Implicit visual learning: How the task set modulates learning by determining the stimulus–response binding

Implicit learning is one of the most fundamental learning mechanisms that enables humans to adapt to regularities inherent in the environment. Despite its high flexibility, it depends on constraints, such as selective attention. Here, we focused on the stimulus-to-response binding which defines the dimensions of the stimuli and the responses participants attend to. In a serial reaction time task with a visual sequence, we investigated whether this stimulus–response binding influences the amount of sequence learning. The results of Experiments 1 and 2 showed that visual sequence learning is reduced when participants do not attend to the relevant response dimension. Furthermore, the findings of Experiment 3 suggest that attention to the relevant response dimension increased the development of explicit knowledge without affecting implicit knowledge. This latter finding is difficult to reconcile with the assumption that explicit learning results from the gradual strengthening of sequence representations.     

Response mode does not modulate the space–time congruency effect: Evidence for a space–time mapping at a conceptual level

Previous studies reported a space–time congruency effect on response time, supporting the notion that people's thinking about time is grounded in their spatial sensorimotor experience. According to a strong view of metaphoric mapping, the congruency effect should be larger for responses that differ in their spatial features than for responses that lack such differences. In contrast, a weaker version of this account posits that the grounding of time is based on higher-level spatial concepts. In this case, response mode should not modulate the size of the space–time congruency effect. In order to assess these predictions, participants in this study responded to temporal stimuli either manually or vocally. Response mode did not modulate the space–time congruency effect which supports the weaker view of metaphoric mapping suggesting that this effect emerges at a higher cognitive level.     

Unlearning a stimulus–response association

After a response has been associated with a particular stimulus, would this association be “unlearned” when the circumstances call for a new response to be made to that stimulus? This question was investigated in the present study with a negative priming (NP) paradigm developed by Shiu and Kornblum (1996). In the study, participants first practiced with a particular pairing of stimuli and responses in a four-choice reaction time (RT) task. Then, in the transfer phase, they switched to a different pairing of the same set of stimuli and responses. The results showed that a transfer response was slow if this response and the stimulus in the preceding trial had been paired in the training phase. Such NP effects persisted even after extended practice with the new pairing, suggesting that the “old” stimulus–response (SR) associations remain despite acquisition of some “new” associations.     

Effects of stimulus–stimulus short-term memory associations in a Simon-like task

The Simon effect refers to faster responding when an irrelevant stimulus location corresponds with the response to a relevant stimulus attribute than when it does not. We investigated whether a memory-based Simon-like effect would occur when the irrelevant spatial attribute was associated with the stimulus during a prior task. In a first task, an association between colour and location was formed by requiring participants to count the occurrences of two colour stimuli, each of which was always presented in a left or right location. In a second task, the colour stimuli were presented centrally and mapped to left and right keypresses, with the mapping being inconsistent or consistent with the prior colour-location associations. A Simon-like effect was evident at the start of the second task, with performance being better when the established colour–position associations were consistent with the colour–response mapping than when they were not. This result indicates that stimulus–stimulus short-term memory associations formed during the first task transferred to the second task. For the remainder of the second task, the data showed a more conservative speed–accuracy criterion for the inconsistent condition than for the consistent condition, though a processing efficiency measure suggested that the prior stimulus–stimulus short-term associations may also continue to directly influence performance. Results suggest that simple declarative knowledge, as represented by stimulus–stimulus STM links, exerts less persistent transfer effects than procedural knowledge as provided by stimulus–response STM links.     

Orthogonal stimulus–response compatibility effects emerge even when the stimulus position is task irrelevant

The above-right/below-left mapping advantage with vertical stimuli and horizontal responses is known as the orthogonal stimulus–response compatibility (SRC) effect. We investigated whether the orthogonal SRC effect emerges with irrelevant stimulus dimensions. In Experiment 1, participants responded with a right or left key press to the colour of the stimulus presented above or below the fixation. We observed an above-right/below-left advantage (orthogonal Simon effect). In Experiment 2, we manipulated the polarity in the response dimension by varying the horizontal location of the response set. The orthogonal Simon effect decreased and even reversed as the left response code became more positive. This result provides evidence for the automatic activation of the positive and negative response codes by the corresponding positive and negative stimulus codes. These findings extended the orthogonal SRC effect based on coding asymmetry to an irrelevant stimulus dimension.     

