The efficient-coding hypothesis asserts that neural and perceptual sensitivity evolved to faithfully represent biologically relevant sensory signals. Here we characterized the spectrotemporal modulation statistics of several natural sound ensembles and examined how neurons encode these statistics in the central nucleus of the inferior colliculus (CNIC) of cats. We report that modulation-tuning in the CNIC is matched to equalize the modulation power of natural sounds. Specifically, natural sounds exhibited a tradeoff between spectral and temporal modulations, which manifests as 1/f modulation power spectrum (MPS). Neural tuning was highly overlapped with the natural sound MPS and neurons approximated proportional resolution filters where modulation bandwidths scaled with characteristic modulation frequencies, a behavior previously described in human psychoacoustics. We demonstrate that this neural scaling opposes the 1/f scaling of natural sounds and enhances the natural sound representation by equalizing their MPS. Modulation tuning in the CNIC may thus have evolved to represent natural sound modulations in a manner consistent with efficiency principles and the resulting characteristics likely underlie perceptual resolution.

Rodríguez FA, Read HL, Escabí MA. Spectral and temporal modulation tradeoff in the inferior colliculus. J Neurophysiol 103: 887-903, 2010. First published December 16, 2009 doi:10.1152/jn.00813.2009. The cochlea encodes sounds through frequency-selective channels that exhibit low-pass modulation sensitivity. Unlike the cochlea, neurons in the auditory midbrain are tuned for spectral and temporal modulations found in natural sounds, yet the role of this transformation is not known. We report a distinct tradeoff in modulation sensitivity and tuning that is topographically ordered within the central nucleus of the inferior colliculus (CNIC). Spectrotemporal receptive fields (STRFs) were obtained with 16-channel electrodes inserted orthogonal to the isofrequency lamina. Surprisingly, temporal and spectral characteristics exhibited an opposing relationship along the tonotopic axis. For low best frequencies (BFs), units were selective for fast temporal and broad spectral modulations. A systematic progression was observed toward slower temporal and finer spectral modulation sensitivity at high BF. This tradeoff was strongly reflected in the arrangement of excitation and inhibition and, consequently, in the modulation tuning characteristics. Comparisons with auditory nerve fibers show that these trends oppose the pattern imposed by the peripheral filters. These results suggest that spectrotemporal preferences are reordered within the tonotopic axis of the CNIC. This topographic organization has profound implications for the coding of spectrotemporal features in natural sounds and could underlie a number of perceptual phenomena.

No abstract

In patients with bilateral hearing loss, the use of two hearing aids (HAs) offers the potential to restore the benefits of binaural hearing, including sound source localization and segregation. However, existing evidence suggests that bilateral HA users’ access to binaural information, namely interaural time and level differences (ITDs and ILDs), can be compromised by device processing. Our objective was to characterize the nature and magnitude of binaural distortions caused by modern digital behind-the-ear HAs using a variety of stimuli and HA program settings. Of particular interest was a common frequency-lowering algorithm known as nonlinear frequency compression, which has not previously been assessed for its effects on binaural information. A binaural beamforming algorithm was also assessed. Wide dynamic range compression was enabled in all programs. HAs were placed on a binaural manikin, and stimuli were presented from an arc of loudspeakers inside an anechoic chamber. Stimuli were broadband noise bursts, 10-Hz sinusoidally amplitude-modulated noise bursts, or consonant–vowel–consonant speech tokens. Binaural information was analyzed in terms of ITDs, ILDs, and interaural coherence, both for whole stimuli and in a time-varying sense (i.e., within a running temporal window) across four different frequency bands (1, 2, 4, and 6 kHz). Key findings were: (a) Nonlinear frequency compression caused distortions of high-frequency envelope ITDs and significantly reduced interaural coherence. (b) For modulated stimuli, all programs caused time-varying distortion of ILDs. (c) HAs altered the relationship between ITDs and ILDs, introducing large ITD–ILD conflicts in some cases. Potential perceptual consequences of measured distortions are discussed.

The aim of this paper is to present a non-exhaustive set of 36 design patterns for interactive social applications used by older adults. This proposal represents a reliable starting point for designers/developers to easily incorporate usability in interfaces for said technology promoting technology acceptance, use and adoption among older adults. The proposed patterns were based on previous efforts commonly presented as a design criteria and guidelines to describe usability issues in this kind of interfaces, reinforcing those alternatives by specifying related usability issues and providing solutions in a pattern-fashion useful for designers/developers. Pertinence of the patterns was analyzed through a usability study implementing «heuristic evaluation» technique (frequently used in Human-Computer Interaction to obtain users’ perception on a particular design). The study was conducted from two perspectives: the vantage point from experts, and the perception of a social group of older adults. The analysis revealed the proposed patterns are conducive to create well-designed interfaces able to provide a better user experience, encouraging a positive impact in the quality of life in older adults. El objetivo de este artículo fue proponer una colección no exhaustiva de 36 patrones para el diseño de interacciones en aplicaciones sociales para adultos mayores. La propuesta representa un punto de partida confiable para facilitar, a diseñadores/desarrolladores, la integración de usabilidad en las interfaces de estas tecnologías con el fin de fomentar su aceptación, uso y adopción entre los adultos mayores. Esta propuesta se basa en esfuerzos previos comúnmente expresados como criterios y guías de diseño para definir los posibles problemas de usabilidad en este tipo de interfaces, y se concentra en reforzar estos enfoques mediante la integración de una mayor descripción de tales anomalías y alternativas de solución bajo una estructura de patrones útil para los diseñadores/desarrolladores. Se realizó un estudio de usabilidad con la técnica «evaluación heurística» (comúnmente utilizada en interacción hombre-máquina para obtener la percepción de los usuarios sobre un diseño particular). El trabajo se llevó a cabo desde dos perspectivas: el punto de vista de expertos técnicos y la percepción de un grupo social de adultos mayores. Los resultados reflejaron que los patrones propuestos propician la creación de interfaces bien diseñadas capaces de ofrecer una mejor experiencia de uso y promueven un impacto positivo en la calidad de vida de los adultos mayores.