Strategies that reduce Stroop interference.

A remarkable example of reducing Stroop interference is provided by the word blindness post-hypnotic suggestion (a suggestion to see words as meaningless during the Stroop task). This suggestion has been repeatedly demonstrated to halve Stroop interference when it is given to highly hypnotizable people. In order to explore how highly hypnotizable individuals manage to reduce Stroop interference when they respond to the word blindness suggestion, we tested four candidate strategies in two experiments outside of the hypnotic context. A strategy of looking away from the target words and a strategy of visual blurring demonstrated compelling evidence for substantially reducing Stroop interference in both experiments. However, the pattern of results produced by these strategies did not match those of the word blindness suggestion. Crucially, neither looking away nor visual blurring managed to speed up incongruent responses, suggesting that neither of these strategies is the likely underlying mechanism of the word blindness suggestion. Although the current results did not unravel the mystery of the word blindness suggestion, they showed that there are multiple voluntary ways through which participants can dramatically reduce Stroop interference.

Hypothesis awareness confounds asynchronous control conditions in indirect measures of the rubber hand illusion.

Reports of changes in experiences of body location and ownership following synchronous tactile and visual stimulation of fake and real hands (rubber hand (RH) effects) are widely attributed to multisensory integration mechanisms. However, existing control methods for subjective report measures (asynchronous stroking and control statements) are confounded by participant hypothesis awareness; the report may reflect response to demand characteristics. Subjective report is often accompanied by indirect (also called 'objective' or 'implicit') measures. Here, we report tests of expectancies for synchronous 'illusion' and asynchronous 'control' conditions across two pre-registered studies (n = 140 and n = 45) for two indirect measures: proprioceptive drift (a change in perceived hand location) and skin conductance response (a measure of physiological arousal). Expectancies for synchronous condition measures were greater than for asynchronous conditions in both studies. Differences between synchronous and asynchronous control condition measures are therefore confounded by hypothesis awareness. This means indirect measures of RH effects may reflect compliance, bias and phenomenological control in response to demand characteristics, just as for subjective measures. Valid control measures are required to support claims of a role of multisensory integration for both direct and indirect measures of RH effects.

Corrigendum to: the Sussex-Waterloo Scale of Hypnotizability (SWASH): measuring capacity for altering conscious experience.

[This corrects the article DOI: 10.1093/nc/niy006.].

Avoiding pitfalls: Bayes factors can be a reliable tool for post hoc data selection in implicit learning.

Research on implicit processes has revealed problems with awareness categorizations based on nonsignificant results. Moreover, post hoc categorizations result in regression to the mean (RTM), by which aware participants are wrongly categorized as unaware. Using Bayes factors to obtain sensitive evidence for participants' lack of knowledge may deal with nonsignificance being nonevidential, but also may prevent regression-to-the-mean effects. Here, we examine the reliability of a novel Bayesian awareness categorization procedure. Participants completed a reward learning task followed by a flanker task measuring attention towards conditioned stimuli. They were categorized as B_Aware and B_Unaware of stimulus-outcome contingencies, and those with insensitive Bayes factors were deemed B_Insensitive. We found that performance for B_Unaware participants was below chance level using unbiased tests. This was further confirmed using a resampling procedure with multiple iterations, contrary to the prediction of RTM effects. Conversely, when categorizing participants using t tests, t_Unaware participants showed RTM effects. We also propose a group boundary optimization procedure to determine the threshold at which regression to the mean is observed. Using Bayes factors instead of t tests as a post hoc categorization tool allows evaluating evidence of unawareness, which in turn helps avoid RTM. The reliability of the Bayesian awareness categorization procedure strengthens previous evidence for implicit reward conditioning. The toolbox used for the categorization procedure is detailed and made available. Post hoc group selection can provide evidence for implicit processes; the relevance of RTM needs to be considered for each study and cannot simply be assumed to be a problem.

Can unconscious intentions be more effective than conscious intentions? Test of the role of metacognition in hypnotic response.

