Dissociating local and global levels of perceptuo-motor control in masked priming

The Inhibition Effect of Affordances in Action Picture Naming: An ERP Study

How quickly are different kinds of conceptual knowledge activated in action picture naming? Using a masked priming paradigm, we manipulated the prime category type (artificial vs. natural), prime action type (precision, power, vs. neutral grip), and target action type (precision vs. power grip) in action picture naming, while electrophysiological signals were measured concurrently. Naming latencies showed an inhibition effect in the congruent action type condition compared with the neutral condition. ERP results showed that artificial and natural category primes induced smaller waveforms in precision or power action primes than neutral primes in the time window of 100-200 msec. Time-frequency results consistently presented a power desynchronization of the mu rhythm in the time window of 0-210 msec with precision action type artificial objects compared with neutral primes, which localized at the supplementary motor, precentral and postcentral areas in the left hemisphere. These findings suggest an inhibitory effect of affordances arising at conceptual preparation in action picture naming and provide evidence for embodied cognition.

The simultaneous oddball: Oddball presentation does not affect simultaneity judgments

The oddball duration illusion describes how a rare or nonrepeated stimulus is perceived as lasting longer than a common or repeated stimulus. It has been argued that the oddball duration illusion could emerge because of an earlier perceived onset of an oddball stimulus. However, most methods used to assess the perceived duration of an oddball stimulus are ill suited to detect onset effects. Therefore, in the current article, I tested the perceived onset of oddball and standard stimuli using a simultaneity judgment task. In Experiments 1 and 2, repetition and rarity of the target stimulus were varied, and participants were required to judge whether the target stimulus and another stimulus were concurrent. In Experiment 3, I tested whether a brief initial stimulus could act as a conditioning stimulus in the oddball duration illusion. This was to ensure an oddball duration illusion could have occurred given the short duration of stimuli in the first two experiments. In both the first two experiments, I found moderate support for no onset-based difference between oddball and nonoddball stimuli. In Experiment 3, I found that a short conditioning stimulus could still lead to the oddball duration illusion occurring, removing this possible explanation for the null result. Experiment 4 showed that an oddball duration illusion could emerge given the rarity of the stimulus and a concurrent sound. In sum, the current article found evidence against an onset-based explanation of the oddball duration illusion.

Activation, Inhibition, or Something Else: An Exploratory Study on Response Priming Using Moving Dots as Primes in Middle-Aged and Old Adults

Response priming refers to the finding that a prime stimulus preceding a target stimulus influences the response to the following target stimulus. With young subjects, using moving dot stimuli as primes indicated faster responses to compatible targets (i.e., prime and target are associated with the same response) with short stimulus onset asynchronies (SOAs). In contrast, with longer SOAs, participants responded faster to incompatible targets. In the present study, we extended the evidence by comparing middle-aged (50-65 years) and old (66-87 years) adults. With two different motion types, the result found in young participants was replicated in the middle-aged adults. In contrast, old adults showed large positive compatibility effects with the short SOA but neither activation nor inhibition effects with the longer SOA. We discuss our findings in light of several theoretical accounts (i.e., inhibitory deficit, deautomatization, evaluation window account, attention, rapid decay).

Prevailing theories of consciousness are challenged by novel cross-modal associations acquired between subliminal stimuli

While theories of consciousness differ substantially, the 'conscious access hypothesis', which aligns consciousness with the global accessibility of information across cortical regions, is present in many of the prevailing frameworks. This account holds that consciousness is necessary to integrate information arising from independent functions such as the specialist processing required by different senses. We directly tested this account by evaluating the potential for associative learning between novel pairs of subliminal stimuli presented in different sensory modalities. First, pairs of subliminal stimuli were presented and then their association assessed by examining the ability of the first stimulus to prime classification of the second. In Experiments 1-4 the stimuli were word-pairs consisting of a male name preceding either a creative or uncreative profession. Participants were subliminally exposed to two name-profession pairs where one name was paired with a creative profession and the other an uncreative profession. A supraliminal task followed requiring the timed classification of one of those two professions. The target profession was preceded by either the name with which it had been subliminally paired (concordant) or the alternate name (discordant). Experiment 1 presented stimuli auditorily, Experiment 2 visually, and Experiment 3 presented names auditorily and professions visually. All three experiments revealed the same inverse priming effect with concordant test pairs associated with significantly slower classification judgements. Experiment 4 sought to establish if learning would be more efficient with supraliminal stimuli and found evidence that a different strategy is adopted when stimuli are consciously perceived. Finally, Experiment 5 replicated the unconscious cross-modal association achieved in Experiment 3 utilising non-linguistic stimuli. The results demonstrate the acquisition of novel cross-modal associations between stimuli which are not consciously perceived and thus challenge the global access hypothesis and those theories embracing it.

