In fact it has been found that voice-hearers with schizophrenia diagnosis have a higher perceptual sensitivity to speech stimuli than individuals with schizophrenia diagnosis but without AVHs (Vercammen, de Haan, & Aleman, 2008). In this study, voice-hearers in a task, where they had to indicate if they heard a certain word that was presented in background noise so that it was hardly perceptible but still audible, indicated more often to have heard this word. Both groups with schizophrenia diagnosis in this study, however, showed lower perceptual sensitivity than healthy participants. Moreover, voice-hearers tended to state more often with a high degree of confidence that they had heard a certain word in the noise, when this specific word was not presented in the noise, which was interpreted as a positive response
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bias or liberal acceptance of the presence of a stimulus (Vercammen et al., 2008). The authors propose that their results might be accounted for by an attentional bias in speech perception.
In that vein, it has been proposed that an imbalance between ―bottom-up‖ and ―top- down‖ factors in the sense of a prevalence of ―top-down‖ factors, such as perceptual expectations, leads to a reduction of influences from ―bottom-up‖ sensory information and consequently may trigger voice-hearing perceptual experiences, in which no one is speaking (Daalman, Verkooijen, Derks, Aleman, & Sommer, 2012). However, the authors found evidence for the influence of ―top-down‖ semantic expectations only in healthy voice-hearers, but not in voice-hearers with schizophrenia diagnosis. As compared to healthy controls, non- clinical voice-hearers indicated more often to have heard a (due to a sentence‘s context) predictable word, where an unpredictable word was presented or no word was presented at all in the sentence. That was not the case for voice-hearers with schizophrenia diagnosis who did not differ from either of the groups in terms of such ―top-down‖ errors. Thus, this study indicated that abnormal ―top-down‖ processing might play a role in voice-hearing in non- psychotic but not in psychotic individuals and there might be different cognitive mechanisms underlying voice-hearing in psychotic and nonpsychotic individuals (Daalman et al., 2012).
Using a different methodology, others have also proposed that ―top-down‖ factors play a critical role in AVHs (Moritz & Larøi, 2008). By means of an online survey they compared sensory (e.g., loudness) and cognitive (e.g., control) features of thoughts, intrusions and voices. Interestingly, they found that only a minority of (self-reported) schizophrenia patients experience their voices as being as loud as external voices. Additionally, they report various similarities between reported sensory and cognitive features of thoughts, intrusions and voices. The authors therefore conclude that AVHs are unlikely a ―pure‖ disorder of input or ―bottom-up‖ processes (e.g., auditory cortex hyperactivity), although voice-hearers in their study reported more vividness and loudness also of intrusions and ―normal‖ thoughts, which, they propose, might contribute to the vulnerability for AVHs. Moritz and Larøi (2008) propose that ―top-down‖ processes including ―false metacognitive beliefs about the controllability of thoughts, liberal acceptance, gain from illness and self-serving biases‖ (p.105) contribute to the experience of voices. Thus, voice-hearers may, in varying combinations, not take their thoughts as controllable, and more readily attribute internal events to external agents. To accept that their experience stems from an external agent, the authors hypothesise, might be a more appealing choice for a voice-hearer than to conclude to ―suffer[…] from voice-hearing‖ (p.104).
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Table 5
Overview over the reviewed studies regarding “top-down”/“bottom-up” factors in voice-hearing.
Authors (year) Participants Type of study Main results
Vercammen et
al. (2008) N = 15 schizophrenia patients with AVHs N = 15 schizophrenia patients without AVHs N = 17 healthy subjects (DSM-IV) Behavioural (speech discrimination task)
- lower perceptual sensitivity in schizophrenia patients as a whole
- patients with AVHs (vs. without AVHs) indicated more often to have heard a word in background noise - patients with AVHs tended to state more often with a high degree of confidence that they had heard a certain word in the noise, when this specific word was not presented in the noise
Daalman et al.
(2012) N = 40 psychotic patients with AVHs (most on antipsychotic medication) N = 40 non-psychotic individuals with AVHs (one on antipsychotic medication) N = 40 healthy subjects. (of patients: 62.5% paranoid schizophrenia, 15%
schizoaffective disorder 22.5% with psychosis not otherwise specified)
Behavioural
(semantic expectation task)
- evidence the influence of ―top-down‖ semantic expectations only in healthy voice-hearers - compared to healthy controls, non-clinical voice- hearers indicated more often to have heard a (due to a sentence‘s context) predictable word, where an unpredictable one or no word was presented
Moritz and Larøi (2008)
N = 45 subjects with schizophrenia diagnosis, N = 55 subjects with obsessive– compulsive disorder diagnosis N = 60 healthy subjects
Online survey (comparison of sensory & cognitive features of thoughts, intrusions & voices)
- minority of schizophrenia patients report their voices as being as loud as external voices
- various similarities between reported sensory and cognitive features of thoughts, intrusions and voices - individuals with AVHs reported more vividness and loudness of intrusions and ―normal‖ thoughts
Although the proposed ―bottom-up‖-―top-down‖ models go beyond conceptions of AVHs as a ―brain-disease‖ by including processes on a phenomenal level, such as delusional beliefs, they are unsatisfactory regarding several points.
It is, for example, to be questioned if there is an ―auditory signal‖ on an experiential level that is first shaped and filled with content and attributed to someone else. We might argue that this is not the case, as the experience of a ―voice‖ can rather be assumed to be immediate and not a ―raw‖ auditory signal that is shaped until becoming a voice.
One may argue that the misattribution process occurs on a subpersonal, unconscious level, and only when the sound is misattributed it is experienced as an ―alien‖ voice, but this explanation would bring with it other problems: on a subpersonal level, we will not find any
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subject that could misattribute a ―signal‖. There arguably is no homunculus in a voice- hearer‘s brain that interprets auditory signals and decides if they are self-generated or not.
Also, why a voice‘s content is emotional for a specific voice-hearer can arguably not be explained in terms of amygdala activity, but only by taking into account his/her life events and the meaning he/she ascribes to them.
Likewise, we might ask: where does this postulated hyper-activation of the auditory cortex come from? And if it is spontaneous, why are voice-experiences not random?