P300 Amplitude

The P300 peak amplitudes, measured at Pz (Table 3), seem to be gradually reduced from the visual task to the semantic task (F(5, 115) = 48.23, p□< 0.001, GG □epsilon = 0.76). Post hoc Tukey-A analyses revealed, however, that the P300 amplitude was about the same in the two shallowest tasks (size and LD-1) and significantly larger in these two tasks than in all other tasks (p< 0.01).

The P300 amplitude in the deepest (semantic) task was significantly smaller than in all other tasks (p□< 0.01).

Post hoc comparisons also showed that the differences between the rhyme, LD-2, and LD-3 tasks were statistically significant (p□< 0.01).

Hence, the P300 data suggest that in the present study, as in other studies in which the level of processing has been manipulated, shallower tasks were performed faster than deeper tasks. Furthermore, assuming that the amplitude of the P300 is influenced by the amount of effort invested in the performance (e.g., Donchin, 1981) and the variance in the latency of the response in individual trials (jitter), the P300 amplitudes elicited by the targets suggest that the responses in the deeper tasks required more mental effort and were more variable than those in shallower tasks.