Reversible-figure perception: Why is voluntary control limited?

Observers can voluntarily avoid reversals of an ambiguous, reversible figure, extending the duration of an intended percept. This is usually attributed to high-level, top-down attentional processes. However, voluntary control is limited. Reversals occur despite attempts to avoid them. In two experiments, observers demonstrated significant, but limited, voluntary control over Necker cube perception. Cube size and cube completeness, variables associated with stimulus-driven processes involving neural adaptation, influenced the frequency of reversals regardless of observers' intentions. Results are consistent with the hybrid hypothesis that both top-down and bottom-up processes contribute to Necker-cube perception and support the hypothesis that the contribution of bottom-up processes is responsible for the limitation on voluntary control.

Why do learners ignore expected feedback in making metacognitive decisions about retrieval practice?

We report two experiments investigating why learners, in making metacognitive judgments, often seem to ignore or otherwise fail to appreciate that feedback following retrieval practice provides a restudy opportunity. Learners practiced word pairs for a final cued-recall test by studying each pair initially, making a judgment of learning (JOL), and then deciding whether to practice the pair again after a short or long spacing interval, or not at all. For different groups in Experiment 1, additional practice involved restudying, retrieval practice without feedback, or retrieval practice with feedback (the full pair). We used procedures (long feedback duration and covert retrieval practice) designed to rule out the possibility that feedback is ignored because it is usually brief or because participants' choices are influenced by a desire to look good by performing well on overt practice tests. In the relearning condition, learners preferred a long spacing interval for items at all JOL levels. Despite the feedback duration and the covert retrieval practice, learners in both retrieval-practice conditions preferred a short spacing interval for hard, low-JOL items and a long spacing interval for easy, high-JOL items, even though this may not be an effective strategy when feedback is provided. In Experiment 2, instructions framed feedback either as a presentation of the correct answer or as a restudy opportunity preceded by retrieval practice. Framing feedback as a restudy opportunity markedly changed the choices learners made. Apparently, the restudy function of feedback does not occur to learners unless they are specifically alerted to it.

Metacognitive control over the distribution of retrieval practice with and without feedback and the efficacy of learners' spacing choices.

In two experiments on self-regulated learning, participants studied word pairs, made judgments of learning (JOLs), and decided whether to continue practicing after a long or short spacing interval prior to a final cued-recall test. When practice involved restudying, learners preferred a long spacing interval. However, when retrieval practice was involved, learners preferred a short spacing interval for items with low and medium JOLs and a long interval for high-JOL items, regardless of whether retrieval practice was followed by feedback or not. Taking retrieval practice after a short rather than a long spacing interval was efficacious when no feedback followed practice tests, leading to superior recall. Given that retrieval practice was successful, a long spacing interval led to better recall than a short one, but learners were insufficiently accurate in determining which items should be given a long spacing interval for this strategy to be effective. Presenting feedback after retrieval practice did not alter learners' spacing strategy, and the frequent selection of short spacing intervals impaired subsequent recall.

Level of initial training moderates the effects of distributing practice over multiple days with expanding, contracting, and uniform schedules: Evidence for study-phase retrieval.

Inconsistent results have been obtained in experiments comparing the effects on retention of expanding, contracting, and uniform practice schedules, in which the spacing between successive practice sessions progressively increases, progressively decreases, or remains constant, respectively. In the present study, we experimentally assessed an apparent trend in the literature for expanding schedules to be more advantageous than other schedules following a low level of training during the initial learning session, but not following a high level of initial training. College students studied pseudocword-word pairs in multiple practice sessions distributed over a 13-day period according to expanding, contracting, and uniform schedules. During their initial learning session, participants received either low-level training (two study trials) or high-level training (one study trial and then five rounds of practice testing with corrective feedback). All participants were treated identically in the subsequent practice sessions. A final cued-recall test after a two-week retention interval revealed an expanding-schedule superiority following low-level initial training but not following high-level initial training. These results are interpreted in terms of a study-phase-retrieval mechanism and help explain the mixed results obtained in the prior literature.

Metacognitive control in self-regulated learning: Conditions affecting the choice of restudying versus retrieval practice.

