Competitive state of movements during planning predicts sequence performance.

Humans can learn and produce skilled movement sequences from memory, yet the nature of sequence planning is not well understood. Previous computational and neurophysiological work suggests that movements in a sequence are planned as parallel graded activations and selected for output through competition. However, the relevance of this planning pattern to sequence production fluency and accuracy, as opposed to the temporal structure of sequences, is unclear. To resolve this question, we assessed the relative availability of constituent movements behaviorally during the preparation of motor sequences from memory. In three separate multisession experiments, healthy participants were trained to retrieve and produce four-element finger press sequences with particular timing according to an abstract sequence cue. We evaluated reaction time (RT) and error rate as markers of movement availability to constituent movement probes. Our results demonstrate that longer preparation time produces more pronounced differences in availability between adjacent sequence elements, whereas no effect was found for sequence speed or temporal grouping. Further, participants with larger position-dependent differences in movement availability tended to initiate correct sequences faster and with a higher temporal accuracy. Our results suggest that competitive preactivation is established gradually during sequence planning and predicts sequence skill, rather than the temporal structure of the motor sequence.NEW & NOTEWORTHY Sequence planning is an integral part of motor sequence control. Here, we demonstrate that the competitive state of sequential movements during sequence planning can be read out behaviorally through movement probes. We show that position-dependent differences in movement availability during planning reflect sequence preparedness and skill but not the timing of the planned sequence. Behavioral access to the preparatory state of movements may serve as a marker of sequence planning capacity.

Action and perception in literacy: A common-code for spelling and reading.

There is strong evidence that reading and spelling in alphabetical scripts depend on a shared representation (common-coding). However, computational models usually treat the two skills separately, producing a wide variety of proposals as to how the identity and position of letters is represented. This article treats reading and spelling in terms of the common-coding hypothesis for perception-action coupling. Empirical evidence for common representations in spelling-reading is reviewed. A novel version of the Start-End Competitive Queuing (SE-CQ) spelling model is introduced, and tested against the distribution of positional errors in Letter Position Dysgraphia, data from intralist intrusion errors in spelling to dictation, and dysgraphia because of nonperipheral neglect. It is argued that no other current model is equally capable of explaining this range of data. To pursue the common-coding hypothesis, the representation used in SE-CQ is applied, without modification, to the coding of letter identity and position for reading and lexical access, and a lexical matching rule for the representation is proposed (Start End Position Code model, SE-PC). Simulations show the model's compatibility with benchmark findings from form priming, its ability to account for positional effects in letter identification priming and the positional distribution of perseverative intrusion errors. The model supports the view that spelling and reading use a common orthographic description, providing a well-defined account of the major features of this representation. (PsycINFO Database Record

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

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

On costs and benefits of n-2 repetitions in task switching: towards a behavioural marker of cognitive inhibition.

Inhibition in task switching is inferred from slower reaction times returning to a recently performed task after one intervening trial (i.e. an ABA sequence) compared to returning to a task not recently performed (CBA sequence). These n-2 repetition costs are thought to reflect the persisting inhibition of a task after its disengagement. As such, the n-2 repetition cost is an attractive tool for the researcher interested in inhibitory functioning in clinical/neurological/neuroscience disciplines. In the literature, an absence of this cost is often interpreted as an absence of inhibition, an assumption with strong implications for researchers. The current paper argues that this is not necessarily an accurate interpretation, as an absence of inhibition should lead to an n-2 repetition benefit as a task's activation level will prime performance. This argument is supported by three instances of a computational cognitive model varying the degree of inhibition present. An inhibition model fits human n-2 repetition costs well. Removal of the inhibition-the activation-only model-predicts an n-2 repetition benefit. For the model to produce a null n-2 repetition cost, small amounts of inhibition were required-the reduced-inhibition model. The authors also demonstrate that a lateral-inhibition locus of the n-2 repetition cost cannot account for observed human data. The authors conclude that a null n-2 repetition cost provides no evidence on its own for an absence of inhibition, and propose reporting of a significant n-2 repetition benefit to be the best evidence for a lack of inhibition. Implications for theories on task switching are discussed.

Unmixing the mixing cost: contributions from dimensional relevance and stimulus-response suppression.