Response priming with motion primes: negative compatibility or congruency effects, even in free-choice trials

How actions are chosen, and what they are influenced by, has been the focus of several research traditions. Influences on actions are often studied using compatibility paradigms, such as response priming. Here, a first stimulus (i.e., the prime) is presented shortly before a second stimulus (i.e., the target) which has to be classified. Reaction times to the target are often reduced when primes and targets are compatible compared to incompatible primes and targets-i.e., a positive compatibility effect (PCE). There are, however, some conditions in which reliably negative compatibility effects (NCEs), with faster reactions to incompatible targets, are found. Actions in real life are often influenced by perceived motion and are less determined by following (target) stimuli as it is the case in typical response priming studies with predetermined stimulus-response mappings. Thus, in the current experiment we used motion primes in forced-choice trials (with >> and << as targets) as well as in free-choice trials (with <> and >< as targets). Essentially, we found PCEs in the short-SOA condition and NCEs in the long-SOA condition. The pattern was not qualified by task (i.e., forced choice/free choice). The results provide evidence that NCEs with motion primes are found even without strong links between target stimuli and responses and that especially PCEs can be found with simpler and smaller targets than have been used in previous experiments.

Word Meaning Frequencies Affect Negative Compatibility Effects In Masked Priming

Negative compatibility effects (NCEs)—that is, slower responses to targets in related than unrelated prime-target pairs, have been observed in studies using stimulus-response (S-R) priming with stimuli like arrows and plus signs. Although there is no consensus on the underlying mechanism, explanations tend to locate NCEs within the motor-response system. A characteristic property of perceptuo-motor NCEs is a biphasic pattern of activation: A brief period in which very briefly presented (typically) masked primes facilitate processing of related targets is followed by a phase of target processing impairment. In this paper, we present data that suggest that NCEs are not restricted to S-R priming with low-level visual stimuli: The brief (50 ms), backward masked (250 ms) presentation of ambiguous words (bank) leads to slower responses than baseline to words related to the more frequent (rob) but not less frequent meaning (swim). Importantly, we found that slowed responses are preceded by a short phase of response facilitation, replicating the biphasic pattern reported for arrows and plus signs. The biphasic pattern of priming and the fact that the NCEs were found only for target words that are related to their prime word’s more frequent meaning has strong implications for any theory of NCEs that locate these effects exclusively within the motor-response system.

The relationship between reversed masked priming and the tri-phasic pattern of the lateralised readiness potential

One of the potential explanations for negative compatibility effects (NCE) in subliminal motor priming tasks has been perceptual prime-target interactions. Here, we investigate whether the characteristic tri-phasic LRP pattern associated with the NCE is caused by these prime-target interactions. We found that both the prime-related phase and the critical reversal phase remain present even on trials where the target is omitted, confirming they are elicited by the prime and mask, not by prime-target interactions. We also report that shape and size of the reversal phase are associated with response speed, consistent with a causal role for the reversal for the subsequent response latency. Additionally, we analysed sequential modulation of the NCE by previous conflicting events, even though such conflict is subliminal. In accordance with previous literature, this modulation is small but significant.

Exaggerated object affordance and absent automatic inhibition in alien hand syndrome

Patients with alien hand syndrome (AHS) experience making apparently deliberate and purposeful movements with their hand against their will. However, the mechanisms contributing to these involuntary actions remain poorly understood. Here, we describe two experimental investigations in a patient with corticobasal syndrome (CBS) with alien hand behaviour in her right hand. First, we show that responses with the alien hand are made significantly more quickly to images of objects which afford an action with that hand compared to objects which afford an action with the unaffected hand. This finding suggests that involuntary grasping behaviours in AHS might be due to exaggerated, automatic motor activation evoked by objects which afford actions with that limb. Second, using a backwards masked priming task, we found normal automatic inhibition of primed responses in the patient's unaffected hand, but importantly there was no evidence of such suppression in the alien limb. Taken together, these findings suggest that grasping behaviours in AHS may result from exaggerated object affordance effects, which might potentially arise from disrupted inhibition of automatically evoked responses.

