Verbal processing deficits in schizophrenia

The authors reported that a subgroup of schizophrenic patients performed well on a tone serial position task but was impaired on an auditory word serial position task (Wexler, Stevens, Bowers, Cerniak, & Goldman-Rakic, 1998). This study assessed 30 schizophrenic and 32 controls (matched for comparable tone discrimination) on 4 versions of the verbal serial position tasks and 2 tone serial position tasks. Patients performed poorly on all verbal tasks but performed comparably to controls when tones served as stimuli. Proactive interference and visual presentation further compounded the verbal deficits. Deficits persisted with pronounceable nonword stimuli. These findings provide evidence of specific deficits in language-related processing, although the authors could not rule out the possibility that the differential effects that were observed between the tone and word tasks, and particularly among the verbal tasks, may result from differing discriminating power of the different tests.     

Hemispheric processing of idioms in schizophrenia and autism spectrum disorder

Studies conducted on individuals with schizophrenia (SZ) and autism spectrum disorder (ASD) show that they find it difficult to comprehend figurative language, and have a tendency to interpret it literally. This study examines hemispheric processing of idioms in patients with SZ, in comparison to individuals with ASD. Seventeen adults with SZ and 18 adults with ASD participated in the study. The two clinical groups were matched in age, vocabulary scores and verbal executive function scores. Using the divided visual field paradigm, the participants performed a lexical decision task for a target word related to either a literal or a figurative interpretation of an idiom. Whereas SZ patients showed the typical right lateralisation for non-salient literal interpretations of idioms, adults with ASD showed atypical bilateral processing. These findings indicate different hemispheric lateralisation in idiom processing in the two clinical groups.     

Hemispheric differences in case processing

Morphosyntactic capacities of normal brain hemispheres were compared in lexical decision studies involving centrally and laterally presented Serbo-Croatian nouns in different cases. Cases are distinguished by different suffixes and syntactic roles. Experiment 1 confirmed and extended previous findings of the nominative superiority effect: words in the nominative case were processed faster and more accurately than words in other three cases, and nonwords in the nominative case led to more false positive reactions than nonwords in other cases. In Experiment 2 this effect was replicated for right visual field stimuli: nominatives had faster reaction times and smaller error rates than accusatives, and the reversed pattern was found for nonwords. For left visual field stimuli, only the word error analysis found the nominative superior, while the other three analyses (word reaction times, nonword reaction times, and nonword error rates) showed no significant case effect. Word familiarity had an equally strong effect in both hemispheres. The results suggest that centrally presented stimuli are processed by the left hemisphere, that laterally presented stimuli are processed by the initially receiving hemisphere, and that the right hemisphere has a frequency-sensitive lexicon. Reduced right-hemisphere sensitivity for case differences may be due to different lexicon structure or the absence of appropriate morphological or syntactic mechanisms.     

Response-selection processes in paranoid and nonparanoid schizophrenia

Previous research (Marshall, 1973) has shown that the most pronounced component of deficit on a choice reaction time task among a mixed schizophrenic sample involved response-selection processes. Other evidence has indicated that paranoids may be more deficient in this respect than nonparanoids. Hence, it was hypothesized that the former subgroup of schizophrenics would display response-selection deficit while the latter subgroup would display either less or no deficit. Response-selection processes were re-examined using the CRT paradigm with comparisons carried out among paranoid and nonparanoid schizophrenics and a group of nonschizophrenic controls. Results indicated that only the paranoid schizophrenics displayed abnormally retarded response-selection operations, the nonparanoid schizophrenics being nonsignificantly discriminable from the controls. It was suggested that past evidence of CRT response-selection deficit among mixed schizophrenics might have been attributable primarily to the performance of the paranoids, whose performance appears to be adversely affected by an increase in the number of dimensions relevant to response selection.     

Sentence processing deficits in two Cantonese aphasic patients

This paper reports the performances of two Cantonese aphasics on tasks examining their sentence processing deficits. The data on sentence comprehension show that thematically noncanonical sentences, full passives, and subject-gap sentences present greater difficulty to these patients than canonical sentences, truncated passives, and object-gap sentences, respectively. These patterns are consistent with previous observations on Chinese aphasics and are expected given the structural differences between Chinese and English. In a Cantonese grammaticality judgment test, a set of structures are identified that can elicit clear judgments from normal subjects and aphasics, contrary to the claim that grammaticality judgments in Chinese are probabilistic and fragile. Most interestingly, the patients' overall performance patterns reveal a double dissociation between sentence comprehension and judgment of sentence well-formedness, suggesting that the two tasks are supported by independent processing mechanisms.     