When participants repeat the same task in a context in which the task may also switch (a mixed block), performance deteriorates compared to when there is only one task repeating (a pure block). Three experiments were designed to assess how perceptual and motor transitions influenced this mixing cost. Experiment 1 provided three pure block baselines for perceptual and motor transitions. Experiments 2 and 3 examined these transitions in a mixed block. Results show that most of the mixing cost comes from two factors: (a) episodic interference in the mixed block when the stimulus changes and the response repeats, and (b) increased suppression in mixed blocks affecting trials where stimulus-response mappings repeat. We propose that these mechanisms are strategically applied when adopting a sustained "switching set" in mixed blocks. The purpose of this set would be to avoid perseveration errors in the most demanding trials (the task-switching trials), but remaining active during task-repetitions. Results regarding the mixing cost are thus relevant to the assessment of models of task-switching, which at present mainly rely on data from task switch trials.

CDF-XL: computing cumulative distribution functions of reaction time data in Excel.

In experimental psychology, central tendencies of reaction time (RT) distributions are used to compare different experimental conditions. This emphasis on the central tendency ignores additional information that may be derived from the RT distribution itself. One method for analysing RT distributions is to construct cumulative distribution frequency plots (CDFs; Ratcliff, Psychological Bulletin 86:446-461, 1979). However, this method is difficult to implement in widely available software, severely restricting its use. In this report, we present an Excel-based program, CDF-XL, for constructing and analysing CDFs, with the aim of making such techniques more readily accessible to researchers, including students (CDF-XL can be downloaded free of charge from the Psychonomic Society's online archive). CDF-XL functions as an Excel workbook and starts from the raw experimental data, organised into three columns (Subject, Condition, and RT) on an Input Data worksheet (a point-and-click utility is provided for achieving this format from a broader data set). No further preprocessing or sorting of the data is required. With one click of a button, CDF-XL will generate two forms of cumulative analysis: (1) "standard" CDFs, based on percentiles of participant RT distributions (by condition), and (2) a related analysis employing the participant means of rank-ordered RT bins. Both analyses involve partitioning the data in similar ways, but the first uses a "median"-type measure at the participant level, while the latter uses the mean. The results are presented in three formats: (i) by participants, suitable for entry into further statistical analysis; (ii) grand means by condition; and (iii) completed CDF plots in Excel charts.

Task preparation and task inhibition: a comment on Koch, Gade, Schuch, & Philipp (2010).

In their recent review article, Koch, Gade, Schuch, & Philipp, (Psychonomic Bulletin & Review, 17, 1-14, 2010) present compelling evidence for the role of inhibition in task switching, as measured by n-2 repetition costs. They promote the view that inhibition targets response-related processes of task performance rather than cue-based preparatory stages. In support of this distinction, they cite the finding in the literature that n-2 repetition costs are not reduced given longer preparation intervals. In this article, we advocate the analysis of whole reaction time distributions for investigating the influence of task preparation on task inhibition. We present such analyses from two of our published experiments that support the view that n-2 repetition costs can be reduced given sufficient preparation. The results suggest that cue-based processes do contribute to inhibition in task switching.

Heightened conflict in cue-target translation increases backward inhibition in set switching.

Backward inhibition (BI) is a performance cost that occurs when an individual returns to a task after 1 (vs. more than 1) intervening trial, and it may reflect the inhibition of task-set components during switching. In 3 experiments, we support the theory that inhibition can target cue-based preparatory stages of a task. Participants performed a cued target-localization task that had been previously shown to produce BI. In Experiment 1, reassignment of arbitrary cue-target pairings midway through the experiment doubled the size of BI, though cue, target, and response sets remained unchanged. In Experiment 2, we controlled for effects of order of conditions or simple change of cue meaning. In Experiment 3, we demonstrated that the effect depends on re-pairing members of the same cue and target sets. The results are attributed to heightened conflict (and hence greater inhibition) during cue-target translation when a previously learned cue-target mapping is remapped.

Cue-switch costs in task-switching: cue priming or control processes?

In the explicitly cued task-switching paradigm, two cues per task allow separation of costs associated with switching cues from costs of switching tasks. Whilst task-switch costs have become controversial, cue-switch costs are robust. The processes that contribute to cue-switch costs are under-specified in the literature: they could reflect perceptual priming of cue properties, or priming of control processes that form relevant working memory (WM) representations of task demands. Across two experiments we manipulated cue-transparency in an attention-switching design to test the contrasting hypotheses of cue-switch costs, and show that such costs emerge from control processes of establishing relevant WM representations, rather than perceptual priming of the cue itself. When the cues were maximally transparent, cue-switch costs were eradicated. We discuss the results in terms of recent theories of cue encoding, and provide a formal definition of cue-transparency in switching designs and its relation to WM representations that guide task performance.

The role of cue-target translation in backward inhibition of attentional set.

