Manuel Rosa

Feature Selection for Sound Classification in Hearing Aids Through Restricted Search Driven by Genetic Algorithms

Hearing loss may disqualify many people from leading a normal life, though the majority do not make use of hearing aids. This is because most hearing aids on the market cannot automatically adapt to the changing acoustical environment the user faces daily. This paper focuses on the development of an automatic sound classifier for digital hearing aids that aims to enhance listening comprehension when the user goes from one sound environment to another. Given the strong complexity constraints of these devices, reducing the number of signal-describing features which feed the automatic classifier is of great importance and becomes a challenging topic. Thus, the use of genetic algorithms with restricted search is explored for the mentioned feature selection. In an effort to evaluate its performance, the algorithm is compared with a standard unconstrained genetic algorithm and with sequential methods. The restricted search driven by the implemented genetic algorithm performs better than both the sequential methods and unconstrained genetic algorithms. It thus allows a subset of signal-describing features with lower cardinality to be selected. This may permit these selected features to be programmed on the digital signal processor that the hearing aid is based on, and to make efficient use of its limited computational facilities.

Early hominin auditory capacities

Hearing in early hominins may have facilitated an increased emphasis on short-range vocal communication in open habitats. Studies of sensory capacities in past life forms have offered new insights into their adaptations and lifeways. Audition is particularly amenable to study in fossils because it is strongly related to physical properties that can be approached through their skeletal structures. We have studied the anatomy of the outer and middle ear in the early hominin taxa Australopithecus africanus and Paranthropus robustus and estimated their auditory capacities. Compared with chimpanzees, the early hominin taxa are derived toward modern humans in their slightly shorter and wider external auditory canal, smaller tympanic membrane, and lower malleus/incus lever ratio, but they remain primitive in the small size of their stapes footplate. Compared with chimpanzees, both early hominin taxa show a heightened sensitivity to frequencies between 1.5 and 3.5 kHz and an occupied band of maximum sensitivity that is shifted toward slightly higher frequencies. The results have implications for sensory ecology and communication, and suggest that the early hominin auditory pattern may have facilitated an increased emphasis on short-range vocal communication in open habitats.

Auditory capacities of human fossils: A new approach to the origin of speech

The origin and evolution of human language has mainly dealt with the reconstruction of the upper respiratory tract of human fossils. After decades of controversy no clear results have arisen from these studies. We propose a new approach to this issue based on the possibility to reconstruct the sound power transmission, through the external and middle ear, in fossil specimens. The results thus obtained in the more than 500 ky old fossils from the Sima de los Huesos site (Sierra de Atapuerca, Spain) show that this hominins had the same auditory capacities as modern human, suggesting an older origin for speech than any previous study.

Evolution of Hearing and Language in Fossil Hominins

This chapter outlines the evolution of auditory capacities during the course of human evolution and the implications for understanding when human language may have evolved. These findings are considered within the context of habitat acoustics, the mathematical theory of communication, and the frame/content theory of speech production. Compared to chimpanzees, the auditory pattern in the early hominin taxa Australopithecus and Paranthropus show a heightened sensitivity between 1.0 and 3.5 kHz but a similarly narrow bandwidth of maximum sensitivity. The early hominin auditory pattern may have facilitated short-range communication in open habitats, but their communication pattern apparently did not involve transmission of information beyond that of a chimpanzee. The early hominins likely were restricted to the frame stage of speech production, a phoneme-based, presyntactic form of communication with only limited word formation. In contrast, the Middle Pleistocene Atapuerca Sima de los Huesos (SH) hominins resemble H. sapiens in showing a broad region of heightened sensitivity between 1 and 5 kHz and a wider bandwidth of maximum sensitivity that is extended toward higher frequencies. The wider bandwidth in the Atapuerca (SH) hominins facilitated specialization in the use of complex, short-range vocal communication, including an emphasis on high-frequency consonant production and increased word formation. The Atapuerca (SH) hominins, then, may have been on the threshold of passing into the frame/content stage of speech production. The evolution of auditory capacities is consistent with the presence of some form of spoken language in the genus Homo prior to the appearance of H. sapiens.