Table 2.

Distinctions among Cochlear Microphonics (CM), Auditory Brainstem Responses, and Cortical Evoked Potentials

	CM	ABR/FFR	Cortical EPs
Origin	Preneural, cochlea	CN, LL, IC	Cortex, may also reflect MGB activity
Recording characteristics
Polarity	Eliminated by alternating polarity	Responses present to alternating polarity	Responses present to alternating polarity
Rate	Unaffected by increasing rate	Latency shifts with stimulus rate	Eliminated at fast rates
Stimulus level	No latency shifts	Latency shifts with stimulus intensity	Latency shifts with stimulus intensity
Recording montage	Within ear canal	Two-channel (horizontal, vertical)	Multiple recording channels
Response characteristics
Fidelity	Reflects stimulus	Reflects stimulus fine-structure and envelope	Reflects gross stimulus envelope
Onset latency	<1 ms	5–10 ms	>50 ms
Size (range)	Microvolts	Nanovolts	Microvolts
Latency variability	Not variable	Normal variability of <1 ms	Large variability in latency (10–25 ms)
Maturation	Very early maturation	Adultlike responses by school age	Protracted development, not adultlike until late adolescence
Subject characteristics
Arousal	Unaffected by subject state	Can be recorded in sleeping subjects	Reduced or eliminated in sleeping subjects
Attention	Unaffected by attention	Largely unaffected by attention	Attention-modulated
Plasticity	Unaffected by experience	Experience modulates responses	Experience modulates responses

CN: cochlear nucleus, LL: lateral lemniscus, IC: inferior colliculus, MGB: medial geniculate body (see Figure 2).