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Abstract Background A traditional concept in bacterial genetics states that housekeeping genes, those involved in basic metabolic functions needed for maintenance of the cell, are encoded in the chromosome, whereas genes required for dealing with challenging environmental conditions are located in plasmids. Exceptions to this rule have emerged from genomic sequence data of bacteria with multipartite genomes. The genome sequence of R. etli CFN42 predicts the presence of panC and panB genes clustered together on the 642 kb plasmid p42f and a second copy of panB on plasmid p42e. They encode putative pantothenate biosynthesis enzymes (pantoate-β-alanine ligase and 3-methyl-2-oxobutanoate hydroxymethyltransferase, respectively). Due to their ubiquitous distribution and relevance in the central metabolism of the cell, these genes are considered part of the core genome; thus, their occurrence in a plasmid is noteworthy. In this study we investigate the contribution of these genes to pantothenate biosynthesis, examine whether their presence in plasmids is a prevalent characteristic of the Rhizobiales with multipartite genomes, and assess the possibility that the panCB genes may have reached plasmids by horizontal gene transfer. Results Analysis of mutants confirmed that the panC and panB genes located on plasmid p42f are indispensable for the synthesis of pantothenate. A screening of the location of panCB genes among members of the Rhizobiales showed that only R. etli and R. leguminosarum strains carry panCB genes in plasmids. The panCB phylogeny attested a common origin for chromosomal and plasmid-borne panCB sequences, suggesting that the R. etli and R. leguminosarum panCB genes are orthologs rather than xenologs. The panCB genes could not totally restore the ability of a strain cured of plasmid p42f to grow in minimal medium. Conclusions This study shows experimental evidence that core panCB genes located in plasmids of R. etli and R. leguminosarum are indispensable for the synthesis of pantothenate. The unusual presence of panCB genes in plasmids of Rhizobiales may be due to an intragenomic transfer from chromosome to plasmid. Plasmid p42f encodes other functions required for growth in minimal medium. Our results support the hypothesis of cooperation among different replicons for basic cellular functions in multipartite rhizobia genomes.

In previous studies, it was established that individuals can implicitly learn spatiotemporal regularities related to how the distribution of target locations unfolds across the time course of a single trial. However, these regularities were tied to the appearance of salient targets that are known to capture attention in a bottom-up way. The current study investigated whether the saliency of target is necessary for this type of learning to occur. In a visual search task, participants were instructed to search for a unique circle with a gap (Landolt C) among two other circles and indicate the location of the gap. Unbeknownst to them, the onset timing of search displays predicted the target location. Specifically, the target appeared more frequently at one peripheral location with an early onset of the search display and at the opposite peripheral location with a late onset of the search display. Additionally, we manipulated the gap size of the Landolt C to create either nonsalient (small gap) or salient (big gap) target events. Results showed that, regardless of prior exposure to salient targets (Experiment 1) or nonsalient targets (Experiment 2), visual search efficiency increased when the target appeared at the temporally valid location compared with the temporally invalid location. In conclusion, the saliency of targets and the associated bottom-up capture is not a prerequisite for learning dynamic distributional regularities of target locations during visual search., Competing Interests: Declarations. Conflicts of interest/Competing interests: The authors declare no conflicts of interest. Ethics approval: This study received approval from the Ethical Review Committee of the Faculty of Behavioral and Movement Sciences at Vrije Universiteit Amsterdam. Consent to participate: Informed consent was obtained from all participants at the beginning of the experiment. Consent for publication: Consent for publication was obtained from all participants in this study. Participants were informed that their data could be used for publication purposes and agreed to the publication of their anonymized data. No identifiable personal information will be disclosed in the publication. Open practices statement: The experimental programs, raw data, processed data, analysis scripts, and power analysis code are available on the Open Science Framework ( https://osf.io/vkn6a/ ). None of the experiments was preregistered., (© 2024. The Author(s).)

