Replotted results from Gardner et al. (1989, experiment 1) showing the dependence of /ru/ and /li/ responses (%) on the ΔF0 (semitones) applied to formant 2 of a four-formant stimulus, irrespective of the number of sources heard. Adapted with permission from the Acoustical Society of America.
Stimuli for experiment 1—standard dichotic stimulus configuration illustrated using a synthetic-formant analogue of the sentence “The yellow lion wore an iron muzzle.” The left ear receives F1 and F3; the right ear receives F2. The upper panels show the amplitude envelopes of the signals presented to each ear, normalized to the maximum value in the left ear. The lower panels show the corresponding spectrograms; narrow-band frequency analysis was used to illustrate clearly the harmonic structure of the stimuli (F0 = 150 Hz). The dashed line in the spectrogram for the left ear depicts the frequency contour of the second-formant competitor (F2C), when present, which corresponds to the time-reversed frequency contour for F2. The F0 of F2C was set either to match or to differ from that of the other formants.
Results for experiment 1—influence of ΔF0 on the effect of competitors (F2Cs) on the intelligibility of synthetic-formant analogues of sentences spoken with almost continuous voicing. Mean scores and inter-subject standard errors (n = 32) are shown for the control conditions (white bars), experimental conditions (gray bars), and the dichotic reference condition (black bar). The experimental conditions are subdivided into the case where the F0 for F2C matches that of the other formants (ΔF0 = 0, dark gray bar) and the cases where it does not (ΔF0 ≠ 0, light gray bars). The top axis indicates which formants were presented to each ear; the bottom axis indicates the ΔF0 for F2C (when present). Also shown are the mean scores following a median split of the data by rank order of the diotic scores for all 64 sentences. The results for the more and less intelligible sentences are indicated by upward- and downward-pointing triangles, respectively (see inset).
Results for experiment 2—effect of a competitor (F2C) with time-reversed frequency and amplitude contours on the intelligibility of synthetic-formant speech in two dichotic configurations, for which ΔF0 = 0. Mean scores and inter-subject standard errors (n = 16) are shown in the absence (black bars) and presence (gray bars) of F2C. The paired columns on the left- and right-hand sides correspond to the results for the standard and Rand configurations, respectively (see top axis). For each condition, the leftward- and rightward-pointing triangles indicate the mean scores when the ear receiving F1 was left or right, respectively (see inset).
Stimulus properties for the conditions used in experiment 1 (main session). The F0 frequency for F1, F2, and F3 was always 150 Hz. The ΔF0 on F2C, when present, was relative to 150 Hz.
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