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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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Results of Experiment 2.(A) Grand averaged VEPs (n = 15) elicited by the central square (dark red) and the four squares (light red) accompanied with the subtraction data (thin gray line). (B) Mean voltage maps illustrating the topographic scalp distribution of the VEP difference (subtractions) averaged within the time-windows of 70 to 130 ms (P1), 130 to 200 ms (N1), and 200 to 260 ms.
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pone-0003505-g003: Results of Experiment 2.(A) Grand averaged VEPs (n = 15) elicited by the central square (dark red) and the four squares (light red) accompanied with the subtraction data (thin gray line). (B) Mean voltage maps illustrating the topographic scalp distribution of the VEP difference (subtractions) averaged within the time-windows of 70 to 130 ms (P1), 130 to 200 ms (N1), and 200 to 260 ms.

Mentions: The stimuli were the same as in Experiment 1 except that real gray squares (mean tonal value of 229/255) were positioned so as to occlude the notches (Figure 3). In the central square figure, the real square was a perfect fit over the illusory square. In the control figure four squares, each a quarter of the illusory square surface (2.2 cm or 2.1° of visual angle), were inserted into the outward facing notches. The presentation parameters and the procedure were the same as in Experiment 1. Participants had to press on one key when the central square appeared and on another key when the four squares appeared.


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)

Results of Experiment 2.(A) Grand averaged VEPs (n = 15) elicited by the central square (dark red) and the four squares (light red) accompanied with the subtraction data (thin gray line). (B) Mean voltage maps illustrating the topographic scalp distribution of the VEP difference (subtractions) averaged within the time-windows of 70 to 130 ms (P1), 130 to 200 ms (N1), and 200 to 260 ms.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0003505-g003: Results of Experiment 2.(A) Grand averaged VEPs (n = 15) elicited by the central square (dark red) and the four squares (light red) accompanied with the subtraction data (thin gray line). (B) Mean voltage maps illustrating the topographic scalp distribution of the VEP difference (subtractions) averaged within the time-windows of 70 to 130 ms (P1), 130 to 200 ms (N1), and 200 to 260 ms.
Mentions: The stimuli were the same as in Experiment 1 except that real gray squares (mean tonal value of 229/255) were positioned so as to occlude the notches (Figure 3). In the central square figure, the real square was a perfect fit over the illusory square. In the control figure four squares, each a quarter of the illusory square surface (2.2 cm or 2.1° of visual angle), were inserted into the outward facing notches. The presentation parameters and the procedure were the same as in Experiment 1. Participants had to press on one key when the central square appeared and on another key when the four squares appeared.

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