PubMed · 6837806
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A Margo. 1983. Auditory hallucinations.. https://doi.org/10.1176/ajp.140.4.aj1404515
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A series of experiments investigated the finding that the fundamental frequency (F0) discrimination of a group of unresolved harmonics (the "target") is impaired more by a masker which starts before and ends after it than when the masker and target are gated on and off together [Carlyon, J. Acoust. Soc. Am. 99, 517-524 (1996)]. Generally, the masker was a group of unresolved harmonics with an F0 of 210 Hz, the target F0s were geometrically centered on 210 Hz, both the targets and the masker were filtered between 3900 and 5400 Hz, and the target duration was 200 ms. The additional deterioration produced by the portion of the masker occurring before the target (the "forward fringe") was greater than that produced by the portion after the target ("backward fringe"), but both had some effect. The forward and backward fringes reduced sensitivity even when the portion of the masker synchronous with the targets was absent, although the reduction was greatest when it was present. The deterioration was markedly reduced by filtering the fringes into a frequency region remote from the target and the synchronous portion of the masker, by attenuating the fringes by 10 dB, or by presenting them either contralaterally to the target or diotically. It could not be reduced by allowing the F0 of the fringes and of the synchronous portion of the masker to differ greatly from that of the target, or by adding a low-frequency portion to the fringe, thereby providing an additional cue to the time of transition between fringe and target. Explanations based on peripheral adaptation and on seemingly similar effects previously observed with brief targets [Massaro, J. Acoust. Soc. Am. 58, 1059-1065 (1975); Kelly and Watson, J. Acoust. Soc. Am. 79, 1934-1938 (1986); Divenyi and Hirsch, Percept. Psychophys. 17, 246-252 (1975)] were rejected. The data are discussed in terms of a central mechanism which includes parts of the fringes in its estimate of the pitch of the target/masker mixture.
The ability to detect frequency changes in transposed sequences of tones was examined in a series of seven experiments. Listeners were asked to judge which of two transposed (i.e., frequency-shifted) comparison patterns preserved the sequence of relative frequencies presented in a preceding standard pattern. The task was performed with five-tone and two-tone patterns under conditions of high and minimal pattern uncertainty. Regardless of pattern length or level of uncertainty, frequency discrimination thresholds for a change in the relative frequency of a single tone were considerably higher when patterns were transposed than when they were not. There was a tendency for performance to worsen with increasing degrees of transposition (primarily under high uncertainty) but most of the detrimental effects of transposition occurred within the first two semitones of transposition. Minimal uncertainty testing resulted in large improvements with five-tone patterns (as much as one order of magnitude), but there was no effect of level of uncertainty on performance with two-tone patterns. Thresholds for changes in two-tone patterns were similar to (although slightly higher than) those for five-tone patterns under minimal-uncertainty testing. This pattern of results reveals that the effects of stimulus complexity (sequence length) and pattern familiarity (level of uncertainty) on relative-frequency discrimination are quite similar to the effects of these variables on absolute-frequency discrimination.
Two experiments examined how listeners weight binaural information of individual components in a multicomponent complex when they are instructed to use this information in various ways. On each experimental trial of the first experiment, a two-component complex consisting of a 553- and 753-Hz pure tone was presented to listeners over headphones. Each component had an interaural difference of time (IDT) that was randomly chosen from a single distribution. Listeners were to indicate the apparent position of the intracranial image relative to the midline on the basis of either the IDT of the 753-Hz component, the sum of the IDTs of the two components, or the difference between the two IDTs. Observer weights for the component IDTs were derived by computing the point-biserial correlations between the IDTs of the components and the listeners' left-right judgments. Three of the four listeners were found to adjust their weighting of the binaural information appropriately for each listening task, while the fourth listener consistently gave almost no weight to the 553-Hz component regardless of the listening condition. In a second experiment, listeners were instructed to attend to the randomly selected IDT of one of three components (553, 753, or 953 Hz) and to indicate whether the intracranial image produced by that component was to the left or right of midline. Only one of six listeners gave greatest weight to the target component regardless of its frequency. The other five listeners gave significant weight to all three components in all listening conditions. In all cases, individual differences in percent correct performance could be attributed largely to individual differences in weights with little variation in internal noise.