While several theories assume that responses to hypnotic suggestions can be implemented without executive intentions, the metacognitive class of theories postulate that the behaviors produced by hypnotic suggestions are intended and the accompanying feeling of involuntariness is only a consequence of strategically not being aware of the intention. Cold control theory asserts that the only difference between a hypnotic and non-hypnotic response is this metacognitive one, that is, whether or not one is aware of one's intention to perform the relevant act. To test the theory, we compared the performance of highly suggestible participants in reducing the Stroop interference effect in a post-hypnotic suggestion condition (word blindness: that words will appear as a meaningless foreign script) and in a volitional condition (asking the participants to imagine the words as a meaningless foreign script). We found that participants had equivalent expectations that the posthypnotic suggestion and the volitional request would help control the conflicting information. Further, participants felt they had more control over experiencing the words as meaningless with the request rather than the suggestion; and they experienced the request largely as imagination and the suggestion largely as perception. That is, we set up the interventions we required for the experiment to constitute a test of cold control theory. Both the suggestion and the request reduced Stroop interference. Crucially, there was Bayesian evidence that the reduction in Stroop interference was the same between the suggestion and the volitional request. That is, the results support the claim that responding hypnotically does not grant a person greater first order abilities than they have non-hypnotically, consistent with cold control theory.

Trait phenomenological control predicts experience of mirror synaesthesia and the rubber hand illusion.

In hypnotic responding, expectancies arising from imaginative suggestion drive striking experiential changes (e.g., hallucinations) - which are experienced as involuntary - according to a normally distributed and stable trait ability (hypnotisability). Such experiences can be triggered by implicit suggestion and occur outside the hypnotic context. In large sample studies (of 156, 404 and 353 participants), we report substantial relationships between hypnotisability and experimental measures of experiential change in mirror-sensory synaesthesia and the rubber hand illusion comparable to relationships between hypnotisability and individual hypnosis scale items. The control of phenomenology to meet expectancies arising from perceived task requirements can account for experiential change in psychological experiments.

Can hypnotic suggestibility be measured online?

Hypnosis and hypnotic suggestions are gradually gaining popularity within the consciousness community as established tools for the experimental manipulation of illusions of involuntariness, hallucinations and delusions. However, hypnosis is still far from being a widespread instrument; a crucial hindrance to taking it up is the amount of time needed to invest in identifying people high and low in responsiveness to suggestion. In this study, we introduced an online assessment of hypnotic response and estimated the extent to which the scores and psychometric properties of an online screening differ from an offline one. We propose that the online screening of hypnotic response is viable as it reduces the level of responsiveness only by a slight extent. The application of online screening may prompt researchers to run large-scale studies with more heterogeneous samples, which would help researchers to overcome some of the issues underlying the current replication crisis in psychology.

The Sussex-Waterloo Scale of Hypnotizability (SWASH): measuring capacity for altering conscious experience.

The ability to respond to hypnotic suggestibility (hypnotizability) is a stable trait which can be measured in a standardized procedure consisting of a hypnotic induction and a series of hypnotic suggestions. The SWASH is a 10-item adaptation of an established scale, the Waterloo-Stanford Group C Scale of Hypnotic Suggestibility (WSGC). Development of the SWASH was motivated by three distinct aims: to reduce required screening time, to provide an induction which more accurately reflects current theoretical understanding and to supplement the objective scoring with experiential scoring. Screening time was reduced by shortening the induction, removing two suggestions which may cause distress (dream and age regression) and by modifications which allow administration in lecture theatres, so that more participants can be screened simultaneously. Theoretical issues were addressed by removing references to sleep, absorption and eye fixation and closure. Data from 418 participants at the University of Sussex and the Lancaster University are presented, along with data from 66 participants who completed a retest screening. The subjective and objective scales were highly correlated. The subjective scale showed good reliability and objective scale reliability was comparable to the WSGC. The addition of subjective scale responses to the post-hypnotic suggestion (PHS) item suggested a high probability that responses to PHS are inflated in WSGC screening. The SWASH is an effective measure of hypnotizability, which reflects changes in conscious experience and presents practical and theoretical advantages over existing scales.