In dynamic environments, statistical learning of spatial and temporal regularities guides visual attention in space and time. In the current study, we explored whether and how combined spatiotemporal regularities regarding target events guide visual attention. In three experiments, participants performed the additional singleton task. They were asked to search for a target stimulus with a unique shape among five non-target distractors and respond to the orientation of a line inside the target. Unbeknownst to the participants, the moment in time that the search display was presented was predictive of the target location. Specifically, the target was more likely to be presented at one high-probability location after a short interval and at another high-probability location after a long interval. The results showed that participants' performance was better for high-probability locations than for low-probability locations. Moreover, visual search efficiency was greater when the target appeared at the high-probability location after its associated interval than when it occurred there after its nonassociated interval, regardless of whether the distribution of intervals was uniform (Experiment 1), exponential (Experiment 2), or anti-exponential (Experiment 3). Taken together, the results indicate that implicitly learned spatiotemporal regularities dynamically guide visual attention towards the probable target location., (© 2022. The Author(s).)

Temporal preparation is the cognitive function that takes place when anticipating future events. This is commonly considered to involve a process that maximizes preparation at time points that yield a high hazard. However, despite their prominence in the literature, hazard-based theories fail to explain the full range of empirical preparation phenomena. Here, we present the formalized multiple trace theory of temporal preparation (fMTP), an integrative model which develops the alternative perspective that temporal preparation results from associative learning. f MTP builds on established computational principles from the domains of interval timing, motor planning, and associative memory. In f MTP, temporal preparation results from associative learning between a representation of time on the one hand and inhibitory and activating motor units on the other hand. Simulations demonstrate that f MTP can explain phenomena across a range of time scales, from sequential effects operating on a time scale of seconds to long-term memory effects occurring over weeks. We contrast f MTP with models that rely on the hazard function and show that f MTP's learning mechanisms are essential to capture the full range of empirical effects. In a critical experiment using a Gaussian distribution of foreperiods, we show the data to be consistent with f MTP's predictions and to deviate from the hazard function. Additionally, we demonstrate how changing f MTP's parameters can account for participant-to-participant variations in preparation. In sum, with f MTP we put forward a unifying computational framework that explains a family of phenomena in temporal preparation that cannot be jointly explained by conventional theoretical frameworks. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

There is growing appreciation for the role of long-term memory in guiding temporal preparation in speeded reaction time tasks. In experiments with variable foreperiods between a warning stimulus (S1) and a target stimulus (S2), preparation is affected by foreperiod distributions experienced in the past, long after the distribution has changed. These effects from memory can shape preparation largely implicitly, outside of participants' awareness. Recent studies have demonstrated the associative nature of memory-guided preparation. When distinct S1s predict different foreperiods, they can trigger differential preparation accordingly. Here, we propose that memory-guided preparation allows for another key feature of learning: the ability to generalize across acquired associations and apply them to novel situations. Participants completed a variable foreperiod task where S1 was a unique image of either a face or a scene on each trial. Images of either category were paired with different distributions with predominantly shorter versus predominantly longer foreperiods. Participants displayed differential preparation to never-before seen images of either category, without being aware of the predictive nature of these categories. They continued doing so in a subsequent Transfer phase, after they had been informed that these contingencies no longer held. A novel rolling regression analysis revealed at a fine timescale how category-guided preparation gradually developed throughout the task, and that explicit information about these contingencies only briefly disrupted memory-guided preparation. These results offer new insights into temporal preparation as the product of a largely implicit process governed by associative learning from past experiences., (© 2021. The Author(s).)

How quickly participants respond to a "go" after a "warning" signal is partly determined by the time between the two signals (the foreperiod) and the distribution of foreperiods. According to Multiple Trace Theory of Temporal Preparation (MTP), participants use memory traces of previous foreperiods to prepare for the upcoming go signal. If the processes underlying temporal preparation reflect general encoding and memory principles, transfer effects (the carryover effect of a previous block's distribution of foreperiods to the current block) should be observed regardless of the sensory modality in which signals are presented. Despite convincing evidence for transfer effects in the visual domain, only weak evidence for transfer effects has been documented in the auditory domain. Three experiments were conducted to examine whether such differences in results are due to the modality of the stimulus or other procedural factors. In each experiment, two groups of participants were exposed to different foreperiod distributions in the acquisition phase and to the same foreperiod distribution in the transfer phase. Experiment 1 used a choice-reaction time (RT) task, and the warning signal remained on until the go signal, but there was no evidence for transfer effects. Experiments 2 and 3 used a simple- and choice-RT task, respectively, and there was silence between the warning and go signals. Both experiments revealed evidence for transfer effects, which suggests that transfer effects are most evident when there is no auditory stimulation between the warning and go signals.

