Individual Differences in Working Memory Capacity Modulate Electrophysiological Correlates of Semantic Negative Priming From Single Words.

In the present study, event-related potentials (ERPs) were registered during a semantic negative priming (NP) task in participants with higher and lower working memory capacity (WMC). On each trial participants had to actively ignore a briefly presented single prime word, which was followed either immediately or after a delay by a mask. Thereafter, either a semantically related or an unrelated target word was presented, to which participants made a semantic categorization judgment. The ignored prime produced a behavioral semantic NP in delayed (but not in immediate) masking trials, and only for participants with a higher-WMC. Both masking type and WMC also modulated ERP priming effects. When the ignored prime was immediately followed by a mask (which impeded its conscious identification) a reliable N400 modulation was found irrespective of participants' WMC. However, when the mask onset following the prime was delayed (thus allowing its conscious identification), an attenuation of a late positive ERP (LPC) was observed in related compared to unrelated trials, but only in the higher-WMC group showing reliable behavioral NP. The present findings demonstrate for the first time that individual differences in WMC modulate both behavioral measures and electrophysiological correlates of semantic NP.

Semantic Negative Priming From an Ignored Single-Prime Depends Critically on Prime-Mask Inter-Stimulus Interval and Working Memory Capacity.

The aim of this study is to examine the link between working memory capacity and the ability to exert cognitive control. Here, participants with either high or low working memory capacity (WMC) performed a semantic negative priming (NP) task as a measure of cognitive control. They were required to ignore a single prime word followed by a pattern mask appearing immediately or after a delay. The prime could be semantically related or unrelated to an upcoming target word where a forced-choice categorization was required. Each type of mask (immediate vs. delayed) appeared randomly from trial to trial. Results demonstrated that, when the ignored prime was immediately followed by the mask, neither of the groups (high or low WMC) showed reliable NP. In clear contrast, when the mask onset was delayed responses latencies were reliably slower for semantically related trials than for unrelated trials (semantic NP), but only for the high WMC group. The present results clearly demonstrate that semantic NP from single ignored primes depends on both the masking pattern that follows the prime (immediate vs. delayed mask), and on working memory capacity.

The implementation of expectancy-based strategic processes is delayed in normal aging.

The present research examined if the time needed to implement expectancy-based strategic processes is different in younger and healthy older adults. In four experiments participants from both age groups performed different strategic priming tasks. These included a greater proportion of incongruent (or unrelated; 80%) than of congruent (or related; 20%) trials. With this procedure performance is worse for congruent (less frequent) than for incongruent (more frequent) trials, thus demonstrating that the relative frequency information can be used to predict the upcoming target. To explore the time course of these expectancy-based effects, the prime-target SOA was manipulated across experiments through a range of intervals: 400, 1000 and 2000 ms. Participants also performed a change localization and an antisaccade task to assess their working memory and attention control capacities. The results showed that increases in age were associated with (a) a slower processing-speed, (b) a decline in WM capacity, and (c) a decreased capacity for attentional control. The latter was evidenced by a disproportionate deterioration of performance in the antisaccade trials compared to the prosaccade ones in the older group. Results from the priming tasks showed a delay in the implementation of expectancies in older adults. Whereas younger participants showed strategic effects already at 1000 ms, older participants consistently failed to show expectancy-based priming during the same interval. Importantly, these effects appeared later at 2000 ms, being similar in magnitude to those by the younger participants and unaffected by task practice. The present findings demonstrate that the ability to implement expectancy-based strategies is slowed down in normal aging.

Expectancy-Based Strategic Processes Are Influenced by Spatial Working Memory Load and Individual Differences in Working Memory Capacity.

