Short-term visual deprivation can enhance spatial release from masking

Highlights

• Brief visual deprivation transiently enhances auditory perception.

• 90 min of visual deprivation boosts out-of-phase competing noise detection.

• Auditory ability returns to baseline after 90 min of light exposure.

Abstract

This research aims to study the effect of short-term visual deprivation on spatial release from masking, a major component of the cocktail party effect that allows people to detect an auditory target in noise. The Masking Level Difference (MLD) test was administered on healthy individuals over three sessions: before (I) and after 90 min of visual deprivation (II), and after 90 min of re-exposure to light (III). A non-deprived control group performed the same tests, but remained sighted between sessions I and II. The non-deprived control group displayed constant results across sessions. However, performance in the MLD test was improved following short-term visual deprivation and performance returned to pre-deprivation values after light re-exposure. This study finds that short-term visual deprivation transiently enhances the spatial release from masking. These data suggest the significant potential for enhancing a process involved in the cocktail party effect in normally developing individuals and adds to an emerging literature on the potential to enhance auditory ability after only a brief period of visual deprivation.

Introduction

Several investigations on the blind have reported significant improvements to a number of auditory abilities [1], [2], [3]. However, little is known regarding the rapidity of these sensory changes following sensory deprivation. Some investigations have shed light on the mechanisms underlying the relative swiftness of this plasticity. For instance, auditory steady-state responses were found to be altered in some individuals following only 6 h of visual deprivation [4] and most recently, Meng et al. [5] found that one week of dark exposure could alter animal primary auditory cortex connectivity. Investigations on the impact of short-term visual deprivation for behavioral auditory processes in human have revealed increased loudness and pitch discrimination [6], reduced sound localization inaccuracies [7], and improved detection of mistuned harmonics [8]. However, further research is required to better understand the specific auditory abilities that can be enhanced within such a short timeframe.

The ability to isolate a target signal from background noise is a major enabling factor in the cocktail effect [9], [10]. This improvement of sound source segregation when the target and competing acoustic information are spatially separated is called the ‘spatial release from masking’ [11], [12]. Spatial release from masking resulting from binaural interaction can be evaluated using a Masking Level Difference (MLD: [13], [14]) test. For this, a target signal is presented binaurally simultaneously with a competing noise. An interaural phase difference of either the target signal or the masking noise is then introduced. This shift in phase produces a perceptual distinction between the spatial locations of the acoustics stimuli, which in turn facilitate the detection of the target signal. The MLD has received significant research interest and has been shown to be highly stable and reproducible [e.g. 15].

In this present study, we investigate the impact of short-term visual deprivation on the MLD test. Previous data have suggested that 90 min of visual deprivation can transiently enhance the perception of auditory cues in non-competing listening situations. Here, we hypothesize that this short-term visual deprivation will lead to an improvement in a competing auditory condition evaluated by the MLD test.

Twenty-six healthy individuals (14 females, 12 males; 20–32 years of age; mean age: 24) participated in the study. All participants gave their written informed consent and research approval was obtained from the Institutional Review Board of the Faculty of Medicine at the Université de Montréal. All participants reported normal or corrected-to-normal vision. Pure-tone detection thresholds at octave frequencies ranging from 250 to 8000 kHz were within normal limits in both ears for all participants.

The MLD test was administered [13], [14]. A 500 Hz pure-tone signal and a narrow-band noise were simultaneously presented binaurally. Detection thresholds were measured in three conditions. In the first condition, the pure tone and the masking noise were presented binaurally in-phase (homophasic condition: S0N0). In the second condition, the pure tone was presented 180° out-of-phase while the masking noise remained in-phase (antiphasic condition: SπN0). Finally, in the third condition, the pure tone was presented in-phase whereas the masking noise is presented 180° out-of-phase (antiphasic condition: S0Nπ). Detection thresholds were determined using a 3-down/1-up adaptive staircase procedure [16], [17] with 1 dB increments. Participants were asked to indicate the detection of the signal by pressing a button. Thresholds were identified when three identical ascending responses were reported. The MLD was calculated from the difference in the binaural detection thresholds between the homophasic and either antiphasic condition (i.e. S0N0 − SπN0; S0N0 − S0Nπ). All participants were blindfolded during the MLD test (Mindfold, Mindfold Incorporated, Tucson, AZ, USA) and no feedback about the correctness of the responses was given to the participants at any time. The stimuli were generated using an Interacoustics AC40 audiometer (Interacoustics, Assens, Denmark) and were presented binaurally through ER 3A insert earphones (Etymotic Research, Elk Grove, California, USA). The output of the acoustic system was calibrated using a sound level meter (model 824, Larson Davis, Provo, Utah) and artificial ear (6 cc coupler, model 4152, Brüel and Kjaër, Denmark).

Participants were separated into two age and gender matched groups. After the first administration of the MLD test (session I), one group (n = 13; visually deprived) kept their blindfold while the other (n = 13; controls) had their blindfolds removed (for an explicit detailing of the visual deprivation procedure, see [8]). Participants were asked to view or listen to a movie during a period of 90 min. The examiner who remained in the room during this time monitored participants. After 90 min, the MLD test was again administered (session II). After the second session, all participants had their blindfolds removed and waited another 90 min. Participants were asked to view a movie during this period. Their thresholds were measured a third time (session III) after this second 90-min period. Each administration of the MLD test lasted approximately 15 min during which the three MLD test conditions (S0N0; SπN0; S0Nπ) were administrated in pseudo-random order.