Modulation of affective face processing deficits in Schizophrenia by congruent emotional sounds

Schizophrenia is a psychiatric disorder resulting in prominent impairments in social functioning. Thus, clinical research has focused on underlying deficits of emotion processing and their linkage to specific symptoms and neurobiological dysfunctions. Although there is substantial research investigating impairments in unimodal affect recognition, studies in schizophrenia exploring crossmodal emotion processing are rare. Therefore, event-related potentials were measured in 15 patients with schizophrenia and 15 healthy controls while rating the expression of happy, fearful and neutral faces and concurrently being distracted by emotional or neutral sounds. Compared with controls, patients with schizophrenia revealed significantly decreased P1 and increased P2 amplitudes in response to all faces, independent of emotion or concurrent sound. Analyzing these effects with regard to audiovisual (in)congruence revealed that P1 amplitudes in patients were only reduced in response to emotionally incongruent stimulus pairs, whereas similar amplitudes between groups could be observed for congruent conditions. Correlation analyses revealed a significant negative correlation between general symptom severity (Brief Psychiatric Rating Scale-V4) and P1 amplitudes in response to congruent audiovisual stimulus pairs. These results indicate that early visual processing deficits in schizophrenia are apparent during emotion processing but, depending on symptom severity, these deficits can be restored by presenting concurrent emotionally congruent sounds.

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title: Crossmodal binding of fear in voice and face
abstract: In social environments, multiple sensory channels are simultaneously engaged in the service of communication. In this experiment, we were concerned with defining the neuronal mechanisms for a perceptual bias in processing simultaneously presented emotional voices and faces. Specifically, we were interested in how bimodal presentation of a fearful voice facilitates recognition of fearful facial expression. By using event-related functional MRI, that crossed sensory modality (visual or auditory) with emotional expression (fearful or happy), we show that perceptual facilitation during face fear processing is expressed through modulation of neuronal responses in the amygdala and the fusiform cortex. These data suggest that the amygdala is important for emotional crossmodal sensory convergence with the associated perceptual bias during fear processing, being mediated by task-related modulation of face-processing regions of fusiform cortex.

title: Audiovisual integration of emotional signals in voice and face: An event-related fMRI study
abstract: In a natural environment, non-verbal emotional communication is multimodal (i.e. speech melody, facial expression) and multifaceted concerning the variety of expressed emotions. Understanding these communicative signals and integrating them into a common percept is paramount to successful social behaviour. While many previous studies have focused on the neurobiology of emotional communication in the auditory or visual modality alone, far less is known about multimodal integration of auditory and visual non-verbal emotional information. The present study investigated this process using event-related fMRI. Behavioural data revealed that audiovisual presentation of non-verbal emotional information resulted in a significant increase in correctly classified stimuli when compared with visual and auditory stimulation. This behavioural gain was paralleled by enhanced activation in bilateral posterior superior temporal gyrus (pSTG) and right thalamus, when contrasting audiovisual to auditory and visual conditions. Further, a characteristic of these brain regions, substantiating their role in the emotional integration process, is a linear relationship between the gain in classification accuracy and the strength of the BOLD response during the bimodal condition. Additionally, enhanced effective connectivity between audiovisual integration areas and associative auditory and visual cortices was observed during audiovisual stimulation, offering further insight into the neural process accomplishing multimodal integration. Finally, we were able to document an enhanced sensitivity of the putative integration sites to stimuli with emotional non-verbal content as compared to neutral stimuli.

title: Audio-visual integration of emotion expression
abstract: Regardless of the fact that emotions are usually recognized by combining facial and vocal expressions, the multisensory nature of affect perception has scarcely been investigated. In the present study, we show results of three experiments on multisensory perception of emotions using newly validated sets of dynamic visual and non-linguistic vocal clips of affect expressions. In Experiment 1, participants were required to categorize fear and disgust expressions displayed auditorily, visually, or using congruent or incongruent audio-visual stimuli. Results showed faster and more accurate categorisation in the bimodal congruent situation than in the unimodal conditions. In the incongruent situation, participant preferentially categorized the affective expression based on the visual modality, demonstrating a visual dominance in emotional processing. However, when the reliability of the visual stimuli was diminished, participants categorized incongruent bimodal stimuli preferentially via the auditory modality. These results demonstrate that visual dominance in affect perception does not occur in a rigid manner, but follows flexible situation-dependent rules. In Experiment 2, we requested the participants to pay attention to only one sensory modality at a time in order to test the putative mandatory nature of multisensory affective interactions. We observed that even if they were asked to ignore concurrent sensory information, the irrelevant information significantly affected the processing of the target. This observation was especially true when the target modality was less reliable. Altogether, these findings indicate that the perception of emotion expressions is a robust multisensory situation which follows rules that have been previously observed in other perceptual domains.

title: The time‐course of intermodal binding between seeing and hearing affective information
abstract: Intermodal binding between affective information that is seen as well as heard triggers a mandatory process of audiovisual integration. In order to track the time course of this audiovisual binding, event related brain potentials were recorded while subjects saw facial expression and concurrently heard auditory fragment. The results suggest that the combination of the two inputs is early in time (110 ms post-stimulus) and translates as a specific enhancement in amplitude of the auditory N1 component. These findings are compatible with previous functional neuroimaging results of audiovisual speech showing strong audiovisual interactions in auditory cortex in the form of magnetic response amplifications, as well as with electrophysiological studies demonstrating early audiovisual interactions (before 200 ms post-stimulus). Moreover, our results show that the informational content present in the two modalities plays a crucial role in triggering the intermodal binding process.

title: Facial expressions modulate the time course of long latency auditory brain potentials.
abstract: Long latency auditory brain potentials were recorded while subjects listened to bi-syllabic words spoken with an emotional expression and concurrently viewed congruent or incongruent facial expressions. Analysis of the auditory waveforms suggests the existence of a positive deflection around 240 ms post-stimulus with a clear posterior topography (the P2b component). This potential is subsequent upon the modality-specific auditory N1-P2 components and precedes the amodal N2-P3 complex. Congruent face-voice trials elicited an earlier P2b component than incongruent trials suggesting that auditory processing is delayed in the presence of an incongruent facial context. These electrophysiological results are consistent with previous behavioural studies showing an acceleration of reaction times for rating voice expressions that are part of congruent bimodal stimulus pairs. A source localisation analysis performed on the scalp EEG during the time-window corresponding to the P2b component disclosed a single dipole solution in the anterior cingulate cortex.