Distraction by a salient object can be reduced when we implicitly learn to suppress its most likely location. The current study investigated whether this suppression can also be tuned to the time at which the distractor is likely to appear. Participants performed the additional singleton task, in which they searched for a unique shape while a color singleton distractor was present. Following the fixation point, the search display was presented either after a short (500 ms) or long (1,500 ms) time interval. Critically, the color singleton distractor was presented relatively frequently at one high probability location after the short interval and at another high probability location after the long interval. The results showed that attentional capture at the two high probability locations was reduced relative to low probability distractor locations. More importantly, this reduction was greater when the color singleton distractor appeared at a high probability location after its associated interval than after the other interval. These findings indicate that participants learn to suppress particular locations at particular moments in time, suggesting that the spatial priority map of attentional selection is dynamically adjusted during the trial. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

In a warned reaction time task, the warning stimulus (S1) initiates a process of temporal preparation, which promotes a speeded response to the impending target stimulus (S2). According to the multiple trace theory of temporal preparation (MTP), participants learn the timing of S2 by storing a memory trace on each trial, which contains a temporal profile of the events on that trial. On each new trial, S1 serves as a retrieval cue that implicitly and associatively activates memory traces created on earlier trials, which jointly drive temporal preparation for S2. The idea that S1 assumes this role as a retrieval cue was tested across eight experiments, in which two different S1s were associated with two different distributions of S1-S2 intervals: one with predominantly short and one with predominantly long intervals. Experiments differed regarding the S1 features that made up a pair, ranging from highly distinct (e.g., tone and flash) to more similar (e.g., red and green flash) and verbal (i.e., "short" vs "long"). Exclusively for pairs of highly distinct S1s, the results showed that the S1 cue modified temporal preparation, even in participants who showed no awareness of the contingency. This cueing effect persisted in a subsequent transfer phase, in which the contingency between S1 and the timing of S2 was broken - a fact participants were informed of in advance. Together, these findings support the role of S1 as an implicit retrieval cue, consistent with MTP., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Experimental studies that manipulate treatment procedures to investigate their direct effects on treatment processes and outcomes are necessary to find out the effective elements and improve the effects of cognitive behavioral therapy (CBT) for depression. The present study randomized mildly to severely depressed participants into a procedure focused on cognitive therapy skill acquisition (CTSA; n = 27) or a control procedure focused on being exposed to theories of automatic thinking (n = 25) and investigated the direct effects on cognitive therapy (CT) skill use, credibility of idiosyncratic dysfunctional beliefs and strength of emotions. After the procedure, participants were exposed to a sad mood induction and given an assignment to test their CT skills. Participants who received the CTSA procedure used more CT skills compared to participants that received the control procedure, but there were no differences between conditions in the decrease of the credibility of idiosyncratic dysfunctional beliefs and strength of emotions. However, in participants with mild levels of depression, those who underwent the CTSA procedure showed larger decrease in the credibility of their most malleable belief (i.e. mostly automatic negative thoughts) compared to those who received the control procedure, but the significance of these findings disappeared when controlling for differences in ratings of the procedures. Future experimental studies should focus on the effects of CT skill training in the long term, the dose of the procedure and individual patient differences to find out under what circumstances the use of CT skills can lead to a reduction in dysfunctional thinking and subsequent symptoms of depression., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Vineyards in many semi-arid regions globally face limited water resources. Monitoring évapotranspiration (ET) of vineyards is critical for water resource management, but remains difficult due to the complex biophysics of the surfaces. Both measurement and modeling approaches for estimating turbulent water vapor transport rely on implicit assumptions that exchanges occur in a reasonably regular fashion over the time scales generally used for averaging. However, heterogeneous vegetation in semi-arid climates, such as many vineyards, presents inherent factors, including canopy row/row space structure and frequent periods of light wind, unstable conditions, that can create episodic transport characteristics. Eddy covariance data were collected above and within the canopy of two vineyards in the Central Valley of California during the Grape Remote sensing Atmospheric Profile & Evapotranspiration experiment (GRAPEX). The goal was to document and quantify the existence of intermittent turbulence transport of water vapor, and associated episodic canopy venting. These effects were found to correlate with periods light winds and highly unstable/convective conditions. Power and cross-spectra for intermittent periods documented enhancement of low-frequency water vapor exchange events compared to more steady periods, and diminished time scale correlation between humidity within the canopy and above the canopy. Analyses show that intermittent cases can necessitate longer flux-averaging periods (up to 2 h) than more steady conditions. Episodic exchange events were isolated and summed to determine their relative contribution to the overall water vapor flux. Since light wind, unstable conditions are relatively common in many arid vineyard regions, these findings have implications for mechanistic ET models that rely on time-averaged vertical gradients, which implies reasonably steady transport., Competing Interests: Conflict of interest On behalf of all authors, the corresponding author states that there is no conflict of interest.