Emotion potentiates response activation and inhibition in masked priming

Previous studies have shown that emotion can have 2-fold effects on perception. At the object-level, emotional stimuli benefit from a stimulus-specific boost in visual attention at the relative expense of competing stimuli. At the visual feature-level, recent findings indicate that emotion may inhibit the processing of small visual details and facilitate the processing of coarse visual features. In the present study, we investigated whether emotion can boost the activation and inhibition of automatic motor responses that are generated prior to overt perception. To investigate this, we tested whether an emotional cue affects covert motor responses in a masked priming task. We used a masked priming paradigm in which participants responded to target arrows that were preceded by invisible congruent or incongruent prime arrows. In the standard paradigm, participants react faster, and commit fewer errors responding to the directionality of target arrows, when they are preceded by congruent vs. incongruent masked prime arrows (positive congruency effect, PCE). However, as prime-target SOAs increase, this effect reverses (negative congruency effect, NCE). These findings have been explained as evidence for an initial activation and a subsequent inhibition of a partial response elicited by the masked prime arrow. Our results show that the presentation of fearful face cues, compared to neutral face cues, increased the size of both the PCE and NCE, despite the fact that the primes were invisible. This is the first demonstration that emotion prepares an individual's visuomotor system for automatic activation and inhibition of motor responses in the absence of visual awareness.

Age-related deficits in efficiency of low-level lateral inhibition

Background: In a masked prime task using a 0 ms prime-target inter-stimulus-interval, responses on trials where prime and target match (compatible trials) are usually faster and more accurate than responses where prime and target mismatch (incompatible trials). This positive compatibility effect (PCE) comprises both behavioral benefits on compatible relative to neutral trials, and behavioral costs on incompatible relative to neutral trials. Comparing performance in 2- vs. 4-alternative-response versions of the task indicates that benefits are due to direct priming (i.e., pre-activation) of a motor response, whereas costs reflect an inhibition of the alternative response tendency. The present study employs this paradigm to test the hypothesis that normal aging is associated with a selective deficit in inhibitory function, affecting both low-level motor and higher-level executive control. Experiment and Results: Testing 20 young and 20 older healthy adults, we found that (1) overall, prime-induced benefits were of similar magnitude across age groups, but inhibition-based costs were smaller in older compared to young adults; (2) increasing the number of response alternatives caused the same pattern of unaltered benefits and reduced costs in both age groups; and (3) costs, but not benefits, in the 2-alternative condition were significantly predicted by scores on the digit symbol substitution task (DSST), independently of age and other background variables. Interpretation: Results demonstrate the possibility of isolating an inhibitory component in low-level perceptuo-motor control. Importantly, this component shows an age-related decline in the absence of a corresponding decline of visuo-motor excitability, and appears to be linked to performance on a higher-level processing speed task. We hypothesize that aging might affect the brain's ability to establish precise short-term lateral inhibitory links, and that even in young adults, the efficiency of such links is a significant contributing factor in higher-level cognitive performance.

Automatic motor activation in the executive control of action

Although executive control and automatic behavior have often been considered separate and distinct processes, there is strong emerging and convergent evidence that they may in fact be intricately interlinked. In this review, we draw together evidence showing that visual stimuli cause automatic and unconscious motor activation, and how this in turn has implications for executive control. We discuss object affordances, alien limb syndrome, the visual grasp reflex, subliminal priming, and subliminal triggering of attentional orienting. Consideration of these findings suggests automatic motor activation might form an intrinsic part of all behavior, rather than being categorically different from voluntary actions.

Dissociating effects of subclinical anxiety and depression on cognitive control

Even at subclinical levels, anxiety and depression are associated with impaired cognitive control. It is unclear, though, to what extent these deficits reflect a common underlying dysfunction. Using a non-affective hybrid masked prime-Simon task, we obtained several measures of within- and between- trial inhibitory behavioral control in 80 young, healthy volunteers, together with measures of their anxiety and depression levels. Neither depression nor anxiety affected low-level within-trial control, or any of the between-trial control measures. However, increased levels of depression, but not of anxiety, were associated with impaired high-level within-trial control (increased Simon effect). Results indicate that depression, but not anxiety, impairs voluntary online response-control mechanisms independent of affective content.