title: Perception of facial and vocal affect by people with schizophrenia in early and late stages of illness
abstract: Emotion recognition impairments have been demonstrated in schizophrenia, but few studies have examined whether these reflect generalised or specific perceptual deficits or are associated with illness course.  To examine the nature of emotion recognition abnormalities in patients with schizophrenia at different stages of illness.  We examined the performance of 50 in-patients with early-stage schizophrenia, 50 with chronic schizophrenia and 50 healthy controls on the Benton Facial Recognition Test, Facial Emotion Recognition Test and Voice Emotion Recognition Test.  Patients with chronic schizophrenia were significantly more impaired than other groups on the emotional tasks, even after controlling for impairments in non-emotional stimuli. Individual emotion recognition accuracy for the two sensory modalities was not significantly positively correlated for either group with schizophrenia.  Emotion recognition deficits in schizophrenia are trait features of the disorder and increase with illness duration.

title: Facial emotion recognition in schizophrenia:When and why does it go awry?
abstract: Schizophrenia patients demonstrate impaired emotional processing that may be due, in part, to impaired facial emotion recognition. This study examined event-related potential (ERP) responses to emotional faces in schizophrenia patients and controls to determine when, in the temporal processing stream, patient abnormalities occur.



16 patients and 16 healthy control participants performed a facial emotion recognition task. Very sad, somewhat sad, neutral, somewhat happy, and very happy faces were each presented for 100 ms. Subjects indicated whether each face was "Happy", "Neutral", or "Sad". Evoked potential data were obtained using a 32-channel EEG system.



Controls performed better than patients in recognizing facial emotions. In patients, better recognition of happy faces correlated with less severe negative symptoms. Four ERP components corresponding to the P100, N170, N250, and P300 were identified. Group differences were noted for the N170 "face processing" component that underlies the structural encoding of facial features, but not for the subsequent N250 "affect modulation" component. Higher amplitude of the N170 response to sad faces was correlated with less severe delusional symptoms. Although P300 abnormalities were found, the variance of this component was explained by the earlier N170 response.



Patients with schizophrenia demonstrate abnormalities in early visual encoding of facial features that precedes the ERP response typically associated with facial affect recognition. This suggests that affect recognition deficits, at least for happy and sad discrimination, are secondary to faulty structural encoding of faces. The association of abnormal face encoding with delusions may denote the physiological basis for clinical misidentification syndromes.

title: The influence of emotion clarity on emotional prosody identification in paranoid schizophrenia
abstract: Identification of emotional facial expression and emotional prosody (i.e. speech melody) is often impaired in schizophrenia. For facial emotion identification, a recent study suggested that the relative deficit in schizophrenia is enhanced when the presented emotion is easier to recognize. It is unclear whether this effect is specific to face processing or part of a more general emotion recognition deficit.  We used clarity-graded emotional prosodic stimuli without semantic content, and tested 25 in-patients with paranoid schizophrenia, 25 healthy control participants and 25 depressive in-patients on emotional prosody identification. Facial expression identification was used as a control task.  Patients with paranoid schizophrenia performed worse than both control groups in identifying emotional prosody, with no specific deficit in any individual emotion category. This deficit was present in high-clarity but not in low-clarity stimuli. Performance in facial control tasks was also impaired, with identification of emotional facial expression being a better predictor of emotional prosody identification than illness-related factors. Of those, negative symptoms emerged as the best predictor for emotional prosody identification.  This study suggests a general deficit in identifying high-clarity emotional cues. This finding is in line with the hypothesis that schizophrenia is characterized by high noise in internal representations and by increased fluctuations in cerebral networks.

title: Facial emotion perception in schizophrenia: a meta-analytic review.
abstract: A considerable body of literature has reported on emotion perception deficits and the relevance to clinical symptoms and social functioning in schizophrenia. Studies published between 1970-2007 were examined regarding emotion perception abilities between patient and control groups and potential methodological, demographic, and clinical moderators.  Eighty-six studies were identified through a computerized literature search of the MEDLINE, PsychINFO, and PubMed databases. A quality of reporting of meta-analysis standard was followed in the extraction of relevant studies and data. Data on emotion perception, methodology, demographic and clinical characteristics, and antipsychotic medication status were compiled and analyzed using Comprehensive Meta-analysis Version 2.0 (Borenstein M, Hedges L, Higgins J and Rothstein H. Comprehensive Meta-analysis. 2. Englewood, NJ: Biostat; 2005).



The meta-analysis revealed a large deficit in emotion perception in schizophrenia, irrespective of task type, and several factors that moderated the observed impairment. Illness-related factors included current hospitalization and--in part--clinical symptoms and antipsychotic treatment. Demographic factors included patient age and gender in controls but not race.



Emotion perception impairment in schizophrenia represents a robust finding in schizophrenia that appears to be moderated by certain clinical and demographic factors. Future directions for research on emotion perception are discussed.

title: Impaired perception of affective prosody in schizophrenia.
abstract: The authors aimed to explore schizophrenia patients' ability to perceive affective prosody. Specifically, certain emotions that may be more troublesome for patients and possible gender differences in prosody perception were assessed. Thirty six schizophrenia patients and 32 age-, education-, and gender-matched healthy comparison subjects assessed on an affective prosody test were examined. Patients were impaired on recognition of affective prosody overall, and their difficulties with prosody perception may be attributed to those emotions with negative valence, specifically anger and sadness. Findings revealed that only male patients were impaired on prosody perception. Deficits in the perception of affective prosody were principally evident in emotions with negative valence and male patients with schizophrenia. Future studies should explore the influence of these deficits on social and interpersonal functioning more directly.

title: Getting the cue: sensory contributions to auditory emotion recognition impairments in schizophrenia.
abstract: Individuals with schizophrenia show reliable deficits in the ability to recognize emotions from vocal expressions. Here, we examined emotion recognition ability in 23 schizophrenia patients relative to 17 healthy controls using a stimulus battery with well-characterized acoustic features. We further evaluated performance deficits relative to ancillary assessments of underlying pitch perception abilities. As predicted, patients showed reduced emotion recognition ability across a range of emotions, which correlated with impaired basic tone matching abilities. Emotion identification deficits were strongly related to pitch-based acoustic cues such as mean and variability of fundamental frequency. Whereas healthy subjects' performance varied as a function of the relative presence or absence of these cues, with higher cue levels leading to enhanced performance, schizophrenia patients showed significantly less variation in performance as a function of cue level. In contrast to pitch-based cues, both groups showed equivalent variation in performance as a function of intensity-based cues. Finally, patients were less able than controls to differentiate between expressions with high and low emotion intensity, and this deficit was also correlated with impaired tone matching ability. Both emotion identification and intensity rating deficits were unrelated to valence of intended emotions. Deficits in both auditory emotion identification and more basic perceptual abilities correlated with impaired functional outcome. Overall, these findings support the concept that auditory emotion identification deficits in schizophrenia reflect, at least in part, a relative inability to process critical acoustic characteristics of prosodic stimuli and that such deficits contribute to poor global outcome.

title: Dysfunction of early-stage visual processing in schizophrenia.
abstract: Schizophrenia is associated with deficits in higher-order processing of visual information. This study evaluated the integrity of early visual processing in order to evaluate the overall pattern of visual dysfunction in schizophrenia.