Backward inhibition (BI) refers to a reaction time cost incurred when returning to a recently abandoned task compared to returning to a task not recently performed. The effect has been proposed to reflect an inhibitory mechanism that aids transition from one task to another. The question arises as to precisely what aspects of a task may be inhibited and when the process takes place. Recent work has suggested a crucial role for response-related components of the task, which occur late in the typical trial structure (cue-target-response). In contrast to this suggestion, the authors present evidence that the way in which the task is cued can also modulate BI. Specifically, they find that the less transparent the cue-target relationship, the greater the level of BI. This also demonstrates that BI can be triggered at early stages of the trial structure, specifically during task preparation and prior to response processes. The authors conclude that BI is not tied to any particular component of the task structure but arises from whatever component generates the greatest intertrial conflict.

Unmasking word processing with ERPs: two novel linear techniques for the estimation of temporally overlapped waveforms.

Masked priming experiments are frequently used to study automatic aspects of word processing. Direct measures of such processing obtained with functional neuroimaging techniques (ERPs, fMRI, etc.) need to isolate the neural activation related to relevant events when they are rapidly followed by others (a situation found in other popular paradigms such as the attentional blink and repetition blindness). Here we examine the assumption of "simple insertion", which underlies the use of subtraction to isolate components of temporally overlapping waveforms. We propose two novel linear methods and illustrate how they extract temporal and spatial ERP components that the subtraction method fails to detect. We show this through the analysis of ERP data from a masked semantic priming procedure. The new techniques reveal activation generated by unconscious (masked) prime words as early as 100 ms and 200 ms post stimulus-onset; a pattern which simple subtraction fails to detect.

Temporal cue-target overlap is not essential for backward inhibition in task switching.

Lag 2 repetition costs are a performance cost observed when participants return to a task after just one intervening trial of a different task, compared to returning after a longer interval (ABA vs. CBA sequences, where A, B, C are tasks). This effect is known as backward inhibition (BI) and is thought to reflect the need to overcome inhibition applied specifically to Task "A" during disengagement at trial n - 1. Druey and Hubner (2007) have suggested that employment of such a specific inhibitory mechanism relies upon the cue and the target of the task overlapping temporally. We provide evidence across three experiments (including a direct replication attempt) that this is not the case, and that the presence of task-specific BI relies to some extent on the need to translate the cue-target relationship into working memory. Additionally, we provide evidence that faster responses in no overlap conditions are driven by low-level perceptual differences between target displays across overlap conditions. We conclude that BI is an effective sequential control mechanism, employed equally in cases of temporally overlapping and temporally separated cues and targets.

N400, the reference electrode, and the semantic activation in prime-task experiments: a reply to Dombrowski and Heil (2006).

In two recent papers, Heil et al. [Heil, M., Rolke, B., Pecchinenda, A., 2004. Automatic semantic activation is no myth: semantic context effects on the N400 in the Letter-Search task in the absence of response time effects. Psychol. Sci., 15 (12), 852-857] and Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293-305] found opposite ERP effects of semantic priming following letter search (as measured by the N400). Dombrowski and Heil [Dombrowski, J.H., Heil, M., 2006. Semantic activation, letter search and N400: a reply to Marí-Beffa, Valdés, Cullen, Catena and Houghton (2005). Brain Res., 1073-1074, 440-443] have argued that the N400 modulation associated to semantic priming found by Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293-305] is due to the use of electrode Cz as reference, rather than to the task manipulation being studied (letter search vs. categorisation). In the current article we argue that the conclusions of Dombrowski and Heil are mistaken and are due in part on a misreading of Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293-305]. We argue instead that the differences between the results of Heil et al. [Heil, M., Rolke, B., Pecchinenda, A., 2004. Automatic semantic activation is no myth: semantic context effects on the N400 in the Letter-Search task in the absence of response time effects. Psychol. Sci., 15 (12), 852-857] and Marí-Beffa et al. [Marí-Beffa, P., Valdés, B., Cullen, D.J.D., Catena, A., Houghton, G., 2005. ERP analyses of task effects on semantic processing from words. Cogn. Brain Res., 23, 293-305] are largely due to differences in experimental method and procedure, rather than to the technique used for the ERP analysis.

Serial order and consonant-vowel structure in a graphemic output buffer model.

We review features of the spelling errors of dysgraphic patients with "Graphemic Buffer Disorder" (GBD). We argue that the errors made by such patients suggest the breakdown of a system used to generate serial order in the output stages of spelling production, and we develop a model for this system based on an existing theory of sequential behaviour--"Competitive Queuing." We show that constraints on response categories may be straightforwardly applied during sequence production in such a model, and this enables us to account for the preservation of consonant-vowel status in the spelling errors of GBD patients. When the sequence generation process is disrupted by the addition of random noise the model shows the major features of GBD. The results are compared in detail against data from a number of patients.