The present research examined whether imposing a high (or low) working memory (WM) load in different types of non-verbal WM tasks could affect the implementation of expectancy-based strategic processes in a sequential verbal Stroop task. Participants had to identify a colored (green vs. red) target patch that was preceded by a prime word (GREEN or RED), which was either incongruent or congruent with the target color on 80% and 20% of the trials, respectively. Previous findings have shown that participants can strategically use this information to predict the upcoming target color, and avoid the standard Stroop interference effect. The Stroop task was combined with different types of non-verbal WM tasks. In Experiment 1, participants had to retain sets of four arrows that pointed either in the same (low WM load) or in different directions (high WM load). In Experiment 2, they had to remember the spatial locations of four dots which either formed a straight line (low load) or were randomly scattered in a square grid (high load). In addition, participants in the two experiments performed a change localization task to assess their WM capacity (WMC). The results in both experiments showed a reliable congruency by WM load interaction. When the Stroop task was performed under a high WM load, participants were unable to efficiently ignore the incongruence of the prime, as they consistently showed a standard Stroop effect, regardless of their WMC. Under a low WM load, however, a strategically dependent effect (reversed Stroop) emerged. This ability to ignore the incongruence of the prime was modulated by WMC, such that the reversed Stroop effect was mainly found in higher WMC participants. The findings that expectancy-based strategies on a verbal Stroop task are modulated by load on different types of spatial WM tasks point at a domain-general effect of WM on strategic processing. The present results also suggest that the impact of loading WM on expectancy-based strategies can be modulated by individual differences in WMC.

The Influence of Working Memory Load on Expectancy-Based Strategic Processes in the Stroop-Priming Task.

The present study investigated whether a differential availability of cognitive control resources as a result of varying working memory (WM) load could affect the capacity for expectancy-based strategic actions. Participants performed a Stroop-priming task in which a prime word (GREEN or RED) was followed by a colored target (red vs. green) that participants had to identify. The prime was incongruent or congruent with the target color on 80 and 20% of the trials, respectively, and participants were informed about the differential proportion of congruent vs. incongruent trials. This task was interleaved with a WM task, such that the prime word was preceded by a sequence of either a same digit repeated five times (low load) or five different random digits (high load), which should be retained by participants. After two, three, or four Stroop trials, they had to decide whether or not a probe digit was a part of the memory set. The key finding was a significant interaction between prime-target congruency and WM load: Whereas a strategy-dependent (reversed Stroop) effect was found under low WM load, a standard Stroop interference effect was observed under high WM load. These findings demonstrate that the availability of WM is crucial for implementing expectancy-based strategic actions.

Individual Differences in Working Memory Capacity Modulates Semantic Negative Priming from Single Prime Words.

The present study investigated whether semantic negative priming from single prime words depends on the availability of cognitive control resources. Participants with high vs. low working memory capacity (as assessed by their performance in complex span and attentional control tasks) were instructed to either attend to or ignore a briefly presented single prime word that was followed by either a semantically related or unrelated target word on which participants made a lexical decision. Individual differences in working memory capacity (WMC) mainly affected the processing of the ignored primes, but not the processing of the attended primes: While the latter produced reliable positive semantic priming for both high- and low-WMC participants, the former gave rise to reliable semantic negative priming only for high WMC participants, with low WMC participants showing the opposite positive priming effect. The present results extend previous findings in demonstrating that (a) single negative priming can reliably generalize to semantic associates of the prime words, and (b) a differential availability of cognitive control resources can reliably modulate the negative priming effect at a semantic level of representation.

The semantic origin of unconscious priming: Behavioral and event-related potential evidence during category congruency priming from strongly and weakly related masked words.

The mechanisms underlying masked congruency priming, semantic mechanisms such as semantic activation or non-semantic mechanisms, for example response activation, remain a matter of debate. In order to decide between these alternatives, reaction times (RTs) and event-related potentials (ERPs) were recorded in the present study, while participants performed a semantic categorization task on visible word targets that were preceded either 167 ms (Experiment 1) or 34 ms before (Experiment 2) by briefly presented (33 ms) novel (unpracticed) masked prime words. The primes and targets belonged to different categories (unrelated), or they were either strongly or weakly semantically related category co-exemplars. Behavioral (RT) and electrophysiological masked congruency priming effects were significantly greater for strongly related pairs than for weakly related pairs, indicating a semantic origin of effects. Priming in the latter condition was not statistically reliable. Furthermore, priming effects modulated the N400 event-related potential (ERP) component, an electrophysiological index of semantic processing, but not ERPs in the time range of the N200 component, associated with response conflict and visuo-motor response priming. The present results demonstrate that masked congruency priming from novel prime words also depends on semantic processing of the primes and is not exclusively driven by non-semantic mechanisms such as response activation.