Steady-state visual-evoked potential responses were recorded over the occipital cortex in patients with schizophrenia and in age- and sex-matched comparison volunteers. Visual-evoked potentials were obtained for stimuli composed of isolated squares that were modulated sinusoidally in luminance contrast, number of squares, or chromatic contrast in order to emphasize magnocellular or parvocellular visual pathway activity.



Responses of patients to magnocellular-biased stimuli were significantly lower than those of comparison volunteers. These lower response levels were observed in conditions using both low luminance contrast and large squares that biased processing toward the magnocellular pathway. In contrast, responses to stimuli that biased processing toward the parvocellular pathway were not significantly different between schizophrenia patients and comparison volunteers. A significant interaction of group and stimulus type was observed in the condition using low luminance contrast.



These findings suggest a dysfunction of lower-level visual pathways, which was more prominent for magnocellular than parvocellular biased stimuli. The magnocellular pathway helps in orienting toward salient stimuli. A magnocellular pathway deficit could contribute to higher-level visual cognitive deficits in schizophrenia.

title: Impaired visual object recognition and dorsal/ventral stream interaction in schizophrenia.
abstract: Schizophrenia is associated with well-documented deficits in high-order cognitive processes such as attention and executive functioning. The integrity of sensory-level processing, however, has been evaluated only to a limited degree. Our study evaluated the ability of patients with schizophrenia to recognize complete objects based on fragmentary information, a process termed perceptual closure. Perceptual closure processes are indexed by closure negativity (N(cl)), a recently defined event-related potential (ERP) component that is generated within the visual association cortex. This study assessed the neural integrity of perceptual closure processes in schizophrenia by examining N(cl) generation. Generation of the preceding positive (P1) and negative (N1) ERP components was also examined.



We evaluated 16 patients with chronic schizophrenia and 16 healthy comparison subjects. Successively less fragmented images were presented during high-density ERP recording, which permitted the monitoring of brain activity during perceptual closure processes prior to object recognition. Analyses were performed at parieto-occipital and occipitotemporal sites consistent with dorsal and ventral stream generators of P1, N1, and N(cl).



Patients with schizophrenia showed significant impairment in the ability to recognize fragmented objects, along with impaired generation of N(cl). The amplitude of visual P1 was significantly reduced, particularly over dorsal stream sites. In contrast, the generation of visual N1 was intact.



Patients with schizophrenia are profoundly impaired in perceptual closure as indicated by both impaired performance and impaired N(cl) generation. The selective impairment in dorsal stream P1 is consistent with prior reports of impaired magnocellular processing in schizophrenia. By contrast, intact ventral N1 generation suggests that the initial stages of ventral stream processing are relatively preserved and that impaired magnocellular dorsal stream functioning in schizophrenia may lead to secondary dysregulation of ventral stream object recognition processing.

title: Early-stage face processing dysfunction in patients with schizophrenia.
abstract: Deficits in emotional processing are evident in patients with schizophrenia. Since recent studies have indicated dysfunctions in cortical areas involved in face processing, this study investigated the early processing of faces in schizophrenia patients through the use of event-related potentials.



Event-related potential responses were obtained from 24 schizophrenia patients and 28 healthy comparison subjects who were presented with pictures of faces and pictures of buildings (control stimuli).



Schizophrenia patients displayed significantly lower differences in the face-specific N170 component between the face and building pictures than did the healthy comparison subjects.



This finding suggests a dysfunction of early-stage visual processing of faces in patients with schizophrenia.

title: Functional MRI of facial emotion recognition deficits in schizophrenia and their electrophysiological correlates
abstract: Empirical evidence suggests impaired facial emotion recognition in schizophrenia. However, the nature of this deficit is the subject of ongoing research. The current study tested the hypothesis that a generalized deficit at an early stage of face‐specific processing (i.e. putatively subserved by the fusiform gyrus) accounts for impaired facial emotion recognition in schizophrenia as opposed to the Negative Emotion‐specific Deficit Model, which suggests impaired facial information processing at subsequent stages. Event‐related potentials (ERPs) were recorded from 11 schizophrenia patients and 15 matched controls while performing a gender discrimination and a facial emotion recognition task. Significant reduction of the face‐specific vertex positive potential (VPP) at a peak latency of 165 ms was confirmed in schizophrenia subjects whereas their early visual processing, as indexed by P1, was found to be intact. Attenuated VPP was found to correlate with subsequent P3 amplitude reduction and to predict accuracy when performing a facial emotion discrimination task. A subset of ten schizophrenia patients and ten matched healthy control subjects also performed similar tasks in the magnetic resonance imaging scanner. Patients showed reduced blood oxygenation level‐dependent (BOLD) activation in the fusiform, inferior frontal, middle temporal and middle occipital gyrus as well as in the amygdala. Correlation analyses revealed that VPP and the subsequent P3a ERP components predict fusiform gyrus BOLD activation. These results suggest that problems in facial affect recognition in schizophrenia may represent flow‐on effects of a generalized deficit in early visual processing.

title: Early visual components (P100, N170) are disrupted in chronic schizophrenic patients: an event-related potentials study
abstract: On the basis of the Positive and Negative Syndrome Scale (PANSS), fourteen schizophrenic patients and 7 normal controls were confronted with pictures from the Ekman & Friesen series in an event-related potentials study.


PROCEDURE
Participants were confronted with a visual face-detection task, in which they had to detect, as quickly as possible, deviant faces amongst a train of standard stimuli (neutral faces). Deviant faces changed either on identity (different identity, neutral expression), or on emotion (same identity, happy, fearful or sad expression).



Schizophrenics exhibited a decrease in amplitude of the face N170, recorded around 170 ms at occipito-temporal sites; this was observed as well for emotional as for identity faces, which suggests a global involvement of face processing. Moreover, this decrease of the face-N170 was positively correlated to positive, but not negative, symptoms of schizophrenia. Finally, the amplitude of P100 was also decreased, which suggests that the N170 decrement would result from a more global deficit in visual processing deficit.