ERP analyses of task effects on semantic processing from words.

Semantic (positive) priming refers to the facilitated processing of a probe word when preceded by a related prime word, and is a widely used technique for investigating semantic activation. However, the effect is interrupted or eliminated when attention is directed to low-level features of the prime word, such as its letters, a result which has been used to question the automaticity of semantic processing. We investigated this issue using both behavioural [reaction time (RT)] and electrophysiological measures [event-related potentials (ERPs)]. Subjects performed semantic categorization (living vs. nonliving) and letter search ("A" or "E") tasks on prime words followed by lexical decision on the probe. RT results showed the expected elimination of semantic priming following letter search. However, both prime tasks were affected by the semantic category of the prime, indicating that the meaning was processed. The ERP results supported this conclusion: an early component previously associated with automatic semantic processing [the Recognition Potential (RP)] was sensitive to the category of the prime word irrespective of the prime task. However, a later component (N400) was significantly affected by the task, in both the prime (categorization task) and probe words (semantic priming). The results dissociate rapid, automatic semantic processing from semantic priming. We suggest that a later inhibitory control mechanism suppresses this semantic activation when it is not relevant to the task, and that this produces the loss of semantic priming.

Dissociating object- and response-based components of negative priming through effects of practice.

The negative priming (NP) effect is the slowing of responses to an imperative stimulus (probe) that has recently been ignored (prime). Prevailing accounts of the phenomenon attribute it to a variety of causes, all centered on a representation of the stimulus event itself. However, we argue that the most commonly used NP paradigms confound stimulus- and response-based factors. In two experiments, we demonstrate the importance of response factors in producing NP and show clear empirical dissociations between object- and response-centered NP when studying their time courses over extended practice. When distractors compete for a response (response-based), the NP effect is both more robust and more resistant to the effects of practice. On the other hand, when prime distractors do not compete for response (object-based), they yield weaker NP effects that disappear with practice. We conclude that the NP effects shown in the most common procedures are produced by a combination of distinct factors that tend to act in the same direction.

Learning artificial phonotactic constraints: time course, durability, and relationship to natural constraints.

G. S. Dell, K. D. Reed, D. R. Adams, and A. S. Meyer (2000) proposed a "breadth-of-constraint" continuum on phoneme errors, using artificial experiment-wide constraints to investigate a putative middle ground between local and language-wide constraints. The authors report 5 experiments that test the idea of the continuum and the location of the experiment-wide constraints within it. Experiments 1 and 2 replicated the findings of Dell et al. on the experiment-wide constraints but showed only chance adherence to the local positional constraints. Experiment 3 showed that the latter constraints are uniquely affected by the form of practice used. Experiments 4 and 5 investigated the time course and robustness of the experimental constraints by reversing them during testing. This caused no difficulty when occurring between blocks (Experiment 4) but caused short-lived disruption when occurring within block (Experiment 5). The authors propose that the results do not support the idea of a continuum, but that the experiment-wide constraints reflect a local biasing of language-wide constraints, probably related to the need for rapid learning.

Normal and impaired spelling in a connectionist dual-route architecture.

This paper presents a dual-route connectionist model of spelling, in which one route maps directly from sound to spelling (phonemes to graphemes), while in the other route the mapping is mediated by a further level of representation. The direct route is implemented as a two-layer associative network, with syllabically structured phonemic (input) and graphemic (output) representations, which comes to behave as a productive sound-to-spelling conversion mechanism through the exposure to a corpus of monosyllabic words. The mediated route is modelled as a frequency-sensitive lexical pathway. Nodes representing more frequent words become activated more rapidly than those of lower-frequency words. Access to both routes occurs in parallel, and the final spelling is determined by the combined output of both routes. We show that the model accounts for a wide range of data from normal spellers (including nonword spelling, the variability in vowel spelling and the effect of surrounding phonological context, frequency effect and its interaction with spelling regularity). We also investigate the effect of a selective lesion to the lexical route in which the ceiling of lexical activation is lowered. This manipulation produces a model with surface dysgraphic characteristics, which is tested against data from two impaired subjects. As well as simulating the classic surface dysgraphic profile, including a frequency by regularity interaction, the model exhibits a phenomenon that has only recently been reported, and which provides strong evidence for the idea that multiple routes are active in parallel, and combine to produce the final spelling.