Isolating informational masking in both pure and complex tone sequences.
OBJECTIVE
Interference between a target and simultaneous maskers occurs both at the cochlear level through energetic masking and more centrally through informational masking (IM). Hence, quantifying the amount of IM requires a strict control of the energetic component. Presenting target and maskers on different sides (i.e., dichotically) reduces energetic masking but provides listeners with important lateralization cues that also drastically reduce IM. The main purpose of this study (Experiment 1) was to evaluate a "switch" manipulation aiming at restoring most of the IM despite dichotic listening. Experiment 2 was designed to investigate the source of the difficulty induced by this switching dichotic condition.


METHODS
In Experiment 1, the authors presented 60 normal-hearing young adults with a detection task in which a regularly repeating target was embedded in a randomly varying background masker. The authors evaluated spatial masking release induced by three different dichotic listening conditions in comparison with a diotic baseline. Dichotic stimuli were presented in either a nonswitching or a switching condition. In the latter case, the presentation sides of dichotic target and maskers alternated several times throughout 10 sec sequences. The impact of the number of switches on IM was investigated parametrically, with both pure and complex tone sequences. In Experiment 2, the authors compared performance of 13 young, normal-hearing listeners in a monotic and dichotic version of the rapidly switching condition, using pure-tone sequences.


RESULTS
When target and maskers switched rapidly within sequences, IM was significantly stronger than in nonswitching dichotic sequences and was comparable with the masking effect induced by diotic sequences. Furthermore, Experiment 2 suggests that rapidly switching target and maskers prevent listeners from relying on lateralization cues inherent to the dichotic condition, hence preserving important amounts of IM.


CONCLUSIONS
This paradigm thus provides an original tool to isolate IM in signal and maskers having overlapping spectra.
1Fonds de la Recherche Scientifique-FNRS (FRS-FNRS); 2Unité de Recherche en Neurosciences Cognitives (UNESCOG), Center for Research in Cognition and Neurosciences (CRCN), Université Libre de Bruxelles (ULB), Brussels, Belgium; 3Sonic Arts Research Centre, School of Creative Arts, Queen's University Belfast, Belfast, United Kingdom; 4Laboratoire des Systèmes Perceptifs, UMR 8248, CNRS and Ecole normale supérieure, Paris, France; and 5Laboratoire de Neurophysiologie Sensorielle et Cognitive, Hopital Brugmann, Université Libre de Bruxelles (ULB), Brussels, Belgium.
Axelle
A
Calcus
Trevor
T
Agus
Régine
R
Kolinsky
Cécile
C
Colin
Paul
P
Deltenre
D000161:Acoustic Stimulation / Q000379:methods; D000293:Adolescent; D000328:Adult; D001299:Audiometry; D001301:Audiometry, Pure-Tone; D001307:Auditory Perception / Q000502:physiology*; D004007:Dichotic Listening Tests / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D010470:Perceptual Masking / Q000502:physiology*; D055815:Young Adult