It is suggested that, in schizophrenics, an involvement of early visual processing might underlie the decreased amplitudes and the higher onset latencies of later P300 and N400 components.

title: The effects of familiarity and emotional expression on face processing examined by ERPs in patients with schizophrenia
abstract: The main objective of the study was to determine whether patients with schizophrenia are deficient relative to controls in the processing of faces at different levels of familiarity and types of emotion and the stage where such differences may occur.



ERPs based on 18 patients with schizophrenia and 18 controls were compared in a face identification task at three levels of familiarity (unknown, familiar, subject's own) and for three types of emotion (disgust, smiling, neutral).



The schizophrenic group was less accurate than controls in the face processing, especially for unknown faces and those expressing negative emotions such as disgust. P1 and N170 amplitudes were lower and P1, N170, P250 amplitudes were of slower onset in patients with schizophrenia. N170 and P250 amplitudes were modulated by familiarity and face expression in a different manner in patients than controls.



Schizophrenia is associated with a genelarized defect of face processing, both in terms of familiarity and emotional expression, attributable to deficient processing at sensory (P1) and perceptual (N170) stages. These patients appear to have difficulty in encoding the structure of a face and thereby do not evaluate correctly familiarity and emotion.

title: Attenuated Modulation of the N170 ERP by Facial Expressions in Schizophrenia
abstract: In psychiatrically-well subjects the modulation of event related potentials (ERPs) by emotional facial expressions is found in several ERPs from −100 ms and later. A face-related EPR, the N170, is abnormally reduced in schizophrenia to faces relative to other complex objects and research suggests emotional modulation of N170 may be reduced as well. To further examine facial emotion modulation of N170, subjects detected neutral facial expressions from among five emotional expressions (happy, sad, fearful, angry, and disgusted). Over occipitotemporal sites, psychiatrically-well subjects showed bilateral differences in N170 amplitude among expressions (P=0.014). Schizophrenia subjects failed to show this modulation (P = 0.551). Accuracy on the task did not differ between groups, nor did the pattern of errors. However, in patients, greater positive and negative symptom ratings were associated with increased failure to button press to neutral faces, suggesting misattribution of emotion to neutral expressions in the more ill patients. Because the N170 is largely specific to faces, these results suggest that an impairment specific to the visual processing of facial expressions contributes to the well-known behavioral abnormalities in facial emotion tasks in schizophrenia.

title: Multisensory integration of emotional faces and voices in schizophrenics
abstract: In their natural environment, organisms receive information through multiple sensory channels and these inputs from different sensory systems are routinely combined into integrated percepts. Previously, we reported that in a population of schizophrenics, deficits in audiovisual integration were observed for complex stimuli (auditory and visual syllables), but not for more simple ones (beeps and light flashes). Here, we investigated multisensory integration of emotional information in a group of schizophrenic patients. In Experiment 1, we found a reduced effect of an emotional voice on the categorization of a facial expression. In Experiment 2, the reverse test situation was presented, and, here, we observed an exaggerated effect of a face expression on the categorization of an emotional voice. Results are discussed in the light of current models of multisensory integration and their relevance for schizophrenia.

title: Audiovisual emotion recognition in schizophrenia: Reduced integration of facial and vocal affect
abstract: Since Kraepelin called dementia praecox what we nowadays call schizophrenia, cognitive dysfunction has been regarded as central to its psychopathological profile. Disturbed experience and integration of emotions are, both intuitively and experimentally, likely to be intermediates between basic, non-social cognitive disturbances and functional outcome in schizophrenia. While a number of studies have consistently proven that, as part of social cognition, recognition of emotional faces and voices is disturbed in schizophrenics, studies on multisensory integration of facial and vocal affect are rare. We investigated audiovisual integration of emotional faces and voices in three groups: schizophrenic patients, non-schizophrenic psychosis patients and mentally healthy controls, all diagnosed by means of the Schedules of Clinical Assessment in Neuropsychiatry (SCAN 2.1). We found diminished crossmodal influence of emotional faces on emotional voice categorization in schizophrenics, but not in non-schizophrenia psychosis patients. Results are discussed in the perspective of recent theories on multisensory integration.

title: Perceiving emotions from bodily expressions and multisensory integration of emotion cues in schizophrenia
abstract: Most studies investigating emotion recognition in schizophrenia have focused on facial expressions and neglected bodily and vocal expressions. Furthermore, little is known about affective multisensory integration in schizophrenia. In the first experiment, the authors investigated recognition of static, face-blurred, whole-body expressions (instrumental, angry, fearful, and sad) with a two-alternative, forced-choice, simultaneous matching task in a sample of schizophrenia patients, nonschizophrenic psychotic patients, and matched controls. In the second experiment, dynamic, face-blurred, whole-body expressions (fearful and happy) were presented simultaneously with either congruent or incongruent human or animal vocalizations to schizophrenia patients and controls. Participants were instructed to categorize the emotion expressed by the body and to ignore the auditory information. The results of Experiment 1 show an emotion recognition impairment in the schizophrenia group and to a lesser extent in the nonschizophrenic psychosis group, and this for all four expressions. The findings of Experiment 2 show that schizophrenia patients are more influenced by the auditory information than controls, but only when the auditory information consists of human vocalizations. This shows that schizophrenia patients are impaired in recognizing whole-body expressions, and they show abnormal affective multisensory integration of bimodal stimuli originating from the same source.

title: Audio-visual integration in schizophrenia
abstract: Integration of information provided simultaneously by audition and vision was studied in a group of 18 schizophrenic patients. They were compared to a control group, consisting of 12 normal adults of comparable age and education. By administering two tasks, each focusing on one aspect of audio-visual integration, the study could differentiate between a spatial integration deficit and a speech-based integration deficit. Experiment 1 studied audio-visual interactions in the spatial localisation of sounds. Experiment 2 investigated integration of auditory and visual speech. The schizophrenic group performed as the control group on the sound localisation task, but in the audio-visual speech task, there was an impairment in lipreading as well as a smaller impact of lipreading on auditory speech information. Combined with findings about functional and neuro-anatomical specificity of intersensory integration, the data suggest that there is an integration deficit in the schizophrenic group that is related to the processing of phonetic information.

title: Impaired multisensory processing in schizophrenia: Deficits in the visual enhancement of speech comprehension under noisy environmental conditions
abstract: Viewing a speaker's articulatory movements substantially improves a listener's ability to understand spoken words, especially under noisy environmental conditions. In this study we investigated the ability of patients with schizophrenia to integrate visual and auditory speech. Our objective was to determine to what extent they experience benefit from visual articulation and to detail under what listening conditions they might show the greatest impairments.



