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Disentangling neural processing of masked and masking stimulus by means of event-related contralateral - ipsilateral differences of EEG potentials.

Verleger R, Jaśkowski P - Adv Cogn Psychol (2008)

Bottom Line: Their major component, the N2pc, is interpreted as indicating preferential processing of stimuli matching the target template, which process can neither be identified with conscious perception nor with shifts of spatial attention.The measurements showed that the triggering of response preparation by the masked stimuli did not depend on their discriminability, and their priming effects on the processing of the following target stimuli were qualitatively different for stimulus identification and for response preparation.These results provide another piece of evidence for the independence of motor-related and perception-related effects of masked stimuli.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University of Lübeck, Germany.

ABSTRACT
In spite of the excellent temporal resolution of event-related EEG potentials (ERPs), the overlapping potentials evoked by masked and masking stimuli are hard to disentangle. However, when both masked and masking stimuli consist of pairs of relevant and irrelevant stimuli, one left and one right from fixation, with the side of the relevant element varying between pairs, effects of masked and masking stimuli can be distinguished by means of the contralateral preponderance of the potentials evoked by the relevant elements, because the relevant elements may independently change sides in masked and masking stimuli. Based on a reanalysis of data from which only selected contralateral-ipsilateral effects had been previously published, the present contribution will provide a more complete picture of the ERP effects in a masked-priming task. Indeed, effects evoked by masked primes and masking targets heavily overlapped in conventional ERPs and could be disentangled to a certain degree by contralateral-ipsilateral differences. Their major component, the N2pc, is interpreted as indicating preferential processing of stimuli matching the target template, which process can neither be identified with conscious perception nor with shifts of spatial attention. The measurements showed that the triggering of response preparation by the masked stimuli did not depend on their discriminability, and their priming effects on the processing of the following target stimuli were qualitatively different for stimulus identification and for response preparation. These results provide another piece of evidence for the independence of motor-related and perception-related effects of masked stimuli.

No MeSH data available.


ERPs evoked by the sequence of primes and targets, from 100 ms before prime						onset until 1 s afterwards. Grand means across 12 participants. Trials with						83 ms SOA between primes and targets are compiled in the left half, trials						with 167 ms in the right half. “Congruent” means that the relevant shape was						on the same side in primes as in targets, “incongruent” means different						sides, “neutral” denotes two irrelevant shapes in the primes. Each panel						displays waveshapes averaged across a pair of symmetrical left and right						positions, from anterior sites of the scalp (top) to occipital sites (2nd						panels from bottom), against a reference at the nose. The bottom panels						display the time course of the forces exerted on the response keys.
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Figure 1: ERPs evoked by the sequence of primes and targets, from 100 ms before prime onset until 1 s afterwards. Grand means across 12 participants. Trials with 83 ms SOA between primes and targets are compiled in the left half, trials with 167 ms in the right half. “Congruent” means that the relevant shape was on the same side in primes as in targets, “incongruent” means different sides, “neutral” denotes two irrelevant shapes in the primes. Each panel displays waveshapes averaged across a pair of symmetrical left and right positions, from anterior sites of the scalp (top) to occipital sites (2nd panels from bottom), against a reference at the nose. The bottom panels display the time course of the forces exerted on the response keys.

Mentions: In fact, ERPs evoked by pairs of masked and masking stimuli will not easily disentangle. This is illustrated in Figure 1. (These data were recorded in Experiment 1 of Jaśkowski, van der Lubbe, Schlotterbeck, & Verleger, 2002, but were not reported in that publication.) In this experiment, both masked and masking stimuli were squares or diamonds (Figure 2), with the outer outlines of the smaller masked stimuli fitting the inner outlines of the masking stimuli, thus being subject to masking by metacontrast. A full account of the experimental methods is provided in the Appendix. ERPs will be reported in this paper from the choice-response part of the experiment. In this part, the masking stimuli were the “targets” to which a manual response had to be made, and the preceding masked stimuli were “primes” because they were expected to affect the manual response to the following target. Participants had to press the left or right key depending on the side of the relevant shape in the target stimulus. (The relevant shape was the diamond for half of the participants, and the square for the other half.) Primes could be congruent, incongruent, or neutral in their relation to the following target, that is, the relevant shape could be on the same side as in the target, on the opposite side, or no relevant shape was included in the prime. Stimulus-onset asynchronies (SOA) between primes and targets were either 83 ms or 167 ms (henceforth SOA83 and SOA167). Prime-target congruence and SOA were randomly varied across trials. The rationale of the SOA variation was to use SOA83 as the condition where primes were indistinguishable and SOA167 as a control condition where primes were still hard to distinguish but above the “threshold” of awareness.