Temporal preparation has been investigated extensively by manipulating the foreperiod, the interval between a warning stimulus and target stimulus requiring a speeded response. Although such research has revealed many effects of both the duration and distribution of foreperiods on reaction times, the underlying cognitive mechanism is still largely unknown. Here, we test a recent proposal that temporal preparation is driven by the retrieval of memory traces of past experiences from long-term memory rather than by knowledge about upcoming events. Two groups of participants received different foreperiod distributions in an acquisition phase, which was followed a week later by a transfer phase, in which both groups received the same distribution of foreperiods. We found that the effects of the different foreperiod distributions presented in the acquisition phase were still apparent a week later during the transfer phase, as the reaction time patterns of both groups reflected the old distributions. This occurred even though both groups were provided with full information about the change in the distribution of foreperiods at the start of the transfer phase. These findings provide compelling evidence that long-term memory plays an important role in temporal preparation.

Theories of visual search assume that selection is driven by an active template representation of the target object. Earlier studies suggest that template activation occurs prior to search, but the temporal dynamics of such preactivation remain unclear. Two experiments employed microsaccades to track both general preparation (i.e., anticipation of the search task as such) and template-specific preparation (i.e., anticipation of target selection) of visual search. Participants memorized a target color (i.e., the template) for an upcoming search task. During the delay period, we presented an irrelevant rapid serial visual presentation (RSVP) of lateralized colored disks. Crucially, at different time points into the RSVP, the template color was inserted, allowing us to measure attentional biases toward the template match as a function of time. Results showed a general suppression of saccades: the closer in time to the search display, the less saccades were produced. This suppression was stronger when a template-matching color was present compared to when absent. However, when microsaccades occurred, they were biased toward the template-matching color and more so just prior to the search display. We conclude that observers adapt search template activation to the anticipated moment of search, and that microsaccades reflect general as well as target-specific preparation effects., (© 2017 Elsevier B.V. All rights reserved.)

The hazard function describes the conditional probability that an event will occur at a given moment, given that it has not yet occurred. In warned reaction time tasks, it is a classical finding that the response to a target stimulus is faster as its hazard is higher, which has led to the widespread belief that hazard somehow drives temporal preparation. Alternatively, recent cognitive theories propose that temporal preparation is driven by memory traces of earlier timing experiences. To distinguish between these views, we presented different groups of participants with different distributions of foreperiods between temporal cues and target stimuli. Three experiments revealed clear transfer effects of this manipulation in a test phase where all participants received, after explicit instruction, the same uniform distribution. These findings demonstrate that temporal preparation is driven by past experience, not by current hazard. (PsycINFO Database Record, ((c) 2016 APA, all rights reserved).)

