Very clever homunculus: Compound stimulus strategies for the explicit task-cuing procedure

In two experiments, subjects were given arbitrary letter cues or meaningful word cues that specified the task to be performed on a subsequent target stimulus. Letter and word cues were presented in separate blocks. There were two cues of each type for each task. Three kinds of transitions separated tasks:cue repetitions, in which both the cue and the task repeated;task repetitions, in which the cue changed but the task repeated; andtask alternations, in which both the cue and the task changed. Responses were faster for cue than for task repetitions for both cue types. With word cues, task repetitions were not reliably faster than task alternations. With letter cues, task repetitions were reliably faster than task alternations in the first block but not in the second block. The results suggest that subjects responded to the compound of the cue and the target rather than switching task set between trials.     

Priming cue encoding by manipulating transition frequency in explicitly cued task switching

Explicitly cued task switching with multiple cues per task permits three types of transitions: cue repetitions (cue and task repeat), task repetitions (cue changes but task repeats), and task alternations (cue and task change). The difference between task alternations and task repetitions can be interpreted as a switch cost, but its magnitude varies substantially across experiments. We investigated how switch cost is affected by transition frequency (how often subjects repeat and switch tasks) with an experiment in which each transition had a frequency of .70 in separate sessions. Switch cost was smallest when task alternations were frequent and largest when task repetitions were frequent. Mathematical modeling of the data indicated that the different “switch costs” reflected priming of cue encoding for frequent transitions. Interpretations of our findings based on automatic priming from memory retrieval of past transitions and strategic priming from transition expectancies are discussed.     

Task switching versus cue switching: using transition cuing to disentangle sequential effects in task-switching performance

Recent methodological advances have allowed researchers to address confounds in the measurement of task-switch costs in task-switching performance by dissociating cue switching from task switching. For example, in the transition-cuing procedure, which involves presenting cues for task transitions rather than for tasks, cue transitions (cue switches and cue repetitions) and task transitions (task switches and task repetitions) can be examined in a complete factorial design. Transition cuing removes the confound between cue transitions and first-order task transitions, but it introduces a confound between cue transitions and longer task sequences. In the present study, transition cuing was studied with two cues per transition (REPEAT and AGAIN for task repetitions; SWITCH and CHANGE for task switches), enabling a partial deconfounding of cue transitions and task sequences. Two experiments revealed robust sequential effects, with higher order task transitions affecting performance when cue transitions were held constant and with cue transitions affecting performance when task sequences were held constant. Methodological and theoretical implications of these findings for research on task switching are discussed.     

Priming or executive control? Associative priming of cue encoding increases “switch costs” in the explicit task-cuing procedure

The explicit task-cuing procedure involves presenting a cue that indicates which task to perform on a target. Responses are typically faster when tasks repeat than when they alternate, and this difference is often interpreted as a measure of the time required for executive control processes to change task set. This article suggests that the difference reflects priming of cue encoding when successive cues are identical or associatively related. Subjects responded to task repetitions more quickly when the cue on the current trial was associatively related to the cue on the previous trial (e.g., day --> night) than when the cues were unrelated (e.g., verb --> night). Models applied to the time course function--generated by manipulating the interval between the onsets of the cue and the target--showed that the facilitation was due to cue encoding, a process that does not require online executive control.     

Phonological and semantic priming: Evidence for task-independent effects

The questions asked in the present experiments concern the generality of semantic and phonological priming effects: Do these effects arise automatically regardless of target task, or are these effects restricted to target tasks that specifically require the retrieval of the primed information? In Experiment 1, subjects produced faster color matching times on targets preceded by a masked rhyming prime than on targets preceded by an orthographic control or an unrelated prime. This result suggests that automatic priming effects on the basis of phonological similarity can be obtained even when the target task does not make use of phonological information. This claim was reinforced in Experiment 2 in which a rhyme priming effect and a semantic priming effect were found in a semantic categorization task. In Experiment 3, the target task was phonological (rhyme detection), and, again, both phonological and semantic priming effects were observed. Finally, in Experiments 4 and 5, in a replication and an extension of Experiment 1, phonological and semantic priming effects were found in a color matching task, a task involving neither phonological nor semantic processing. These results are most straightforwardly interpreted by assuming that both semantic and phonological priming effects are, at least in part, due to automatic activation of memorial representations.     