Subliminal Gestalt grouping: evidence of perceptual grouping by proximity and similarity in absence of conscious perception.

Previous studies making use of indirect processing measures have shown that perceptual grouping can occur outside the focus of attention. However, no previous study has examined the possibility of subliminal processing of perceptual grouping. The present work steps forward in the study of perceptual organization, reporting direct evidence of subliminal processing of Gestalt patterns. In two masked priming experiments, Gestalt patterns grouped by proximity or similarity that induced either a horizontal or vertical global orientation of the stimuli were presented as masked primes and followed by visible targets that could be congruent or incongruent with the orientation of the primes. The results showed a reliable priming effect in the complete absence of prime awareness for both proximity and similarity grouping principles. These findings suggest that a phenomenal report of the Gestalt pattern is not mandatory to observe an effect on the response based on the global properties of Gestalt stimuli.

Unconscious congruency priming from unpracticed words is modulated by prime-target semantic relatedness.

Participants performed a 2-choice categorization task on visible word targets that were preceded by novel (unpracticed) prime words. The prime words were presented for 33 ms and followed either immediately (Experiments 1-3) or after a variable delay (Experiments 1 and 4) by a pattern mask. Both subjective and objective measures of prime visibility were used in all experiments. On 80% of the trials the primes and targets belonged to different categories (incongruent trials), whereas in the remaining 20% (congruent trials) they could be either strong or weak semantically related category members. Positive congruency effects (reaction times faster on congruent than on incongruent trials) were consistently found, but only when the mask immediately followed the primes, and participants reported being unaware of the identity of the primes. Primes followed by a delayed mask (such that participants reported being aware of their identity) produced either nonreliable facilitation or reliable reversed priming (strategic), depending on whether the prime-target stimulus onset asynchrony was either short (200 ms; Experiments 1 and 4) or long (1,000 ms; Experiment 4). Facilitatory priming with immediate mask was found strong (a) even for participants who performed at chance in prime visibility tests; and (b) for high but not for weakly semantically related category coordinates, irrespective of category size (animals, body parts). These findings provide evidence that unconscious congruency priming by unpracticed words from large stimulus sets critically depends on associative strength and/or semantic similarity between category coexemplars.

Influence of spatial attention on conscious and unconscious word priming.

We used a qualitative dissociation procedure to assess semantic priming from spatially attended and unattended masked words. Participants categorized target words that were preceded by parafoveal prime words belonging to either the same (20%) or the opposite (80%) category as the target. Using this paradigm, only non-strategic use of the prime would result in facilitation of the target responses in related trials. Primes were immediately masked or masked with a delay, while spatial attention was allocated to the primes' location or away from the primes' location. Immediate masked, strongly related primes facilitated target responses irrespective of the spatial attention. Delayed masked, related primes led to reversed (strategic) or facilitatory priming depending on whether they were cued or uncued. These findings demonstrate that perceiving a stimulus with or without awareness depends on both stimulus quality and attention orienting and that non-strategic priming can be observed from clear visible but spatially unattended words.

