Figure 1.
Grand average “raw” ERPs elicited by the standard pairs in the oddball conditions.
In this and all other figures, positivity at the scalp relative to the reference is indicated by an upward deflection. The first 80–80 dB SPL standards in the increment and decrement conditions are superimposed. The morphology of these ERPs are essentially equivalent. Both include an N1s occurring approximately 100 ms followed by a positive deflection and another N1 approximately 140 ms following the onset of the second. These standard ERPs were subsequently subtracted from the ERPs elicited by the deviant 80–80 dB SPL pairs in the psychological increment and decrement conditions in order to isolate processing associated with the change detection process.
Figure 2.
Grand average difference waves in the psychological increment condition.
Difference waves were created by subtracting frequently occurring 80–80 dB SPL standard pairs in the oddball decrement condition (80–80…80–80…80–60…80–80) from deviant occurrences of these pairs in the psychological increment condition (80–60…80–60…80–80…80–60). The onset of the second stimulus (when deviance from the standard pattern occurs) is set at 0 ms in this figure. A large amplitude MMN was evident over fronto-central areas of the scalp between 150 and 200 ms following presentation of the psychological increment. The MMN inverted in polarity at the mastoids. However, this inversion failed to reach significance at either the M1 or M2 electrode sites. A centrally maximum non-significant P3a-like wave is evident at approximately 280 ms.
Figure 3.
Grand average difference waves in the psychological decrement condition.
Difference waves were created by subtracting frequently occurring 80–80 dB SPL standard pairs in the oddball increment condition (80–80…80–80…80–90…80–80) from deviant occurrences of these pairs in the psychological decrement condition (80–90…80–90…80–80…80–90). Again, the onset of the second (deviant) member of the pair is set at 0 ms in this figure. The psychological decrement elicited a smaller and relatively delayed (peaking between 200–250 ms) but significant MMN. The small inversion of the mastoids was not significant. No P3a-like positivity was present.
Figure 4.
Grand average “raw” ERPs elicited by the same standard 80 dB SPL tones in the psychological increment and decrement conditions.
ERPs corresponding to the standards in the two conditions are superimposed in the figure. N1, peaking at about 100(60 dB SPL) tone in the decrement condition but alternated with a higher intensity (90 dB SPL) tone in the increment condition.
Figure 5.
Grand average difference waves in the psychological increment condition.
A large amplitude front-central maximum MMN occurring between 150 and 200 ms was evident following presentation of the psychological increment. A significant P3a-like centro-frontal maximum positivity peaking between 200 and 250 ms was also evident in the grand average waveform.
Figure 6.
Grand average difference waves in the psychological decrement condition.
The psychological decrement elicited a smaller non-significant negativity corresponding to the typical scalp distribution and latency of an MMN. No P3a-like positivity was apparent.
Figure 7.
Spline scalp distribution maps of the MMN following presentation of the psychological decrements and increments.
Although the MMN elicited by the psychological decrement did not attain significance, its scalp distribution was very similar to that elicited by the psychological increment. The MMNs were maximum over fronto-central areas and inverted in amplitude over inferior-lateral regions.