References
- Heil & Irvine. J Physiol 1997; 78:2438-54
- Fishbach et al. J Neurophysiol 2001; 85:2303-23
- Khimich et al. Nature 2005; 434:889-94
- Leshowitz et al. J Acoust Soc Am 1971; 49, Suppl 2:462-6
- Parsons. Nature 2006; 444:1013-4
Great questionI will provide an answer in 2 parts. The first part is a theoretical approach based on the absolute possible minimum (as measured by the number of discussions it raisedmy original answer)!
After looking into this question and discussing for quite a while with @Dustin. The second part focuses on experiments in the peripheral auditory system - I am, however, afraid I cannot give a conclusive(added edited answer).
Firstly, I was not able to find any literature that investigated duration thresholds on tone bursts or auditory clicks, let alone as a function of acoustic frequency. Secondly, asPART I: Absolute theoretical minimum (original answer) As you inquire about electrical signals in the auditory human system I have to say that electrophysiological data at such a fundamental level is scarce in humans.
That having said, we can start off by looking at auditory clicks, which are generally the shortest possible well-defined auditory stimuli. The shortest auditory click I was able to find, and which was used in a psychophysical context (i.e., audible to a human) was 10 microseconds (Leshowitz, 1971).
I hope this theoretical approach helpsEDIT: PART II. Phsyiological experiments. As you somewhatare also interested in electrical signals, but itwe might take another approach and start looking at experimental (animal) data. The temporal limits of the auditory system are generally assumed to reside in the ribbon synapse that is highly advisablesituated between the inner hair cells and the auditory nerve fiber (Parsons, 2006):
This synapse is considered to start testing minimal durationsbe the limiting factor in the temporal limits of the auditory system (Khimich, 2005). Analyzing this synapse using very short tone bursts, it was shown that the vesicles of glutamate (the neurotransmitter activating the auditory nerve fibers that lead the signal to the brain) were released as shortly as 2 ms after tone onset. Tone bursts were 8 - 16 kHz, 10 ms plateau, 1 ms rise/fall (Khimich, 2005). Note the tone burstduration and think about whether clicks would suffice your purposerise fall times mentioned in answer PART I.
Indeed, when first spike times in auditory nerve fibers were determined, spikes with the shortest latency occurred just under 2 ms (Heil and Irvine, 1997).
SR in the figure means spike rate, showing that higher spike rates are accompanied by shorter latencies. A1 means auditory cortex neurons, which would make lifeobviously have longer latencies.
Hence, from these experiments I dare say that 2 ms would be sufficient to elicit at least one spike.
Why then leave part I of the answer? The problem is that the experimental data do not show that a lot easierspike wouldn't have been generated at shorter stimuli. The data merely show that with an ongoing stimulus the first spike appears at 2 ms. It does not show whether (but less informative2 ms of temporal summation is necessary, and that is why I have left part I of my answer in place, as well)a theoretical lower bound.
As a side note: the spike rates are highly dependent on loudness levels. Lower sound levels result in longer latencies. Specificaly, acceleration of the stereocilia on the inner hair cells in the cochlea is the primary parameter. The faster the cilia move, the faster the spike response.
References
Heil & Irvine. J Physiol 1997; 78:2438-54
Fishbach et al. J Neurophysiol 2001; 85:2303-23
Khimich et al. Nature 2005; 434:889-94
Leshowitz et al. J Acoust Soc Am 1971; 49, Suppl 2:462-6
Parsons. Nature 2006; 444:1013-4
Great question (as measured by the number of discussions it raised)!
After looking into this question and discussing for quite a while with @Dustin - I am, however, afraid I cannot give a conclusive answer.
Firstly, I was not able to find any literature that investigated duration thresholds on tone bursts or auditory clicks, let alone as a function of acoustic frequency. Secondly, as you inquire about electrical signals in the auditory human system I have to say that electrophysiological data at such a fundamental level is scarce in humans.
That having said, we can start off by looking at auditory clicks, which are generally the shortest possible well-defined auditory stimuli. The shortest auditory click I was able to find, and which was used in a psychophysical context (i.e., audible to a human) was 10 microseconds (Leshowitz, 1971).
I hope this theoretical approach helps you somewhat, but it is highly advisable to start testing minimal durations and think about whether clicks would suffice your purpose, which would make life a lot easier (but less informative as well).
References
Fishbach et al. J Neurophysiol 2001; 85:2303-23
Leshowitz et al. J Acoust Soc Am 1971; 49, Suppl 2:462-6
I will provide an answer in 2 parts. The first part is a theoretical approach based on the absolute possible minimum (my original answer). The second part focuses on experiments in the peripheral auditory system (added edited answer).
PART I: Absolute theoretical minimum (original answer) As you inquire about electrical signals in the auditory human system I have to say that electrophysiological data at such a fundamental level is scarce in humans. That having said, we can start off by looking at auditory clicks, which are generally the shortest possible well-defined auditory stimuli. The shortest auditory click I was able to find, and which was used in a psychophysical context (i.e., audible to a human) was 10 microseconds (Leshowitz, 1971).
EDIT: PART II. Phsyiological experiments. As you are also interested in electrical signals, we might take another approach and start looking at experimental (animal) data. The temporal limits of the auditory system are generally assumed to reside in the ribbon synapse that is situated between the inner hair cells and the auditory nerve fiber (Parsons, 2006):
This synapse is considered to be the limiting factor in the temporal limits of the auditory system (Khimich, 2005). Analyzing this synapse using very short tone bursts, it was shown that the vesicles of glutamate (the neurotransmitter activating the auditory nerve fibers that lead the signal to the brain) were released as shortly as 2 ms after tone onset. Tone bursts were 8 - 16 kHz, 10 ms plateau, 1 ms rise/fall (Khimich, 2005). Note the tone burstduration and rise fall times mentioned in answer PART I.
Indeed, when first spike times in auditory nerve fibers were determined, spikes with the shortest latency occurred just under 2 ms (Heil and Irvine, 1997).
SR in the figure means spike rate, showing that higher spike rates are accompanied by shorter latencies. A1 means auditory cortex neurons, which obviously have longer latencies.
Hence, from these experiments I dare say that 2 ms would be sufficient to elicit at least one spike.
Why then leave part I of the answer? The problem is that the experimental data do not show that a spike wouldn't have been generated at shorter stimuli. The data merely show that with an ongoing stimulus the first spike appears at 2 ms. It does not show whether 2 ms of temporal summation is necessary, and that is why I have left part I of my answer in place, as a theoretical lower bound.
As a side note: the spike rates are highly dependent on loudness levels. Lower sound levels result in longer latencies. Specificaly, acceleration of the stereocilia on the inner hair cells in the cochlea is the primary parameter. The faster the cilia move, the faster the spike response.
References
Heil & Irvine. J Physiol 1997; 78:2438-54
Fishbach et al. J Neurophysiol 2001; 85:2303-23
Khimich et al. Nature 2005; 434:889-94
Leshowitz et al. J Acoust Soc Am 1971; 49, Suppl 2:462-6
Parsons. Nature 2006; 444:1013-4