We assessed the ability to recognize auditory and audiovisual speech in different levels of noise in 18 patients with schizophrenia and compared their performance with that of 18 healthy volunteers. We used a large set of monosyllabic words as our stimuli in order to more closely approximate performance in everyday situations.



Patients with schizophrenia showed deficits in their ability to derive benefit from visual articulatory motion. This impairment was most pronounced at signal-to-noise levels where multisensory gain is known to be maximal in healthy control subjects. A surprising finding was that despite known early auditory sensory processing deficits and reports of impairments in speech processing in schizophrenia, patients' performance in unisensory auditory speech perception remained fully intact.



Thus, the results showed a specific deficit in multisensory speech processing in the absence of any measurable deficit in unisensory speech processing and suggest that sensory integration dysfunction may be an important and, to date, rather overlooked aspect of schizophrenia.

title: Incongruence effects in crossmodal emotional integration
abstract: Emotions are often encountered in a multimodal fashion. Consequently, contextual framing by other modalities can alter the way that an emotional facial expression is perceived and lead to emotional conflict. Whole brain fMRI data was collected when 35 healthy subjects judged emotional expressions in faces while concurrently being exposed to emotional (scream, laughter) or neutral (yawning) sounds. The behavioral results showed that subjects rated fearful and neutral faces as being more fearful when accompanied by screams than compared to yawns (and laughs for fearful faces). Moreover, the imaging data revealed that incongruence of emotional valence between faces and sounds led to increased activation in the middle cingulate cortex, right superior frontal cortex, right supplementary motor area as well as the right temporoparietal junction. Against expectations no incongruence effects could be found in the amygdala. Further analyses revealed that, independent of emotional valence congruency, the left amygdala was consistently activated when the information from both modalities was emotional. If a neutral stimulus was present in one modality and emotional in the other, activation in the left amygdala was significantly attenuated. These results indicate that incongruence of emotional valence in audiovisual integration activates a cingulate-fronto-parietal network involved in conflict monitoring and resolution. Furthermore in audiovisual pairing amygdala responses seem to signal also the absence of any neutral feature rather than only the presence of an emotionally charged one.

title: A method for obtaining 3-dimensional facial expressions and its standardization for use in neurocognitive studies
abstract: Facial expressions of emotion are increasingly being used in neuroscience as probes for functional imaging and as stimuli for studying hemispheric specialization for face and emotion processing. Available facial stimuli are 2-dimensional and therefore, their orientation is fixed and poorly suited for examining asymmetries, they are often obtained under poorly specified conditions, usually posed, lack ethnic diversity, and are of restricted age range. We describe a method for accurately acquiring and reconstructing the geometry of the human face and for display of this reconstruction in a 3-dimensional format. We applied the method in a sample of 70 actors and 69 actresses expressing happiness, sadness, anger, fear and disgust, as well as neutral expressions. Each emotion was expressed under three levels of intensity and under both posed and evoked conditions. Resulting images are of high technical quality and are accurately identified by raters. The stimuli can be downloaded in digital form as 'movies' where angle and orientation can be manipulated for inclusion in functional imaging probes or in tests that can be administered as measures of individual differences in facial emotion processing. The database of emotional expressions can also be used as a standard for comparison with clinical populations.

title: A new method for off-line removal of ocular artifact.
abstract: A new off-line procedure for dealing with ocular artifacts in ERP recording is described. The procedure (EMCP) uses EOG and EEG records for individual trials in an experimental session to estimate a propagation factor which describes the relationship between the EOG and EEG traces. The propagation factor is computed after stimulus-linked variability in both traces has been removed. Different propagation factors are computed for blinks and eye movements. Tests are presented which demonstrate the validity and reliability of the procedure. ERPs derived from trials corrected by EMCP are more similar to a 'true' ERP than are ERPs derived from either uncorrected or randomly corrected trials. The procedure also reduces the difference between ERPs which are based on trials with different degrees of EOG variance. Furthermore, variability at each time point, across trials, is reduced following correction. The propagation factor decreases from frontal to parietal electrodes, and is larger for saccades than blinks. It is more consistent within experimental sessions than between sessions. The major advantage of the procedure is that it permits retention of all trials in an ERP experiment, irrespective of ocular artifact. Thus, studies of populations characterized by a high degree of artifact, and those requiring eye movements as part of the experimental task, are made possible. Furthermore, there is no need to require subjects to restrict eye movement activity. In comparison to procedures suggested by others, EMCP also has the advantage that separate correction factors are computed for blinks and movements and that these factors are based on data from the experimental session itself rather than from a separate calibration session.

title: Effects of the anticonvulsant benzodiazepine clonazepam on event-related brain potentials in humans.
abstract: The effects of the benzodiazepine clonazepam (a drug used as anticonvulsant) on event-related brain potentials were investigated in healthy human subjects. Thirty-six male student volunteers (mean age 30 years) received clonazepam or a placebo in a double-blind setting. VEPs (visual evoked potentials) were obtained from the standard checkerboard reversal procedure; AEPs (auditory evoked potentials) and slow cortical potentials (CNV) were measured during a 2-stimulus reaction time paradigm, in which the quality of the acoustic S1 signalled whether the acoustic S2 would follow after 2 sec or after 6 sec. Each S2 requested a speeded button press. Compared to placebo, clonazepam significantly reduced P100 amplitude of the VEP and the amplitudes of the AEP components N1 and P3. On the other hand, clonazepam boosted the development of a distinct N2 which was not apparent in placebo subjects. The CNV was significantly reduced and reaction time increased under clonazepam compared to placebo. Specific versus non-specific damping effects of the benzodiazepine are discussed, comparing the present result with the pattern of ERP effects of the anticonvulsant carbamazepine that had been obtained using the same experimental paradigms.

title: Antipsychotic Dose Equivalents and Dose-Years: A Standardized Method for Comparing Exposure to Different Drugs
abstract: A standardized quantitative method for comparing dosages of different drugs is a useful tool for designing clinical trials and for examining the effects of long-term medication side effects such as tardive dyskinesia. Such a method requires establishing dose equivalents. An expert consensus group has published charts of equivalent doses for various antipsychotic medications for first- and second-generation medications. These charts were used in this study.



Regression was used to compare each drug in the experts' charts to chlorpromazine and haloperidol and to create formulas for each relationship. The formulas were solved for chlorpromazine 100 mg and haloperidol 2 mg to derive new chlorpromazine and haloperidol equivalents. The formulas were incorporated into our definition of dose-years such that 100 mg/day of chlorpromazine equivalent or 2 mg/day of haloperidol equivalent taken for 1 year is equal to one dose-year.



