The firing of the action potential only occurs at a particular point. In sound, this means the potential only fires at a certain frequency. Having an accurate phase-locked representation generally needs averaging across several cells rather than a single cell. This helps with telling where you are in a cycle, because the neuron will only fire at a certain point in that cycle. 

phase-locked action potentials

In practice, pitch perception is explained by a combination of the temporal and place theories, with their respective contributions depending on the sound's frequency. For frequencies up to approximately 4000 Hz, both the firing rate of neurons (temporal cues) and the specific location of stimulation on the basilar membrane (place cues) work together to determine pitch. However, for frequencies above this 4000 Hz threshold, pitch is encoded exclusively through place cues.

Hybrid Model of Pitch Perception

Directly encoding the auditory stimuli at the rate of auditory neurons. If there is a sound at 500 Hz, there will be neurons firing 500 action potentials per second. The firing is phase-locked to the stimuli, and the representation is averaged across ceveral cells. High-frequency sounds closer to the frequency of the action potential instead of the encoded auditory frequency.

Encoding multiple frequency allows the system to have higher than the maximal neural firing rate. 

Grinnell College

People can discriminate changes in frequency between two tones by about 2 Hz for sounds up to 2000 Hz. Pitch relies on the subjective expereince of sound, which means frequency of sound is not the only determinant of pitch. There are two complementary ways that pitch information is encoded.

Encoding pitch information

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

The physical location of a sound can be distinguished based on the activation of receptors near the base of the cochlea and near the apex. Treble sounds vibrate at the base of the cochlea while basss sounds at the apex. Coplex sounds activate multiple areas of the cochlea with simultanious peaks of vibration along the basilar membrane. 

Place Coding

Temporal coding

Tonality refers to two types of sounds:

* *Tonal sounds*, which are more musical in nature, including melody, motif, and harmony
* *Atonal sounds* (also called non-harmonic sound), which resemble everyday sounds or noise – they don’t conform to traditional musical compositions

Sounds can be designed using tonal or atonal elements, and sometimes a sound will be comprised of both. Tonal sounds work best to communicate personality, emotion, and state changes, whereas atonal sounds better support motion transitions and express a sense of haptic feedback.

Tonality

Audible frequency range is the span of sound frequencies a species can hear, and this range differs across species. In the textbook examples, chickens hear roughly $$125$$ to $$2000$$ Hz, mice hear roughly $$1000$$ to $$91000$$ Hz, beluga whales hear roughly $$1000$$ to $$123000$$ Hz, dogs hear about $$70$$ to $$45000$$ Hz, and cats hear about $$45$$ to $$64000$$ Hz.

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