Size matters, but not for everyone:Individual differences for contrast discrimination

It is very well known that contrast detection thresholds improve with the size of a grating-type stimulus, but it is thought that the benefit of size is abolished for contrast discriminations well above threshold (e.g., Legge, G. E., & Foley, J. M. (1980)]. Here we challenge the generality of this view. We performed contrast detection and contrast discrimination for circular patches of sine wave grating as a function of stimulus size. We confirm that sensitivity improves with approximately the fourth-root of stimulus area at detection threshold (a log-log slope of -0.25) but find individual differences (IDs) for the suprathreshold discrimination task. For several observers, performance was largely unaffected by area, but for others performance first improved (by as much as a log-log slope of -0.5) and then reached a plateau. We replicated these different results several times on the same observers. All of these results were described in the context of a recent gain control model of area summation [Meese, T. S. (2004)], extended to accommodate the multiple stimulus sizes used here. In this model, (i) excitation increased with the fourth-root of stimulus area for all observers, and (ii) IDs in the discrimination data were described by IDs in the relation between suppression and area. This means that empirical summation in the contrast discrimination task can be attributed to growth in suppression with stimulus size that does not keep pace with the growth in excitation. © 2005 ARVO.

British racial discourse: a study of political discourse about race and race-related matters at parliamentary and borough council levels

'British Racial Discourse' is a study of political discourse about race and race-related matters. The explanatory theory is adapted from current sociological studies of ideology with a heavy emphasis on the tradition developed from Marx and Engels's Feuerbach. The empirical data is drawn from the parliamentary debates on immigration and the Race Relations Bills, Conservative and Labour Party Conference Reports, and a set of interviews with Wolverhampton Borough councillors. Although the thesis has broader significance for British political discourse about race, it is particularly concerned with the responses of members of the two main political parties, rather than with the more overt and sensational racism of certain extreme Right-wing groups. Indeed, as the study progresses, it focuses more and more narrowly on the phenomenon of 'deracialised' discourse, and the details of the predominantly class-based justificatory systems of the Conservative and Labour Parties. Of particular interest are the argument forms (used in the debates on immigration and race relations) which manage to obscure the white electorate's responsibility for prejudice and discrimination. Such discoursive forms are of major significance for understanding British race relations, and their detailed examination provides an insight into the way in which 'ideological facades' are created and maintained.