Search for a target stimulus among distractors is subject to both goal-driven and stimulus-driven influences. Variables that selectively modify these influences have shown strong interaction effects on saccade trajectories toward the target, suggesting the involvement of a shared spatial orienting mechanism. However, subsequent manual response times (RTs) have revealed additive effects, suggesting that different mechanisms are involved. In the present study, we tested the hypothesis that an interaction for RTs is obscured by preceding multisaccade trajectories, promoted by the continuous presence of distractors in the display. In two experiments, we compared a condition in which distractors were removed soon after the presentation of the search display to a standard condition in which distractors were not removed. The results showed additive goal-driven and stimulus-driven effects on RTs in the standard condition, but an interaction when distractors were removed. These findings support the view that both variables influence a shared spatial orienting mechanism.

We outline a new multiple trace theory of temporal preparation (MTP), which accounts for behavior in reaction time (RT) tasks in which the participant is presented with a warning stimulus (S1) followed by a target stimulus (S2) that requires a speeded response. The theory assumes that during the foreperiod (FP; the S1-S2 interval) inhibition is applied to prevent premature response, while a wave of activation occurs upon the presentation of S2. On each trial, these actions are stored in a separate memory trace, which, jointly with earlier formed memory traces, starts contributing to preparation on subsequent trials. We show that MTP accounts for classic effects in temporal preparation, including mean RT-FP functions observed under a variety of FP distributions and asymmetric sequential effects. We discuss the advantages of MTP over other accounts of these effects (trace-conditioning and hazard-based explanations) and suggest a critical experiment to empirically distinguish among them.

It is generally agreed that attention can be captured in a stimulus-driven or in a goal-driven fashion. In studies that investigated both types of capture, the effects on mean manual response time (reaction time [RT]) are generally additive, suggesting two independent underlying processes. However, potential interactions between the two types of capture may fail to be expressed in manual RT, as it likely reflects multiple processing steps. Here we measured saccadic eye movements along with manual responses. Participants searched a target display for a red letter. To assess contingent capture, this display was preceded by an irrelevant red cue. To assess stimulus-driven capture, the target display could be accompanied by the simultaneous onset of an irrelevant new object. At the level of eye movements, the results showed strong interactions between cue validity and onset presence on the spatiotemporal trajectories of the saccades. However, at the level of manual responses, these effects cancelled out, leading to additive effects on mean RT. We conclude that both types of capture influence a shared spatial orienting mechanism and we provide a descriptive computational model of their dynamics., (PsycINFO Database Record (c) 2014 APA, all rights reserved.)

In manual choice reaction time (RT) tasks, people respond faster to a visual target stimulus when it is accompanied by a task-irrelevant tone than when it is presented alone. This intersensory facilitation effect is often attributed to multisensory integration, but here we show it to be a reflection of temporal preparation. According to this view, the more rapidly processed tone serves as a warning signal (S1), which initiates preparation for the more sluggish visual target (S2). To test this view, we varied the delay between S1 and S2 in conjunction with the modality of S1 (auditory or visual). For brief delays, responses to S2 were faster when S1 was auditory than when it was visual. Crucially, however, this intersensory facilitation effect disappeared after correction for the difference in S1-detection time, equating the effective preparation period. This shows that sound speeds response to a visual target only through preparation.

During the foreperiod (FP) of a warned reaction task, participants engage in a process of temporal preparation to speed response to the impending target stimulus. Previous neurophysiological studies have shown that inhibition is applied during FP to prevent premature response. Previous behavioral studies have shown that the duration of FP on both the current and the preceding trial codetermine response time to the target. Integrating these findings, the present study tested the hypothesis that the behavioral effects find their origin in response inhibition on the preceding trial. In two experiments the variable-FP paradigm was combined with a go/no-go task, in which no-go stimuli required explicit response inhibition. The resulting data pattern revealed sequential effects of both FP (long or short) and response requirement (go or no-go), which could be jointly understood as expressions of response inhibition, consistent with the hypothesis., (Copyright © 2013 Elsevier B.V. All rights reserved.)