In two experiments, learners studied word pairs one or two times and took a final cued recall test. They studied each pair upon its initial presentation and decided whether they would restudy it later, take a practice test on it later (retrieval practice), or forego all further practice with the pair. Whether learners preferred restudying or testing depended upon conditions. Regardless of whether practice tests were followed by feedback, they chose to take practice tests relatively more often when items were easy and the lag or spacing interval between the first and second occurrence was short, whereas they chose to restudy relatively more when items were hard and the lag was long. That is, they preferred testing under conditions in which successful retrieval on the practice test was likely. In Experiment 2, we varied the number of points each item was worth if recalled on the final test. A high point value led to a marked increase in both the preference for testing when the lag was short and the preference for restudying when the lag was long. Results support the hypothesis that learners appreciate at some level that retrieval practice can be a more effective learning strategy than restudying. However, they appear to believe that successful retrieval is necessary to reap the benefits of retrieval practice. As a consequence, their tendency to choose testing is influenced by conditions (item difficulty and spacing interval) that affect the likelihood of successful practice-test retrieval.

Relearn Faster and Retain Longer.

Both repeated practice and sleep improve long-term retention of information. The assumed common mechanism underlying these effects is memory reactivation, either on-line and effortful or off-line and effortless. In the study reported here, we investigated whether sleep-dependent memory consolidation could help to save practice time during relearning. During two sessions occurring 12 hr apart, 40 participants practiced foreign vocabulary until they reached a perfect level of performance. Half of them learned in the morning and relearned in the evening of a single day. The other half learned in the evening of one day, slept, and then relearned in the morning of the next day. Their retention was assessed 1 week later and 6 months later. We found that interleaving sleep between learning sessions not only reduced the amount of practice needed by half but also ensured much better long-term retention. Sleeping after learning is definitely a good strategy, but sleeping between two learning sessions is a better strategy.

Time for a change: what dominance durations reveal about adaptation effects in the perception of a bi-stable reversible figure.

The effect of adaptation on the perception of a reversible figure was examined in the context of the so-called "reverse-bias effect" in which prolonged exposure to an unambiguous version of a bi-stable ambiguous stimulus serves to bias an observer to report the alternative version of the subsequently viewed ambiguous stimulus. Exposure to the unambiguous stimulus presumably selectively adapts and weakens the neural structures underlying that particular interpretation of the ambiguous figure. We extended previous research by examining the dominance durations for the two alternatives of the reversible figure (i.e., how long each alternative was perceived when it was dominant) in addition to the measures of response rate and choice preference used by other researchers. We replicated earlier findings with the previously used measures. Interestingly, adaptation with an unambiguous version of the ambiguous stimulus produced an asymmetrical effect on the dominance durations of the subsequently presented ambiguous stimulus, relative to a no-adaptation control. The dominance durations were lengthened for the perceptual organization that was the opposite of the adaptation stimulus while they were relatively unaffected for the perceptual organization that was the same as the adaptation stimulus. Our findings are consistent with the argument that adaptation effects play an important role in perceptual bistability. The asymmetrical dominance-duration findings further suggest that adaptation operates in a perceptual system in which the alternative perceptual representations of an ambiguous figure reciprocally inhibit one another via cross-inhibitory processes, consistent with views developed in other forms of bistable perception (e.g., binocular rivalry).

Optimising retention through multiple study opportunities over days: The benefit of an expanding schedule of repetitions.

Few studies have investigated how scheduling repeated studies of the same material over several days influences its subsequent retention. The study-phase retrieval hypothesis predicts that, under these circumstances, expanding intervals between repetitions will promote the greatest likelihood that the participant will be reminded of previous occurrences of the item, thus leading to a benefit for subsequent recall. In the present article, participants studied vocabulary pairs that were repeated according to one of three schedules. In the expanding schedule, pairs were presented on days 1, 2 and 13; in the uniform schedule, on days 1, 7 and 13; and in the contracting schedule, on days 1, 12 and 13. Cued-recall was assessed after a retention interval (RI) of 2, 6 or 13 days. Consistent with predictions, the expanding schedule generally led to better performance than the other schedules. However, further analyses suggested that the benefit of an expanding schedule may be greater when the RI is longer.

Contribution of degraded perception and insufficient encoding to decisions to mass or space study.