The effect of alcohol and repetition at encoding on implicit and explicit false memories.

RATIONALE: Alcohol impairs explicit memory, whilst leaving implicit memory relatively intact. Less is known about its effects on false memories. AIM: The present study examines the effects of alcohol on explicit and implicit false memories using study list repetition as a tool for modulating learning at encoding. METHODS: Thirty-two participants were given either an alcohol (0.6 g/kg) or placebo beverage before undergoing an encoding phase consisting of 10 lists of nine associated words (veridical items). Each list was associated to a word, which was not presented at encoding (semantically associated non-studied lure; critical item), serving as the measure for false memory. Half of the lists were presented once, and half were repeated three times. The next day, participants underwent an implicit (stem completion and post hoc awareness measurements), and an explicit (free recall) task. RESULTS: Alcohol decreased veridical and false explicit memory for singularly presented lists compared to placebo; no group difference existed for repeated lists. Implicit veridical memory was not affected by alcohol. Awareness memory measures demonstrated in placebo participants an increased ability with repetition in rejecting false memories. The reverse was found in intoxicated participants who with repetition accepted more false memories. CONCLUSION: Alcohol appears to decrease semantic activation leading to a decline in false memories. Increased learning with repetition, which increases the rejection of false memories under placebo, is reversed under alcohol leading to a decrease in rejection of false memories. The latter effect of alcohol may be due to its ability to impair monitoring processes established at encoding.

State-dependent effects of alcohol on recollective experience, familiarity and awareness of memories.

RATIONALE: Explicit memory (EM) is the memory for events which occurs with full awareness of where and how the recalled events took place, whereas implicit memory (IM) is the memory which is unfolded without any awareness of these events and usually becomes apparent when performance is facilitated by its presence. These two types of memory can be understood as different systems. Findings attempting to differentiate between the two systems in normal subjects have been controversial, with some researchers arguing that there is a single memory system and only the match in processes used during learning and later at retrieval can be important. OBJECTIVES: The present study compared the effects of alcohol (0.8 g/kg) or placebo administered prior to encoding and/or retrieval on measures of explicit and implicit memory in terms of recollective experience and familiarity. METHODS: At encoding subjects studied a list of 80 words presented in pairs. At retrieval, participants first carried out an implicit stem completion task, followed by an explicitly cued recall task (stem completion) which measured IM and EM respectively. After stem completion participants were required to indicate whether the items from the studied list were consciously recollected ("remember" response) or was known for a fact that were presented in the studied list ("know" response). In the IM task completed items from the studied list but not recognised by the subjects as such indicated memory without awareness. Studied items were of high and low associations. Forty-eight participants were tested in one of four drug conditions: alcohol-alcohol, placebo-placebo, placebo-alcohol, alcohol-placebo. RESULTS: In the implicit stem completion task, alcohol did not affect overall correct completion rates. However, participants who received alcohol prior to encoding reported lower awareness of correctly completed study items. In the cued recall task, alcohol also did not affect overall performance. However, participants in the same drug-state conditions (SS) reported greater recollection than familiarity with study material, whereas participants who encoded and retrieved material in different drug-state conditions (DS) reported recollection and familiarity to the same extent. In addition, DS participants showed more familiarity with study material compared to SS participants. Direct comparisons between IM and EM tasks demonstrated that alcohol at retrieval decreased the cued recall of items from high associations compared to placebo, but did not have any effect on implicit stem completion. CONCLUSIONS: In summary, these results demonstrate a dissociation of alcohol effects on measures of EM and IM. Alcohol administered prior to encoding reduced awareness of implicitly retrieved material, but did not impair IM per se, confirming previous findings with alcohol. In addition, the data provided new evidence for state-dependent retrieval effects on EM but not IM. It was also shown that for explicitly retrieved items, recollective experience benefits from same drug state, whereas familiarity benefits from different drug state between encoding and retrieval.

