Hockenbury Discovering Psychology 5th txtbk

104 CHAPTER 3 Sensation and Perceptionfrequency theoryThe view that the basilar membrane vibratesat the same frequency as the sound wave.place theoryThe view that different frequencies causelarger vibrations at different locations alongthe basilar membrane.olfactionTechnical name for the sense of smell.gustationTechnical name for the sense of taste.Table 3.2Decibel Level of Some Common SoundsDecibels Examples Exposure Danger180 Rocket launching pad Hearing loss inevitable140 Shotgun blast, jet plane Any exposure is dangerous120 Speakers at rock concert, sandblasting, thunderclap Immediate danger100 Chain saw, pneumatic drill 2 hours90 Truck traffic, noisy home appliances, lawn mower Less than 8 hours80 Subway, heavy city traffic, alarm clock at 2 feet More than 8 hours70 Busy traffic, noisy restaurant Critical level begins withconstant exposure60 Air conditioner at 20 feet, conversation, sewingmachine50 Light traffic at a distance, refrigerator40 Quiet office, living room30 Quiet library, soft whisper0 Lowest sound audible to human earThe hair cells bend as the basilar membrane ripples. It is here that transductionfinally takes place: The physical vibration of the sound waves is converted into neuralimpulses. As the hair cells bend, they stimulate the cells of the auditory nerve,which carries the neural information to the thalamus and the auditory cortex in thebrain (Recanzone & Sutter, 2008).Distinguishing PitchHow do we distinguish between the low-pitched throb of a bass guitar and thehigh-pitched tones of a piccolo? Remember, pitch is determined by the frequency ofa sound wave. The basilar membrane is a key structure involved in our discriminationof pitch. Two complementary theories describe the role of the basilar membranein the transmission of differently pitched sounds.According to frequency theory, the basilar membrane vibrates at the same frequencyas the sound wave. Thus, a sound wave of about 100 hertz would exciteeach hair cell along the basilar membrane to vibrate 100 times per second, andneural impulses would be sent to the brain at the same rate. However, there’s alimit to how fast neurons can fire. Individual neuronscannot fire faster than about 1,000 times per second.But we can sense sounds with frequencies that aremany times higher than 1,000 hertz. A child, for example,can typically hear pitches ranging from about 20 to20,000 hertz. Frequency theory explains how lowfrequencysounds are transmitted to the brain, but itcannot explain the transmission of higher-frequencysounds.So how do we distinguish higher-pitched sounds? Accordingto place theory, different frequencies causelarger vibrations at different locations along the basilarmembrane. High-frequency sounds, for example, causemaximum vibration near the stirrup end of the basilarmembrane. Lower-frequency sounds cause maximum vibrationat the opposite end. Thus, different pitches excitedifferent hair cells along the basilar membrane.Higher-pitched sounds are interpreted according to theplace where the hair cells are most active.