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Apr 2012

Volume 8, Issue 2, pp. 8-56

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Select this Article		Acoustical Tests of Middle‐Ear and Cochlear Function in Infants and Adults Douglas H. Keefe Acou. Today Volume 8, Issue 2, pp. 8-17 (2012); (10 pages) Full Text: \| Download PDF
	+ -	Show Abstract The peripheral processing of sound by the external ear, middle ear and cochlea precedes the neural encoding of sound. The external ear collects sound power that is transmitted and reflected within the ear canal, absorbed by the middle ear, and transmitted as a coupled mechanical‐fluid wave motion within the cochlea. The cochlea analyzes the time‐varying frequency components of the incident sound and converts them into a spatial‐temporal distribution of neural spikes in the fibers of the auditory nerve. This encoded signal is subsequently analyzed by the brain through detection and classification processes, which enables the human listener to construct a perceptual and cognitive map of the auditory world. This article describes how acoustical measurements in the ear canal in response to sound are used to study and clinically assess hearing in children and adults.

Select this Article		Spatial Release from Masking Ruth Y. Litovsky Acou. Today Volume 8, Issue 2, pp. 18-25 (2012); (8 pages) Full Text: \| Download PDF
	+ -	Show Abstract In complex auditory environments multiple sounds occur, such as people uttering speech that is of interest, as well as speech sounds with uninteresting content. Additionally, humans spend a great deal of their awake hours in social, work‐related and learning environments that contain maskers: background noise, music and various other environmental sounds, all of which can vary in direction, amplitude and familiarity to the listener, and have the potential to interfere with information transmitted by the speech signal. To communicate using spoken language, listeners must be able to use auditory cues to attend to the speech source of interest and ignore other sounds. When you next find yourself in a “cocktail party” environment, imagine what incredible processes the auditory system has to segregate speech from noise.

Select this Article		Tonal Language Processing Fan‐Gang Zeng Acou. Today Volume 8, Issue 2, pp. 26-28 (2012); (3 pages) Full Text: \| Download PDF
	+ -	Show Abstract A tonal language uses changes in tone or pitch of a voiced sound to differentiate words. A classic example is the consonant‐vowel combination /ma/ in Mandarin Chinese. The same /ma/, depending upon the tonal pattern of vowel /a/, can mean mother, numb, horse, or curse. According to the late linguist, Yuen‐Ren Chao, tones have been used to differentiate words in Chinese for at least 3,000 years. Today, about 70% of the world's languages are tonal languages, which are spoken by over 2‐billion people, mostly in sub‐Saharan Africa and South East Asia. So, our ancestors out of Africa invented tonal languages, but why?

Select this Article		Hearing Loss and Frequency Analysis of Complex Sounds Marjorie Leek and Michelle Molis Acou. Today Volume 8, Issue 2, pp. 29-33 (2012); (5 pages) Full Text: \| Download PDF
	+ -	Show Abstract The sounds that surround us in our everyday lives range from very simple and tonal, such as one might hear from a flute or a whistle, to highly complex containing multiple tones and noises, such as listening to a single speaker in the presence of background noise or the babble of many other talkers at the same time. For the most part, the sounds that are relevant to us are complex, which, by definition, means they are made up of multiple frequencies with multiple sound levels. Some may be tonal, some may have a noisy quality, and often there will be important temporal features such as sequence or order effects. Speech is just such a signal—perhaps the most relevant and complex signal heard by humans. The auditory system is exquisitely designed to encode information from these complex sounds. Encoding, combining, and recombining information allows us to sort out our sound environment and gain information about who (or what) is near or in the distance, who is speaking, if we are in danger, or if there is something good to eat out there. The study of psychoacoustics and physiology allows us to understand what those encoding mechanisms are, how they work separately and together, and how they might fail us from time to time.

Select this Article		Physiological Correlates of Perceptual Deficits Following Sensorineural Hearing Loss Michael G. Heinz Acou. Today Volume 8, Issue 2, pp. 34-40 (2012); (7 pages) Full Text: \| Download PDF
	+ -	Show Abstract Several translational issues related to sensorineural hearing loss (SNHL) have recently re‐invigorated an active debate in the field of psychological and physiological acoustics regarding the perceptual role of the temporal structure of sound. Much of this recent interest over the last decade has centered on the mathematical fact that any sound can be separated into slowly‐varying temporal envelope (ENV) and rapidly varying temporal fine‐structure (TFS) components. This dichotomy has been motivated in part from cochlear implants, which are neural prostheses that can restore the sense of hearing for patients with profound deafness through electrical stimulation of remaining cochlear neurons. Although often quite successful in understanding speech in quiet conditions, cochlear‐implant patients often struggle to understand speech in noisy conditions or to appreciate music. These limitations have motivated numerous perceptual studies to understand the relative perceptual importance of ENV and TFS cues because cochlear implants currently only provide the slowly varying ENV cues and are unable to provide the rapidly varying TFS cues.

Select this Article		Auditory Cortical Function: Insights from Current Approaches Christoph E. Schreiner, Patrick O. Kanold, Hisayuki Ojima, Shihab A. Shamma, and Steven G. Lomber Acou. Today Volume 8, Issue 2, pp. 42-50 (2012); (9 pages) Full Text: \| Download PDF
	+ -	Show Abstract Over the last decade, an expanding array of innovative approaches has been used to explore the organization, processing, and behavioral/perceptual contributions of the auditory cortex in various animal models. Several investigators were invited to present an overview of current developments in the field of auditory cortical processing at the occasion of Acoustics 2012 Hong Kong held 14–18 May 2012. In this article, a brief overview of five different aspects of these influential approaches represented at that meeting are presented to provide a mosaic of current progress in our understanding of auditory cortical function.

Select this Article		Wind Turbines and Ghost Stories: The Effects of Infrasound on the Human Auditory System Hsuan‐hsiu Annie Chen and Peter Narins Acou. Today Volume 8, Issue 2, pp. 51-56 (2012); (6 pages) Full Text: \| Download PDF
	+ -	Show Abstract Climate change and fossil fuel depletion have pushed many countries to seek and invest in alternative clean energy sources, such as wind energy. By converting kinetic energy from the wind into mechanical or electrical energy, wind farms in California, for example, power nearly 850,000 households each year, while producing negligible green house gases and contributing little to water pollution. Nevertheless, several ecological and environmental concerns remain. High levels of infrasound and low frequency sounds generated by wind turbines pose a potentially serious threat to communities near wind farms. Wind energy companies remain largely dismissive, claiming that wind turbine noise is subaudible, undetectable by humans, and therefore presents minimal risk to human health. However, various cochlear microphonic, distortion product otoacoustic emission, and functional magnetic resonance imaging (fMRI) studies have demonstrated the detection of infrasound by the human inner ear and auditory cortex. Additional psychosomatic stress and disorders, including the “wind turbine syndrome” and paranormal experiences, are also linked to infrasound exposures. With wind turbines generating substantial levels of infrasound and low frequency sound, modifications and regulations to wind farm engineering plans and geographical placements are necessary to minimize community exposure and potential human health risks.