Schizophrenia Research Trends

Latent Inhibition and Learned Irrelevance Paradigms … 145take place in one and the same individual, i.e. a within-subject study design is applied. TheUS consists of the target which commands the subjects to respond. As the dependent variablethe time to find the target, i.e. the response time (RT) is measured.In another new visual LI paradigm (61;62) subjects are preexposed to a coloredrectangular field that contains six small windows (preexposed “PE-CS”). In the conditioningphase, one of the windows is shaded by a black square which changes its position every trial.The subjects are instructed to try to predict the position of the square (US) by pressing one ofsix keys which represent the six windows. One specific position is indicated by a field stainedwith the preexposed color, while another distinct position is predicted by a field of a differentcolor (non-preexposed “NPE-CS”). The remaining four positions are not predicted at all andthe black square appears on a blank background. The dependent variables are the CR and thetime to predict the black square’s position (RT) in the trials with colored (PE and NPE)backgrounds.Response time as the dependent variableIt is unique that these visual LI paradigms measure the response time (RT) as thedependent variable and not the conditioned response as instrumental learning to criterionparadigms. The conditioned responses (number of correct responses) are measured as well,but they do not indicate a LI effect (61;62). This is thought to be because the associations ofthe multiple CS and the US are much harder to learn than those in the instrumental learningtasks, e.g. in the paradigm of Ginton et al. (23). In the visual LI paradigms the subjects onlyscarcely learn the rule underlying the task and, therefore, do not reach the criterion of aspecific number of consecutive correct responses. However, it is debatable whether this newgeneration of paradigms takes us away from those used in animal LI studies. They mightmake it more difficult to compare and contrast the results obtained with physiological andpharmacological manipulations across species (21).The masking taskHuman LI paradigms can be divided into two groups: paradigms that require a maskingtask (MT) to produce a LI effect and paradigms that do not. While CTA and Pavlovianconditioning of autonomic responses can obtain a LI effect without an additional task,instrumental learning to criterion as well as eyeblink conditioning and visual LI paradigmsneed masking (17;58).A MT is a simple task administered to all subjects in the preexposure phase or in both thepreexposure and the conditioning phase. In the frequently replicated paradigm of Ginton etal. (23), the MT involves a recording of a list of nonsense syllables which is played severaltimes to PE as well as NPE subjects during preexposure and conditioning. In the preexposurephase, subjects are instructed to pick one specific syllable and to count how many times it isrepeated. For the PE group, the noise bursts (CS) are interspersed with the syllables, while