How do learners decide whether to mass or space an item during study? Results from Son (2004) indicate that these decisions are influenced by the degree to which an item is judged to be encoded sufficiently during an initial study episode, whereas others (Toppino, Cohen, Davis, & Moors, 2009) have proposed that degraded perceptual processing contributed to participants' decisions to mass or space study. To reconcile these conflicting conclusions, the current experiments used eye tracking technology to evaluate the contribution of degraded perception and insufficient encoding on learners' study decisions. Participants studied synonym pairs from the graduate record exam (GRE) that varied in item difficulty for 1 s (Experiment 1) or 5 s (Experiment 2) each while their eye movements were recorded. Participants then decided whether to mass, space, or drop each pair in future study. For pairs that were never fixated, and hence not perceived, participants overwhelmingly chose to mass their study, presumably so that they could read the target. For pairs that were processed sufficiently to be perceived, preference for massing and spacing pairs increased with item difficulty (i.e., both increased as pairs became less likely to be fully encoded). Taken together, these data demonstrate a contribution of degraded perception and insufficient encoding for learners' decisions to mass (or space) their study.

A deeper analysis of the spacing effect after "deep" encoding.

The most common encoding strategies used by participants in word list studies include rehearsal and using the story mnemonic. Previous studies have suggested that with a rote-rehearsal strategy, mixed lists lead people to borrow rehearsal time from massed items and to give it to spaced items. Using rehearse-aloud methodologies, we demonstrated in Experiment 1 that the borrowing effect does not occur in the story mnemonic. However, the rates of rehearsal of individual items provided a good prediction of their subsequent recall rates, with spaced items being rehearsed more often in both mixed and pure lists. In experiment 2, we demonstrated that creating "story links" between items enhanced recall, but it did not affect the magnitude of the spacing effect. These results suggest that a massed-item deficit in encoding may underlie the spacing effect in the story mnemonic.

Metacognitive control and spaced practice: clarifying what people do and why.

What do learners do when they control whether to engage in massed or spaced practice? According to theories by Son (2004) and by Metcalfe and Kornell (2005), the tendency for learners to choose spaced practice over massed practice should decline as item difficulty becomes greater. Support originally was obtained when pairs containing unfamiliar words were presented briefly for study, but subsequent research has suggested that, under these conditions, learners had difficulty initially encoding the members of the to-be-learned pairs. In Experiments 1 and 2, we failed to support the previously mentioned prediction in conditions in which the difficulty of learning was not correlated with the difficulty of initially encoding the pair members. Learners' relative preference for spaced practice increased, rather than decreased, with greater item difficulty, consistent with either a discrepancy-reduction-like account or an agenda-based-regulation account. In Experiment 3, we independently varied item difficulty and the point value that items were worth on the final test. Learners' relative preference for spaced practice was greater for high- than for low-value items but was unaffected by item difficulty. These results are more consistent with an agenda-based-regulation account than with a discrepancy-reduction account. More generally, learners' choices appear to be strategic and to reflect theory-based decisions, suggesting some level of appreciation for the relative benefits of massed versus spaced practice.

Metacognitive control over the distribution of practice: when is spacing preferred?

The authors clarify the source of a conflict between previous findings related to metacognitive control over the distribution of practice. In a study by L. Son (2004), learners were initially presented pairs of Graduate Record Examination (GRE) vocabulary words and their common synonyms for 1 s, after which they chose to study the pair again immediately (massed practice), later (spaced practice), or not at all (done). Learners chose spaced practice less as pair difficulty increased. A. S. Benjamin and R. D. Bird (2006), using different materials and procedures and a longer presentation duration (5 s), concluded just the opposite. The authors adopted Son's materials and procedures and replicated her findings with a 1-s stimulus duration. However, the declining choice of spacing as item difficulty increased largely reflected learners' failure to fully perceive items with brief presentations. With longer presentations, ensuring full perception, the choice of spaced practice increased with greater pair difficulty, in agreement with Benjamin and Bird. Theoretical implications are discussed in the context of discrepancy-reduction and proximal-learning perspectives.

The testing effect and the retention interval: questions and answers.

People learn from tests. Providing tests often enhances retention more than additional study opportunities, but is this testing effect mediated by processes related to retrieval that are fundamentally different from study processes? Some previous studies have reported that testing enhances retention relative to additional studying, but only after a relatively long retention interval. To the extent that this interaction with retention interval dissociates the effects of studying and testing, it may provide crucial evidence for different underlying processes. However, these findings can be questioned because of methodological differences between the study and the test conditions. In two experiments, we eliminated or minimized the confounds that rendered the previous findings equivocal and still obtained the critical interaction. Our results strengthen the evidence for the involvement of different processes underlying the effects of studying and testing, and support the hypothesis that the testing effect is grounded in retrieval-related processes.

