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Temporal brain dynamics of multiple object processing: the flexibility of individuation.

Mazza V, Caramazza A - PLoS ONE (2011)

Bottom Line: In three ERP experiments, participants saw a variable number of target elements among homogenous distracters and performed either an enumeration task (Experiment 1) or a detection task, reporting whether at least one (Experiment 2) or a specified number of target elements (Experiment 3) was present.While in the enumeration task the N2pc response increased as a function of the number of targets, no such modulation was found in Experiment 2, indicating that individuation of multiple targets is not mandatory.However, a modulation of the N2pc similar to the enumeration task was visible in Experiment 3, further highlighting that object individuation is a flexible mechanism that binds indexes to object properties and locations as needed for further object processing.

View Article: PubMed Central - PubMed

Affiliation: Center for Mind/Brain Sciences (CIMeC), University of Trento, Trento, Italy. veronica.mazza@unitn.it

ABSTRACT
The ability to process concurrently multiple visual objects is fundamental for a coherent perception of the world. A core component of this ability is the simultaneous individuation of multiple objects. Many studies have addressed the mechanism of object individuation but it remains unknown whether the visual system mandatorily individuates all relevant elements in the visual field, or whether object indexing depends on task demands. We used a neural measure of visual selection, the N2pc component, to evaluate the flexibility of multiple object individuation. In three ERP experiments, participants saw a variable number of target elements among homogenous distracters and performed either an enumeration task (Experiment 1) or a detection task, reporting whether at least one (Experiment 2) or a specified number of target elements (Experiment 3) was present. While in the enumeration task the N2pc response increased as a function of the number of targets, no such modulation was found in Experiment 2, indicating that individuation of multiple targets is not mandatory. However, a modulation of the N2pc similar to the enumeration task was visible in Experiment 3, further highlighting that object individuation is a flexible mechanism that binds indexes to object properties and locations as needed for further object processing.

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Grand-average ERP waveforms obtained in Experiment 1 in the 600 ms post-stimulus interval at posterior electrodes PO7/PO8 contralateral (solid lines) and ipsilateral (dashed lines) to the target hemifield, as a function of target numerosity (left column: one-target condition; middle column: two-target condition; right column: three-target condition).Topographical ERP scalp distribution maps of the N2pc (180–270 ms) are shown for each condition, obtained by computing the contralateral minus ipsilateral difference activity, and mirrored across the midline. The scale was optimized for each experiment (Experiment 1: ±4 µV). Both the N2pc and CDA increased as a function of target numerosity.
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pone-0017453-g002: Grand-average ERP waveforms obtained in Experiment 1 in the 600 ms post-stimulus interval at posterior electrodes PO7/PO8 contralateral (solid lines) and ipsilateral (dashed lines) to the target hemifield, as a function of target numerosity (left column: one-target condition; middle column: two-target condition; right column: three-target condition).Topographical ERP scalp distribution maps of the N2pc (180–270 ms) are shown for each condition, obtained by computing the contralateral minus ipsilateral difference activity, and mirrored across the midline. The scale was optimized for each experiment (Experiment 1: ±4 µV). Both the N2pc and CDA increased as a function of target numerosity.

Mentions: The N2pc was clearly modulated by the number of targets presented in the visual field, being larger for the larger target numerosities (Figure 2). In addition, the N2pc was followed by a CDA showing the same modulation, with larger amplitudes for larger target numerosities. Statistical analyses confirmed these observations.


Temporal brain dynamics of multiple object processing: the flexibility of individuation.

Mazza V, Caramazza A - PLoS ONE (2011)

Grand-average ERP waveforms obtained in Experiment 1 in the 600 ms post-stimulus interval at posterior electrodes PO7/PO8 contralateral (solid lines) and ipsilateral (dashed lines) to the target hemifield, as a function of target numerosity (left column: one-target condition; middle column: two-target condition; right column: three-target condition).Topographical ERP scalp distribution maps of the N2pc (180–270 ms) are shown for each condition, obtained by computing the contralateral minus ipsilateral difference activity, and mirrored across the midline. The scale was optimized for each experiment (Experiment 1: ±4 µV). Both the N2pc and CDA increased as a function of target numerosity.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3046149&req=5

pone-0017453-g002: Grand-average ERP waveforms obtained in Experiment 1 in the 600 ms post-stimulus interval at posterior electrodes PO7/PO8 contralateral (solid lines) and ipsilateral (dashed lines) to the target hemifield, as a function of target numerosity (left column: one-target condition; middle column: two-target condition; right column: three-target condition).Topographical ERP scalp distribution maps of the N2pc (180–270 ms) are shown for each condition, obtained by computing the contralateral minus ipsilateral difference activity, and mirrored across the midline. The scale was optimized for each experiment (Experiment 1: ±4 µV). Both the N2pc and CDA increased as a function of target numerosity.
Mentions: The N2pc was clearly modulated by the number of targets presented in the visual field, being larger for the larger target numerosities (Figure 2). In addition, the N2pc was followed by a CDA showing the same modulation, with larger amplitudes for larger target numerosities. Statistical analyses confirmed these observations.

Bottom Line: In three ERP experiments, participants saw a variable number of target elements among homogenous distracters and performed either an enumeration task (Experiment 1) or a detection task, reporting whether at least one (Experiment 2) or a specified number of target elements (Experiment 3) was present.While in the enumeration task the N2pc response increased as a function of the number of targets, no such modulation was found in Experiment 2, indicating that individuation of multiple targets is not mandatory.However, a modulation of the N2pc similar to the enumeration task was visible in Experiment 3, further highlighting that object individuation is a flexible mechanism that binds indexes to object properties and locations as needed for further object processing.

View Article: PubMed Central - PubMed

Affiliation: Center for Mind/Brain Sciences (CIMeC), University of Trento, Trento, Italy. veronica.mazza@unitn.it

ABSTRACT
The ability to process concurrently multiple visual objects is fundamental for a coherent perception of the world. A core component of this ability is the simultaneous individuation of multiple objects. Many studies have addressed the mechanism of object individuation but it remains unknown whether the visual system mandatorily individuates all relevant elements in the visual field, or whether object indexing depends on task demands. We used a neural measure of visual selection, the N2pc component, to evaluate the flexibility of multiple object individuation. In three ERP experiments, participants saw a variable number of target elements among homogenous distracters and performed either an enumeration task (Experiment 1) or a detection task, reporting whether at least one (Experiment 2) or a specified number of target elements (Experiment 3) was present. While in the enumeration task the N2pc response increased as a function of the number of targets, no such modulation was found in Experiment 2, indicating that individuation of multiple targets is not mandatory. However, a modulation of the N2pc similar to the enumeration task was visible in Experiment 3, further highlighting that object individuation is a flexible mechanism that binds indexes to object properties and locations as needed for further object processing.

Show MeSH