Timing of finger tapping to frequency modulated acoustic stimuli

This study examined the timing of synchronous finger tapping to continuous frequency modulation (FM) and to click trains. Tapping to click trains was found to statistically significantly anticipate the acoustic stimulus. Tapping to continuous FM occurred before the instantaneous frequency rose through its mean value (i.e. at zero phase of the sinusoidal FM). The anticipation of zero phase of the FM was similar in magnitude to the anticipation of the click stimuli. However, there was a systematic departure from this timing when the FM depth was varied, the cause of which is unclear. The perceived timing of acoustic stimuli will influence the timing of motor responses to the stimuli. These results may therefore be relevant to the timing of perceptual centres of acoustic stimuli including speech

Sound localisation during illusory self-rotation

Auditory elevation localisation was investigated under conditions of illusory self-rotation (i.e., vection) induced by movement of wide-field visual stimuli around participants' z-axes. Contrary to previous findings which suggest that auditory cues to sound-source elevation are discounted during vection, we found little evidence that vection affects judgements of source elevation. Our results indicate that the percept of auditory space during vection is generally consistent with the available head-centered auditory cues to source elevation. Auditory information about the head-centered location of a source appears to be integrated, without modification, with visual information about head motion to determine the perceived exocentric location of the source

Variability in the headphone-to-ear-canal transfer function

Headphone-to-ear-canal transfer functions (HpTFs) for 20 headphone placements were measured for each ear of three participants and an acoustic manikin. Head-related transfer functions (HRTFs) were measured for nine sound-source locations within a 14.5° radius of each of eight representative locations. Noises were convolved with these functions and passed through a cochlear filter model to estimate cochlear excitation. The variability of the magnitudes of the filtered HpTFs was much less than the variability of the magnitudes of the unfiltered HpTFs. It was also considerably less than the variability of the magnitudes of the filtered HRTFs. In addition, the variability of the group delays of the HpTFs for the three human participants was considerably less than the minimum discriminable interaural time difference. It follows that much of the information in HRTFs that could provide a cue to sound-source location will not be masked by the variability of HpTFs across headphone placements. The spatial fidelity of an individualized virtual audio display, therefore, will not necessarily be compromised by variability in HpTFs

Phase effects in forward masking of the compound action potential: A comparison of responses to stimulus and distortion frequencies

When a complex stimulus is presented, new frequencies (distortion products, DPs) are generated within the cochlea. The most intense DPs are lower in frequency than the stimulus tones (primaries). It is not clear whether the relative phase of stimuli is encoded by neural channels tuned to the primaries or by channels tuned to the DPs. We estimated the response of auditory nerve fibres tuned to each of these channels as a function of the relative phase of harmonic stimuli. The compound action potential (CAP) evoked by probes at the primary or distortion frequencies was masked by harmonic 2-tone maskers and cochlear generated DPs. The degree of masking reflected the response to the masker of fibres tuned to the probe. Changes in relative phase of the primaries resulted in a large modulation of the response of fibres tuned to the DPs. Except for a primary frequency ratio of 1:2, the response of fibres tuned to the primaries was only shallowly modulated by changes in relative phase. However, the level of response to the DPs was much lower than the response to the stimulus tones

Spectral hyperacuity in the cat: neural response to frequency modulated tone pairs

When two tones are presented to the ear, distortion products are generated which are lower in frequency than the presented (primary) tones. We studied the responses of neurons from the inferior colliculus of the cat to small frequency modulations (FM) of primary tone combinations which gave rise to distortion products within the neuron\u27s response area. Neural discharges were modulated in response to the FM of the distortion product in a similar manner to modulation of discharges by FM of a pure tone to which these neurons were sensitive. However, very shallow, neurally-insignificant FM of high-frequency primaries could be transposed into significant FM of lower frequency distortion products. Because the sensitivity of a low-frequency neuron to a transposed FM exceeds that of neurons sensitive to a single tone with the same FM, the effect is termed hyperacuity

Spectral integration time of the auditory localisation system

For the elevation and front-versus-back hemifield of a sound source to be accurately determined, the sound must contain a broad range of frequencies. Experiment 1 of this study examined the spectral integration time of the auditory localisation system by measuring the accuracy with which frequency-modulated (FM) tones of modulation periods ranging from 0.5 to 200 ms can be localised. For each of the four participants, judgements of sound-source elevation and front-back hemifield were most accurate for a modulation period of 5 ms. Accuracy levels for the 5 ms modulation period approached those for a pink-noise stimulus. This suggests that the spectral integration time of the auditory localisation system is around 5 ms. Supporting evidence for this conclusion was sought in experiment 2, in which two participants localised noise stimuli that had magnitude spectra identical to those of 5 ms equivalent-rectangular-duration samples of the FM tones from experiment 1. For both participants, functions relating localisation error measures (i.e., elevation error and frequency of front-back confusion) to modulation period for spectrally matched noises were similar to those for FM tones. Crow