Rethinking volitional control over task choice in multitask environments: Use of a stimulus set selection strategy in voluntary task switching

Under conditions of volitional control in multitask environments, subjects may engage in a variety of strategies to guide task selection. The current research examines whether subjects may sometimes use a top-down control strategy of selecting a task-irrelevant stimulus dimension, such as location, to guide task selection. We term this approach a stimulus set selection strategy. Using a voluntary task switching procedure, subjects voluntarily switched between categorizing letter and number stimuli that appeared in two, four, or eight possible target locations. Effects of stimulus availability, manipulated by varying the stimulus onset asynchrony between the two target stimuli, and location repetition were analysed to assess the use of a stimulus set selection strategy. Considered across position condition, Experiment 1 showed effects of both stimulus availability and location repetition on task choice suggesting that only in the 2-position condition, where selection based on location always results in a target at the selected location, subjects may have been using a stimulus set selection strategy on some trials. Experiment 2 replicated and extended these findings in a visually more cluttered environment. These results indicate that, contrary to current models of task selection in voluntary task switching, the top-down control of task selection may occur in the absence of the formation of an intention to perform a particular task.     

Modeling task switching without switching tasks: a short-term priming account of explicitly cued performance

Switch costs in task switching are commonly attributed to an executive control process of task-set reconfiguration, particularly in studies involving the explicit task-cuing procedure. The authors propose an alternative account of explicitly cued performance that is based on 2 mechanisms: priming of cue encoding from residual activation of cues in short-term memory and compound cue retrieval of responses from long-term memory. Their short-term priming account explains the repeated cue encoding benefit, switch cost, reduction in switch cost with preparation time, and other effects. The authors develop a mathematical model of their priming account and fit it to data from 3 experiments, demonstrating that a set of basic psychological processes can produce several effects--including putative switch costs--without switching tasks.     

Out with the old, in with the new: More valid measures of switch cost and retrieval time in the task span procedure

Two experiments provided new measures of switch cost and retrieval time in the task span procedure. In Experiment 1, subjects were given lists of six task names to remember, followed by six targets on which to perform the tasks named in the list. The lists contained alternations and repetitions, and switch costs were estimated by comparing reaction time (RT) on alternation and repetition trials. The experiment also included memory span and single task conditions, so switch costs could be estimated by subtracting the sum of the RT in those conditions from the task span RT, as in the original report (Logan, 2004). The data suggested that the original measure of switch cost was invalid and that the new measure was preferable. In Experiment 2, subjects performed each task on the list twice. Retrieval was required on the first but not on the second trial in each pair. Retrieval time was estimated by comparing the RT on trials that required retrieval with trials that did not require retrieval. This measure was more valid than the RT in the memory span condition of Experiment 1, which was used in the original report.     

Voluntary task switching: chasing the elusive homunculus

In the voluntary task switching procedure, subjects choose the task to perform on a series of bivalent stimuli, requiring top-down control of task switching. Experiments 1-3 contrasted voluntary task switching and explicit task cuing. Choice behavior showed small, inconsistent effects of external stimulus characteristics, supporting the assumption of top-down control of task choice. Switch costs were smaller when subjects chose to switch tasks than when instructed by an external cue. Experiments 4-6 separated choice costs from switch costs. These findings support models of task switching that incorporate top-down processes in accounts of switch costs. The degree to which task switching procedures capture top-down versus bottom-up processes may depend on the extent of environmental support provided by the procedure.     

Memory retrieval given two independent cues: cue selection or parallel access?

