No abstract

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.

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.

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 investigatedwhether 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 alternativewas 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.

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 ofthe preceding prime following briefpreexposure 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.