Fig. 4. Study of the effect of the number of comparison images on the amplitude of the novelty response. (A) The amplitude of the novelty responses elicited by a single odd event (left) and an increase-and-hold pattern (middle) are not significantly different (t-test, P<0.05, N=20). In the right plot, normalized intervals (1-I/I₀) obtained using both experimental paradigms are plotted one-to-one, according to their ordinal number. The linear relationship indicates a similar time course for both novelty responses. (B) Amplitude of the novelty response as a function of difference between baseline and comparison amplitudes (PP) obtained applying a single-odd-event pattern (open symbols) and an increase-and-hold pattern (filled symbols). The experimental protocols are illustrated in the inset. Starting from a single baseline level (43 mV cm^-1 in the example), each trial consisted of a pair of stimuli: a single odd event followed 30 s later by a 4 s held stimulus of identical PP, or vice versa. In successive trials PP was varied in a random fashion.