All comparisons to chlorpromazine and haloperidol were highly linear with R(2) values greater than .9. A power transformation further improved linearity.



By deriving a unique formula that converts doses to chlorpromazine or haloperidol equivalents, we can compare otherwise dissimilar drugs. These equivalents can be multiplied by the time an individual has been on a given dose to derive a cumulative value measured in dose-years in the form of (chlorpromazine equivalent in mg) x (time on dose measured in years). After each dose has been converted to dose-years, the results can be summed to provide a cumulative quantitative measure of lifetime exposure.

title: Processing of environmental sounds in schizophrenic patients: disordered recognition and lack of semantic specificity
abstract: The recognition of environmental sounds is an important feature of higher auditory processing and essential for everyday life. The present study aimed to investigate the potential impairment of this mental function in schizophrenia. This work on immediate sound recognition is complementary to recent studies on auditory linguistic processing. Fifteen schizophrenic patients and 30 control subjects were asked to identify 43 complex environmental sounds from different categories and rate their familiarity when naïve to the sounds. In consecutive experiments, patients and control subjects rated the sounds according to emotional valence and arousal, as well as imageability. In both groups, correct identification of non-verbal sounds was highly associated with familiarity. Statistical analysis by group demonstrated a significantly higher error rate in identifying sounds in patients suffering from schizophrenia compared to healthy control subjects. In contrast, the affective recognition of the complex sounds was preserved in the schizophrenic patients. These results suggest a disturbance of higher-order, auditory mnemonic processing in schizophrenic patients in the non-linguistic domain. We discuss their abnormal responses in the context of recent theories of auditory physiological and semantic processing deficits in schizophrenia.

title: Using event related potentials to explore stages of facial affect recognition deficits in schizophrenia.
abstract: Schizophrenia patients show impairments in identifying facial affect; however, it is not known at what stage facial affect processing is impaired. We evaluated 3 event-related potentials (ERPs) to explore stages of facial affect processing in schizophrenia patients. Twenty-six schizophrenia patients and 27 normal controls participated. In separate blocks, subjects identified the gender of a face, the emotion of a face, or if a building had 1 or 2 stories. Three ERPs were examined: (1) P100 to examine basic visual processing, (2) N170 to examine facial feature encoding, and (3) N250 to examine affect decoding. Behavioral performance on each task was also measured. Results showed that schizophrenia patients' P100 was comparable to the controls during all 3 identification tasks. Both patients and controls exhibited a comparable N170 that was largest during processing of faces and smallest during processing of buildings. For both groups, the N250 was largest during the emotion identification task and smallest for the building identification task. However, the patients produced a smaller N250 compared with the controls across the 3 tasks. The groups did not differ in behavioral performance in any of the 3 identification tasks. The pattern of intact P100 and N170 suggest that patients maintain basic visual processing and facial feature encoding abilities. The abnormal N250 suggests that schizophrenia patients are less efficient at decoding facial affect features. Our results imply that abnormalities in the later stage of feature decoding could potentially underlie emotion identification deficits in schizophrenia.

title: Morphological and latency abnormalities of the mid-latency auditory evoked responses in schizophrenia: a preliminary report
abstract: Evoked potential (EP) amplitude and latency abnormalities have been extensively examined in schizophrenia. Morphological abnormalities of the mid-latency auditory evoked responses (MLAERs; P50, N100, P200), on the other hand, received very little attention.



Based on a priori defined set of morphological criteria, the morphology and latency of the MLAERs were blindly compared between stable outpatients with schizophrenia (N=27) and age- and gender-matched healthy control subjects (N=22). The morphology of the MLAERs was considered abnormal if one or more of the components fell outside the expected latency range, if one or more of the components were missing, or if a later occurring component was smaller in amplitude than an earlier occurring one.



Of the 27 schizophrenia subjects, 20 had waveforms that were deemed atypical, while only 8 from the control group were classified as atypical (chi(2)=5.52, p<0.02). The latencies of the P50 and N100 components, identified based on morphology, were significantly prolonged in schizophrenia patients.



These preliminary data suggest that morphological abnormalities of the MLAERs in schizophrenia patients are significant and should be taken into consideration when examining the MLAERs of this patient population.

title: Meta-analysis of the P300 and P50 waveforms in schizophrenia
abstract: To determine whether patients with schizophrenia have abnormalities in the P300 and P50 waves and to quantify the magnitude of any differences from controls.



We conducted a systematic search for articles published between January 1994 and August 2003 that reported P50 or P300 measures in schizophrenic patients and controls. Metaregression analyses were performed using a random effects model. The pooled standardised effect size (PSES) was calculated as the difference between the means of the two groups divided by the common standard deviation.



We identified 46 studies suitable for analysis of P300 measures, including 1443 patients and 1251 controls. There were 20 P50 studies including 421 patients and 401 controls. The PSES for the P300 amplitude was 0.85 (95% CI: 0.65 to 1.05; p<0.001), and for the P300 latency was -0.57 (95% CI: -0.75 to -0.38; p<0.001). The PSES of the P50 ratio was -1.56 (95% CI: -2.05 to -1.06; p<0.001). There were no significant differences between patients and controls in P50 latency. Across-study variations in filters, task difficulty, antipsychotic medication and duration of illness did not influence the PSES significantly.



This meta-analysis confirms the existence of ERP deficits in schizophrenia. The magnitude of these deficits is similar to the most robust findings reported in neuroimaging and neuropsychology in schizophrenia.

title: Profile of auditory information-processing deficits in schizophrenia
abstract: Schizophrenia patients exhibit abnormalities in several different auditory event-related potential (ERP) measures. It is unclear how these abnormalities relate to each other, since multiple measures are rarely acquired from the same sample. This study addressed two related questions: 1) Are specific auditory ERP measures differentially impaired in schizophrenia? 2) Do abnormalities co-aggregate within the same patients? Nine auditory ERP measures were acquired in a single testing session from 23 schizophrenia patients and 22 healthy subjects. Hierarchical oblique factor analysis revealed that these measures aggregated into four factors, with each loading primarily on a single factor. Patient deficits were observed for two independent factors: N100/mismatch negativity (MMN) and P3a/P3b. N100/MMN abnormalities were associated with symptoms of alogia and formal thought disorder. P3a/P3b abnormalities were associated with avolition, attentional disturbances and delusions. We conclude that deficits in different ERP measures of early sensory processing at the level of the auditory cortex co-occur in patients. These likely represent a single differential deficit indexing the physiological abnormality underlying impaired language and verbal processing. This is relatively independent of a higher cortical deficit that mediates cognitive stimulus evaluation and underlies deficits in motivation, attention and reality testing. Such multidimensional profiling of ERP abnormalities may help to clarify the clinical and genetic heterogeneity of schizophrenia.

