Latent inhibition and psychometrically defined schizotypy: An experimental investigation

The thesis adopted a personality-based approach to experimental psychopathology testing alternative interpretations of latent inhibition deficits as a function of psychotic-like features in non-clinical participants. Chapter 1 reviews the evidence on the continuity of psychotic-like experiences, describes the historical origins of dimensional views of psychosis, and discusses methodological advantages and pitfalls in schizotypy research. Chapter 2 reviews different sources of evidence on a link between disruption of latent inhibition and the schizophrenia continuum, as well different theories of latent inhibition, and discusses methodological issues in terms of the existing latent inhibition paradigms. The review suggests that the interpretation of the disruption of latent inhibition within the schizophrenia continuum remains elusive due to a number of methodological and theoretical problems. In Chapter 3, a preliminary evaluation of self-report psychotic-like experiences was examined in terms of the capacity of different psychometric scales to predict perceptual and decision biases, akin to those observed in schizophrenia, when searching for fast moving words. Additionally, this chapter examined whether various schizotypy traits were associated with the ability to identify fast moving words, prior to the development of this paradigm as a latent inhibition procedure (Experiments 1 & 2). In Chapter 4, a novel latent inhibition paradigm was introduced. Visual search of fast moving words was examined as a function of target preexposure, amount of pre-exposure, and schizotypy (STA), without the target/ distractor reversal employed in most past investigations of latent inhibition in humans, and without including a masking task (Experiment 3 & 4). Latent inhibition was found to be relatively disrupted in high-schizotypy scores, but intact in their low-schizotypy counterparts. In Chapter 5, latent inhibition was examined in relation to schizotypy after procedural changes were introduced to address possible confounds in the previous experiments. In addition, in effort to evaluate attentional accounts, performance after stimulus preexposure was examined under individual testing (Experiment 5) and group testing (Experiment 6) conditions. In Chapter 6, in order to evaluate context effects on latent inhibition, and test predictions derived from opposing accounts, latent inhibition was assessed in high- and low-schizotypy scorers within a stable context (Experiment 7), and after a context change (Experiment 8). In Chapter 7, in order to evaluate whether the latent inhibition deficits are due to enhanced stimulus salience (related to a putative heightened perceptual awareness in high-schizotypy scorers), participants were conjointly tested in terms of latent inhibition and their ability to discriminate between different levels of stimulus salience, as assessed by a visual pop-out task (Experiments 9 & 10). In Chapter 8, a compound-stimulus discrimination paradigm was developed (Experiment 11), in order to test target/distractor shift-learning in different schizotypy dimensions (Experiment 12). In Chapter 9, a theoretical integration of the findings is proposed. The data obtained are discussed in terms of a two-component (attentional + associative) model of latent inhibition deficits