Hemispheric visual processing in face recognition

Two experiments tested how facial details are used in recognizing face drawings presented to either the left or right visual field (VF). Subjects used inner and outer features about equally in both the left and right VFs. The major finding was a very strong tendency to recognize the upper facial features more accurately than the lower facial features. The top-to-bottom recognition difference occurred in both VFs, in contrast to an earlier study by J. Sergent (1982, Journal of Experimental Psychology: Human Perception and Performance, 8, 1-14). Methodological differences between the present experiments and Sergent's studies were discussed. It was concluded that both the left and right hemispheres recognize novel faces using top-to-bottom serial processing.     

Hemispheric differences in processing handwritten cursive

Hemispheric asymmetry was examined for native English speakers identifying consonant-vowel-consonant (CVC) non-words presented in standard printed form, in standard handwritten cursive form or in handwritten cursive with the letters separated by small gaps. For all three conditions, fewer errors occurred when stimuli were presented to the right visual field/left hemisphere (RVF/LH) than to the left visual field/right hemisphere (LVF/RH) and qualitative error patterns indicated that the last letter was missed more often than the first letter on LVF/RH trials but not on RVF/LH trials. Despite this overall similarity, the RVF/LH advantage was smaller for both types of cursive stimuli than for printed stimuli. In addition, the difference between first-letter and last-letter errors was smaller for handwritten cursive than for printed text, especially on LVF/RH trials. These results suggest a greater contribution of the right hemisphere to the identification of handwritten cursive, which is likely related visual complexity and to qualitative differences in the processing of cursive versus print.     

Hemispheric differences in processing visual patterns

The dichotomies verbal/visuospatial, serial/parallel and analytic/holistic are reviewed with respect to differences in hemispheric processing. A number of experimental parameters may be varied in such tasks, and together with certain frequently-occurring weaknesses of experimental design may account for the often discrepant results hitherto reported. The above factors are systematically reviewed, and three further experiments are reported which attempt to fill in the missing designs. Further evidence is given in support of the hypothesis that right-hemisphere superiority is most apparent in processes leading to identity matching. It is quantitative rather than qualitative, and may depend upon operations on the entire gestalt, such as holistic matching, mental rotation, reflection, distortion, etc., rather than, e.g., simultaneous (parallel) processing of discretely analysed or isolated features or elements. On the other hand left-hemisphere involvement in visuospatial processing is thought to reflect analysis of the configuration into its separable components; such processing may be either serial or parallel, and may frequently lead to a judgement different.     

Decisional processing in paranoid and non-paranoid schizophrenics

40 schizophrenic subjects, divided into paranoid/non-paranoid categories and 14 normal controls were presented a task which involved making "same-different" judgments during random presentations of a series of visual comparison stimuli with a standard which represented the midpoint of the stimulus continuum. Using Sternberg's Choice RT paradigm for studying the locus of cognitive deficit, difficulty at the response-selection stage was manipulated while holding other stages constant. It was predicted that paranoids would have shorter RTs at easy decision points and longer RTs at difficult decision points relative to non-paranoids. The directions of the differences were as predicted but did not attain statistical significance. Both schizophrenic groups, compared to normals, made significantly fewer "same" responses on those trials where the comparison and standard were most similar.     

Hemispheric processing of multi-element displays

A visual detection paradigm was employed in two experiments to explore the relationship between stimulus configuration and hemispheric processing. Stimulus arrays composed of small vertical lines were presented tachistoscopically to the left and right hemispheres. Subjects judged whether all the lines within an array were vertically oriented (same) or whether a horizontal line was present (different). In general, right hemisphere presentations demonstrated a faster detection than the left for arrays consisting of all identical elements, whereas left hemisphere presentations demonstrated a faster detection than the right for arrays containing a different element. Similar results were obtained for both experiments, although the response patterns and error rates varied somewhat with the inter-item spacing and organization of stimulus elements. These effects suggest that differential hemispheric processing for target detection tasks is determined by the nature of the stimulus materials which governs the relative efficacy of the hemispheric and decision outcomes.     

Social processing errors among paranoid personalities

The present study tested clinical hypotheses about the social processing attributes of paranoid personalities (PP). Eighteen PPs and 18 normal controls (NC) viewed standardized role plays (Dodge, 1986) in which a provocation occurred but the protagonist's intention varied (i.e., ambiguous, accidental, hostile, or prosocial). Subjects identified the intention behind the action and then chose a response to that action (e.g., ignore what he did). The results indicated that PPs and NCs did not differ on intentioncue detection when the intention was clear, but PPs had a significantly higher rate of misreading ambiguous situations. Furthermore, when intentions were ambiguous, PPs were more likely than NCs to identify them as hostile intentions. Finally, PPs' reactions to the vignettes were different from normal controls' when the perceived intention was either prosocial or accidential. PPs were more likely to respond with anger and less likely to ignore the event, compared to NCs. These data provide initial support for clinical notions about the aberrant social processing of paranoid personalities.     

