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.

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.

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.

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

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.

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, 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.

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.

Adaptation effects and reversible figures: a comment on Horlitz and O'Leary

Horlitz and O'Leary have provided further evidence for the important role of such top-down processes as attention and familiarity on reported reversals of ambiguous figures. As such, these results are consistent with the claims of several other investigators who have argued that any theory of phenomenal reversal that is based solely on passive neural processes is likely to be incomplete. However, Horlitz and O'Leary make the additional claims (1) that the several reports of adaptation effects in the literature are readily reinterpreted within an information-access framework and (2) that their own empirical work demonstrates a basic failure of neural-adaptation effects with reversible figures. It is proposed here that these claims must be viewed with caution. First, Horlitz and O'Leary's explanation for the discrepancy of their results from those of ostensibly similar experimental procedures in the reversible-figure literature is not the only, or the most likely, possibility. A plausible alternative model that posits critical procedural differences (specifically, duration of adaptation) across studies has been offered, and supporting empirical work for this latter suggestion has been presented. Second, the empirical efforts of Horlitz and O'Leary, while providing further evidence for top-down processes, do not eliminate the likely role of adaptation effects with reversible figures. There is strong reason to believe that the viewing conditions selected by these researchers may not have been sufficient to produce appreciable adaptation. Moreover, there is excellent reason to believe that both bottom-up and top-down processes moderate reported reversals of these figures.(ABSTRACT TRUNCATED AT 250 WORDS)

A new twist on the rotating-trapezoid illusion: evidence for neural-adaptation effects

In a series of experiments, the selective-adaptation paradigm was applied to the rotating-trapezoid illusion in an effort to demonstrate neural-adaptation effects in the figural reversal of this classic illusion. Prior to viewing the standard trapezoid, the observer adapted to a rectangle rotating unambiguously in the same direction as the trapezoid or in the opposite direction. In accordance with the neural hypothesis, illusion strength was greatest when the two figures rotated in the same direction and weakest when the two figures rotated in opposite directions. Results were confirmed with two separate dependent variables: the observer's 'first look' at the illusion after adaptation and the observer's reversal rate during a test period. These findings were discussed in terms of (a) the basic similarity of results for the rotating trapezoid and reversible figures such as the Necker cube and (b) the need for a multiprocess model of both classes of illusions which emphasizes bottom-up and top-down processes.

Prime time: fatigue and set effects in the perception of reversible figures

Subjects viewed unambiguous versions of both stationary and rotating Necker cube illusions for varying durations prior to the presentation of the standard ambiguous figure. In each case, the subjects were more likely to report the ambiguous figure to be (1) in the same configuration as that of the preceding prime following brief preexposure periods and (2) in the opposite configuration from that of the preceding prime following long preexposure periods. In addition, the number of reversals of the figure during the test period was also strongly related to the duration of the preexposure period, with progressively fewer reversals reported following longer preexposure periods. The results are interpreted as revealing the concurrent roles of "set" effects in the brief preexposure conditions and neural fatigue effects in the long preexposure conditions. Furthermore, the ability of the proposed two-process model to integrate the myriad of empirical effects in the reversible-figure literature is emphasized.

The spacing effect in young children's free recall: support for automatic-process explanations

The effect of spacing repetitions on children's free recall was investigated in two experiments. In Experiment 1, both 4-year-old children and 7-year-old children exhibited a spacing effect in free recall, and the magnitude of the effect did not change with age. In Experiment 2, free recall was examined as a function of spacing, age (3 years old vs. 4 years old) and presentation rate (1 vs. 2 vs. 5 sec per stimulus). A spacing effect was obtained that did not differ as a function of age or presentation rate. Of particular interest was the fact that 3-year-olds exhibited a strong spacing effect even when stimuli were presented at a very rapid 1-sec rate. The results support the hypothesis that fundamental memory mechanisms that operate relatively automatically are sufficient to produce a spacing effect in free recall.

The effect of spacing repetitions on the recognition memory of young children and adults

In Experiment 1, preschoolers, first graders, and third graders were presented a list of pictures that included twice-presented items separated by varying numbers of intervening items. Performance on a subsequent recognition test improved as the spacing between repetitions increased, but the effect of spacing did not interact reliably with grade level. In Experiment 2a, we replicated the spaced-repetition effect in young children and found a similar effect in college students. In Experiment 2b, we varied the conditions under which lists were presented to college students and again found a spacing function that was comparable to that of very young children. The results are consistent with the hypothesis that spaced-repetition effects in recognition are produced by fundamental memory mechanisms that are operational at a very early age and which undergo little change with development.

The lag effect and differential organization theory: Nine failures to replicate

In our first experiment, we tried to replicate and extend previous results that had provided seemingly convincing support for a differential organization explanation of the monotonically increasing lag effect in free recall. However, we failed to obtain the lag effect. Eight additional experiments also failed to replicate the lag effect. In all, we made 918 observations of performance on items repeated at each of three lags, and the mean percentage of correct free recall varied by less than one percentage point. These results suggest that there are boundary conditions limiting the generality of the monotonically increasing lag effect in free recall. In addition, caution should be exercised in accepting certain previous findings as strong evidence for a differential organization explanation of the phenomenon.

The lag effect and differential organization theory: nine failures to replicate

In our first experiment, we tried to replicate and extend previous results that had provided seemingly convincing support for a differential organization explanation of the monotonically increasing lag effect in free recall. However, we failed to obtain the lag effect. Eight additional experiments also failed to replicate the lag effect. In all, we made 918 observations of performance on items repeated at each of three lags, and the mean percentage of correct free recall varied by less than one percentage point. These results suggest that there are boundary conditions limiting the generality of the monotonically increasing lag effect in free recall. In addition, caution should be exercised in accepting certain previous findings as strong evidence for a differential organization explanation of the phenomenon.

Multiple representations of the same reversible figure: implications for cognitive decisional interpretations

Observations are reported with the side-by-side presentation of rotating Necker cubes and other well-known reversible (ambiguous) figures. The fact that the two representations can be seen in the opposite direction of rotation, or perspective, at the same time is regarded as a serious difficulty for the cognitive or decisional interpretations of the spontaneous alternations in these figures. It is suggested that separate and fatiguable cortical 'channels' are a more likely basis for the dual-presentation effect than multiple decisional or attentional processes. The relationship between this proposal and recent research consistent with the visual system as a multichannel processor is noted.