Scalp potentials evoked by amplitude-modulated tones in dyslexia

We recorded the far-field EEG potential evoked by amplitude modulation of acoustic stimuli (the amplitude modulation following response, AMFR) in adults with developmental dyslexia and in a matched control group of adults with no history of reading problems. The mean AMFR recorded from participants with dyslexia was significantly smaller than that recorded from members of the control group. In contrast, the amplitude of the click-evoked auditory brainstem response [ABR) was not significantly different between participant groups. Also, there was no difference between participant groups in the latency of the AMFR or ABR. The reduced AMFR in listeners with dyslexia may reflect impaired ability of the auditory system to follow rapid changes in stimulus energy, a cue believed to be important in the perception of speech

Spatial audio displays improve the detection of target messages in a continuous monitoring task

Objective: The detection of target messages in a background of competing speech and the identification of the color/number combinations in those messages were examined in a continuous monitoring task. Background: Previous research has shown that if listeners know when and where to listen, speech-on-speech intelligibility is improved when signals are presented via a 3-D audio display as compared with a diotic display. However, the effect of display type on detection of infrequent target messages in a continuous monitoring task has not been examined. Method: Participants were required to monitor five communications channels conveying messages at random intervals under each of three audio display conditions: diotic, all channels in front, and channels separated in azimuth (3-D). Results: Message detection sensitivity was significantly higher for the 3-D condition than for the in-front condition but did not differ significantly between the in-front and the diotic conditions. There were no differences in response criteria across conditions. Color/number identification sensitivity also was significantly higher for the 3-D condition than for the in-front condition but did not differ significantly between the in-front and the diotic conditions. Conclusion: A 3-D audio display enhances both message detection and message identification in a continuous monitoring task. Application: Three-dimensional audio displays would be particularly beneficial in environments such as aviation, in which the information conveyed to operators via the auditory modality can be crucial to the safe and effective performance of their work

Sound localization with head movement: implications for 3-d audio displays

Previous studies have shown that the accuracy of sound localization is improved if listeners are allowed to move their heads during signal presentation. This study describes the function relating localization accuracy to the extent of head movement in azimuth. Sounds that are difficult to localize were presented in the free field from sources at a wide range of azimuths and elevations. Sounds remained active until the participants’ heads had rotated through windows ranging in width of 2°, 4°, 8°, 16°, 32°, or 64° of azimuth. Error in determining sound-source elevation and the rate of front/back confusion were found to decrease with increases in azimuth window width. Error in determining sound-source lateral angle was not found to vary with azimuth window width. Implications for 3-d audio displays: The utility of a 3-d audio display for imparting spatial information is likely to be improved if operators are able to move their heads during signal presentation. Head movement may compensate in part for a paucity of spectral cues to sound-source location resulting from limitations in either the audio signals presented or the directional filters (i.e., head-related transfer functions) used to generate a display. However, head movements of a moderate size (i.e., through around 32° of azimuth) may be required to ensure that spatial information is conveyed with high accuracy

Silabo de Evaluación de Proyectos de Inversión

Tanto en su formulación como en la evaluación, los proyectos de inversión requieren no sólo de la intuición y el sentido empresarial, sino de una rigurosa metodología de cálculo y contrastación de variables que nos permita determinar su viabilidad. La evaluación de proyectos, aplicada de manera conveniente, resulta fundamental en la elección de oportunidades de inversión de estudios y proyectos que impliquen la asignación de recursos en pos de obtener un resultado financiero a favor del inversionista. Sin embargo, Los principios de la evaluación de proyectos, por su validez universal y practicidad, son de aplicación no sólo en los casos de proyectos de inversión propiamente, sino en cualquier situación en la que se requiera medir los posibles resultados que podrían arrojar una elección de inversión. En tal sentido, los conceptos a desarrollarse en el curso constituyen herramientas de gran importancia para todo aquel que esté interesado en maximizar sus decisiones financieras, cualquiera que sea su contexto, campo de aplicación y complejidad