title: Neural response to emotional prosody in schizophrenia and in bipolar affective disorder
abstract: Evidence suggests a reversal of the normal left-lateralised response to speech in schizophrenia.  To test the brain's response to emotional prosody in schizophrenia and bipolar disorder.  BOLD contrast functional magnetic resonance imaging of subjects while they passively listened or attended to sentences that differed in emotional prosody.  Patients with schizophrenia exhibited normal right-lateralisation of the passive response to ‘pure’ emotional prosody and relative left-lateralisation of the response to unfiltered emotional prosody. When attending to emotional prosody, patients with schizophrenia activated the left insula more than healthy controls. When listening passively, patients with bipolar disorder demonstrated less activation of the bilateral superior temporal gyri in response to pure emotional prosody, and greater activation of the left superior temporal gyrus in response to unfiltered emotional prosody. In both passive experiments, the patient groups activated different lateral temporal lobe regions.  Patients with schizophrenia and bipolar disorder may display some left-lateralisation of the normal right-lateralised temporal lobe response to emotional prosody.

title: Altered lateralisation of emotional prosody processing in schizophrenia
abstract: Alterations of cerebral lateralisation in schizophrenia have been reported consistently, and a reduced left-lateralisation has been suggested for language functions. Speech contains non-verbal information, e.g. prosody, and on a behavioural level, the extraction of emotional information from prosody is often impaired in schizophrenia. A previous functional magnetic resonance imaging study suggests increased left-lateralisation in schizophrenia during prosody processing, but did not disentangle effects of speech processing as such and emotional prosody processing. Here, we used meaningless syllables spoken with neutral, angry or fearful speech melody and measured blood oxygen level-dependent (BOLD) responses in 15 in-patients with schizophrenia and 15 healthy control participants matched for age and gender. Lateralisation indices were calculated for responses to emotional versus neutral prosody, and for all types of prosody versus baseline. Compared to control participants, patients with schizophrenia showed an increased right-lateralisation of emotional and non-emotional prosody processing in the temporal and parietal cortex. This right-lateralisation was increased in patients with reduced right-handedness and decreased in patients with stronger negative symptoms, particularly affective blunting, and with longer hospitalisation. Although patients with schizophrenia performed worse in emotion identification, this deficit was not related to lateralisation indices. Enhanced right-lateralisation to prosody resembles previous findings on laterality changes in speech processing and might suggest a common underlying cause in the organization of language functions.

title: EVENT-RELATED POTENTIALS TO VISUAL, AUDITORY, AND BIMODAL (COMBINED AUDITORY-VISUAL) STIMULI
abstract: The purpose of this study was to investigate the response properties of event related potentials to unimodal and bimodal stimulations. The amplitudes of N1 and P2 were larger during bimodal evoked potentials (BEPs) than auditory evoked potentials (AEPs) in the anterior sites and the amplitudes of P1 were larger during BEPs than VEPs especially at the parieto-occipital locations. Responses to bimodal stimulation had longer latencies than responses to unimodal stimulation. The N1 and P2 components were larger in amplitude and longer in latency during the bimodal paradigm and predominantly occurred at the anterior sites. Therefore, the current bimodal paradigm can be used to investigate the involvement and location of specific neural generators that contribute to higher processing of sensory information. Moreover, this paradigm may be a useful tool to investigate the level of sensory dysfunctions in clinical samples.

title: Event-related potentials and event-related oscillations during identity and facial emotional processing in schizophrenia.
abstract: Impairments in emotional recognition have been consistently reported in schizophrenic patients. The main aim of the present study was to evaluate time-sequenced responses in ERPs and event-related oscillations during emotional recognition of happiness and fear compared to facial identity recognition in schizophrenic patients (SCH) versus healthy controls (CON). Ten paranoid SCH and ten CON subjects performed three oddball paradigm tasks, evaluating face identity recognition and facial emotional recognition of happiness and fear. Event-related potentials and event-related theta and alpha oscillations were obtained for each task. N170 and P2 components appeared with higher amplitude in SCH than in CON at the occipital locations. An early prefrontally distributed P3a component was observed while doing the identity task with lower amplitude in SCH than in CON. Comparatively, P3b amplitude was lower in SCH than in CON over parietal leads in the identity and happiness tasks. Additionally, theta oscillations showed significantly lower RMS values in SCH between 250 and 500 ms post-stimuli in frontal and central regions. On the other hand, the grand-averaged alpha oscillations demonstrated higher RMS values in the occipital leads in SCH compared to CON and the opposite over the frontal regions. Results are interpreted in the framework of a functional disruption in the distributed neuronal networks involved both in facial identity and emotional recognition in schizophrenics as indexed by the brain oscillatory activity and related ERP components.

title: EEG-correlates of facial affect recognition and categorisation of blurred faces in schizophrenic patients and healthy volunteers
abstract: The ability to recognise emotional expressions of faces and the ability to categorise blurred and non-blurred faces and complex objects was tested in 16 schizophrenic in-patients and 16 healthy volunteers. EEGs were recorded during performance of the tasks and event-related potentials were compared between groups. Patients performed worse than healthy volunteers in recognition of facial affect but not in categorisation of blurred faces. Furthermore, within a 180-250ms latency range patients showed reduced amplitudes during affect recognition compared with controls but not during categorisation of blurred faces. Amplitudes recorded at frontal electrode sites were associated with performance in facial affect recognition. These results provide a first clue to the neurophysiological basis of the widely reported facial affect recognition deficit in schizophrenic patients.

title: Visual sensory processing deficits in Schizophrenia and their relationship to disease state
abstract: ContextVisual Evoked Potential (VEP) abnormalities have been a fairly consistent finding in patients with schizophrenia, and it has been suggested that electrophysiological markers of early sensory processing may be useful as trait markers for the illness, and for development as potential diagnostic measures.ObjectiveClear amplitude reductions in the occipital P1 component of the VEP (~100 ms), have been repeatedly demonstrated in patients with schizophrenia. Here, we investigated whether the extent of this deficit was related to age, clinical symptoms, medication status and length of illness, in a large cohort of ethnically homogenous patients. and participantsVEP responses to simple isolated-check stimuli were examined in 52 DSM-IV diagnosed patients with schizophrenia, and compared with responses from 26 healthy age-matched control subjects. Using high-density electrical scalp recordings, we assessed the integrity of the visual P1 component across the two groups. This study was conducted at St.Vincent’s Psychiatric Hospital in Fairview, Dublin, Ireland.ResultsSubstantially reduced P1 amplitude was demonstrated in the patient group compared to controls. The deficit was not linked to age, length of illness or medication status. A small positive correlation, accounting for about 11% of the variance, was found between P1 amplitude and clinical symptoms scales (BPRS and SANS). In addition, we found that a slightly later (~110 ms) fronto-central component was relatively increased in the patient group, and was inversely correlated with the occipital P1 amplitude in the patients, but not in the healthy control subjects.ConclusionsOur findings clearly demonstrate a deficit in early visual processing in patients with schizophrenia (with a large effect size; Cohen’s d = 0.7) that is unrelated to chronicity. The results are consistent with recent findings showing that the P1 deficit is endophenotypic of the disorder and related to genetic risk factors rather than the disease process itself.