Centre-surround inhibition is a general aspect of famous-person recognition: evidence from negative semantic priming from clearly visible primes

A centre-surround attentional mechanism was proposed by Carr and Dagenbach (Journal of Experimental Psychology: Learning, Memory, and Cognition 16: 341-350, 1990) to account for their observations of negative semantic priming from hard-to-perceive primes. Their mechanism cannot account for the observation of negative semantic priming when primes are clearly visible. Three experiments (Ns = 30, 46, and 30) used a familiarity decision with names of famous people, preceded by a prime name with the same occupation as the target or with a different occupation. Negative semantic priming was observed at a 150- or 200-ms SOA, with positive priming at shorter (50-ms) and longer (1,000-ms) SOAs. In Experiment 3, we verified that the primes were easily recognisable in the priming task at an SOA that yielded negative semantic priming, which cannot be predicted by the original centre-surround mechanism. A modified version is proposed that explains transiently negative semantic priming by proposing that centre-surround inhibition is a normal, automatically invoked aspect of the semantic processing of visually presented famous names.

Supplementary motor area activations in unconscious inhibition of voluntary action

It is widely accepted that regions within the dorsal medial frontal cortex are involved in the control of voluntary action. However, recent evidence suggests that a subset of these regions may also be important for unconscious and involuntary motor processes. Indeed, Sumner et al. (Neuron 54:697-711, 2007) showed that two patients with micro-lesions of the supplementary motor area (SMA) and supplementary eye field (SEF) demonstrated an absence of unconscious inhibition as evoked by masked-prime stimuli, while pre-SMA damage had no such effect. Here, we employ fMRI and a similar masked-prime task to test whether SMA and pre-SMA are similarly dissociated in healthy volunteers. Reaction times (RT) revealed that responses to compatible trials were slower than those to incompatible trials (negative compatibility effect, NCE), indicating automatic inhibition in every participant. BOLD signals in the SMA were modulated by prime compatibility, showing greater signal for compatible trials, but there was no change in pre-SMA. There was also no modulation in the hand motor cortex (HMC). These findings imply that the SMA is involved in automatic suppression of manual motor plans.

Tight coupling between positive and reversed priming in the masked prime paradigm

When associations between certain visual stimuli and particular actions are learned, those stimuli become capable of automatically and unconsciously activating their associated action plans. Such sensorimotor priming is assumed to be fundamental for efficient responses, and can be reliably measured in masked prime studies even when the primes are not consciously perceived. However, when the delay between prime and target is increased, reversed priming effects are often found instead (the negative compatibility effect, NCE). The main accounts of the NCE assume that it too is a sensorimotor phenomenon, predicting that it should occur only when the initial positive priming phase also occurs. Alternatively, reversed priming may reflect a perceptual process entirely independent from positive motor priming (which is simply evident at a different temporal delay), in which case no dependency is expected between the NCE and positive priming. We tested these predictions while new sensorimotor associations were learned, and found a remarkable symmetry between positive and reversed priming during all such learning phases, supporting the idea that reversed priming is a sensorimotor process that automatically follows the positive priming phase.

Self-specific priming effect

Priority of the "self" is thought to be evolutionarily advantageous. However, evidence for this priority has been sparse. In this study, subjects performed a gender categorization task on self- and non-self target faces preceded by either congruent (same gender as target) or incongruent (different gender) periliminal (33ms) or subliminal (17ms) primes. We found that subliminal primes induced a priming effect only on self target faces. This discovery of a self-specific priming effect suggests that functional specificity for faces may include timing as well as spatial adaptations.

Unconscious inhibition separates two forms of cognitive control

In the human brain, cognitive-control processes are generally considered distinct from the unconscious mechanisms elicited by subliminal priming. Here, we show that cognitive control engaged in situations of response conflict interacts with the negative (inhibitory) phase of subliminal priming. Thus, cognitive control may surprisingly share common processes with nonconscious brain mechanisms. In contrast, our findings reveal that subliminal inhibition does not, however, interact with control adaptation--the supposed modulation of current control settings by previous experience of conflict. Therefore, although influential models have grouped immediate cognitive control and control adaptation together as products of the same conflict detection and control network, their relationship to subliminal inhibition separates them. Overall, these results suggest that the important distinction lies not between cognitive or top-down processes on the one hand and nonconscious priming mechanisms on the other hand but between responsive (poststimulus) mechanisms that deal with sensorimotor activation after it has occurred and preparatory (prestimulus) mechanisms that are modulated before stimulus arrival.

