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On the functional significance of the P1 and N1 effects to illusory figures in the notch mode of presentation.

Brodeur M, Bacon BA, Renoult L, Prévost M, Lepage M, Debruille JB - PLoS ONE (2008)

Bottom Line: In response to these "real" figures, no P1 effect was found but a N1 effect comparable to the one obtained with illusory figures was observed.Taken together, these results suggest that the P1 effect observed with illusory figures is likely specific to the processing of the illusory features of the figures.Conversely, the fact that the N1 effect was also obtained with real figures indicates that this effect may be due to more global processes related to depth segmentation or surface/object perception.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, Douglas Mental Health McGill University Institute, Montreal, Quebec, Canada.

ABSTRACT
The processing of Kanizsa figures have classically been studied by flashing the full "pacmen" inducers at stimulus onset. A recent study, however, has shown that it is advantageous to present illusory figures in the "notch" mode of presentation, that is by leaving the round inducers on screen at all times and by removing the inward-oriented notches delineating the illusory figure at stimulus onset. Indeed, using the notch mode of presentation, novel P1 and N1 effects have been found when comparing visual potentials (VEPs) evoked by an illusory figure and the VEPs to a control figure whose onset corresponds to the removal of outward-oriented notches, which prevents their integration into one delineated form. In Experiment 1, we replicated these findings, the illusory figure was found to evoke a larger P1 and a smaller N1 than its control. In Experiment 2, real grey squares were placed over the notches so that one condition, that with inward-oriented notches, shows a large central grey square and the other condition, that with outward-oriented notches, shows four unconnected smaller grey squares. In response to these "real" figures, no P1 effect was found but a N1 effect comparable to the one obtained with illusory figures was observed. Taken together, these results suggest that the P1 effect observed with illusory figures is likely specific to the processing of the illusory features of the figures. Conversely, the fact that the N1 effect was also obtained with real figures indicates that this effect may be due to more global processes related to depth segmentation or surface/object perception.

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Mean amplitudes of the figure effect (illusory square vs. control figure in Experiment 1 and central square vs. peripheral squares in Experiment 2) for the four subsets of electrodes.
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pone-0003505-g004: Mean amplitudes of the figure effect (illusory square vs. control figure in Experiment 1 and central square vs. peripheral squares in Experiment 2) for the four subsets of electrodes.

Mentions: The VEPs to both figures presented in Figure 3 included a P1 peaking at 110 ms. The electrode×modality (F(27,378) = 2.51, p<.001, ε = .223) and modality×figure (F(1,14) = 11.5, p = .004) interactions both achieved significance, which suggests that the ERPs evoked in the two experiments were modulated differently across the scalp and that the figure effect varied depending on whether the figures were real or illusory. In fact, no P1 effect was found in the posterior region. Posterior amplitudes were indeed almost identical for the central square (2.1 µv ±1.4) and for the four squares (2.2±1.8). The only significant effect was found for the anterior subset (F(1,14) = 12.2, p = .004). Analyses with the four subsets of electrodes were also conducted on the data of Experiment 1 but no significant figure effects were found outside the posterior region. It has to be noted that the triple interaction was not significant, which suggests that the topography of the figure effect was not different across experiments. Figure 4 depicts the distribution of the effects across the four subsets of electrodes for each experiment and explains this surprising absence of interaction.


On the functional significance of the P1 and N1 effects to illusory figures in the notch mode of presentation.

Brodeur M, Bacon BA, Renoult L, Prévost M, Lepage M, Debruille JB - PLoS ONE (2008)

Mean amplitudes of the figure effect (illusory square vs. control figure in Experiment 1 and central square vs. peripheral squares in Experiment 2) for the four subsets of electrodes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2567430&req=5

pone-0003505-g004: Mean amplitudes of the figure effect (illusory square vs. control figure in Experiment 1 and central square vs. peripheral squares in Experiment 2) for the four subsets of electrodes.
Mentions: The VEPs to both figures presented in Figure 3 included a P1 peaking at 110 ms. The electrode×modality (F(27,378) = 2.51, p<.001, ε = .223) and modality×figure (F(1,14) = 11.5, p = .004) interactions both achieved significance, which suggests that the ERPs evoked in the two experiments were modulated differently across the scalp and that the figure effect varied depending on whether the figures were real or illusory. In fact, no P1 effect was found in the posterior region. Posterior amplitudes were indeed almost identical for the central square (2.1 µv ±1.4) and for the four squares (2.2±1.8). The only significant effect was found for the anterior subset (F(1,14) = 12.2, p = .004). Analyses with the four subsets of electrodes were also conducted on the data of Experiment 1 but no significant figure effects were found outside the posterior region. It has to be noted that the triple interaction was not significant, which suggests that the topography of the figure effect was not different across experiments. Figure 4 depicts the distribution of the effects across the four subsets of electrodes for each experiment and explains this surprising absence of interaction.

Bottom Line: In response to these "real" figures, no P1 effect was found but a N1 effect comparable to the one obtained with illusory figures was observed.Taken together, these results suggest that the P1 effect observed with illusory figures is likely specific to the processing of the illusory features of the figures.Conversely, the fact that the N1 effect was also obtained with real figures indicates that this effect may be due to more global processes related to depth segmentation or surface/object perception.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, Douglas Mental Health McGill University Institute, Montreal, Quebec, Canada.

ABSTRACT
The processing of Kanizsa figures have classically been studied by flashing the full "pacmen" inducers at stimulus onset. A recent study, however, has shown that it is advantageous to present illusory figures in the "notch" mode of presentation, that is by leaving the round inducers on screen at all times and by removing the inward-oriented notches delineating the illusory figure at stimulus onset. Indeed, using the notch mode of presentation, novel P1 and N1 effects have been found when comparing visual potentials (VEPs) evoked by an illusory figure and the VEPs to a control figure whose onset corresponds to the removal of outward-oriented notches, which prevents their integration into one delineated form. In Experiment 1, we replicated these findings, the illusory figure was found to evoke a larger P1 and a smaller N1 than its control. In Experiment 2, real grey squares were placed over the notches so that one condition, that with inward-oriented notches, shows a large central grey square and the other condition, that with outward-oriented notches, shows four unconnected smaller grey squares. In response to these "real" figures, no P1 effect was found but a N1 effect comparable to the one obtained with illusory figures was observed. Taken together, these results suggest that the P1 effect observed with illusory figures is likely specific to the processing of the illusory features of the figures. Conversely, the fact that the N1 effect was also obtained with real figures indicates that this effect may be due to more global processes related to depth segmentation or surface/object perception.

Show MeSH
Related in: MedlinePlus