Volume 135, Issue 1, January 2014
Index of content:
- PSYCHOLOGICAL ACOUSTICS 
Plasticity and modified loudness following short-term unilateral deprivation: Evidence of multiple gain mechanisms within the auditory system135(2014); http://dx.doi.org/10.1121/1.4835715View Description Hide Description
Auditory deprivation and stimulation can change the threshold of the acoustic middle ear reflex as well as loudness in adult listeners. However, it has remained unclear whether changes in these measures are due to the same mechanism. In this study, deprivation was achieved using a monaural earplug that was worn by listeners for 7 days. Acoustic reflex thresholds (ARTs) and categorical loudness ratings were measured using a blinded design in which the experimenter was unaware of which ear had been plugged. Immediately after terminating unilateral deprivation, ARTs were obtained at a lower sound pressure level in the ear that had been fitted with an earplug and at a higher sound pressure level in the control ear. In contrast, categorical judgments of loudness changed in the same direction in both ears with a given stimulus level reported as louder after unilateral deprivation. The relationship between changes to the ART and loudness judgments was not statistically significant. For both the ARTs and the categorical loudness judgments, most of the changes had disappeared within 24 h after earplug removal. The changes in ARTs, as a consequence of unilateral sound deprivation, are consistent with a gain control mechanism; however, the lack of relationship with the categorical loudness judgments, and the different pattern of findings for each measure, suggests the possibility of multiple gain mechanisms.
Effects of tonotopicity, adaptation, modulation tuning, and temporal coherence in “primitive” auditory stream segregationa)135(2014); http://dx.doi.org/10.1121/1.4845675View Description Hide Description
The perceptual organization of two-tone sequences into auditory streams was investigated using a modeling framework consisting of an auditory pre-processing front end [Dau et al., J. Acoust. Soc. Am. 102, 2892–2905 (1997)] combined with a temporal coherence-analysis back end [Elhilali et al., Neuron 61, 317–329 (2009)]. Two experimental paradigms were considered: (i) Stream segregation as a function of tone repetition time (TRT) and frequency separation (Δf) and (ii) grouping of distant spectral components based on onset/offset synchrony. The simulated and experimental results of the present study supported the hypothesis that forward masking enhances the ability to perceptually segregate spectrally close tone sequences. Furthermore, the modeling suggested that effects of neural adaptation and processing though modulation-frequency selective filters may enhance the sensitivity to onset asynchrony of spectral components, facilitating the listeners' ability to segregate temporally overlapping sounds into separate auditory objects. Overall, the modeling framework may be useful to study the contributions of bottom-up auditory features on “primitive” grouping, also in more complex acoustic scenarios than those considered here.
135(2014); http://dx.doi.org/10.1121/1.4835735View Description Hide Description
The purpose of this study was to determine the extent to which cochlear implant (CI) rate discrimination can be improved through training. Six adult CI users took part in a study that included 32 h of training and assessment on rate discrimination measures. Rate difference limens (DLs) were measured from 110 to 3520 Hz in octave steps using 500 ms biphasic pulse trains; the target and standard stimuli were loudness-balanced with the target always at an adaptively lower rate. DLs were measured at four electrode positions corresponding to basal, mid-basal, mid-apical, and apical locations. Procedural variations were implemented to determine if rate discrimination was impacted by random variations in stimulus amplitude or by amplitude modulation. DLs improved by more than a factor of 2 across subjects, electrodes, and standard rates. Factor analysis indicated that the effect of training was comparable for all electrodes and standard rates tested. Neither level roving nor amplitude modulation had a significant effect on rate DLs. In conclusion, the results demonstrate that training can significantly improve CI rate discrimination on a psychophysical task.
135(2014); http://dx.doi.org/10.1121/1.4838995View Description Hide Description
The discrimination of interaural phase differences (IPDs) requires accurate binaural temporal processing and has been used as a measure of sensitivity to temporal envelope and temporal fine structure (TFS). Previous studies found that TFS-IPD discrimination declined with age and with sensorineural hearing loss (SNHL), but age and SNHL have often been confounded. The aim of this study was to determine the independent contributions of age and SNHL to TFS and envelope IPD discrimination by using a sample of adults with a wide range of ages and SNHL. A two-interval, two-alternative forced-choice procedure was used to measure IPD discrimination thresholds for 20-Hz amplitude-modulated tones with carrier frequencies of 250 or 500 Hz when the IPD was in either the stimulus envelope or TFS. There were positive correlations between absolute thresholds and TFS-IPD thresholds, but not envelope-IPD thresholds, when age was accounted for. This supports the idea that SNHL affects TFS processing independently to age. Age was positively correlated with envelope-IPD thresholds at both carrier frequencies and TFS-IPD thresholds at 500 Hz, when absolute thresholds were accounted for. These results suggest that age negatively affects the binaural processing of envelope and TFS at some frequencies independently of SNHL.