We examined the time course of temporal preparation in the practice of computer gaming. Participants held an infrared rifle to shoot animated figures ("terrorists") that appeared from an elevator that opened briefly after the sound of a bell. The sound was either loud or soft and the interval between the sound and the opening of the elevator varied between 100 and 600ms. We found that shooting latency decreased exponentially as a function of interval, reflecting growing temporal preparation towards an optimum. When the sound was soft, this function was shifted to the right as compared to when the sound was loud. These findings are consistent with a model assuming that preparation starts upon the detection of a warning (i.e., later for the soft than for the loud sound) and continues until the detection of a target (i.e., longer as the interval increases). These results signify a successful application of a theoretical model in an applied setting., (© 2013.)

This study examined whether the process of temporal preparation for a target stimulus is the same regardless of the task required by the target stimulus. To this end, the same variable-foreperiod design was used in a temporal discrimination task (Experiment 1) and a reaction time task (Experiment 2). In Experiment 1, both temporal sensitivity and perceived duration increased as a function of foreperiod, whereas in Experiment 2, foreperiod did not influence reaction time. Furthermore, both temporal sensitivity and perceived duration revealed an asymmetric sequential effect of foreperiod, but the pattern of this effect was opposite to the pattern observed in the reaction time task. Together these dissociative patterns of foreperiod effects suggest that the mechanism of temporal preparation depends on the task required by the target stimulus.

Recent studies have shown that switch costs (i.e., slower responding on task-alternation trials than on task-repetition trials) are not observed when on the preceding trial a no-go signal instructed the participant to withhold the response to the target stimulus. This finding suggests that neither task set is inhibited on no-go trials, and that the origin of switch costs is located in the application of the task set to the target stimulus. However, these studies also showed that responding after a no-go trial is substantially slower than after a go trial. This suggests that both task sets are inhibited on no-go trials and that switch costs originate from the preparation of a task set. In two experiments we created conditions that revealed an absence of switch costs in conjunction with relatively fast responding after no-go trials. Together these findings confirm that switch costs originate from the application of the task set.

In reaction time (RT) research on nonspecific preparation, the preparation period is often identified with the foreperiod (FP), the interval between the offset of a neutral warning stimulus (S1) and the onset of the reaction stimulus (S2). However, the "effective preparation period" may be longer than FP: nonspecific preparation may start prior to FP (e.g., at the onset of S1) and/or continue after it (i.e., in parallel with the reaction process). In four experiments, we factorially varied FP and an additional factor (S1-duration; S2-luminance; stimulus-response compatibility) that probed the effective preparation period outside the bounds of FP. By examining how equivalent RT-FP functions obtain at the different levels of the additional factor, we showed that nonspecific preparation (1) starts at the onset of S1 for brief FPs but at its offset for longer FPs and (2) continues in parallel with S2-encoding but stops prior to response selection.

In the study of nonspecific preparation, the response time (RT) to an imperative stimulus is analyzed as a function of the foreperiod (FP), the interval between a warning stimulus and the imperative stimulus. When FP is varied within blocks of trials, a downward sloping FP-RT function is usually observed. The slope of this function depends on the distribution of FPs (the more negative the skewness, the steeper the slope) and on intertrial sequences of FP (the longer the FP on the preceding trial, the steeper the slope). Because these determinants are confounded, we examined whether FP-RT functions, observed under three different FP distributions (i.e., uniform, exponential, and peaked) can be predicted, one from the other, by reweighting sequential effects. It turned out that reweighting explained very little variance of the difference between the FP-RT functions, suggesting a dominant role of temporal orienting strategies.

The authors hypothesized that there are distinct intentional and unintentional influences on nonspecific preparation for a future event. In 2 experiments, participants responded to an imperative stimulus (S-sub-2) that was presented equiprobably either 400 ms or 1,200 ms after the offset of a warning stimulus (S-sub-1). During the S-sub-1-S-sub-2 interval, the authors measured the contingent negative variation (CNV), an event-related brain potential reflecting nonspecific preparation. S-sub-1 provided either no information or reliable information about the duration of the impending S-sub-1-S-sub-2 interval, thereby allowing an intentional influence on the state of preparation. The effect of S-sub-1 information on the CNV was approximately additive to the effect of the S-sub-1-S-sub-2 interval that was used on the preceding trial. This supports the view that the preceding S-sub-1-S-sub-2 interval contributes unintentionally to the state of nonspecific preparation guided by a process of trace conditioning., (((c) 2005 APA, all rights reserved).)

