A.S. David

Explicit and Implicit Neural Mechanisms for Processing of Social Information From Facial Expressions: A Functional Magnetic Resonance Imaging Study

The processing of changing nonverbal social signals such as facial expressions is poorly understood, and it is unknown if different pathways are activated during effortful (explicit), compared to implicit, processing of facial expressions. Thus we used fMRI to determine which brain areas subserve processing of high‐valence expressions and if distinct brain areas are activated when facial expressions are processed explicitly or implicitly. Nine healthy volunteers were scanned (1.5T GE Signa with ANMR, TE/TR 40/3,000 ms) during two similar experiments in which blocks of mixed happy and angry facial expressions (“on” condition) were alternated with blocks of neutral faces (control “off” condition). Experiment 1 examined explicit processing of expressions by requiring subjects to attend to, and judge, facial expression. Experiment 2 examined implicit processing of expressions by requiring subjects to attend to, and judge, facial gender, which was counterbalanced in both experimental conditions. Processing of facial expressions significantly increased regional blood oxygenation level‐dependent (BOLD) activity in fusiform and middle temporal gyri, hippocampus, amygdalohippocampal junction, and pulvinar nucleus. Explicit processing evoked significantly more activity in temporal lobe cortex than implicit processing, whereas implicit processing evoked significantly greater activity in amygdala region. Mixed high‐valence facial expressions are processed within temporal lobe visual cortex, thalamus, and amygdalohippocampal complex. Also, neural substrates for explicit and implicit processing of facial expressions are dissociable: explicit processing activates temporal lobe cortex, whereas implicit processing activates amygdala region. Our findings confirm a neuroanatomical dissociation between conscious and unconscious processing of emotional information. Hum. Brain Mapping 9:93–105, 2000.

An investigation into the perception of dominance from schematic faces: a study using the World-Wide Web.

The World-Wide Web (WWW) is considered to be a viable tool for scientific research, and several investigators have already made use of it in their studies. Although the WWW allows researchers to access a vast subject pool, questions of reliability and validity need to be addressed before it is incorporated into mainstream research. By replicating, on the Internet, an existing study (Keating, Mazur, & Segall, 1977) on the perception of schematic faces, we were able to conclude that experimental work carried out in this manner is not necessarily biased by the medium. One difference from previous work was the effect of a smiling versus a nonsmiling face on the perception of dominance, given an identical brow position for the two faces. This was replicated on a different occasion with different subjects, which may represent a shift in attitudes to this facial configuration since the original study was conducted. Young North American males were overrepresented in our sample, but comparison with other surveys indicates that the population sampled by the Internet is becoming more representative.

A cognitive neuropsychological approach to the study of delusions in late-onset schizophrenia

Objective. Hypotheses to explain delusion formation include distorted perceptual processing of meaningful stimuli (eg faces), abnormal reasoning, or a combination of both. The study investigated these hypotheses using standardized neuropsychological tests.

Is semantic fluency differentially impaired in schizophrenic patients with delusions

The study of cognitive deficits in schizophrenia has recently focused upon semantics: the study of meaning. Delusions are a plausible manifestation of abnormal semantics because by definition they involve changes in personal meaning and belief. A symptom-based approach was used to investigate semantic and phonological fluency in a group of schizophrenic patients subdivided into those with delusions and those with no current delusions. The results demonstrated that deluded patients only were differentially impaired on a test of semantic fluency in comparison to phonological fluency. All subjects showed the same decline in performance over the time course of both tests indicating that retrieval speed in schizophrenia is no different from that of normal controls. Further analysis of word associations in two semantic categories (animals and body parts), revealed that deluded subjects have a more idiosyncratic organisation for animals. The findings of reduced semantic fluency production and poor logical word associations may represent a disorganised storage of semantic information in deluded patients, which in turn affects efficient access.

Sentence verification and delusions: A content-specific deficit

BACKGROUND A sentence verification task was developed to investigate semantic memory in schizophrenia. METHODS The test consisted of three types of sentence (true, unlikely and nonsense) and seven different types of content (neutral, persecutory, grandiose, political, religious, relationships and somatic) representing common delusional themes present in schizophrenic patients. Sixty-three schizophrenic patients and 66 matched control subjects were asked to make true/false judgements to 143 sentences. RESULTS Overall accuracy was similar across the two groups; sentences with some emotional themes and sentences of the unlikely type produced the most violations. Significant differences between the two subject groups were found specifically on nonsense sentences with persecutory and religious themes. Patients made significantly more incorrect responses (acceptance) to nonsense sentences that had an emotional content congruent with their delusional beliefs, past or present, and also on unlikely sentences (incorrect rejections) whose content was not congruent with their delusions. Further analysis of response bias in the patients showed, overall, that there were more incorrect rejections (a reflection of the large number of unlikely sentence errors) and more incorrect responses to sentences congruent with patients delusions. Furthermore, analysis of those patients currently experiencing delusions revealed more incorrect responses to sentences congruent with their delusional ideas compared with patients not currently deluded. CONCLUSIONS These findings are indicative of cognitive bias in schizophrenia towards certain emotional themes that may underlie illogical semantic connections and delusions.