Visual Signal Detection Measured by Event-Related Potentials

Signal Detection tasks typically involve within-subject signal changes. Such a procedure does not lend itself to event-related potential (ERP) experiments where the need for averaging necessitates the maintenance of consistent stimulus parameters. In the present ERP study we adopt a novel approach to thresholding that allows within-subject signal manipulation. The Signal Detection task required the identification of letter targets, formed from dots, in a random dot field. ERP waveforms were segmented into three windows corresponding to N1, N2, and P300 components. Analysis shows that ERP variations are dependent on both task demands and response characteristics for N1, N2, and P300 components.     

Psychocultural Interpretations and Dramas: Identity Dynamics in Ethnic Conflict

Ethnic identity connects individuals through perceived common past experiences and expectations of shared future ones. Identity is concerned with group judgments and judgments about groups and their motives. This article explores identity through the case of Loyal Order Protestant parades in Northern Ireland and the concepts of psychocultural interpretations (shared, deeply held worldviews found in group narratives) and psychocultural dramas (conflicts over competing, and apparently irresolvable, claims that engage the central elements of a group's historical experience). Psychocultural dramas are polarizing events whose manifest content involves non-negotiable cultural claims, threats, and/or rights that become important because of their connections to core metaphors and group narratives that embody a group's identity. In ethnic conflicts, psychocultural dramas arise over competing claims that evoke deeply rooted dimensions of the conflict which cannot be settled by reference to more general rules or higher authority. Psychocultural dramas are tools of analysis for understanding the centrality of cultural identity and ritual in ethnic conflict and for the redefinition of such conflicts in ways that increase the chances for managing them constructively. Examining the psychocultural dramas surrounding parades disputes in Northern Ireland suggests why and how some conflicts are more amenable to constructive outcomes than others.     

Concept learning and feature interpretation

Models of categorization often assume that people classify new instances directly on the basis of the presented, observable features. Recent research, however, has suggested that the coherence of a category may depend in part on more abstract features that can link together observable features that might otherwise seem to have little similarity. Thus, category learning may also involve the determination of the appropriate abstract features that underlie a category and link together the observable features. We show in four experiments that observable features of a category member are often interpreted as congruent with abstract features that are suggested by observable features of other highly available category members. Our discussion focuses on the implications of these findings for future research.     

Cleomedes (c. 1st century AD) on the celestial illusion, atmospheric enlargement, and size-distance invariance

Cleomedes (Kleomedes) is a little-known Greek author (c. 1st century AD) who produced what is probably the earliest extant statement of size-distance invariance. He supported the Stoic philosophy and was concerned to discredit the Epicurean position that we perceive objects as having their true size. He explained the celestial illusion (the apparent enlargement of the sun near the horizon) in two ways: partly as a refractive effect of the atmosphere similar to angular enlargement when looking into water; and partly as a linear enlargement due to increased apparent distance in a misty atmosphere. He is the earliest extant author to offer apparent distance as a clear explanation of the celestial illusion. He attributed these views to Posidonius (c. 135-50 BC). His explanations remained at the geometrical level, and he did not speculate on sensory mechanisms.     

Mean performance and the factor analysis of learning data

The difference in factor structure resulting from the factorization of correlations, covariances, and cross products is discussed. Factoring cross products has the advantage of retaining information on both means and variances; this method of factoring learning data is recommended. The conditions under which factoring covariances and cross products lead to the same essential structure are investigated.