How do participants adapt to temporal variation of preparatory foreperiods? For reaction times, specific sequential effects have been observed. Responses become slower when the foreperiod is shorter on the current than on the previous trial. If this effect is due to changes in motor activation, it should also be visible in force of responses and in EEG measures of motor preparation, the contingent negative variation (CNV) and the lateralized readiness potential (LRP). These hypotheses were tested in a two-choice reaction task, with targets occurring 500, 1500, or 2500 ms after an acoustic warning signal. The reaction time results showed the expected pattern and were accompanied by similar effects on a fronto-central CNV and the LRP. In contrast, the increase of response force with brief current foreperiods did not depend on previous foreperiods. Thus, EEG measures confirm that sequential effects on RT are at least partially due to changes in motor activation originating from previous trials. Effects found on response force may be related to general response readiness rather than activation of motor-hand areas, which may explain the absence of a sequential effect on force in the current experiment.

I examined the relation between two inhibitory processes operating on spatial and temporal representations. In two experiments, participants had to detect a peripheral target that was presented after a variable interval following the onset of an uninformative peripheral cue. For the shortest cue-target interval, target detection was faster at the cued than at the uncued location, but this effect was reversed for the longer cue-target intervals. This finding has been taken to reflect a buildup of space-related inhibition over time, known as inhibition of return. Also, target detection was slower when the cue-target interval of the preceding trial was longer than that of the current trial than when this was not so. This sequential effect has been taken to reflect an intertrial carryover of time-related inhibition. Crucially, the spatial and temporal effects were additive in both experiments, suggesting a modular organization of the underlying inhibitory processes.

According to the asynchronous discrete coding model of Miller, two manipulations should display underadditive effects on reaction time if they slow down noncontingent stages associated with the processing of two separable dimensions of a stimulus. Underadditive effects are also predicted by a dual route model when a task variable is factorially varied with design type (mixed vs blocked). Interpretations of both underadditive effects and their combination were evaluated. Intact and degraded stimuli were presented to 18 young adults either in a single block (mixed) or in separate blocks (blocked). Spatial stimulus-response (S-R) compatibility was manipulated in all conditions. Stimulus degradation and S-R compatibility interacted underadditively, but only in blocked presentations. Both interpretations of underadditive effects were supported. Eye-movement registrations provided additional support for the alternative routes model.

The nonspecific preparation that follows a warning stimulus (WS) to speed responding to an impending imperative stimulus (IS) is generally viewed as a strategic, intentional process. An alternative view holds that WS acts as a conditioned stimulus that unintentionally elicits a tendency to respond at the moment of IS presentation as a result of a process of trace conditioning. These views were contrasted as explanatory frameworks for classical effects on reaction time of the duration and intertrial variability of the foreperiod, the interval between WS and IS. It is shown that the conditioning view accounts for the available data at least as well as the strategic view. In addition, the results of 3 experiments provide support for the conditioning view by showing that unintentional contributions to nonspecific preparation can be dissociated from intentional contributions.

The foreperiod (FP) is the interval between a warning stimulus and the imperative stimulus. It is a classical finding that both the duration and the intertrial variability of FP considerably affects response time. These effects are invariably attributed to the participant's state of nonspecific preparation at the moment the imperative stimulus is presented. In this article, we examined a proposal by Los, S. A. (1996) [On the origin of mixing costs: exploring information processing in pure and mixed blocks of trials. Acta Psychologica, 94, 145-188] that the real-time development of nonspecific preparation during FP relies on the same principle as trace conditioning. To this end, we adjusted the formal conditioning model developed by Machado, A. (1997) [Learning the temporal dynamics of behavior. Psychological Review, 104 (2), 241-265], and fitted this model to a representative data set we obtained from nine participants. Although the model accounted for only a moderate proportion of the variance, it accurately reproduced several key features of the data. We therefore concluded that the model is a promising first step toward a theory of nonspecific preparation.

