Schizotypy and Perceptual Learning: Aberrant Salience or Disrupted Inhibition?

Schizophrenia is a complex, heterogenous diagnostic category characterised by hallucinations, the possession of unusual beliefs and disorganised cognitions and behaviours. Symptoms vary on a continuum throughout the population and the extent to which one displays traits can be examined with measures of 'schizotypy'. Latent inhibition (LI) refers to the phenomenon that prior exposure to a conditioned stimulus (CS) in the absence of an unconditioned stimulus (US) impairs subsequent learning about the relationship between the CS and US, compared to a CS that has not been pre-exposed. Contemporary models of learning suggest that attention to the CS declines during pre-exposure, as participants learn that the stimulus does not signal a significant event. LI is disrupted in individuals with a diagnosis of schizophrenia and is inversely related to schizotypal traits. Lubow (2005) suggested that LI serves to direct attention towards relevant stimuli and away from irrelevant stimuli. These studies indicate that individuals with high schizotypy allocate attention less efficiently, maintaining greater attention towards irrelevant stimuli. It has been postulated that hallucinations occur consequential to the aberrant assignment of salience to internal stimuli and that delusions arise when one attempts to understand these experiences.
Whilst these theories provide a comprehensive account of the positive symptoms of schizophrenia, they neglect the negative symptoms. However, Kapur's (2005) theory can be extended to account for depressive symptomology (DS), a common negative symptom. Seminal research indicated that the perceived absence of the ability to modulate environmental contingencies entails a causal role in depression; one can conceptualise this as an association between an environmental outcome (US) and one's actions (CS). Crucially, the context in which this occurs also develops an association with the US, such that the CS-US relationship is in competition with the context-US relationship for behavioural control. As contextual information is redundant, its salience should decline. However, if non-predictive stimuli acquire greater salience in individuals with high schizotypy, the context's salience will remain higher for longer. As salience is central to learning, the context-US association will be relatively stronger and the CS-US association will be relatively weaker in individuals with high schizotypy, culminating in DS.
'Perceptual learning' refers to the phenomenon that pre-exposure to stimuli aids subsequent discrimination between the stimuli. McLaren et al (1989) explained this by suggesting that stimuli comprise a number of elements, composed of those that are unique to each stimulus and those that are common to both stimuli. Pre-exposure to both stimuli (e.g. CS-A and CS-B) results in relatively greater LI of the common elements than the unique elements. Accordingly, learning about CS-A generalises less readily to CS-B, facilitating discrimination. Moreover, the unique elements of CS-A become conditioned inhibitors of the unique elements of CS-B. The authors suggested that the common elements become independently associated with the unique elements of both stimuli, due to concurrent presentation. Therefore, presentation of CS-A in the absence of the unique elements of CS-B manifests a prediction error, resulting in conditioned inhibition of the unique elements. Despite evidence that perceptual learning is dependent upon both LI and conditioned inhibition, phenomena which are disrupted in individuals with high schizotypy, it remains to be examined whether perceptual learning is abnormal in individuals with high schizotypy. This research will examine the influence of schizotypy on perceptual learning and elucidate whether any abnormality is attributable to disrupted LI and/or disrupted inhibitory associations. Moreover, this study aims to elucidate whether DS is related to either LI or the development of inhibitory associa