Auditory Occlusion Research Articles

A disjointed account of the illusion of auditory continuity: in favor of hearing everyday sounds but against hearing semantic properties

ABSTRACT I will investigate the auditory illusion of continuity, which is the phenomenon of auditory occlusion in which we are able to hear a sound as continuous even though it has been masked by another sound. This phenomenon seems to have a perceptual nature when it occurs in the context of everyday sounds, while it seems to have a cognitive nature when it occurs in the context of speech sounds. This difference has the following consequences: (1) We need to have a differentiated approach to the study of this phenomenon; (2) the perceptual explanation of the phenomenon involving everyday sounds indicates that everyday sounds can be auditorily perceived; and (3) the cognitive explanation of the phenomenon involving speech sounds suggests, instead, that semantic properties cannot be auditorily perceived. From (2) and (3) it follows that while we have a good argument for the rich view when focusing on everyday sounds, we seem to lack an analogous argument to support the rich view in the context of speech sounds. Thus, I will suggest a new argument for the view that we do not hear semantic properties, as language understanding seems to be primarily a cognitive ability.

Implementation of a simplified, artificial external ear test fixture for measurement of the earplug induced auditory occlusion effect

Earplugs remain a frequently used short-term solution for occupational hearing conservation. Due to comfort limitations, as induced by, e.g., the occlusion effect, workers often only wear earplugs for limited amounts of time and are likely to develop professional hearing loss. The occlusion effect expresses itself in the low frequencies through an altered perception of the wearer’s own voice and the amplification of physiological noises that occur upon earplug insertion. While many studies examined the occlusion effect experimentally, no study was found that attempted to implement an artificial external ear model dedicated to the measurement of the objective occlusion effect. A simplified external ear test fixture can help to better assess and design earplugs, because it allows standardized experimental testing. This work describes the implementation of a cylindrical artificial test fixture of the human outer ear that comprises the auditory canal as well as the bony, cartilaginous, and skin tissues that are made up of rigid polyurethane foam and two different types of silicone, respectively. Obtained measurement results are compared to literature findings.

A simplified axi-symmetric finite element model of the human outer ear to determine the earplug induced auditory occlusion effect

Earplugs are a frequently used short-term solution for hearing conservation in the workplace environment. Due to limited auditory comfort, however, workers often only wear them for short periods of time and become prone to hearing loss. An important source of discomfort is the auditory occlusion effect, which expresses itself through the distortion of the wearer's voice and the amplification of physiological noises upon earplug insertion. Simplified numerical modeling can help to better assess and design earplugs, because it requires few system resources and is simpler in terms of numerical and experimental implementation than an equivalent complex model. This work describes a novel coupled linear elasto-acoustic two dimensional finite element (FE) model of the human outer ear. The model comprises the auditory canal as well as the bony, cartilaginous, and skin tissues whose material parameters were approximated using literature findings. The outlined model can compute the transfer functions between the sound pressure levels at the eardrum and a structure-borne excitation for both an unoccluded ear and an ear occluded by a molded earplug. Simulated occlusion effects are examined as a function of excitation, earplug, and insertion depth. Predicted model results are compared to literature findings and to findings obtained from an equivalent three dimensional FE-model.

Investigation of the Auditory Occlusion Effect with Implications for Hearing Protection and Hearing Aid Design

Previous research has shown that auditory occlusion effects could inhibit people from using hearing protection devices or hearing aids, which raises safety and usability concerns. The objective of this study was to evaluate occlusion effects as a function of insertion depth (shallow and deep), earplug type (foam earplug and medical balloonbased earplug), and excitation source (bone vibrator and self vocal utterance). Ten participants, six male and four female, completed the experiment. The ANOVA and post hoc tests conducted on the measured occlusion effects revealed main effects of insertion depth and earplug type, as well as an interaction effect between insertion depth and earplug type. The occlusion effect of deeply inserted earplugs was smaller than that of shallowly inserted earplugs by 11.2 dB. At deep insertion, the balloon-based earplugs produced an occlusion effect of 14.9 dB while the foam earplugs produced 5.9 dB.

Low Frequency Sound as a Navigational Tool for People with Visual Impairments

For decades, a mistaken assumption in the habilitation of travel for people with visual impairments has been that the use of “echolocation” is a dominant feature of acoustic information for the guidance of locomotion. This paper outlines a theoretical model of acoustic information available in many travel situations. The acoustic information consists of a build up of low frequency sound along large structures such as walls. Useful frequencies are low enough that the experience of this build up is often one of feeling rather than hearing. Experimental validation of this model was accomplished by having participants with visual impairments walk along walls with varying types of auditory occlusion and through laboratory based manipulations of acoustic information. Results indicate that the model is appropriate. Useful acoustic information appears to extend up to 1 m from a wall. There is strong evidence that participants make use of binaural information, gauging the similarity of acoustic information reaching each ear to maintain orientation to a wall. Motion through the sound field near the wall makes the information more useful but it is unclear whether motion in certain directions or conditions is more useful than others.

Perception of acoustic occlusion using body-scaled judgments

Occlusion has been found to compel visual perception of object position and scene analysis [G. A. Kaplan, Percept. Psychophys. 6, 193–198 (1969); W. H. Warren and S. Wang, J. Exp. Psychol. 13, 371–383 (1987)]. Auditory occlusion may also provide salient information about the locations of both sound sources and surfaces in an acoustic scene. In the current experiment, blindfolded participants were asked to listen to sound occluded by an aperture and judge whether unobstructed passage was afforded for various aperture sizes (e.g., W. H. Warren and S. Wang, 1987). Judgments were found to be highly accurate, suggesting the salience of occlusion information for auditory perception. Information from the relative loudness between aperture sizes may have contributed to this ability.

Kinesthetic Sensing for the EMG Controlled "Boston Arm"

The contribution of a novel cutaneous display of elbow angle to an amputee's ability to position an EMG-controlled externally powered elbow prosthesis was objectively evaluated. Comparisons were made between the amputee's positional control of his conventional mechanical cable-operated elbow and the EMG "Boston Arm"l elbow, with and without angle feedback, in REACHING tasks with vision occluded in all cases and with and without auditory occlusion. MATCHING tasks compared his ability to position the EMG limb to conform with the flexion of his normal (contralateral) elbow. Computer reduction of almost 9000 individual trials and analysis of variance indicated that for the EMG limb the tactile feedback with sound occluded reduced errors by 50 percent. Terminal device load did not significantly affect positioningperformance due to the force proprioception built into the Boston Arm. In comparison with the standard mechanical prosthesis, the EMG limb with feedback achieves virtually identical kinesthetic performance. The display is completely compatible with the EMG control, causes no discomfort to the wearer, and is not significantly degraded by the environmental conditions of the limb socket.