236 research outputs found
The psychophysics of absolute threshold and signal duration: A probabilistic approach
The absolute threshold for a tone depends on its duration; longer tones have lower thresholds. This effect has traditionally been explained in terms of ?temporal integration? involving the summation of energy or perceptual information over time. An alternative probabilistic explanation of the process is formulated in terms of simple equations that predict not only the time=duration dependence but also the shape of the psychometric function at absolute threshold. It also predicts a tight relationship between these two functions. Measurements made using listeners with either normal or impaired hearing show that the probabilistic equations adequately fit observed threshold-duration functions and psychometric functions. The mathematical formulation implies that absolute threshold can be construed as a two-valued function: (a) gain and (b) sensory threshold, and both parameters can be estimated from threshold-duration data. Sensorineural hearing impairment is sometimes associated with a smaller threshold=duration effect and sometimes with steeper psychometric functions. The equations explain why these two effects are expected to be linked. The probabilistic approach has the potential to discriminate between hearing deficits involving gain reduction and those resulting from a raised sensory threshold
Frequency decoding of periodically timed action potentials through distinct activity patterns in a random neural network
Frequency discrimination is a fundamental task of the auditory system. The
mammalian inner ear, or cochlea, provides a place code in which different
frequencies are detected at different spatial locations. However, a temporal
code based on spike timing is also available: action potentials evoked in an
auditory-nerve fiber by a low-frequency tone occur at a preferred phase of the
stimulus-they exhibit phase locking-and thus provide temporal information about
the tone's frequency. In an accompanying psychoacoustic study, and in agreement
with previous experiments, we show that humans employ this temporal information
for discrimination of low frequencies. How might such temporal information be
read out in the brain? Here we demonstrate that recurrent random neural
networks in which connections between neurons introduce characteristic time
delays, and in which neurons require temporally coinciding inputs for spike
initiation, can perform sharp frequency discrimination when stimulated with
phase-locked inputs. Although the frequency resolution achieved by such
networks is limited by the noise in phase locking, the resolution for realistic
values reaches the tiny frequency difference of 0.2% that has been measured in
humans.Comment: 16 pages, 5 figures, and supplementary informatio
The TA Framework: Designing Real-time Teaching Augmentation for K-12 Classrooms
Recently, the HCI community has seen increased interest in the design of
teaching augmentation (TA): tools that extend and complement teachers'
pedagogical abilities during ongoing classroom activities. Examples of TA
systems are emerging across multiple disciplines, taking various forms: e.g.,
ambient displays, wearables, or learning analytics dashboards. However, these
diverse examples have not been analyzed together to derive more fundamental
insights into the design of teaching augmentation. Addressing this opportunity,
we broadly synthesize existing cases to propose the TA framework. Our framework
specifies a rich design space in five dimensions, to support the design and
analysis of teaching augmentation. We contextualize the framework using
existing designs cases, to surface underlying design trade-offs: for example,
balancing actionability of presented information with teachers' needs for
professional autonomy, or balancing unobtrusiveness with informativeness in the
design of TA systems. Applying the TA framework, we identify opportunities for
future research and design.Comment: to be published in Proceedings of the 2020 CHI Conference on Human
Factors in Computing Systems, 17 pages, 10 figure
Across-Channel Timing Differences as a Potential Code for the Frequency of Pure Tones
When a pure tone or low-numbered harmonic is presented to a listener, the resulting travelling wave in the cochlea slows down at the portion of the basilar membrane (BM) tuned to the input frequency due to the filtering properties of the BM. This slowing is reflected in the phase of the response of neurons across the auditory nerve (AN) array. It has been suggested that the auditory system exploits these across-channel timing differences to encode the pitch of both pure tones and resolved harmonics in complex tones. Here, we report a quantitative analysis of previously published data on the response of guinea pig AN fibres, of a range of characteristic frequencies, to pure tones of different frequencies and levels. We conclude that although the use of across-channel timing cues provides an a priori attractive and plausible means of encoding pitch, many of the most obvious metrics for using that cue produce pitch estimates that are strongly influenced by the overall level and therefore are unlikely to provide a straightforward means for encoding the pitch of pure tones
The Frequency Following Response (FFR) May Reflect Pitch-Bearing Information But is Not a Direct Representation of Pitch
The frequency following response (FFR), a scalp-recorded measure of phase-locked brainstem activity, is often assumed to reflect the pitch of sounds as perceived by humans. In two experiments, we investigated the characteristics of the FFR evoked by complex tones. FFR waveforms to alternating-polarity stimuli were averaged for each polarity and added, to enhance envelope, or subtracted, to enhance temporal fine structure information. In experiment 1, frequency-shifted complex tones, with all harmonics shifted by the same amount in Hertz, were presented diotically. Only the autocorrelation functions (ACFs) of the subtraction-FFR waveforms showed a peak at a delay shifted in the direction of the expected pitch shifts. This expected pitch shift was also present in the ACFs of the output of an auditory nerve model. In experiment 2, the components of a harmonic complex with harmonic numbers 2, 3, and 4 were presented either to the same ear (“mono”) or the third harmonic was presented contralaterally to the ear receiving the even harmonics (“dichotic”). In the latter case, a pitch corresponding to the missing fundamental was still perceived. Monaural control conditions presenting only the even harmonics (“2 + 4”) or only the third harmonic (“3”) were also tested. Both the subtraction and the addition waveforms showed that (1) the FFR magnitude spectra for “dichotic” were similar to the sum of the spectra for the two monaural control conditions and lacked peaks at the fundamental frequency and other distortion products visible for “mono” and (2) ACFs for “dichotic” were similar to those for “2 + 4” and dissimilar to those for “mono.” The results indicate that the neural responses reflected in the FFR preserve monaural temporal information that may be important for pitch, but provide no evidence for any additional processing over and above that already present in the auditory periphery, and do not directly represent the pitch of dichotic stimuli
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