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Electrophysiological activation by masked primes: Independence of prime-related and target-related activities

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Klotz W., Heumann M., Ansorge U., Neumann O.

Advances in Cognitive Psychology

2007

vol. 3

issue 4

449-465

Visual stimuli that are made invisible by metacontrast masking (primes) have a marked influence on behavioral and psychophysiological measures such as reaction time (RT) and the lateralized readiness potential (LRP). 4 experiments are reported that shed light on the effects that masked primes have on the LRP. Participants had a go-nogo task in which the prime was associated with 1 of 2 responses even if the target required participants to refrain from responding. To analyze the electrophysiological responses, we computed the LRP and applied an averaging method separating the activation due to the prime and the target. The results demonstrated that (a) masked primes activate responses even in a nogo situation, (b) this prime-related activation is independent of masking, (c) and is also independent of whether prime and target require the same responses (congruent condition) or different responses (incongruent condition).

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

75%

Verleger R., Jaśkowski P.

Advances in Cognitive Psychology

2007

vol. 3

issue 1-2

193-210

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.

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2 Advances in Cognitive Psychology

1 Ansorge U.

1 Heumann M.

1 Jaśkowski P.

1 Klotz W.

1 Neumann O.

1 Verleger R.

2 2007

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Electrophysiological activation by masked primes: Independence of prime-related and target-related activities

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