Electrophysiological correlates of encoding processes in a full-report visual working memory paradigm

Why are some visual stimuli remembered, whereas others are forgotten? A limitation of recognition paradigms is that they measure aggregate behavioral performance and/or neural responses to all stimuli presented in a visual working memory (VWM) array. To address this limitation, we paired an electroencephalography (EEG) frequency-tagging technique with two full-report VWM paradigms. This permitted the tracking of individual stimuli as well as the aggregate response. We recorded high-density EEG (256 channel) while participants viewed four shape stimuli, each flickering at a different frequency. At retrieval, participants either recalled the location of all stimuli in any order (simultaneous full report) or were cued to report the item in a particular location over multiple screen displays (sequential full report). The individual frequency tag amplitudes evoked for correctly recalled items were significantly larger than the amplitudes of subsequently forgotten stimuli, regardless of retrieval task. An induced-power analysis examined the aggregate neural correlates of VWM encoding as a function of items correctly recalled. We found increased induced power across a large number of electrodes in the theta, alpha, and beta frequency bands when more items were successfully recalled. This effect was more robust for sequential full report, suggesting that retrieval demands can influence encoding processes. These data are consistent with a model in which encoding-related resources are directed to a subset of items, rather than a model in which resources are allocated evenly across the array. These data extend previous work using recognition paradigms and stress the importance of encoding in determining later VWM retrieval success.     

The bar-cross-ellipse illusion: alternating percepts of rigid and nonrigid motion based on contour ownership and trackable feature assignment

We present a new multistable stimulus generated by continuously rotating an ellipse behind four fixed occluders. Despite the stimulus remaining constant, observers can alternate between one of four percepts: (1) a continuously morphing cross; (2) two independent perpendicular bars oscillating in depth; (3) a rigidly rotating ellipse observed behind the occluders; (4) a fixed cross observed through a continuously rotating, elliptical aperture. Interestingly, the initial percept naive observers tend to see is percept 1, which is the only nonrigid motion percept. This appears to be a violation of the hypothesized 'rigidity heuristic' in which rigid motion percepts tend to be perceived over retinally equivalent nonrigid ones. Here, we describe the relationships between each of the percepts and the assignment of contour ownership and figure/ground segmentation.     

The concept of validity

This article advances a simple conception of test validity: A test is valid for measuring an attribute if (a) the attribute exists and (b) variations in the attribute causally produce variation in the measurement outcomes. This conception is shown to diverge from current validity theory in several respects. In particular, the emphasis in the proposed conception is on ontology, reference, and causality, whereas current validity theory focuses on epistemology, meaning, and correlation. It is argued that the proposed conception is not only simpler but also theoretically superior to the position taken in the existing literature. Further, it has clear theoretical and practical implications for validation research. Most important, validation research must not be directed at the relation between the measured attribute and other attributes but at the processes that convey the effect of the measured attribute on the test scores.     

Surprises: low probabilities or high contrasts?

Outcome expectations can be expressed prospectively in terms of probability estimates, and retrospectively in terms of surprise. Surprise ratings and probability estimates differ, however, in some important ways. Surprises are generally created by low-probability outcomes, yet, as shown by several experiments, not all low-probability outcomes are equally surprising. To account for surprise, we propose a contrast hypothesis according to which the level of surprise associated with an outcome is mainly determined by the extent to which it contrasts with the default, expected alternative. Three ways by which contrasts can be established are explored: contrasts due to relative probabilities, where the obtained outcome is less likely than a default alternative; contrasts formed by novelty and change, where a contrast exists between the obtained outcome and the individual's previous experience; and contrasts due to the perceptual or conceptual distance between the expected and the obtained. In all these cases, greater contrast was accompanied by higher ratings of surprise.     

What is constructive empiricism?

An earlier (and much funnier) version of this paper was presented as Constructive Empiricism and Everyday Life at a conference on laws of nature at the University of Michigan in April, 1990. I am grateful to Bas van Fraassen for his generous response at the conference, and also to Paul Benacerraf, Lisa Eckstrom, Sally Haslanger, Jim Joyce, Peter Railton, Larry Sklar, Jamie Tappenden, Paul Thomson and Steve Yablo for comments, conversations, etc.     

Suicide and self-inflicted injuries

The present study addressed itself to the problem of self-inflicted injuries (SII) in the Israeli army, and to the wider question whether non-fatal self injuries and suicide are part of the same phenomenon. The findings show that in some cases SII is an unsucessful suicide while in others SII is anything but a reflection of a death wish. It appears that the modus operandi is a major indication as to the intentions of the actor. The study also demonstrates the difference between the population of the suiciders and that of the SII victims. While suiciders seem to score higher on the Performance Prediction Score (PPS) and Combat Suitability Scale, the SII population seems to be overly represented in the lower parts of the PPS and the Combat Suitability Scale. The study used a data set that represents a 5 year period, and followed the consequences of the SII in terms of medical status and occupational assignment of the actors. The findings yielded some possible policy implications, in terms of a better classification of the relevant populations, and a possible attribution of a more refined meaning to the behavior. © 1994 Wiley-Liss, Inc.     

Selective pressures on the once and future contents of ethnic stereotypes: effects of the communicability of traits

It is hypothesized that traits that are most likely to be the subject of social discourse (i.e., most communicable) are most likely to persist in ethnic stereotypes over time and that this effect is moderated by the extent to which an ethnic group is the subject of social discourse. Study 1 yielded communicability ratings of 76 traits. Study 2 tested the relation between a trait's communicability and its presence in stereotypes of 4 Canadian ethnic groups. Study 3 tested the relation between a trait's communicability and its persistence over time in stereotypes of 8 American ethnic groups. Results supported the hypotheses. A communication-based analysis of stereotypes appears helpful in predicting persistence and change in the contents of stereotypes of real groups in the real world.     

Framing, intentions, and trust–choice incompatibility

The present paper examines how framing of messages and the intentions inferred from different—positive vs. negative—framings, interact with the development of trust. Empirical evidence is presented showing that different, logically equivalent, frames are supposedly interpreted as implying different intentions. Next, the relationship between different frames (and the corresponding intentions reflected from these frames) and trust are explored. Finally, and most important, the relationship between the assessment of trust, inferred from different frames, and the corresponding choice behavior resulting from these frames, are investigated. Specifically, consider agents A and B offering to sell exactly the same commodity, except that one agent formulates it in a positive and the other in a negative frame. The different frames may lead to different assessments of the trustworthiness of the two agents. Following common wisdom, if agent A is trusted more than B, then one should prefer to conduct transactions with the former rather than with the latter agent. Several experiments are presented that are incompatible with this conjecture. For example, when faced with a choice between two butchers, whose ground beef is advertised as containing 25% fat (negative frame) or 75% lean (positive frame), respectively, most people have more trust in the former yet most indicate they would buy their meat from the latter butcher. This phenomenon, in which negative framing weighs more in trust assessments, and positive framing weighs more in choice, is labeled trust–choice incompatibility. The robustness of the phenomenon is further demonstrated in several experiments, and possible explanations for its occurrence are discussed.