Phases in the experimental design for both training and control groups of participants.
Experimental procedure for a single trial. During the pre, control 1, control 2, post 1, and post 2 phases of the experiment, only “test” portion of the procedure (steps 1–3) was implemented. During the training phases (train 1 and train 2), all steps of the procedure were implemented: .
Interaural time difference (ITD) as a function of source azimuth angle (two-pole coordinates, with source elevation fixed at 0°) based on HRTF verification measurements of the 3D sound card apparatus (solid symbols). These data are well approximated by a model of ITD change based on a spherical head (solid line) with a diameter of (Woodworth and Schlosberg, 1954). For comparison purposes, ITD data based on HRTF measurements from one of the participants in this study (listener SLO) are also shown (open symbols).
(Color online) HRTF magnitude spectrum contours for the left and right ear as a function of source azimuth angle (upper panels) and elevation angle (lower panels) based on the HRTF verification measurements of the 3D sound card apparatus. For the azimuth angle analyses, source elevation was fixed at 0°. For elevation angle analyses, source azimuth was fixed at 0°. Note the changes in spectral pattern, especially in the right (ipsilateral) ear, as azimuth angle increases form 0° to 180°. In general, front hemifield sources (0°–90° azimuth) appear to have greater level in the ipsilateral (right) ear in the bandwidth than do sources in the rear hemifield (90°–180° azimuth). More complicated changes in spectral patterns are observed for changes in source elevation, where the frequencies of various spectral notches in the bandwidth change as a function of source elevation.
(Color online) Same as Fig. 4, but for HRTF data from listener SLO. Note generally more complicated patterns of spectral change as a function of both azimuth (front-back location) and elevation relative to the HRTF data from the 3D sound card apparatus (Fig. 4).
HRTF level differences (ipsilateral ear only) in -octave bands between front and rear hemifield locations that are symmetrically displaced from 90° azimuth along the horizontal plane (0° elevation) from the 3D sound card apparatus. Displacements ranging from to (directly in front versus directly behind) are shown. Positive level differences indicate greater level for the frontal source. Note for this HRTF set, frontal sources produce consistently greater level in the bandwidth for all displacements.
Same as Fig. 6, but for HRTF data from listener SLO. Note for this HRTF set, frontal sources also produce consistently greater level in the bandwidth, although the effect is less pronounced than for the HRTF data from the 3D sound card apparatus (Fig. 6). In other lower and higher frequency regions, rear hemifield locations have greater level.
Scatterplots of target sound source angle versus orienting response angle for a single representative listener in the training group (listener SCD). The data are displayed in the three-pole coordinate system for each phase in the experimental procedure (indicated in column headings). Reversals in the front-back dimension are indicated by open symbols. Mean unsigned error, , for the data displayed in each panel (reversals resolved) is also indicated. This listener shows a large reduction in the number of reversals during and following the training procedures.
Same as Fig. 8, but for data from listener SLO in the training group. Note that this listener shows little to no effect of the training procedures, although overall localization accuracy for this listener was quite high initially.
Same as Fig. 8, but for data from listener SCI in the control group.
Same as Fig. 8, but for data from listener SCG in the control group.
Summary of mean unsigned error, , for each dimension in the three-pole coordinate system. Each data point represents the mean across listeners in the training or control groups for a given phase in the experiment. Bars represent one standard error of the mean across listeners in each group . All responses identified as front-back reversals were resolved to the correct hemifield prior to computation. Within each group, no statistically significant differences are observed in mean throughout the phases of the experiment.
Proportion of responses identified as front-back reversals before (pre) and after (post 1) either training or control. Chi-square statistics are indicated for those listeners who showed a significant difference in front-back reversals in the pre versus post 1 phases ( ; ; ).
Proportion of responses identified as front-back reversals before (prc) and after (post 2) traning. Chi-square statistics are indicated for thsoe listeners who showed a significant difference in front-back reversals in the pre versus post 2 phase ( ; ; ).
Breakdown of front-back reversal direction in initial localization testing (pre phase) for all listeners. Back-to-front reversals represent responses to front hemifield sources that were incorrectly localized to the rear hemifield. Front-to-back reversals represent responses to rear hemifield sources that were incorrectly localized to the front hemifield. The proportions of the total number of responses that fall in each category are displayed.
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