Toward a unified fielder theory: what we do not yet know about how people run to catch a ball.

Linear optic trajectory theory claims that people catch balls by running in a direction that keeps an optic trajectory of the ball linear. The authors show a range of ball trajectories for which departures of the optic trajectory from linearity do not predict which direction people will run, and the direction they choose does not correct these departures. Data from a wide range of ball trajectories show that people run so that the angle of elevation of gaze to the ball increases at a decreasing rate. But it is not yet known why people choose the particular path they do from the many that would achieve this.

The effects of cigarette smoking on negative priming.

Nicotine administration has been found to enhance performance on tasks of selective attention. It has been proposed that efficient attentional filtering depends on the successful inhibition of distracting information. In the work reported here, a negative priming paradigm was adopted to test whether smoking enhanced the inhibition of irrelevant information. Thirty-six minimally deprived smokers, half of whom smoked and half of whom sham smoked, completed the negative priming task. A significantly larger negative priming effect was found in participants who had smoked in comparison with those who sham smoked. These results support the hypothesis that nicotine enhances the inhibition of distracting information and thus suggest a possible mechanism by which smoking may enhance selective attention.

A theory of implicit and explicit knowledge.

The implicit-explicit distinction is applied to knowledge representations. Knowledge is taken to be an attitude towards a proposition which is true. The proposition itself predicates a property to some entity. A number of ways in which knowledge can be implicit or explicit emerge. If a higher aspect is known explicitly then each lower one must also be known explicitly. This partial hierarchy reduces the number of ways in which knowledge can be explicit. In the most important type of implicit knowledge, representations merely reflect the property of objects or events without predicating them of any particular entity. The clearest cases of explicit knowledge of a fact are representations of one's own attitude of knowing that fact. These distinctions are discussed in their relationship to similar distinctions such as procedural-declarative, conscious-unconscious, verbalizable-nonverbalizable, direct-indirect tests, and automatic-voluntary control. This is followed by an outline of how these distinctions can be used to integrate and relate the often divergent uses of the implicit-explicit distinction in different research areas. We illustrate this for visual perception, memory, cognitive development, and artificial grammar learning.

The role of implicit memory in controlling a dynamic system.

The relationship between implicit memory and implicit learning is explored. Dienes and Fahey (1995) showed that learning to control a dynamic system was mediated by a look-up table consisting of previously successful responses to specific situations. The experiment reported in this paper showed that facilitated performance on old situations was independent of the subjects' ability to recognize those situations as old, suggesting that memory was implicit. Further analyses of the Dienes and Fahey data replicated this independence of control performance on recognition. However, unlike the implicit memory revealed on fragment completion tasks, successful performance on the dynamic control tasks was remarkably resilient to modality shifts. The results are discussed in terms of models of implicit learning and the nature of implicit memory.

Incorporation of rhodopsin in laterally structured supported membranes: observation of transducin activation with spatially and time-resolved surface plasmon resonance.

Rhodopsin-transducin coupling was used as an assay to investigate a laterally patterned membrane reconstituted with a receptor and its G protein. It served as a model system to show the feasibility to immobilize G protein-coupled receptors on solid supports and investigate receptor activation and interaction with G proteins by one-dimensional imaging surface plasmon resonance. Supported membranes were formed by the self-assembly of lipids and rhodopsin from detergent solution onto functionalized gold surfaces. They formed micrometer-sized alternating regions of pure fluid phospholipid bilayers separated by bilayers composed of an outer phospholipid leaflet on a gold-attached inner thiolipid. Rhodopsin was found to incorporate preferentially into the phospholipid bilayer regions, whereas transducin was uniformly distributed over the entire outer surface of the supported patterned membrane. The influence of rhodopsin on the dark binding of transducin to lipid membranes was described quantitatively and compared with previously published data. Coupling reactions with transducin resembled closely the native system, indicating that the native functionality of rhodopsin was preserved in the supported membranes. The spatially varying properties of the membranes resulted in a pattern of rhodopsin activity on the surface. This combination of techniques is very promising for the investigation of the lateral diffusion of transducin, can be extended to include signalling proteins downstream of the G protein, and may be applied to functional screening of other G protein-coupled receptors. In the future, it may also serve as a basis for constructing biosensors based on receptor proteins.

