Auditory cortical responses in the cat to sounds that produce spatial illusions

Humans and cats can localize a sound source accurately if its spectrum is fairly broad and flat(1-3), as is typical of most natural sounds. However, if sounds are filtered to reduce the width of the spectrum, they result:in illusions of sources that are very different from the actual locations, particularly in the up/down and front/back dimensions(4-6). Such illusions reveal that the auditory system relies on specific characteristics of sound spectra to obtain cues for localization(7). In the-auditory cortex of cats, temporal firing patterns of neurons can signal the locations of broad-band sounds(8-9). Here we show that such spike patterns systematically mislocalize sounds that have been passed through a narrow-band filter. Both correct and incorrect locations signalled by neurons can be predicted quantitatively by a model of spectral processing that also predicts correct and incorrect localization judgements by human listeners(6). Similar cortical mechanisms, if present in humans, could underlie human auditory spatial perception.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62778/1/399688a0.pd

A volumetric display for visual, tactile and audio presentation using acoustic trapping

Science-fiction movies such as Star Wars portray volumetric systems that not only provide visual but also tactile and audible 3D content. Displays, based on swept volume surfaces, holography, optophoretics, plasmonics, or lenticular lenslets, can create 3D visual content without the need for glasses or additional instrumentation. However, they are slow, have limited persistence of vision (POV) capabilities, and, most critically, rely on operating principles that cannot also produce tactile and auditive content. Here, we present for the first time a Multimodal Acoustic Trap Display (MATD): a mid-air volumetric display that can simultaneously deliver visual, auditory, and tactile content, using acoustophoresis as the single operating principle. Our system acoustically traps a particle and illuminates it with red, green, and blue light to control its colour as it quickly scans through our display volume. Using time multiplexing with a secondary trap, amplitude modulation and phase minimization, the MATD delivers simultaneous auditive and tactile content. The system demonstrates particle speeds of up to 8.75m/s and 3.75m/s in the vertical and horizontal directions respectively, offering particle manipulation capabilities superior to other optical or acoustic approaches demonstrated to date. Beyond enabling simultaneous visual, tactile and auditive content, our approach and techniques offer opportunities for non-contact, high-speed manipulation of matter, with applications in computational fabrication and biomedicine

Spike-Timing-Based Computation in Sound Localization

Spike timing is precise in the auditory system and it has been argued that it conveys information about auditory stimuli, in particular about the location of a sound source. However, beyond simple time differences, the way in which neurons might extract this information is unclear and the potential computational advantages are unknown. The computational difficulty of this task for an animal is to locate the source of an unexpected sound from two monaural signals that are highly dependent on the unknown source signal. In neuron models consisting of spectro-temporal filtering and spiking nonlinearity, we found that the binaural structure induced by spatialized sounds is mapped to synchrony patterns that depend on source location rather than on source signal. Location-specific synchrony patterns would then result in the activation of location-specific assemblies of postsynaptic neurons. We designed a spiking neuron model which exploited this principle to locate a variety of sound sources in a virtual acoustic environment using measured human head-related transfer functions. The model was able to accurately estimate the location of previously unknown sounds in both azimuth and elevation (including front/back discrimination) in a known acoustic environment. We found that multiple representations of different acoustic environments could coexist as sets of overlapping neural assemblies which could be associated with spatial locations by Hebbian learning. The model demonstrates the computational relevance of relative spike timing to extract spatial information about sources independently of the source signal

Perception of Vibrotactile Cues in Musical Performance

We suggest that studies on active touch psychophysics are needed to inform the design of haptic musical interfaces and better understand the relevance of haptic cues in musical performance. Following a review of the previous literature on vibrotactile perception in musical performance, two recent experiments are reported. The first experiment investigated how active finger-pressing forces affect vibration perception, finding significant effects of vibration type and force level on perceptual thresholds. Moreover, the measured thresholds were considerably lower than those reported in the literature, possibly due to the concurrent effect of large (unconstrained) finger contact areas, active pressing forces, and long-duration stimuli. The second experiment assessed the validity of these findings in a real musical context by studying the detection of vibrotactile cues at the keyboard of a grand and an upright piano. Sensitivity to key vibrations in fact not only was highest at the lower octaves and gradually decreased toward higher pitches; it was also significant for stimuli having spectral peaks of acceleration similar to those of the first experiment, i.e., below the standard sensitivity thresholds measured for sinusoidal vibrations under passive touch conditions

The Role of Haptic Cues in Musical Instrument Quality Perception

We draw from recent research in violin quality evaluation and piano performance to examine whether the vibrotactile sensation felt when playing a musical instrument can have a perceptual effect on its judged quality from the perspective of the musician. Because of their respective sound production mechanisms, the violin and the piano offer unique example cases and diverse scenarios to study tactile aspects of musical interaction. Both violinists and pianists experience rich haptic feedback, but the former experience vibrations at more bodily parts than the latter. We observe that the vibrotactile component of the haptic feedback during playing, both for the violin and the piano, provides an important part of the integrated sensory information that the musician experiences when interacting with the instrument. In particular, the most recent studies illustrate that vibrations felt at the fingertips (left hand only for the violinist) can lead to an increase in perceived sound loudness and richness, suggesting the potential for more research in this direction

Thresholds for the perception of hand-transmitted vibration: dependence on contact area and contact location

The detection of vibration applied to the glabrous skin of the hand varies with contact conditions. Three experiments have been conducted to relate variations in the perception of hand-transmitted vibration to previously reported properties of tactile channels. The effects of a surround around the area of contact, the size of the area of contact, the location of the area of contact, the contact force, and the hand posture on perception of thresholds were determined for 8–500?Hz vibration. Removal of a surround around a contact area on the fingertip elevated thresholds of the NP II channel (FA I fibres) at frequencies less than 31.5?Hz and reduced thresholds of the Pacinian channel (FA II fibres) at frequencies greater than about 63?Hz. When no surround was present, thresholds reduced systematically as the contact area increased from the fingertip to the whole hand at frequencies from 16 to 125?Hz, although the decrease was not inversely proportional to the increase in contact area. The results are partly explained by spatial summation in the Pacinian channel (FA II fibres) and the involvement of the NP II channel (SA II) with some influence of biodynamic responses and contact pressures. There were regional differences in sensitivity over the hand within the NP I channel but not within the Pacinian channel: the NP I thresholds (less than 31.5?Hz) decreased from proximal to distal regions of the hand, whereas the Pacinian thresholds (125?Hz) were independent of contact location over the hand