The role of fingerprints in the coding of tactile information probed with a biomimetic sensor

In humans, the tactile perception of fine textures (spatial scale <200 micrometers) is mediated by skin vibrations generated as the finger scans the surface. To establish the relationship between texture characteristics and subcutaneous vibrations, a biomimetic tactile sensor has been designed whose dimensions match those of the fingertip. When the sensor surface is patterned with parallel ridges mimicking the fingerprints, the spectrum of vibrations elicited by randomly textured substrates is dominated by one frequency set by the ratio of the scanning speed to the interridge distance. For human touch, this frequency falls within the optimal range of sensitivity of Pacinian afferents, which mediate the coding of fine textures. Thus, fingerprints may perform spectral selection and amplification of tactile information that facilitate its processing by specific mechanoreceptors.Comment: 25 pages, 11 figures, article + supporting materia

Decoding neural responses to temporal cues for sound localization

The activity of sensory neural populations carries information about the environment. This may be extracted from neural activity using different strategies. In the auditory brainstem, a recent theory proposes that sound location in the horizontal plane is decoded from the relative summed activity of two populations in each hemisphere, whereas earlier theories hypothesized that the location was decoded from the identity of the most active cells. We tested the performance of various decoders of neural responses in increasingly complex acoustical situations, including spectrum variations, noise, and sound diffraction. We demonstrate that there is insufficient information in the pooled activity of each hemisphere to estimate sound direction in a reliable way consistent with behavior, whereas robust estimates can be obtained from neural activity by taking into account the heterogeneous tuning of cells. These estimates can still be obtained when only contralateral neural responses are used, consistently with unilateral lesion studies. DOI: http://dx.doi.org/10.7554/eLife.01312.001

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

Retinal Microscotomas Revealed with Adaptive-Optics Microflashes

PURPOSE. To develop a sensitive psychophysical test for detecting visual defects such as microscotomas. METHODS. Frequency-of-seeing curves were measured with 0.75' and 7.5' spots. On each trial, from 0 to 4 stimuli were randomly presented at any of eight equally spaced loci 0.5° from fixation. By correcting the aberrations of the eye, adaptive optics produced retinal images of the 0.75' spot that were 3.0 μm wide at half height, small enough to be almost entirely confined within the typical cone diameter at this eccentricity. Data were collected from a patient with deuteranopia (AOS1) whose retina, imaged with adaptive optics, suggested that ≈30% of his cones were missing or abnormal. Patients with protanomalous trichromacy (1 subject), deuteranopia (1 subject), and trichromacy (5 subjects) served as controls (all had normal cone density and complete cone mosaics). Psychophysical results were modeled by a Monte Carlo simulation incorporating measured properties of the cone mosaic. RESULTS. Frequency-of-seeing curves for AOS1 obtained with 0.75' spots showed lower asymptote, slope, and sensitivity than for controls. The 7.5' results showed that these differences were the result of the small spot size, which on some trials was confined mostly to the locus of the putatively missing cones. A two-parameter model satisfactorily described the data and was highly sensitive to the proportion of missing cones simulated. CONCLUSIONS. Adaptive-optics microperimetry is a powerful psychophysical test for assessing the loss of neural elements, even in retinas that appear otherwise normal in standard clinical tests. This technique may prove useful in estimating the proportion of missing cones in different patients and in detecting other visual losses such as those associated with glaucoma

Detection of keyboard vibrations and effects on perceived piano quality

Two experiments were conducted on an upright and a grand piano, both either producing string vibrations or conversely being silent after the initial keypress, while pianists were listening to the feedback from a synthesizer through insulating headphones. In a quality experiment, participants unaware of the silent mode were asked to play freely and then rate the instrument according to a set of attributes and general preference. Participants preferred the vibrating over the silent setup, and preference ratings were associated to auditory attributes of richness and naturalness in the low and middle ranges. Another experiment on the same setup measured the detection of vibrations at the keyboard, while pianists played notes and chords of varying dynamics and duration. Sensitivity to string vibrations was highest in the lowest register and gradually decreased up to note D5. After the percussive transient, the tactile stimuli exhibited spectral peaks of acceleration whose perceptibility was demonstrated by tests conducted in active touch conditions. The two experiments confirm that piano performers perceive vibratory cues of strings mediated by spectral and spatial summations occurring in the Pacinian system in their fingertips, and suggest that such cues play a role in the evaluation of quality of the musical instrument

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

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