Disentangling neural processing of masked and masking stimulus by means of event-related contralateral - ipsilateral differences of EEG potentials.

Verleger R, Jaśkowski P - Adv Cogn Psychol (2008)

ERPs evoked by the sequence of primes and targets, from 100 ms before prime						onset until 1 s afterwards. Grand means across 12 participants. Trials with						83 ms SOA between primes and targets are compiled in the left half, trials						with 167 ms in the right half. “Congruent” means that the relevant shape was						on the same side in primes as in targets, “incongruent” means different						sides, “neutral” denotes two irrelevant shapes in the primes. Each panel						displays waveshapes averaged across a pair of symmetrical left and right						positions, from anterior sites of the scalp (top) to occipital sites (2nd						panels from bottom), against a reference at the nose. The bottom panels						display the time course of the forces exerted on the response keys.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2864968&req=5

Figure 1: ERPs evoked by the sequence of primes and targets, from 100 ms before prime onset until 1 s afterwards. Grand means across 12 participants. Trials with 83 ms SOA between primes and targets are compiled in the left half, trials with 167 ms in the right half. “Congruent” means that the relevant shape was on the same side in primes as in targets, “incongruent” means different sides, “neutral” denotes two irrelevant shapes in the primes. Each panel displays waveshapes averaged across a pair of symmetrical left and right positions, from anterior sites of the scalp (top) to occipital sites (2nd panels from bottom), against a reference at the nose. The bottom panels display the time course of the forces exerted on the response keys.
Mentions: In fact, ERPs evoked by pairs of masked and masking stimuli will not easily disentangle. This is illustrated in Figure 1. (These data were recorded in Experiment 1 of Jaśkowski, van der Lubbe, Schlotterbeck, & Verleger, 2002, but were not reported in that publication.) In this experiment, both masked and masking stimuli were squares or diamonds (Figure 2), with the outer outlines of the smaller masked stimuli fitting the inner outlines of the masking stimuli, thus being subject to masking by metacontrast. A full account of the experimental methods is provided in the Appendix. ERPs will be reported in this paper from the choice-response part of the experiment. In this part, the masking stimuli were the “targets” to which a manual response had to be made, and the preceding masked stimuli were “primes” because they were expected to affect the manual response to the following target. Participants had to press the left or right key depending on the side of the relevant shape in the target stimulus. (The relevant shape was the diamond for half of the participants, and the square for the other half.) Primes could be congruent, incongruent, or neutral in their relation to the following target, that is, the relevant shape could be on the same side as in the target, on the opposite side, or no relevant shape was included in the prime. Stimulus-onset asynchronies (SOA) between primes and targets were either 83 ms or 167 ms (henceforth SOA83 and SOA167). Prime-target congruence and SOA were randomly varied across trials. The rationale of the SOA variation was to use SOA83 as the condition where primes were indistinguishable and SOA167 as a control condition where primes were still hard to distinguish but above the “threshold” of awareness.

Bottom Line: Their major component, the N2pc, is interpreted as indicating preferential processing of stimuli matching the target template, which process can neither be identified with conscious perception nor with shifts of spatial attention.The measurements showed that the triggering of response preparation by the masked stimuli did not depend on their discriminability, and their priming effects on the processing of the following target stimuli were qualitatively different for stimulus identification and for response preparation.These results provide another piece of evidence for the independence of motor-related and perception-related effects of masked stimuli.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, University of Lübeck, Germany.

ABSTRACT
In spite of the excellent temporal resolution of event-related EEG potentials (ERPs), the overlapping potentials evoked by masked and masking stimuli are hard to disentangle. However, when both masked and masking stimuli consist of pairs of relevant and irrelevant stimuli, one left and one right from fixation, with the side of the relevant element varying between pairs, effects of masked and masking stimuli can be distinguished by means of the contralateral preponderance of the potentials evoked by the relevant elements, because the relevant elements may independently change sides in masked and masking stimuli. Based on a reanalysis of data from which only selected contralateral-ipsilateral effects had been previously published, the present contribution will provide a more complete picture of the ERP effects in a masked-priming task. Indeed, effects evoked by masked primes and masking targets heavily overlapped in conventional ERPs and could be disentangled to a certain degree by contralateral-ipsilateral differences. Their major component, the N2pc, is interpreted as indicating preferential processing of stimuli matching the target template, which process can neither be identified with conscious perception nor with shifts of spatial attention. The measurements showed that the triggering of response preparation by the masked stimuli did not depend on their discriminability, and their priming effects on the processing of the following target stimuli were qualitatively different for stimulus identification and for response preparation. These results provide another piece of evidence for the independence of motor-related and perception-related effects of masked stimuli.

No MeSH data available.