The role of task rules and stimulus–response mappings in the task switching paradigm

Switch costs occur whenever participants are asked to switch between two or more task sets. In a typical task switching experiment, participants have to switch between two task sets composed of up to four different stimuli per task set. These 2 (task sets) x 4 (stimuli) contain only 8 different stimulus-response (S-R) mappings, and the question is why participants base their task performance on task sets instead of S-R mappings. The current experiments compared task performance based on task rules with performance based on single stimulus-response mappings. Participants were led to learn eight different S-R mappings with or without fore-knowledge about two underlying task sets. Without task set information no difference between shifts and repetitions occurred, whereas introducing task sets at the beginning led to significant switch costs. Most importantly, introducing task sets in the middle of the experiment also resulted in significant switch costs. Furthermore, introducing task rules at the beginning of the experiment lead to slower RTs when simple stimuli (Experiment 1) had to be processed. This detrimental effect disappeared with more complex stimuli (Experiment 2). Results will be discussed with respect to cognitive control.     

"1-2-3": is there a temporal number line? Evidence from a serial comparison task

Evidence suggests that numbers are intimately related to space (Dehaene, Bossini, & Giraux, 1993; Hubbard, Piazza, Pinel, & Dehaene, 2005). Recently, Walsh (2003) suggested that numbers might also be closely related to time. To investigate this hypothesis we asked participants to compare two digits that were presented in a serial manner, i.e., one after another. Temporally ascending digit pairs (such as 2-3) were responded to faster than temporally descending pairs (3-2). This effect was, in turn, qualified by a local SNARC (spatial numerical association of response codes) effect and a local semantic congruity effect (SCE). Moreover, we observed a global numerical SCE only for temporally descending digit pairs. However, we did not observe a global SNARC effect, i.e., an interaction of numerical magnitude and the right/left response hand. We discuss our results in terms of overlearned forward-associations ("1-2-3") as formed by our ubiquitous cognitive routines to count off objects or events.     

Transfer of orthogonal stimulus–response mappings to an orthogonal Simon task

When up–down stimulus locations are mapped to left–right keypresses, an overall advantage for the up–right/down–left mapping is often obtained that varies as a function of response eccentricity. This orthogonal stimulus–response compatibility (SRC) effect also occurs when stimulus location is irrelevant, a phenomenon called the orthogonal Simon effect, and has been attributed to correspondence of stimulus and response code polarities. The Simon effect for horizontal stimulus–response (S–R) arrangements has been shown to be affected by short-term S–R associations established through the mapping used for a prior SRC task in which stimulus location was relevant. We examined whether such associations also transfer between orthogonal SRC and Simon tasks and whether correspondence of code polarities continues to contribute to performance in the Simon task. In Experiment 1, the orthogonal Simon effect was larger after practising with an up–right/down–left mapping of visual stimuli to responses than with the alternative mapping, for which the orthogonal Simon effect tended to reverse. Experiment 2 showed similar results when practice was with high (up) and low (down) pitch tones, though the influence of practice mapping was not as large as that in Experiment 1, implying that the short-term S–R associations acquired in practice are at least in part not modality specific. In Experiment 3, response eccentricity and practice mapping were shown to have separate influences on the orthogonal Simon effect, as expected if both code polarity and acquired S–R associations contribute to performance.     

How sequence learning creates explicit knowledge: the role of response–stimulus interval

Destrebecqz and Cleeremans (Psychon bull rev 8:343-350, 2001; Attention and implicit learning. John Benjamins Publishing Company, Amsterdam, pp 181-213, 2003) reported that increasing the response-stimulus interval (RSI) during incidental sequence learning improved participants' ability to discriminate old and new sequences in a recognition test. However, the original experimental design confounded RSI effects during training and test. I therefore repeated the experiment with an improved design in which RSI was varied systematically during the training phase and the recognition task. Participants learned a sequence of response locations either incidentally or intentionally. As a result, sequence recognition was not affected by the RSI manipulations in the group of incidental learners. With intentional learning instructions, recognition was unaffected by training RSI, but a long RSI in the test phase improved recognition performance over a short RSI. Response latencies while executing the test sequences indicated no effect of training RSI on sequence learning. However, sequence knowledge was expressed more readily when the RSI in the test phase matched the RSI in the training phase.     

The influence of the response–stimulus interval on implicit and explicit learning of stimulus sequence

Three experiments investigated the influence of the response-stimulus interval (RSI) on implicit and explicit learning of stimulus sequences. Participants responded to numerals presented in predetermined positions with alternating long and short RSIs. Half of the participants were instructed explicitly to learn the position sequence. In the transfer phase of Experiments 1 and 2, changing RSI patterns reduced the expression of incidental and intentional learning of position sequence. In Experiment 3 the position sequence was transformed, except that sub-sequences demarcated by long RSIs remained unchanged; this greatly reduced the expression of intentional learning, and slightly reduced that of incidental learning. These results indicate that in implicit learning, stimulus sequences are learned under the constraints of RSIs, whereas in explicit learning, learning independent of RSIs, as well as learning constrained by RSIs, occurs.     

