Evoked Cortical Responses to Stimulus Change

The presentation of any sensory stimulus of sufficient intensity produces a widespread evoked potential from the human brain. This can be recorded from scalp electrodes. These responses can also be elicited by any fairly abrupt change or alteration of the sensory environment. An evoked response occurs when the frequency of an auditory stimulus, the color of a visual stimulus, or the rate of tactile stimulation is changed perceptibly from an established condition. The response wave form is insensitive to direction of frequency change, but it has greater amplitude with intensity in crement than with a decrement. The evoked response amplitude and latency are related to the magnitude of the stimulus change. Evoked responses are also elicited when a tone being presented to one ear is changed to the other ear. Any perceptible alteration of one’s sensory environment from an established condition appears capable of eliciting not only behavioral alerting but also an accompanying evoked cortical response.