title: Visual scanning of facial expressions in schizophrenia.
abstract: The authors previously observed that schizophrenic patients generated fewer fixations of < or = 50.1 ms in response to faces than did a clinical control group. This study examined whether deficits in short-duration eye movements were related to patients' problems in gestalt perception of faces. Faces were presented in upright and inverted orientations to examine the effects of distorting facial gestalts on eye movements. Normal subjects generated more saccades of < or = 50.1 ms to upright than to inverted faces. Patients' saccades of < or = 50.1 ms did not differ between orientations. Patterns of fixations and of saccades > 50.1 ms did not differ between groups. The results may indicate deficits in these patients in search strategies that underlie perception of facial gestalts.

title: Visual scanpaths to positive and negative facial emotions in an outpatient schizophrenia sample
abstract: We used a psychophysiological marker of visual attention (visual scanpath) to investigate facial emotion processing in schizophrenia (n= 65) and healthy control (n = 61) groups. Visual scanpaths to 'happy', *sad' and 'neutral' faces (two exposures each) were recorded using video-oculography. Emotion recognition accuracy was assessed under both 'difficult' (exposure 1) and 'limited choice' (exposure 2) conditions. Compared to controls, schizophrenia subjects showed 'restricted' scanning and reduced attention to salient facial features (eyes, nose, mouth), that was particularly apparent for happy and neutral faces: accuracy was correspondingly reduced for the 'difficult' condition. The schizophrenia deficit in positive emotion perception may reflect a failure to integrate salient features due to dysfunctions in local processing of detailed, relevant information (fewer fixations, less attention to facial features), and in the networks that synchronise local and global processing of biologically-relevant face stimuli (generally restricted scanning style).

title: The combined perception of emotion from voice and face: early interaction revealed by human electric brain responses
abstract: Judgement of the emotional tone of a spoken utterance is influenced by a simultaneously presented face expression. The time course of this integration was investigated by measuring the mismatch negativity (MMN). In one condition, the standard stimulus was an angry voice fragment combined with a (congruous) angry face expression. In the deviant pair, the voice expression was kept the same and only the face expression changed to an (incongruous) sad face. The pairs with a deviant visual item evoked a negative electric brain response showing the characteristics of the MMN, which is usually evoked only by auditory deviations. Similar results were obtained by employing incongruous standard and congruous deviant pairs. These findings provide compelling evidence of an early integration of face with voice information in the processing of affect.

title: Underconstrained perception: a theoretical approach to the nature and function of verbal hallucinations.
abstract: We do not see the world as it is. Perception forms a subjective image of the world in a language that has proven to be adaptive to our interaction with the external world. Perception is mainly determined by current needs of the organism and goals of behavior. Sensory processing itself does not culminate in perception and is not essential for perception, since perception derives from representations of internal symbols and their features. The current stimulation of sensory organs does, however, constrain our perception. Perception might be less constrained by the external world in cases of (1) increased attention, (2) decreased sensory stimulation, or (3) facilitated formation of cortical associations between representations of expectations and internal symbols. Hallucinations are perceptions that are underconstrained by external sensory stimulation. Verbal hallucinations that allow the patient to infer about his self-image might constitute the core psychopathology in a subset of schizophrenia. Commenting and discussing voices might be perceived under the pressure of increased attention to environmental factors that relate to the patient's social fears and wishes. Secondarily, delusions about the possession of thoughts and disorders of self-experience may develop.

title: How hallucinations may arise from brain mechanisms of learning, attention, and volition
abstract: This article suggests how brain mechanisms of learning, attention, and volition may give rise to hallucinations during schizophrenia and other mental disorders. The article suggests that normal learning and memory are stabilized through the use of learned top-down expectations. These expectations learn prototypes that are capable of focusing attention upon the combinations of features that comprise conscious perceptual experiences. When top-down expectations are active in a priming situation, they can modulate or sensitize their target cells to respond more effectively to matched bottom-up information. They cannot, however, fully activate these target cells. These matching properties are shown to be essential towards stabilizing the memory of learned representations. The modulatory property of top-down expectations is achieved through a balance between top-down excitation and inhibition. The learned prototype is the excitatory on-center in this top-down network. Phasic volitional signals can shift the balance between excitation and inhibition to favor net excitatory activation. Such a volitionally mediated shift enables top-down expectations, in the absence of supportive bottom-up inputs, to cause conscious experiences of imagery and inner speech and thereby to enable fantasy and planning activities to occur. If these volitional signals become tonically hyperactive during a mental disorder, the top-down expectations can give rise to conscious experiences in the absence of bottom-up inputs and volition. These events are compared with data about hallucinations. The article predicts where these top-down expectations and volitional signals may act in the laminar circuits of visual cortex and, by extension, in other sensory and cognitive neocortical areas, and how the level of abstractness of learned prototypes may covary with the abstractness of hallucinatory content. A similar breakdown of volition may lead to delusions of control in the motor system.

title: Cognitive basis of hallucinations in schizophrenia: role of top-down information processing
abstract: Hallucinations in schizophrenia have been regarded to result from the erroneous attribution of internally generated information to an external source. Distortions in mental imagery may underlie such confusions. We investigated performance of 77 subjects on multiple behavioral measures of auditory and visual mental imagery and perception, and a measure of reality monitoring. Comparisons were made between performance of schizophrenia patients with (N=22) and without (N=35) hallucinations and matched normal comparison subjects (N=20), after controlling for attentional factors. No differences emerged on any of the mental imagery measures, nor on reality monitoring accuracy. This suggests that there is no stable disposition towards abnormal mental imagery associated with hallucinations. However, for patients with active hallucinations (N=12), hallucination severity correlated positively with a measure of imagery-perception interaction in the auditory modality, r=0.70, p=0.01. Although preliminary, this finding is consistent with recent theoretical proposals in which hallucinations have been suggested to result from an increased influence of top-down sensory expectations on conscious perception.