Effects of response–stimulus interval manipulation and articulatory suppression on task switching

We conducted three experiments using a list paradigm to examine how articulatory suppression and response–stimulus interval (RSI) manipulation affected task switching. Experiments 1 and 2 tested task-switching performance under a short and long RSI and three concurrent task conditions (control, articulatory suppression, and tapping) without external task cues. The results indicated that alternation had a greater effect under articulatory suppression than under the control and tapping conditions, and that articulatory suppression costs were unrelated to the RSI. In Experiment 3, an external task cue was provided with each stimulus, and the negative effect of articulatory suppression on alternation cost was eliminated. These results indicated that articulatory suppression effects did not differ between conditions of short and long RSI and that the availability of verbal representations of task information was independent of RSI length. This paper discussed the possible roles played by the phonological loop in task-switching paradigms.     

Integrated cross-domain object storage in working memory: Evidence from a verbal–spatial memory task

Working-memory theories often include domain-specific verbal and visual stores (e.g., the phonological and visuospatial buffers of Baddeley, 1986), and some also posit more general stores thought to be capable of holding verbal or visuospatial materials (Baddeley, 2000; Cowan, 2005). However, it is currently unclear which type of store is primarily responsible for maintaining objects that include components from multiple domains. In these studies, a spatial array of letters was followed by a single probe identical to an item in the array or differing systematically in spatial location, letter identity, or their combination. Concurrent verbal rehearsal suppression impaired memory in each of these trial types in a task that required participants to remember verbal–spatial binding, but did not impair memory for spatial locations if the task did not require verbal–spatial binding for a correct response. Thus, spatial information might be stored differently when it must be bound to verbal information. This suggests that a cross-domain store such as the episodic buffer of Baddeley (2000) or the focus of attention of Cowan (2001) might be used for integrated object storage, rather than the maintenance of associations between features stored in separate domain-specific buffers.     

Decomposing serial learning: What is missing from the learning curve?

Our current understanding of serial learning relies on the form of the learning curve and on changes in the serial position curve over repeated study-test trials (Ward, 1937). The averaging of data that produces these functions obscures the detailed history of memory for individual items over the course of study-test trials. Extending Tulving’s (1964) analysis of free recall learning, we present a new analysis of serial learning that tracks the acquisition and forgetting of item and order information at the level of individual items. Applying this analysis to two large data sets on serial list learning allows us to discern among hypotheses that are indistinguishable solely on the basis of the learning curve.     

Repetition costs in word identification: evaluating a stimulus–response integration account

Stimulus repetition facilitates performance in many experimental contexts. However, an episodic approach to interpreting repetition effects suggests that repetition effects should depend on how stimuli are encoded. In Experiments 1-3, stimulus repetition in a word identification task led to a cost rather than a benefit in performance, but only when the prime was presented for a relatively long duration. One account of these results is that long prime durations allow integration between stimulus and response codes to occur, which in turn can interfere with responding to a following identical target. In Experiment 4, a stimulus intensity based episodic specificity effect that was insensitive to the proportion of repeated trials supported this stimulus-response integration account.     

Monitoring of learning at the category level when learning a natural concept: Will task experience improve its resolution?

Researchers have recently begun to investigate people's ability to monitor their learning of natural categories. For concept learning tasks, a learner seeks to accurately monitor learning at the category level — i.e., to accurately judge whether exemplars will be correctly classified into the appropriate category on an upcoming test. Our interest was in whether monitoring resolution at the category level would improve as participants gain task experience across multiple study-test blocks, as well as within each block. In four experiments, exemplar birds (e.g., American Goldfinch, Cassin's Finch) paired with each family name (e.g., Finch) were studied, and participants made a judgment of learning (JOL) for each exemplar. Of most interest, before and after studying the exemplars, participants made category learning judgments (CLJs), which involved predicting the likelihood of correctly classifying novel birds into each family. Tests included exemplars that had been studied or exemplars that had not been studied (novel). This procedure was repeated for either one or two additional blocks. The relative accuracy of CLJs did not improve across blocks even when explicit feedback was provided, whereas item-by-item JOL accuracy improved across blocks. Category level resolution did improve from pre-study to post-study on an initial block, but it did not consistently increase within later blocks. The stable accuracy of CLJs across blocks poses a theoretical and empirical challenge for identifying techniques to improve people's ability to judge their learning of natural categories.     