Negative semantic priming from consciously vs. unconsciously perceived single words

El presente estudio investiga si la obtención depriming semántico negativo ante una única palabra ignorada depende delnivel de conciencia de dicha palabra. En cada ensayo aparecía brevementeuna palabra previa seguida inmediatamente o tras un intervalo de demora,por una máscara de patrón. A continuación aparecía una palabra objetivoante la que los participantes debían realizar una tarea de categorizaciónsemántica o una tarea de identificación de elección forzada. Se instruyó alos sujetos a que atendieran la palabra objetivo e ignoraran la palabra previa,considerándola como un distractor. Las palabras previa y objetivopertenecían a la misma categoría semántica en la mitad de los ensayos, y adistintas categorías en los ensayos restantes. Los resultados mostraron unpatrón diferencial de efectos de priming semántico en función del tipo deenmascaramiento: Priming negativo con la máscara demorada, y facilitacióncon la máscara inmediata. Estos resultados demuestran que el tipo deenmascaramiento, que supuestamente afecta a la percepción consciente vs.no consciente de la palabra previa, constituiría una variable crítica paraobtener priming semántico negativo ante una única palabra. También sonconsistentes con la idea de que la percepción con y sin conciencia produceconsecuencias comportamentales cualitativamente diferentes, que reflejan lacontribución de procesos controlados y automáticos, respectivamente(AU)

The present research explores whether obtaining semantic negative primingfrom a single ignored word depends on whether that word is eitherconsciously or unconsciously perceived. On each trial a prime word wasbriefly displayed and followed either immediately or after a delay by apattern mask. The mask offset was followed by a probe display containing asingle target word that participants were required to either categorize oridentify. Participants were instructed to attend to the target while ignoringthe prime word. On half of trials the prime-target pairs were highlyassociated words belonging to the same semantic category, whereas on theremaining half they belonged to different semantic categories. A differentialpriming pattern as a function of the masking condition was found: Semanticnegative priming when the mask presentation was delayed, and positivepriming when the prime word was immediately masked, thus preventing itsconscious identification. These results suggest that masking type, whichsupposedly affects prime awareness, would be a critical factor to obtainnegative semantic priming from single words. They also provide evidencethat perceiving a stimulus with or without awareness can lead toqualitatively different behavioral consequences, which reflect thecontribution of controlled and automatic components, respectively(AU)

Semantic priming effects from single words in a lexical decision task.

The present research examines the semantic priming effects of a centrally presented single prime word to which participants were instructed to either "attend and remember" or "ignore". The prime word was followed by a central probe target on which the participants made a lexical decision task. The main variables manipulated across experiments were prime duration (50 or 100 ms), the presence or absence of a mask following the prime, and the presence (or absence) and type of distractor stimulus (random set of consonants or pseudowords) on the probe display. There was a consistent interaction between the instructions and the semantic priming effects. Relative to the "attend and remember" instruction, an "ignore" instruction produced reduced positive priming from single primes presented for 100 ms, irrespective of the presence or absence of a prime mask, and regardless of whether the probe target was presented with or without distractors. Additionally, reliable negative priming was found from ignored primes presented for briefer durations (50 ms) and immediately followed by a mask. Methodological and theoretical implications of the present findings for the extant negative priming literature are discussed.

Semantic priming effects with and without perceptual awareness

Elpresente trabajo pretende replicar y extender los resultados de algunosestudios previos que demuestran que la percepción consciente vs. noconscientede palabras puede producir efectos comportamentales diferentes.Los participantes realizaban una tarea de categorización semántica sobre unapalabra objetivo que era precedida por una palabra previa que podíapertenecer o a la misma categoría (20% de los ensayos) o a una categoríasemántica diferente (80%). La palabra previa se presentaba brevemente y eraseguida inmediatamente o tras una demora por una máscara visual. Adiferencia de trabajos previos, el tipo de máscara variaba de forma aleatoriade ensayo a ensayo. En los ensayos con la máscara inmediata se encontró unefecto facilitatorio de priming semántico. Con la máscara demorada (quepermitía la identificación consciente de la palabra previa) se encontró unefecto opuesto (negativo) de priming. Estos resultados proporcionan pruebasadicionales de que la percepción con y sin conciencia produceconsecuencias comportamentales cualitativamente diferentes, las cualesreflejan la contribución de procesos controlados (estratégicos) yautomáticos, respectivamente