Either or neither, but not both: locating the effects of masked primes

Execution of a response that has been primed by a backward-masked stimulus is inhibited (negative compatibility effect; NCE). Three experiments investigated the locus of this inhibition. Masked primes (left- or right-pointing arrows) were followed either by an arrow or a circle target. Arrow targets always required a left- or right-hand response, but the experiments differed in the response required to circles: press neither, either or both response keys (i.e. nogo, free choice and bimanual, respectively). Arrow targets showed the usual NCEs. Circle targets showed NCEs in the form of a response bias away from the primed response in the nogo and free-choice tasks; primes and targets differed on these trials, ruling out a perceptual explanation of the NCE. The bimanual task showed no such bias, suggesting that the NCE is located at a level of abstract response codes rather than specific muscle commands.

Negative and positive masked-priming - implications for motor inhibition

Masked stimuli can prime responses to subsequent target stimuli, causing response benefits when the prime is similar to the target. However, one masked-prime paradigm has produced counter-intuitive negative compatibility effects (NCE), such that performance costs occur when prime and target are similar. This NCE has been interpreted as an index of an automatic self-inhibition mechanism that suppresses the partial motor activation caused by the prime. However, several alternative explanations for the NCE have been proposed and supported by new evidence. As a framework for discussion, I divide the original theory into five potentially separable issues and briefly examine each with regard to alternative theories and current evidence. These issues are: 1) whether the NCE is caused by motor inhibition or perceptual interactions; 2) whether inhibition is self-triggered or stimulus-triggered; 3) whether prime visibility plays a causal role; 4) whether there is a threshold for triggering inhibition; 5) whether inhibition is automatic. Lastly, I briefly consider why NCEs have not been reported in other priming paradigms, and what the neural substrate for any automatic motor inhibition might be.

The negative compatibility effect: A case for self-inhibition

In masked priming, a briefly presented prime stimulus is followed by a mask, which in turn is followed by the task-relevant target. Under certain conditions, negative compatibility effects (NCNCEs) occur, with impaired performance on compatible trials (where prime and target indicate the same response) relative to incompatible trials (where they indicate opposite responses). However, the exact boundary conditions of NCEs, and hence the functional significance of this effect, are still under discussion. In particular, it has been argued that the NCE might be a stimulus-specific phenomenon of little general interest. This paper presents new findings indicating that the NCE can be obtained under a wider variety of conditions, suggesting that it reflects more general processes in motor control. In addition, evidence is provided suggesting that prime identification levels in forced choice tasks - usually employed to estimate prime visibility in masked prime tasks - are affected by prior experience with the prime (Exp. 1) as well as by direct motor priming (Exp. 2 & 3).

Mask-induced priming and the negative compatibility effect

Under certain conditions, masked primes have produced counter-intuitive negative compatibility effects (NCE), such that RT is increased, not decreased, when the target is similar to the prime. This NCE has been interpreted as an index of automatic motor inhibition, triggered to suppress the partial motor activation caused by the prime. An alternative explanation is that perceptual interactions between prime and mask produce positive priming in the opposite direction to the prime, explaining the NCE without postulating inhibition. Here the potential role of this "mask-induced priming" was investigated in two experiments, using masks composed of random lines. Experiment 1 compared masks that included features of the primes and targets with masks that did not. The former should create more mask-induced priming, but the NCE did not differ between masks. Experiment 2 employed masks that contained features of either one target or the other, but not both. These asymmetric masks produced significant mask-induced priming, but it was insufficient in size to account for the prime-related NCE. Thus mask composition can contribute to NCEs, but when random line masks are employed, the major source of the NCE seems to be motor-inhibition.

Human medial frontal cortex mediates unconscious inhibition of voluntary action

Within the medial frontal cortex, the supplementary eye field (SEF), supplementary motor area (SMA), and pre-SMA have been implicated in the control of voluntary action, especially during motor sequences or tasks involving rapid choices between competing response plans. However, the precise roles of these areas remain controversial. Here, we study two extremely rare patients with microlesions of the SEF and SMA to demonstrate that these areas are critically involved in unconscious and involuntary motor control. We employed masked-prime stimuli that evoked automatic inhibition in healthy people and control patients with lateral premotor or pre-SMA damage. In contrast, our SEF/SMA patients showed a complete reversal of the normal inhibitory effect--ocular or manual--corresponding to the functional subregion lesioned. These findings imply that the SEF and SMA mediate automatic effector-specific suppression of motor plans. This automatic mechanism may contribute to the participation of these areas in the voluntary control of action.