Figure 5

Echoic memory and change-related cortical response under various paradigms. A) repetitive standard sounds followed by a deviant, the so-called oddball paradigm usually used to obtain MMN. When the duration of the standard is short, the increase in memory strength during repetition of the same standard sound should be minimal, because of the small difference between storage and decay for each sound, which would result in a weak change response in spite of a long recording time. It should be noted that a deviant (rare) sound can be a standard for the next standard (frequent) sound. B) a standard sound followed without a blank by a deviant. Since memory decay does not occur, the amplitude of the change response reflects the degree of memory storage [17, 20]. This paradigm would be useful when a patient possibly suffers from memory storage abnormalities. C) a long-duration standard followed by a deviant. When the duration of the interval between the standard and deviant is increased, the evoked change response decreases because of the decay [17]. This paradigm would be useful to detect a faster than normal decay of memory in a certain patient. It is important to note that there may be a group of patients in which the change-detecting system itself is disturbed. In such cases, any kind of stimulation paradigm can evoke only a weak, if any, change response. One such candidate is schizophrenia. In schizophrenics, it is known that both the On-response and MMN is weak, and in addition, sound-evoked responses are resistant to repetition (little activity to adapt).