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The subjective transfer function (STF) approach is a method developed to evaluate Air Force command and control systems, and is applicable to other complex systems that are impossible to evaluate through traditional quantitative means. Based on the principles of hypothesis formulation and testing, the method incorporates features of the algebraic modeling approach to measurement where meaningful subjective scale values derive from tested theories. It also provides features for coalescing judgments obtained from different groups of system experts into an overall perceptual system outcome. This report introduces and is a primer of the STF method. It outlines the steps involved in the approach, describes how those steps can be accomplished, and discusses measurement principles and techniques to aid the reader's understanding of the basis for the approach.

Subjective transfer function method. --- System analysis.

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Coherence (Optics) --- Optical data processing. --- Optical transfer function.

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Human sound localization helps to pay attention to spatially separated speakers using interaural level and time differences as well as angle-dependent monaural spectral cues. In a monophonic teleconference, for instance, it is much more difficult to distinguish between different speakers due to missing binaural cues. Spatial positioning of the speakers by means of binaural reproduction methods using head-related transfer functions (HRTFs) enhances speech comprehension. These HRTFs are influenced by the torso, head and ear geometry as they describe the propagation path of the sound from a source to the ear canal entrance. Through this geometry-dependency, the HRTF is directional and subject-dependent. To enable a sufficient reproduction, individual HRTFs should be used. However, it is tremendously difficult to measure these HRTFs. For this reason this thesis proposes approaches to adapt the HRTFs applying individual anthropometric dimensions of a user. Since localization at low frequencies is mainly influenced by the interaural time difference, two models to adapt this difference are developed and compared with existing models. Furthermore, two approaches to adapt the spectral cues at higher frequencies are studied, improved and compared. Although the localization performance with individualized HRTFs is slightly worse than with individual HRTFs, it is nevertheless still better than with non-individual HRTFs, taking into account the measurement effort.

Engineering. --- Construction --- Industrial arts --- Technology --- Head-related transfer function --- Spatial audio --- Binaural hearing --- Anthropometry --- Sound localization

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Time series models estimation --- Forecasting of time series --- Time series models identification --- Transfer function models --- Seasonal time series --- Feedback control --- Time series forecasting --- Time series control --- Autocorrelation functions

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Spatial-hearing ability has been found to vary widely across listeners. A survey of the existing auditory-space perception literature suggests that three main types of factors may account for this variability: - physical factors, e.g., acoustical characteristics related to sound-localization cues, - perceptual factors, e.g., sensory/cognitive processing, perceptual learning, multisensory interactions, - and methodological factors, e.g., differences in stimulus presentation methods across studies. However, the extent to which these–and perhaps other, still unidentified—factors actually contribute to the observed variability in spatial hearing across individuals with normal hearing or within special populations (e.g., hearing-impaired listeners) remains largely unknown. Likewise, the role of perceptual learning and multisensory interactions in the emergence of a multimodal but unified representation of “auditory space,” is still an active topic of research. A better characterization and understanding of the determinants of inter-individual variability in spatial hearing, and of its relationship with perceptual learning and multisensory interactions, would have numerous benefits. In particular, it would enhance the design of rehabilitative devices and of human-machine interfaces involving auditory, or multimodal space perception, such as virtual auditory/multimodal displays in aeronautics, or navigational aids for the visually impaired. For this Research Topic, we have considered manuscripts that: - present new methods, or review existing methods, for the study of inter-individual differences; - present new data (or review existing) data, concerning acoustical features relevant for explaining inter-individual differences in sound-localization performance; - present new (or review existing) psychophysical or neurophysiological findings concerning spatial hearing and/or auditory perceptual learning, and/or multisensory interactions in humans (normal or impaired, young or older listeners) or other species; - discuss the influence of inter-individual differences on the design and use of assistive listening devices (rehabilitation) or human-machine interfaces involving spatial hearing or multimodal perception of space (ergonomy).

Directional hearing. --- Space perception. --- Learning --- HRTF (head related transfer function) --- Sound Localization --- spatial hearing --- adaptation --- training --- binaural cues --- spectral cues --- mulltisensory interaction