The spacing effect in intentional and incidental free recall by children and adults: Limits on the automaticity hypothesis.

Preschoolers, elementary school children, and college students exhibited a spacing effect in the free recall of pictures when learning was intentional. When learning was incidental and a shallow processing task requiring little semantic processing was used during list presentation, young adults still exhibited a spacing effect, but children consistently failed to do so. Children, however, did manifest a spacing effect in incidental learning when an elaborate semantic processing task was used. These results limit the hypothesis that the spacing effect in free recall occurs automatically and constrain theoretical accounts of why the spacing between repetitions affects recall performance.

Articulatory suppression and the irrelevant-speech effect in short-term memory: does the locus of suppression matter?

Immediate serial recall for letter sequences was impaired when irrelevant speech (IS) was presented throughout stimulus input and a subsequent rehearsal interval. This irrelevant-speech effect was eliminated when participants engaged in articulatory suppression (repeated articulation of one or more digits) during stimulus input but not when suppression occurred during the postinput rehearsal period. Also, changing-state suppression (articulation of multiple items) impaired the overall level of performance more than did steady-state suppression (repetition of a single item), whereas both forms of suppression had the same influence on the IS effect. Our results suggest that the locus of suppression (during or after stimulus input) may have contributed to discrepant findings in the prior literature regarding the influence of articulatory suppression on the IS effect. We consider the implications of our findings for three prominent models of immediate memory: the working memory model, the object-oriented episodic record model, and the feature model.

Enduring interest in perceptual ambiguity: alternating views of reversible figures.

Research favoring the so-called bottom-up and top-down classes of explanations for reversible figures that dominated the literature in last half of the 20th century is reviewed. Two conclusions are offered. First, any single-process model is extremely unlikely to be able to accommodate the wide array of empirical findings, suggesting that the "final" explanation will almost certainly involve a hybrid conceptualization of interacting sensory and cognitive processes. Second, the utility of distinguishing between 2 components of the observer's experience with reversible figures is emphasized. This distinction between the observer's ability to access multiple representations from the single stimulus pattern (ambiguity) and the observer's phenomenal experience of oscillation between those representations (reversibility) permits the literature to be segregated into useful categories of research that expose overlapping but distinctive cortical processes.

Reversible-figure perception: mechanisms of intentional control.

Observers can exert a degree of intentional control over the perception of reversible figures. Also, the portion of the stimulus that is selected for primary or enhanced processing (focal-feature processing) influences how observers perceive a reversible figure. Two experiments investigated whether voluntary control over perception of a Necker cube could be explained in terms of intentionally selecting appropriate focal features within the stimulus for primary processing. In Experiment 1, varying observers' intentions and the focus of primary processing produced additive effects on the percentage of time that one alternative was perceived. In Experiment 2, the effect of varying the focus of primary processing was eliminated by the use of a small cube, but the effect of intention was unaltered. The results indicate that intentional control over perception can be exerted independently of focal-feature processing, perhaps by top-down activation or priming of perceptual representations. The results also reveal the limits of intentional control.

The spacing effect in the free recall of homogeneous lists: present and accounted for.

Memory performance nearly always improves as a function of the spacing between repetitions. However, previous studies indicated that college students exhibited no spacing effect in the free recall of lists composed exclusively of words sampled from a single semantic category. We explored this puzzling phenomenon in two experiments. We found that the spacing effect in free recall can occur with homogeneous lists. Most interestingly, the effect seems to depend on the number of items (lag) separating spaced repetitions. Short lags between spaced repetitions yield a spacing effect, whereas longer lags do not.

The spacing effect, free recall, and two-process theory: a closer look.

Two experiments used procedures similar to those used by R. L. Greene (1989) to test the 2-process theory of the spacing effect and, in particular, the contextual-variability subtheory that applies to free-recall performance. Experiment 1 obtained a spacing effect in free recall following intentional learning but not following incidental learning, contrary to a previous result supporting the 2-process theory. Experiment 2 replicated the incidental-learning results when a slow presentation rate was used. However, with a faster presentation rate, a spacing effect was obtained, and performance exceeded that of the slow-presentation-rate condition at the longest lag. Neither the contextual-variability subtheory of 2-process theory nor an alternative deficient-processing hypothesis was able to account for all of the data.