Autobiographical memory deficits in schizophrenia

This study investigated autobiographical memory processes in a group of individuals diagnosed with schizophrenia and matched controls. The schizophrenia group displayed an overgeneral style of autobiographical memory retrieval on two widely used measures, and displayed problems retrieving both autobiographical facts and events. They showed a specific impairment in the recall of autobiographical events and facts in early adulthood, around the time of onset of their illness. Retrieval deficits were independent of mood state and premorbid intellectual functioning. The magnitude of the deficits in autobiographical memory retrieval specificity were considerably greater than any general impairments in episodic and working memory.     

Word production deficits in schizophrenia

Fronto-cerebellar circuitry is implicated in word production. Data suggest that the cerebellum is involved in word search, whereas the prefrontal cortex underlies the selection of words from among competing alternatives. We explored the role of search and selection processes in word production deficits in schizophrenia patients. In Experiment 1, patients were impaired in a verb generation task under both high and low selection conditions but were more impaired in the high selection condition. In Experiment 2, when the difficulty level of search and selection conditions was equated in a word stem completion task, patients were only impaired in the search condition. Word search deficits underlie word production problems in schizophrenia, and may involve fronto-cerebellar dysfunction.     

Neurophysiological evidence for disturbances of conflict processing in patients with schizophrenia

Deficits in cognition are a hallmark of schizophrenia. In the present study, the authors investigated the effects of schizophrenia on the neural correlates of conflict processing in a single-trial version of the Stroop task by using event-related brain potentials. Relative to matched controls, patients with schizophrenia showed increased Stroop interference in response time, but this effect was eliminated when the effect of response slowing was controlled. In controls, conflict processing was associated with a negative wave peaking between 400 and 500 ms (N450) and conflict sustained potential (SP) peaking between 600 and 800 ms after stimulus onset. In patients with schizophrenia, the amplitude of the N450 was significantly attenuated and the conflict SP was absent. These results provide evidence for the existence of altered neural processes associated with conflict processing that may be associated with dysfunction of the anterior cingulate and prefrontal cortex in patients with schizophrenia.     

Hemispheric local/global processing revisited

Hemispheric differences for local and global processing were assessed with square and rectangular stimulus shapes which contained either squares or rectangles within them. Experiment 1 manipulated the overall size and area of the stimulus items, while experiment 2 kept stimulus area constant and manipulated the number of shapes inside the stimulus. In different conditions subjects judged whether the inside shapes (local processing) or whether the outside shapes (global processing) were squares or rectangles. Reaction time measures revealed that hemispheric differences were unrelated to the local or global processing requirements as well as the spatial frequency of the stimulus texture. A left hemisphere advantage generally was obtained across stimulus and processing conditions, with the pattern of task effects dependent on the specific stimuli employed. The results suggest that the overall stimulus shape rather than processing mode or specific spatial frequency is a primary determinant of hemispheric differences for visual information.     

Hemispheric asymmetries in visual pattern processing in infancy

A right hemisphere advantage was observed in a previous study of 4- to 9-month old infants presented with a face discrimination task (de Schonen & Mathivet, 1990). The present study was designed to investigate pattern processing by the two hemispheres and the interhemispheric communication of this processing. Infants aged 4 to 9 months were tested with divided visual field presentations in one or two discrimination tasks. Under both task conditions, the infants had to discriminate between two patterns in which only two local components differed. Under one condition the components of the patterns were arranged so as to produce a face-like pattern. Under the other condition the same components were arranged into arbitrary patterns that were not "good form" patterns. No performance asymmetry was observed with the arbitrary patterns; whereas, a right hemisphere (RH) disadvantage was observed with the face-like patterns compared with both the RH performances on the arbitary patterns and the left hemisphere (LH) performances on the face-like patterns. These results show that the RH advantage for individual face recognition is not due to a general immaturity or inability of the LH in pattern processing at this period of development, nor to a more specific inability in a local mode of pattern processing. On the other hand, the RH does not completely lack local processing capacity, but is at a disadvantage when this local mode of processing has to be used with face-like (or good form) patterns. The interhemispheric communication of visual discrimination learning was tested by measuring learning transfer between the visual fields. Contrary to de Schonen and Bry's study (1987) on faceness recognition, no data in favor of interhemispheric communication were recorded in the present study.