Responding to stimuli of different perceptual categories is usually faster when the categories are presented isolated from each other, in pure blocks, than when they are presented randomly intermixed, in mixed blocks; a difference denoted as perceptual mixing costs. The present study examined the contribution of strategic and stimulus-driven factors to these costs. The first two experiments showed that perceptual mixing costs were not reduced when participants were informed at the start of each trial in mixed blocks about the impending category. Furthermore, Experiments 1 and 3 showed that mixing costs were concentrated on those trials of mixed blocks where the perceptual category was different from that of the preceding trial. These results support the view that perceptual mixing costs derive from stimulus-driven trial-by-trial adjustments in processing. Some general implications for processing models are discussed.

Responding to stimuli of different perceptual categories is usually faster when the categories are presented isolated from each other, in pure blocks, than when they are presented intermixed, in mixed blocks. According to criterion models, these perceptual mixing costs result from the use of a less conservative response criterion in pure than in mixed blocks. According to alternate processing models, mixing costs result from time-consuming switching in mixed blocks between different computational processes called on by the different perceptual categories. In 5 experiments, participants had to identify number stimuli of different categories. The results showed clear mixing costs whenever these categories differed in their assumed computational processing requirements but not when they differed on features that seemed trivial from a computational viewpoint. The results favor the alternate processing conception.

Purpose: To evaluate a dental adhesive system that uses a single conditioning/primer agent., Materials and Methods: Twenty-five flat enamel and dentin bonding sites were prepared to 600 grit on human molar teeth. The Clearfil Liner Bond 2 adhesive system was used to bond Clearfil AP-X composite to both enamel and dentin. After 24 hours of water storage, shear bond strengths were determined using an Instron testing machine. Fifty V-shaped cavity preparations were prepared in human molar teeth with an enamel and cementum margin. Composite restorations were placed using the new adhesive system. The teeth were stored for 24 hours, thermocycled, stained with AgNO3 , sectioned and examined for microleakage. SEM examinations were also completed to evaluate the effects of the treatment steps on enamel and dentin surfaces., Results: Mean shear bond strengths for the experimental adhesive to enamel and dentin were 28.2 +/- 4.9 and 19.4 +/- 3.1 MPa. A t-test revealed that the enamel bond strength was significantly greater (P<0.05) than the dentin strength. No marginal leakage was observed from the enamel margins of the restorations. Three restorations showed minimal leakage from the cementum margins. SEM examinations showed resin penetration into both the conditioned enamel and dentin surfaces. The adhesive system produced high bond strengths to both enamel and dentin, exhibited very minimal microleakage and was easy to use.

Shear bond strengths to dentin were determined with six current-generation resin adhesive systems following air abrasion of the dentin surface with aluminum oxide and hydroxyapatite. In addition, scanning electron microscopy was used to examine the effects of air abrasive techniques and conditioners/primers on the dentin surfaces. Altering the dentin surface with air abrasion using aluminum oxide and hydroxyapatite did not enhance dentin bond strengths with current-generation adhesive systems. Air abrasion of dentin with aluminum oxide created more surface irregularity than hydroxyapatite. Dentin surfaces air abraded with aluminum oxide and the treated with conditioners that removed the smear layer appeared more irregular than flat ground dentin surfaces treated with the same conditioners.

In three experiments, the extent to which the processing of a visual stimulus profits from equal processing demands of a preceding stimulus was examined. Subjects identified two subsequently presented digits (S1 and S2) that were either intact or degraded by noise, yielding four combinations of stimulus quality. In Experiments 1 and 2, S1 and S2 differed with respect to the values of the digits, so that stimulus quality was the only dimension of possible agreement. The results revealed a faster response to S2 when the stimulus pairs were homogeneous (both intact or both degraded stimuli) than when they were not homogeneous (degraded-intact pairs and intact-degraded pairs, respectively). The occurrence of equal values of S1 and S2 (Experiment 3) tended to magnify this homogeneous-stimulus effect, but was not a prerequisite for its occurrence. Relative to conditions considered to be neutral, the homogeneous-stimulus effect proved to be due to deviant behavior following the processing of a degraded S1. The suggestion that this reflects the involvement of controlled processing is discussed.