Hearing and Auditory Perception Part 3: Introduction and Human Ear

The Human Auditory System

• The Pinna collects sound waves and directs them through the external canal to the inner ear.

Middle Ear Structure

• The middle ear contains three parts: the malleus, incus, and stapes.

Sound Conversion in the Cochlea

• The cochlea converts sound waves to mechanical vibrations.
• Hair cells along the basilar membrane convert neural activity to motion.

Neural Signal Transmission

• The auditory nerve transmits neural signals from the cochlea to the brain.

Central Processing in the Brain

• Central processing in the brain involves uniform spectral analysis.

Sound Perception

• The perceived loudness of a tone is directly related to its sound pressure level.
• The threshold of audibility is the sound pressure level at which a tone can no longer be heard by an adult with normal hearing.
• Low frequencies must be less intense than frequencies in mid-range to be perceived.

Auditory Sensitivity

• The auditory system is most sensitive to high frequencies above 6KHz.
• A 100Hz tone must have a sound pressure level of about 50 dB to be perceived equal in loudness to a 1KHz tone with a sound pressure level of 60 dB.

Basilar Membrane Function

• The basilar membrane performs uniform frequency analysis through a set of bandpass filters.
• Bandpass filters in the cochlea have a constant effective bandwidth of 200Hz for center frequencies below 500 Hz.

Critical Bandwidth

• The formula to calculate the critical bandwidth delta fc is: $\delta f_c = 25 + 75[1 + 1.4( f_c / 1000) ^ 2]^{0.69}$

Critical Bands and Perception

• Critical bands play a significant role in pitch perception, loudness perception, and masking.
• Pitch is a subjective attribute of sound and not a physical attribute of acoustic waveform.
• The relationship between pitch (mel-scale) and frequency of a pure tone is linear.
• At frequencies above 1kHz, the pitch scale becomes nearly linear.

Auditory Masking

• Auditory masking occurs when loud tones cause weak vibrations at a point on the basilar membrane.
• Noise can only mask other noise, and pure tones can only mask other pure tones.
• Masking effect is more pronounced for frequencies below the masking frequency than above it.