Schizophrenia Research Trends

Latent Inhibition and Learned Irrelevance Paradigms … 151As it is characteristic for a within-subject LI paradigm, this LIrr task also involves twodifferent kinds of CSs, preexposed CSs (PE-CS) and non-preexposed CSs (NPE-CS).General descriptionThe paradigm involves a visual target detecting task in which the subject is instructed topress a key on the computer keyboard as soon as the target, the letter X, appears on thescreen. In addition to the target, there are 10 different characters constituting the test. Thesenon-target characters are divided in two groups, NPE and PE, containing five capital Latinletters each. In the studies of Orosz et al. the five vowels (A, E, I, O and U) are assigned to bethe NPE letters, while a selection of five consonants (B, D, T, Y and Z) form the PE charactergroup (101; 102).All characters are yellow and are presented on a blue background which covers the entirecomputer screen (Fig. 2). The letters are all of the same size and are positioned in the centerof the screen. Each letter persists for one second and changes directly without anyinterstimulus interval to the subsequent characters. A test session consists of 450 letters,hence the test duration is 450 seconds which is equal to 7.5 minutes.Composition of a test sessionThere are 75 targets in a test session which are presented according to the schedules ofthree different conditions. These are preexposed (PE), non-preexposed (NPE) and random(R). The three conditions, in turn, are segmented in five blocks each. Thus, there is a total of15 blocks in a test session. Regardless of the condition, all blocks contain 30 characters: fivetargets, 5 CSs, and 20 filler letters. Depending on the condition, the CS letters consist ofcharacters from either the NPE or the PE group and they are always presented immediatelybefore the target. Because of their specific role they are also called target predictor letters orcues. Filler letters consist of characters of the PE group shown in a pseudorandom order.They serve to “fill” the intertrial intervals between the CS-target contingencies. On average,there are four filler letters between a target and the next CS, whereas the range is betweenone and eight. Filler letters never predict the target.While the target and the filler letters always involve the same characters, the predictorletters (CSs) are different across the three conditions (Fig. 3):NPEIn the NPE condition, letters of the NPE group (A, E, I, O and U) serve as CSs. In a NPEblock the target is preceded five times by the same NPE-CS, e.g. five times by A. Each letteris used only in one block as target predictor in a test session. Consequently, the five differentletters of the NPE group are distributed to the five NPE blocks. Note that NPE letters appearonly as target predictors in the NPE blocks and are not presented elsewhere in the test.