The present research was aimed to reply and extend several recent findingsshowing qualitatively different behavioral effects produced by wordsperceived with vs. without awareness. Participants made a semanticcategorization task on a target that was preceded by a prime word belongingeither to the same (20% of trials) or to a different category (80%). The primewas always presented briefly and followed either immediately or after adelay by a pattern mask. In contrast to prior studies, the masking type variedrandomly from trial to trial. For trials with an immediate mask (whichavoided conscious identification of the prime), a significant facilitatorysemantic priming was found. For trials with a delayed mask (on whichparticipants were able to identify the prime), a significant “reversed”semantic priming was observed. The present findings provide furtherevidence that perceiving a stimulus with or without awareness can lead toqualitatively different behavioral consequences, which reflect thecontribution of strategy-based (controlled) and automatic components,respectively

Repetition priming effects from attended vs. ignored single words in a semantic categorization task.

The present research examines priming effects from a centrally presented single-prime word to which participants were instructed to either attend or ignore. The prime word was followed by a single central target word to which participants made a semantic categorization (animate vs. inanimate) task. The main variables manipulated across experiments were attentional instructions (attend vs. ignore the prime word), presentation duration of the prime word (20, 50, 80 or 100 ms), prime-target stimulus onset asynchrony (SOA; 300 vs. 800 ms), and temporal presentation of instructions (before vs. after the prime word). The results showed (a) a consistent interaction between attentional instructions and repetition priming and (b) a qualitatively different ignored priming pattern as a function of prime duration: reduced positive priming (relative to the attend instruction) for prime exposures of 80 and 100 ms, and reliable negative priming for the shorter prime exposures of 20 and 50 ms. In addition (c), the differential priming pattern for attend and ignore trials was observed at a prime-target SOA of 800 ms (but not at a shorter 300-ms SOA) and only when instructions were presented before the prime word. Methodological and theoretical implications of the present findings for the extant negative priming literature are discussed.

Influence of prime-target relationship on semantic priming effects from words in a lexical-decision task.

The present research examines the influence of prime-target relationship (associative and categorical versus categorical only) on priming effects from attended and ignored parafoveal words. Participants performed a lexical-decision task on a single central target, which was preceded by two parafoveal prime words, one of which (the attended prime) was spatially precued. The results showed reliable positive and negative priming effects from attended and ignored words, respectively. However, this priming pattern was observed only for the "associative and categorical", but not for the "categorical only" relationship condition. These results suggest that the lack of semantic priming effects from words in some prior studies may be attributed to the kind of material used (i.e. weakly-associated word pairs).

Semantic activation in the absence of perceptual awareness.

Participants performed a semantic categorization task on a target that was preceded by a prime word belonging either to the same category (20% of trials) or to a different category (80% of trials). The prime was presented for 33 msec and followed either immediately or after a delay by a pattern mask. With the immediate mask, reaction times (RTs) were shorter on related than on unrelated trials. This facilitatory priming reached significance at prime-target stimulus onset asynchronies (SOAs) of 400 msec or less and remained unaffected by task practice. With the delayed mask, RTs were longer on related than on unrelated trials. This reversed (strategic) semantic priming proved to be significant (1) only at a prime-target SOA of 400 msec or longer and (2) after the participants had some practice with the task. The present findings provide further evidence that perceiving a stimulus with and without phenomenological awareness can lead to qualitatively different behavioral consequences.

Perception without awareness: further evidence from a Stroop priming task.

In the present research, we examined the influence of prime-target stimulus onset asynchrony (SOA) on Stroop-priming effects from masked words. Participants indicated the color of a central target, which was preceded by a 33-msec prime word followed either immediately or after a variable delay by a pattern mask. The prime word was incongruent or congruent with the target color on 75% and 25% of the trials, respectively. The words followed by an immediate mask produced reliable Stroop interference at SOAs of 300 and 400 msec but not at SOAs of 500 and 700 msec. The words followed by a delayed mask produced a reversed (i.e., facilitatory) Stroop effect, which reached significance at an SOA of 400 msec or longer, but never at the shorter 300-msec SOA. Such an differential time course of both types of Stroop priming effects provides further evidence for the existence of qualitative differences between conscious and nonconscious perceptual processes.