for these patients, estimates of auditory acuity based solely on static laboratory settings may underestimate their real-world localization abilities.

In the visual domain, a stationary object that is difficult to detect usually becomes far more salient if it moves while the objects around it do not. This “pop out” effect is important for parsing the visual world into figure/ground relationships that allow creatures to detect food, threats, etc. We tested for an auditory correlate to this visual effect by asking listeners to identify a single word, spoken by a female, embedded with two or four masking words spoken by males. Percentage correct scores were analyzed and compared between conditions where target and maskers were presented from the same position vs. when the target was presented from one position while maskers were presented from different positions. In some trials, the target word was moved across the speaker array using amplitude panning, while in other trials that target was played from a single, static position. Results showed a spatial release from masking for all conditions where the target and maskers were not located at the same position, but there was no statistically significant difference between identification performance when the target was moving vs. when it was stationary. These results suggest that, at least for short stimulus durations (0.75 s for the stimuli in this experiment), there is unlikely to be a “pop out” effect for moving target stimuli in the auditory domain as there is in the visual domain.

Objectives-We investigated the ability of single-sided deaf listeners implanted with a cochlear implant (SSD-CI) to (i) determine the front-back and left-right location of sound sources presented from loudspeakers surrounding the listener and (ii) use small head rotations to further improve their localization performance. The resulting behavioral data were used for further analyses investigating the value of so-called "monaural" spectral shape cues for front-back sound source localization.Design-Eight SSD-CI patients were tested with their CI on and off. Eight NH listeners, with one ear plugged during the experiment, and another group of eight NH listeners, with neither ear plugged, were also tested. Gaussian noises of three-second duration were bandpass filtered to 2-8 kHz and presented from one of six loudspeakers surrounding the listener, spaced 60° apart. Perceived sound source localization was tested under conditions where the patients faced forward with the head stationary, and under conditions where they rotated their heads between ±30°. Results-(i)Under stationary listener conditions, unilaterally-plugged NH listeners and SSD-CI listeners (with their CIs both on and off) were nearly at chance in determining the front-back location of high-frequency sound sources. (ii) Allowing rotational head movements improved performance in both the front-back and left-right dimensions for all listeners. (iii) For SSD-CI patients with their CI turned off, head rotations substantially reduced front-back reversals, and the combination of turning on the CI with head rotations led to near-perfect resolution of front-back sound source location. (iv) Turning on the CI also improved left-right localization performance. (v) As expected, NH listeners with both ears unplugged localized to the correct front/back and leftright hemifields both with and without head movements.Conclusions-Although SSD-CI listeners demonstrate a relatively poor ability to distinguish the front-back location of sound sources when their head is stationary, their performance is substantially improved with head movements. Most of this improvement occurs when the CI is off, suggesting that the NH ear does most of the "work" in this regard, though some additional gain is introduced with turning the CI on. During head turns, these listeners appear to primarily rely on comparing changes in head position to changes in monaural level (ML) cues produced by the direction-dependent attenuation of high-frequency sounds that result from acoustic head