Trends in married couples' time use: Evidence from 1977–78 and 1987–88

Conflicting evidence regarding married couples' time use trends has recently emerged in the literature. A critical review of this literature suggests that variations in data quality and methodological approaches may be responsible for many of the observed differences. Capitalizing on the insights gained from this review, a trend analysis of couples' time use is presented in this paper. The analysis is based on two cross-sections of time diary data collected from two-parent, two-child households. The results suggest that the relationships between socioeconomic variables and couples' time use changed during the period from 1977–78 to 1987–88. On average, these changes lead to an increase of over seven hours per week in married women's productive work time (i.e., market work plus household work). Correspondingly, the productive work time of husbands increased by an average of three and one-half hours per week. Both increases came at the expense of time that was formerly spent in more leisure-oriented activities.Financial support for the collection of the data used in this study was provided by the Utah State Agricultural Experiment Station and the University of Utah Research Committee. A grant of computer time from the Utah Supercomputing Institute, which is funded by the State of Utah and the IBM Corporation, is greatfully acknowledged. Additional support has been provided by the Department of Home Economics and Consumer Education at Utah State University where Dr. Zick was on leave during the 1989–90 academic year. W. Keith Bryant, Ken R. Smith, and an anonymous reviewer each gave helpful comments on an earlier draft of this article.     

Reaction time measures in deception research: Comparing the effects of irrelevant and relevant stimulus–response compatibility

Evidence regarding the validity of reaction time (RT) measures in deception research is mixed. One possible reason for this inconsistency is that structurally different RT paradigms have been used. The aim of this study was to experimentally investigate whether structural differences between RT tasks are related to how effective those tasks are for capturing deception. We achieved this aim by comparing the effectiveness of relevant and irrelevant stimulus–response compatibility (SRC) tasks. We also investigated whether an intended but not yet completed mock crime could be assessed with both tasks. Results showed (1) a larger compatibility effect in the relevant SRC task compared to the irrelevant SRC task, (2) for both the completed and the intended crime. These results were replicated in a second experiment in which a semantic feature (instead of color) was used as critical response feature in the irrelevant SRC task. The findings support the idea that a structural analysis of deception tasks helps to identify RT measures that produce robust group effects, and that strong compatibility effects for both enacted crimes as well as merely intended crimes can be found with RT measures that are based on the manipulation of relevant SRC.     

What matters in implicit task sequence learning: perceptual stimulus features, task sets, or correlated streams of information?

Implicit task sequence learning may be attributed to learning the order of perceptual stimulus features associated with the task sequence, learning a series of automatic task set activations, or learning an integrated sequence that derives from 2 correlated streams of information. In the present study, our purpose was to distinguish among these 3 possibilities. In 4 separate experiments, we replicated and extended a previous study by Heuer, Schmidtke, and Kleinsorge (2001). The presence or absence of a sequence of tasks, as well as that of a sequence of different task-to-response mappings, was manipulated independently within experiments. Evidence of implicit sequence learning was found only when correlated sequences of tasks and mappings were present. No sequence learning effects were found when only a single task sequence or a single mapping sequence was present, even when the structure of the single sequence was identical to the structure of the integrated sequence of task-mapping combinations. These results suggest that implicit task sequence learning is not dependent on either perceptual learning of stimulus features or automatic task-set activation per se. Rather, it appears to be driven by correlated streams of information.     

How do speakers resist distraction? Evidence from a taboo picture-word interference task

Even in the presence of irrelevant stimuli, word production is a highly accurate and fluent process. But how do speakers prevent themselves from naming the wrong things? One possibility is that an attentional system inhibits task-irrelevant representations. Alternatively, a verbal self-monitoring system might check speech for accuracy and remove errors stemming from irrelevant information. Because self-monitoring is sensitive to social appropriateness, taboo errors should be intercepted more than neutral errors are. To prevent embarrassment, speakers might also speak more slowly when confronted with taboo distractors. Our results from two experiments are consistent with the self-monitoring account: Examining picture-naming speed (Experiment 1) and accuracy (Experiment 2), we found fewer naming errors but longer picture-naming latencies for pictures presented with taboo distractors than for pictures presented with neutral distractors. These results suggest that when intrusions of irrelevant words are highly undesirable, speakers do not simply inhibit these words: Rather, the language-production system adjusts itself to the context and filters out the undesirable words.     

The effect of corpus size in predicting reaction time in a basic word recognition task: Moving on from Kučera and Francis

Word frequency is one of the strongest determiners of reaction time (RT) in word recognition tasks; it is an important theoretical and methodological variable. The Ku?era and Francis (1967) word frequency count (derived from the 1-million-word Brown corpus) is used by most investigators concerned with the issue of word frequency. Word frequency estimates from the Brown corpus were compared with those from a 131-million-word corpus (the HAL corpus; conversational text gathered from Usenet) in a standard word naming task with 32 subjects. RT was predicted equally well by both corpora for high-frequency words, but the larger corpus provided better predictors for low- and medium-frequency words. Furthermore, the larger corpus provides estimates for 97,261 lexical items; the smaller corpus, for 50,406 items.