Abstract
Cognitive models have suggested that auditory hallucinations occur when internal mental events, such as inner speech or auditory verbal imagery (AVI), are misattributed to an external source. This has been supported by numerous studies indicating that individuals who experience hallucinations tend to perform in a biased manner on tasks that require them to distinguish self-generated from non-self-generated perceptions. However, these tasks have typically been of limited relevance to inner speech models of hallucinations, because they have not manipulated the AVI that participants used during the task. Here, a new paradigm was employed to investigate the interaction between imagery and perception, in which a healthy, non-clinical sample of participants were instructed to use AVI whilst completing an auditory signal detection task. It was hypothesized that AVI-usage would cause participants to perform in a biased manner, therefore falsely detecting more voices in bursts of noise. In Experiment 1, when cued to generate AVI, highly hallucination-prone participants showed a lower response bias than when performing a standard signal detection task, being more willing to report the presence of a voice in the noise. Participants not prone to hallucinations performed no differently between the two conditions. In Experiment 2, participants were not specifically instructed to use AVI, but retrospectively reported how often they engaged in AVI during the task. Highly hallucination-prone participants who retrospectively reported using imagery showed a lower response bias than did participants with lower proneness who also reported using AVI. Results are discussed in relation to prominent inner speech models of hallucinations.
Highlights
The first key finding from Experiment 1 was that when participants were instructed to use auditory verbal imagery (AVI) during a signal detection task, there was a significant drop in response bias
The interaction between task condition and hallucination-proneness indicated that the effect of AVI on response bias was specific to participants who scored highly on self-reported hallucination-proneness, whilst there was no difference between the imagery conditions in participants who reported few hallucinatory experiences
That is, when participants prone to hallucinations generate mental imagery, they are more likely to respond ‘present’, regardless of whether the stimulus was present or not. This is consistent with models that suggest AVHs may occur when inner speech is misattributed to an external source, which may link to excessively vivid mental imagery, low levels of cognitive effort, and/or aberrant predictive processes (Brookwell et al, 2013; Ford & Mathalon, 2005)
Summary
The most prominent cognitive model of AVHs suggests that they occur when an internal mental event (such as inner speech or auditory verbal imagery – AVI) is misattributed to an external source (Ditman & Kuperberg, 2005; Frith, 1992; Jones & Fernyhough, 2007b). This strand of research has been embedded in the source monitoring framework, which attempts to explain how we make judgements regarding the origin of information (i.e., its source; Johnson, Hashtroudi, & Lindsay, 1993).
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