Absolute auditory threshold: testing the absolute

Abstract

The mechanisms underlying the detection of sounds in quiet, one of the simplest tasks for auditory systems, are debated. Several models proposed to explain the threshold for sounds in quiet and its dependence on sound parameters include a minimum sound intensity ('hard threshold'), below which sound has no effect on the ear. Also, many models are based on the assumption that threshold is mediated by integration of a neural response proportional to sound intensity. Here, we test these ideas. Using an adaptive forced choice procedure, we obtained thresholds of 95 normal-hearing human ears for 18 tones (3.125 kHz carrier) in quiet, each with a different temporal amplitude envelope. Grand-mean thresholds and standard deviations were well described by a probabilistic model according to which sensory events are generated by a Poisson point process with a low rate in the absence, and higher, time-varying rates in the presence, of stimulation. The subject actively evaluates the process and bases the decision on the number of events observed. The sound-driven rate of events is proportional to the temporal amplitude envelope of the bandpass-filtered sound raised to an exponent. We find no evidence for a hard threshold: When the model is extended to include such a threshold, the fit does not improve. Furthermore, we find an exponent of 3, consistent with our previous studies and further challenging models that are based on the assumption of the integration of a neural response that, at threshold sound levels, is directly proportional to sound amplitude or intensity.

Temporal integration of infrasound at threshold

“…The spontaneous rate of the model is below 1/s. This agrees with the parameter values reported in [ 25 ] (i.e., λ 1 = 1.59/s and λ 1 = 0.58/s in their Fig 11) and in [ 32 ] (i.e., λ 1 = 0.09/s in their Fig 3 ). The attenuation is considerably higher than those for the classical audio-frequency range (after converting the gain factor using Eq (1) ), but this was expected for the considered frequencies (8 Hz and 16 Hz), because the thresholds for these frequencies are considerably higher than for the frequencies that were considered in the literature for the fitting of the model.…”

“…A similar processing mechanism is supported also by the results of the modelling. The exponent of the model used to account for the infrasound data of the present study is close to 3, the integer exponent found to describe well a variety of temporal-integration data (e.g., [25,32,41]), spectral-and spectrotemporal integration data [42], and binaural integration data [46] for stimuli in the classical audio-frequency range. The spontaneous rate of the model is below 1/s.…”

“…For example, Gerken, Bhat, and Hutchison-Clutter [24] as well as Heil, Matysiak, and Neubauer [25] showed that detection thresholds of equally long stimuli with a plateau in the envelope (plateau burst, PB) are lower than those for a sequence of fully flanked stimuli (multiple bursts, MB). For an MB stimulus, the duration of the gaps between individual bursts has also been shown to affect thresholds [24,25,[31][32][33][34]. It is likely that the shape of the envelope also affects the detection of infrasound stimuli, but this has not yet been confirmed experimentally.…”

Inconsistent effects of stochastic resonance on human auditory processing

“…It is unclear, however, whether a hard threshold exists in the auditory system. Heil and Matysiak 23 performed experiments specifically designed to address the question of whether there is a hard threshold at the perceptual level but found no evidence for the existence of such a threshold (see also 24 ). In fact, detection thresholds for tones presented in quiet, and the dependence of threshold on tone duration and envelope, can be well understood without a hard threshold (e.g., 23,25 ).…”

“…Heil and Matysiak 23 performed experiments specifically designed to address the question of whether there is a hard threshold at the perceptual level but found no evidence for the existence of such a threshold (see also 24 ). In fact, detection thresholds for tones presented in quiet, and the dependence of threshold on tone duration and envelope, can be well understood without a hard threshold (e.g., 23,25 ). Ward et al 22 argue that SR might also be observed in the case of a "soft threshold", i.e., a non-linear transfer function between instantaneous input and output, such as an exponential or logistic function, if sufficiently steep.…”