A basic but unresolved issue in the study of memory retrieval is whether multiple independent cues can be used concurrently (i.e., in parallel) to recall a single, common response. A number of empirical results, as well as potentially applicable theories, suggest that retrieval can proceed in parallel, though set forth a model that denies that possibility. In this paper, five quantitative models are developed to test broad candidate principles. In multiple experiments, subjects were trained to retrieve a vocal digit response for each member of a set of letter or color cues. In subsequent test and transfer phases, single cue trials were randomly mixed with dual cue trials on which the two cues always required the same response. For the first few repetitions of each new set of dual cue items, there was no evidence of parallel retrieval over any part of the RT distribution. After more repetitions, dual cue trials were performed faster than single cue trials, but only under conditions that were favorable to development of a "chunked" dual cue representation. These results indicate that associative independence is an important modulating variable that must be heeded in any general model of attention and memory retrieval. Further, the results are most consistent with a model that places the performance bottleneck prior to the retrieval stage of processing.     

Differential effects of aging on processes underlying task switching

In this study, we used event-related brain potentials (ERPs) to examine the effects of aging on processes underlying task switching. The response time data revealed an age-related increase in mixing costs before controlling for general slowing and no effect of aging on switching costs. In the cue-locked epoch, the ERP data revealed little effect of age on the parietal P3 related to cue encoding, an age-related decrease in parietal activity related to cue retrieval, and an age-related increase in the amplitude of the parietal and frontal activity related to task set configuration and rule mapping. In the target-locked epoch, there was differential neural recruitment in younger and older adults in response to task mixing. These data are consistent with the idea that older adults may not fully implement task set before onset of the target stimulus.     

Sensory generalization and learning about novel colours by poultry chicks

Previous research has shown semantic influence from irrelevant peripheral cues on the spatial allocation of covert visual attention. The present study explored whether the task set determines the extent of such semantic influence. A spatial cueing paradigm with strict eye movement control was used, where cues were either first names (male or female) or emotionally charged words (positive or negative) followed by a face target. Participants discriminated either the gender (male or female) or the emotion (positive or negative) of the face. When there was high information overlap between cue and task set, responses were faster when the cue and target value were semantically congruent than when they were incongruent. It was concluded that the semantically related cues primed a task-influencing response independently of spatial attention allocation processes, showing that semantic influences from brief peripheral cues depend on the degree of information overlap between cue and task set.     

Testing probability matching and episodic retrieval accounts of response repetition effects in task switching

This study takes inventory of available evidence on response repetition (RR) effects in task switching, in particular the evidence for RR cost when the task switches. The review reveals that relatively few task-switching studies in which RR effects were addressed have shown statistical support for RR cost, and that almost all are affected by 1 of 2 potential artifacts, either a response bias caused by disallowing stimulus repetitions or the effect of including stimulus repetitions in data analysis. New results with these factors controlled support an episodic retrieval model in which features of the retrieved trace, including the stimulus but also the task, task cue, and response, facilitate or interfere with performance depending on whether they match or mismatch the current processing context.     

Intelligence as the efficiency of cue-driven retrieval from secondary memory

Complex-span (working-memory-capacity) tasks are among the most successful predictors of intelligence. One important contributor to this relationship is the ability to efficiently employ cues for the retrieval from secondary memory. Presumably, intelligent individuals can considerably restrict their memory search sets by using such cues and can thereby improve recall performance. We here test this assumption by experimentally manipulating the validity of retrieval cues. When memoranda are drawn from the same semantic category on two successive trials of a verbal complex-span task, the category is a very strong retrieval cue on its first occurrence (strong-cue trial) but loses some of its validity on its second occurrence (weak-cue trial). If intelligent individuals make better use of semantic categories as retrieval cues, their recall accuracy suffers more from this loss of cue validity. Accordingly, our results show that less variance in intelligence is explained by recall accuracy on weak-cue compared with strong-cue trials.     

Separating cue encoding from target processing in the explicit task-cuing procedure: are there "true" task switch effects?

Six experiments were conducted to separate cue encoding from target processing in explicitly cued task switching to determine whether task switch effects could be separated from cue encoding effects and to determine the nature of the representations produced by cue encoding. Subjects were required to respond to the cue, indicating which cue was presented (Experiments 1, 3a, and 4a) or which task was cued (Experiments 2, 3b, and 4b), before performing the cued task on the target. Cue encoding was successfully separated from target processing when the cue response indicated which task was cued but not when it indicated which cue was presented. Task switch effects were found when this separation was successful, suggesting that there are "true" task switch effects independent of cue encoding. Analysis of the conditions required for successful separation suggested that cue encoding results in a semantic categorical representation of the task to be performed rather than verbal or phonological representations of individual cues. Implications for the authors' past modeling of task-switching performance are discussed.     

