Temporal effects in simultaneous masking with on- and off-frequency noise maskers: effects of signal frequency and masker level.

International audienceTemporal effects in simultaneous masking were measured as a function of masker level for anon-frequency broadband masker and an off-frequency narrow-band masker for signal frequencies of750, 1730, and 4000 Hz. The on-frequency masker was 10 equivalent rectangular bandwidths~ERBs! wide and centered at the signal frequency; the off-frequency masker was 500 Hz wide andits lower frequency edge was 1.038 ERBs higher in frequency than the signal. The primary goal ofthe study was to determine whether previously observed differences regarding the effects of signalfrequency and masker level on the temporal effect for these two different types of masker might bedue to considerably different signal levels at threshold. Despite similar masked thresholds, theeffects of signal frequency and masker level in the present study were different for the two maskertypes. The temporal effect was significant for the two highest frequencies and absent for the lowestfrequency in the presence of the broadband masker, but was more or less independent of frequencyfor the narrow-band masker. The temporal effect increased but then decreased as a function of levelfor the broadband masker ~at the two higher signal frequencies, where there was a temporal effect!,but increased and reached an asymptote for the narrow-band masker. Despite the different effects ofsignal frequency and masker level, the temporal effects for both types of masker can be understoodin terms of a basilar-membrane input–output function that becomes more linear during the courseof masker stimulation

Effect of contralateral precursor type on the temporal effect in simultaneous masking with tone and noise maskers.

International audienceA sound ~contralateral precursor! presented to the nontest ear prior to the onset of a masker andprobe has been shown to reduce the temporal effect in simultaneous masking with noise maskers butnot with tonal maskers. The present study examined this further. The probe was a 4.0-kHz tone. Inexperiment 1a, the masker was a 4.4-kHz tone and the precursor was a 4.4-kHz tone or anunmodulated ~UM! or amplitude-modulated ~AM! band of noise ~4.4–8.0 kHz!. In experiment 1b,the masker was a broadband noise and the precursor was a UM or an AM broadband noise. In bothexperiments the precursor consistently reduced the temporal effect for only one of the seven or eightsubjects, regardless of precursor type. These largely negative results indicate that it may not bepossible to use contralateral precursors to gain much insight into the mechanisms underlyingtemporal effects in simultaneous masking

Effectiveness of narrow-band versus tonal off-frequency maskers.

International audienceThe present study was a follow-up to a pilot study in which it was found that a 500-Hz-widenarrow-band noise ~NBN! masker produced more masking than a tonal ~T! masker for signalfrequencies both above and below the masker frequency. The aim of the present study was todetermine to what extent these results were influenced by an interaction of the relatively rapidtemporal envelope fluctuations of the NBN and the short ~10-ms! duration of the signal. In the firstexperiment, the masking produced by a regular NBN, a low-noise noise ~LNN!, and a T wascompared. The LNN produced less masking than the NBN, and about as much as the T, suggestingthat the inherent amplitude fluctuations in the NBN were largely responsible for the greater maskingproduced by that masker. In the second experiment, the masking produced by a regular NBN wascompared with that by a T for a signal duration of 10 or 200 ms. The difference in masking betweenthe two maskers was reduced or eliminated when the signal duration was 200 ms, because thethreshold in the presence of the NBN masker decreased more with increasing signal duration. Thiscould reflect a decreased ‘‘confusion’’ between the signal and the inherent fluctuations of the NBNmasker

Effect of aspirin on the temporal effect in simultaneous masking with on- and off-frequency maskers

International audienceThis psychoacoustical study examined individual differences in spatial hearing and aims to develop learning methods to improve auditory localization performance in virtual environments. Nowadays, acoustic cues that are extracted by the human auditory system to localize sound sources (interaural time and level differences, monaural spectral cues, distance cues...) have been well identified. Many technological tools are now designed to produce a 3-dimensional perception of sounds emitted through headphones. To create the illusion of a sound originating from outside the head, these tools use Head-Related Transfer Functions (HRTFs) that are not individualized. Hence, the "realism" of the simulation is not perfect, since these listeners "listen with someone else's ears". The study presented here is an attempt to find the best way to adapt listeners to these "distorted" 3-D auditory environments. At the first place, we examined the individual differences existing in auditory-localization capacity for real sound sources. We also looked at the type of systematic errors in localization responses as well as spatial asymmetries in these errors. To do so, we measured auditory localization responses of 22 right-handed and 10 left-handed normal-hearing subjects in an anechoic room. Twelve loudspeakers were placed behind a curtain at +/- 7, 21, 35, 49, 63 and 77° in the horizontal plane, at 2.10 meters from the listener's head. The curtain was graduated every 10° (from -90° to +90°) to help listeners to give their answers. The signal was a burst of narrow-band noise (250-2000 Hz) lasting 50 ms repeated at a rate of 10 bursts/sec, for a total duration of 500 ms and an overall level of 80 dB SPL (measured at the theoretical center of the head). Listeners had to indicate where they had heard the source, by placing a cursor on a computer screen displaying a picture of the curtain with its graduations. They received no feedback on their answers. The signal was presented twice from each of the 12 loudspeakers, so that a "run" consisted in 24 randomized trials (24 localization responses). Each subject completed 30 runs. The results showed that (1) individual performance was very stable along the 30 trials, (2) most of the subjects underestimated (rather than overestimated) the azimuth of the source, (3) there was a great inter-individual variability in the size of the absolute error (mean angular distance between actual and estimated angle), (4) there was an effect of handiness on spatial asymmetries observed on the absolute error: While the error was of similar size for left and right sources for 8 out of the 10 left-handed subjects, this error was significantly greater with right sources than with left ones for 16 out of the 22 right-handed subjects. In a second experiment, we showed that the use of a visual-auditory feedback eliminated this asymmetry after a few (less than 10) learning runs. Future experiments will aim to identify the cause of these spatial asymmetries, the best way to eliminate them, and learning methods for localization distorted acoustical environments

Auditory streaming without spectral cues in hearing-impaired subjects

International audienc

Spectral integration in bands of modulated or unmodulated noise

International audienc

Auditory stream segregation on the basis of amplitude-modulation rate

International audienc