The minimum contrast requirements for stereopsis.

A number of researchers have compared the contrast requirements for stereopsis with those for detection of the stereoscopic stimulus, but they have generally failed to allow for the fact that stereopsis requires a detectable stimulus in both eyes at the same time. It is argued that the most appropriate detection threshold for this comparison is that for simultaneous monocular detection (SMD) of the stereoscopic half images. Experiments in which this comparison threshold has been used are summarised and the hypothesis generated that, on using stimuli that are localised in both space and spatial frequency (e.g. Gabor patches or differences of Gaussians), a range of disparities can always be found over which contrast thresholds for depth identification are less than or equal to this SMD threshold (the SMD hypothesis). It is argued that the success of this hypothesis in describing data obtained with these stimuli is consistent with the notions of labelled lines for disparity sign and the size--disparity correlation. Last, experiments are reported in which contrast thresholds for stereoscopic depth identification (front/back) were measured with interocular differences in contrast. The data obtained are consistent with the presence of both inhibitory and excitatory interactions between the eyes when unequal monocular contrasts are presented. The implications of these results and the SMD hypothesis for theories of stereopsis and binocular function are discussed.     

Tailored interventions for motivating smoking cessation: using placebo tailoring to examine the influence of expectancies and personalization.

The present study examined mechanisms underlying the effectiveness of tailored interventions for motivating smoking cessation. The study used a placebo-tailoring design to test whether the efficacy of tailoring was due, in part, to personalized features in addition to the theoretically based content. Two hundred forty adult smokers were randomized to 1 of 3 conditions: standard booklet, minimally personalized booklet, or extensively personalized booklet. The interventions varied in their degree of ostensible tailoring, yet the actual smoking-related content of the booklets was identical. A dose-response relationship was hypothesized, with the greatest apparent tailoring producing the most positive outcomes. This pattern was found for evaluation of the booklets, with trends for readiness to change and self-efficacy increases. Moreover, as hypothesized, the effect of the interventions on readiness was moderated by participants' expectancies about tailoring.