Evidence of schizophrenia patients' reduced perceptual biases in response to emotion chimera.

The goal of the study was to determine whether dextral individuals with schizophrenia display atypical perceptual biases in response to faces in general, or whether they display atypical perceptual biases in response to emotional facial cues. To this end, we assessed perceptual processing in schizophrenia patients with four types of free-vision chimeric stimuli. Perceptual biases were evaluated in 45 schizophrenia patients and in 46 controls using two face (emotion, gender) tasks and two nonface (dots, gradients) tasks. In response to the emotion chimera, the patients with schizophrenia displayed a reduced left perceptual bias. The two groups did not differ significantly in their response to the gender chimera or to the two nonface chimera. These findings are consistent with the assertion that schizophrenia patients have impaired emotional perception. In the discussion we consider possible reasons for schizophrenia patients' difficulty comprehending emotional facial stimuli. We suggest that schizophrenia patients' reduced perceptual bias in response to the emotion chimera reflects a hypothesized affective information-processing deficit.

Left-hemisphere activation and deficient response modulation in psychopaths.

Psychopathic offenders have difficulty processing contextual or secondary cues once they have initiated goal-directed behavior or allocated attention to a primary task. To test the hypothesis that this deficit in response modulation is specific to conditions in which psychopaths' left-hemisphere resources are engaged, we administered a serial recall task to 21 incarcerated psychopaths and 21 control subjects. Subjects were instructed to memorize eight words that were presented one at a time, each in one of the four corners of the visual display. Subjects' primary task was to recall the words in serial order. Then, without forewarning, they were asked to recall the words' locations. As predicted, psychopaths performed as well as control subjects in recalling words from the left and right spatial fields, but recalled significantly fewer locations from the right spatial field. Thus, psychopaths' deficient response modulation was specific to conditions in which their left-hemisphere resources were actively engaged.

Perceptual biases in psychosis-prone individuals.

College students screened for psychosis-proneness using the Chapman scales were compared on 4 free-vision tasks that typically yield left-spatial-field biases. The tasks included 2 chimeric face tests, consisting of happy/neutral faces and male/female faces, and 2 nonface tasks, consisting of pairs of dot-filled or gradient-filled rectangles. Participants endorsing perceptual aberration items, magical ideation items, or both (n = 98) and control participants (n = 112) were left-biased on all tasks but gradients and were most biased on emotion faces; in contrast, i.e., social anhedonia participants (n = 40) displayed very little or no left-field biases. For all groups, task intercorrelations were greatest between the 2 face tasks and between the 2 nonface tasks. These findings suggest patterns of atypical perceptual asymmetry in psychosis-prone individuals.

Cerebral asymmetries in processing strategies for letter and symbol trigrams.

Several studies have shown that laterally presented consonant-vowel-consonant (CVC) strings produce both superior performance, and a more wholistic processing strategy in the right visual field/left hemisphere (RVF/LHEM), and a more sequential strategy in the inferior left visual field (LVF). To determine whether these strategies are applied to other types of trigrams subjects (n = 30) were asked to identify consonant and symbol trigrams briefly projected unilaterally to the LVF or RVF, or bilaterally (the same trigram in both fields--BVF). A second group of subjects (n = 30) first practiced pronouncing consonant trigrams and then viewed them tachistoscopically. Both tasks yield RVF advantages. Symbols are processed more wholistically in the LVF, more sequentially in the RVF and in an intermediate pattern when presented bilaterally. In contrast, subjects seem to chunk letters as bigrams, and do so equally well in all fields, and visual field differences in strategies emerge for consonants only when they are pronounced. Pronounceability of consonant trigrams, assessed with ratings and vocal reaction times, was predicted by orthographic regularity. Since the RHEM has limited phonetic skills, but it, like the LHEM, is privy to information on orthographic regularity, the error pattern on consonant strings indicates non-phonetic processing, whereas the RVF wholistic strategy for consonant-vowel-consonant strings appears to reflect phonetic processing.

Left- and right-handers see people differently: free-vision perceptual asymmetries for chimeric stimuli.

We examined perceptual biases of 72 left-handers on six free-vision chimeric tasks, four entailing judgments of emotion (EP and EC tasks) or femininity (GP and GC tasks) in photographic and cartoon chimeric faces, and two of visuospatial properties in dot-filled rectangles (DN-dots nonface task) and asymmetrical shapes (SN-shapes nonface task), and compared to them to those of 72 right-handers previously described by Luh, Rueckert, and Levy (1991). Neither handedness group had an asymmetric bias on the SN task. Both had left hemispatial biases on all other tasks, which were equal across tasks for left-handers, larger on the EP and EC than other tasks for right-handers, and larger for right- than left-handers only on the EP and EC tasks. Task-specific reliable variance was decreased and variance common to all tasks was increased for left- compared to right-handers, which suggests less differentiation of processes in left- than right-handers.

Perceptual asymmetries for free viewing of several types of chimeric stimuli.

We examined perceptual biases of right-handers on six free-vision chimeric tasks; two involving a judgement of happiness of a facial expression in photographic and cartoon chimeras, two involving a judgement of femininity in male/female photographic and cartoon chimeras, and two involving a spatial judgement of nonface chimeric stimuli. All four of the face tasks and one of the nonface tasks elicited left spatial field biases of varying magnitudes, and perceptual asymmetries on all tasks were positively correlated. However, multiple correlational analyses revealed that these tests shared differing proportions of variance with each other. Results indicate that, in addition to a common factor or set of factors contributing to lateral biases that is independent of both the nature of the stimulus and whether the stimulus engages lateralized mechanisms, there are distinct lateralized mechanisms which yield different patterns of perceptual asymmetries for different stimuli.

Impairments in orienting to visual stimuli in monkeys following unilateral lesions of the superior sulcal polysensory cortex.

Monkeys were tested for head and eye orientation to illuminated lamps in a hemisphere before and after serial, unilateral lesions of the polysensory superior temporal cortex (STS) or control lesions. Following STS lesions they were impaired in orienting to contralateral lamps; this impairment was more severe and persistent when a ipsilateral stimulus in the mirror-image position was simultaneously presented. These findings, together with deficits in manual reaching and grasping observed following STS lesions, support the view that the STS is part of a polysensory system controlling attention and exploratory movements.