Modeling graded response congruency effects in task switching

Compound cue retrieval is a computational model of a mediated route for response selection in task-switching situations. In previous studies, the model has been shown to account for response congruency effects when switching between two tasks, where response congruency reflects the degree of match between relevant and irrelevant task responses associated with a target stimulus. In the present study, the author derived a model prediction of graded response congruency effects in situations involving three tasks. The predicted pattern was observed for both response time and error rate in an experiment in which numerical categorization tasks were performed on single-digit targets. Implications for understanding response congruency effects and for developing models of task-switching performance are discussed.     

Components of Stroop-like interference in picture naming

The semantic interference effect observed in Stroop tasks and picture-word interference tasks might be due to the previous confounding of semantic similarity with task relevance (in the Stroop task) and with perceptual similarity (in the picture-word interference task). A picture-word variant of the Stroop task was devised in which the factors of task relevance and perceptual similarity were controlled. The distractor conditions allowed for the examination of four types of context effects. The results show that the overall Stroop-like interference effect can be decomposed into interference effects due to (1) a semantic relation between distractor and target, (2) the semantic relevance of the distractor word in the task at hand, (3) the presence of the distractor word in the response set, and (4) the mere presence of a word. Implications of these findings for the locus or loci of Stroop and picture-word interference effects are discussed. It is concluded that distractor words in Stroop-like naming tasks interfere mainly in the process of name retrieval.     

The cost of a voluntary task switch

Task-switching paradigms are widely used to study executive control. However, standard paradigms may not require active control to switch tasks. We examined voluntary task switching by having subjects choose which task to perform on a series of bivalent stimuli. Subjects performed parity or magnitude judgments on single digits. Instructions were to perform the two tasks equally often and in a random order. The response-to-stimulus interval (RSI) was either 100 or 1,000 ms, manipulated between blocks. Task alternations were slower than task repetitions, and this switch cost was greater at the short RSI than at the long RSI (310 and 94 ms, respectively). Additionally, subjects produced more task repetitions than expected if the tasks were performed in a random sequence. These results show costs associated with a voluntary task switch, when subjects must actively control the choice of the task to be performed.     

Encoding specificity in the recall of pictures and words in children and adults

In this study, the modality of the retrieval cues (pictures or words) was varied in a cued recall task to determine how second and fourth grade children and college adults encode words (Experiment 1) and pictures (Experiment 2). According to the assumptions of the encoding specificity principle, cue modality should affect recall only to the degree to which subjects focus on modality specific (sensory) rather than nonmodality specific (semantic) information in stimuli. In both experiments, the results showed progressively smaller encoding specificity effects with increasing age. To ensure that differences in encoding activity were responsible for these effects, comparisons were made of recall patterns under intentional learn conditions, and under incidental conceptual and sensory orienting conditions. The recall patterns of the children in the conceptual orienting condition were similar to the adult patterns in the learn condition, and the adult recall patterns in the sensory orienting conditions were similar to those of the children in the learn conditions. These results suggest that there are developmental differences in encoding the sensory and semantic information in stimuli that may result from differences in the efficiency with which the semantic information in stimuli is processed. The results suggest that young children typically encode stimuli in a fashion that stresses the sensory aspects of the stimuli, and that recall suffers as a result.     

Comparing word fragment completion and cued recall with letter cues

Cued recall with word stems as cues and fragment completion rely on different types of letter cues and also differ in the explicit-implicit nature of the retrieval orientation. Despite these differences, variables effective in one task may be effective in the other because both rely on letter cues. Two variables known to affect cued recall were manipulated: Lexical set size (number of words that fit the letter cue) and meaning set size (number of associates generated to the studied words). Across four experiments, subjects in each task were less likely to recover targets from larger lexical sets. However, meaning set size affected cued recall but not fragment completion. These results indicate that fragment completion and letter-cued recall are based on lexical search but that cued recall also involves a semantic search component. Furthermore, type of retrieval cue had a greater effect than type of retrieval orientation.