Reversible oriented surface immobilization of functional proteins on oxide surfaces.

Reversible and oriented immobilization of proteins in a functionally active form on solid surfaces is a prerequisite for the investigation of molecular interactions by surface-sensitive techniques. We demonstrate a method generally applicable for the attachment of proteins to oxide surfaces. A nitrilotriacetic acid group serving as a chelator for transition metal ions was covalently bound to the surface via silane chemistry. Reversible binding of the green fluorescent protein, modified with a hexahistidine extension, was monitored in situ using total internal reflection fluorescence. The association constant and kinetic parameters of the binding process were determined. The reversible, directed immobilization of proteins on surfaces as described here opens new ways for structural investigation of proteins and receptor-ligand interactions.

How to catch a cricket ball.

A cricket or baseball fielder can run so as to arrive at just the right place at just the right time to catch a ball. It is shown that if the fielder runs so that d2(tan alpha)/dt2 = 0, where alpha is the angle of elevation of gaze from fielder to ball, then the ball will generally be intercepted before it hits the ground. This is true whatever the aerodynamic drag experienced by the ball. The only exception is if the ball is not approaching the fielder before he starts to run.

Levels of processing for visual stimuli in an "extinguished" field.

Volpe et al. (Nature 282, 722, 1979 [19]) described an experimental study of four patients with parietal tumours who were able to judge whether two simultaneous stimuli were identical or different, even when they were unable to name the stimulus contralateral to their brain injury. We report the case of another patient, E.M., in whom we have investigated this phenomenon further. E.M. had undergone a right temporal lobectomy to prevent recurrent seizures. She could correctly name photographs of objects presented in isolation to either the left or right visual field, at 150 msec exposure (although she was impaired for single objects on the left at 10 msec exposures). She was able to judge correctly whether two simultaneous objects on the left and right had the same or different names, even though she was often unable to name the object on the left. These judgements remained above chance when same-name pairs of stimuli showed the same object but seen from two different viewpoints, or even when they showed visually dissimilar exemplars of the same name category. This implies that the patient based her same-different judgements on categorical information about the pair of objects, even though she was often unable to name the contralateral object.

Motion coherence and conjunction search: implications for guided search theory.

Feature integration theory has recently been revised with two proposals that visual conjunction search can be parallel under some circumstances--either because items with nontarget features are inhibited, or because items with target features are excited. We examined whether excitatory or inhibitory guidance controlled conjunction search for an X oscillating in one direction among Os oscillating in that direction and Xs oscillating in another. Search was affected by whether items oscillated in phase with each other, and it was exceptionally difficult when items with target motion moved out of phase with each other and items with nontarget motion moved out of phase. The results suggest that conjunction search can be guided both by excitation of target features and by inhibition of nontarget features.

Are direction and speed coded independently by the visual system? Evidence from visual search.

Three visual search experiments examined whether motion is coded as two separate features, speed and direction. Increasing the heterogeneity of the directions in which stimuli moved disrupted detection of a target defined by speed (fast among medium and slow nontargets), suggesting that speed is coded integrally with direction. However, heterogeneity in speed did not disrupt detection of a target moving in a particular direction among nontargets with different directions. This suggests that direction is coded independently of speed. The apparent paradox raised by these contrasting conclusions is consistent with neurophysiological and computational models of motion-detection, which suggest that low-levels of the visual system contain direction-detectors insensitive to speed, while speed is coded at higher levels by detectors which are also sensitive to direction. Evidence consistent with the existence of the latter conjunction detectors was obtained in a final experiment which found search for a conjunction of speed and direction to be parallel.