Article

''Masked'' Span of Apprehension in Schizophrenic Subgroups

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Abstract

Background. This study explored the possible impairment in inhibiting irrelevant stimuli (as reflected in the backward masking version of the forced-choice span of apprehension task) in subgroups of individuals with schizophrenia. Method. Subjects included 48 schizophrenics and 54 nonpsychiatric controls. Letter arrays were presented at three stimulus onset asynchronies (SOAs; 60, 100, 250msec) and three levels of complexity (3, 7, 11 distractor letters). Results. As a group, schizophrenics (n = 54) were impaired relative to nonpsychiatric controls (n = 48) for 7-distractor displays at 60msec and 250msec SOA. Cluster analysis of SAPS and SANS ratings produced four symptom subgroups. Opposing masking performances were found for Psychomotor Poverty (impaired for long SOAs) and Reality Distortion (enhanced at short SOAs) subgroups, whereas the Disorganisation subgroup was globally impaired, and the Episodic subgroup performed similarly overall to controls. Conclusion. The results highlight the potential importance of symptomatology in further elucidating the span of apprehension impairment in schizophrenia.

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Forward and backward masking of contour by light was investigated with stimulus onset asynchronies from 20 to 180 ms in a group of 22 schizophrenic patients and 22 matched normal controls. Individuals with schizophrenia were selected using American Psychiatric Association (1987) criteria and were also assessed using the Andreasen scales for the presence of positive and negative symptoms (N.C. Andreasen, 1981, 1983). The Andreasen scales were used to divide schizophrenic patients into 2 subgroups (positive and negative symptoms). Positive-symptom schizophrenic patients showed no differences in their target duration thresholds or in their backward masking functions. Negative-symptom schizophrenic patients showed significantly longer target duration thresholds and experienced significantly more backward masking. There was no difference between schizophrenic patients and controls in forward masking.
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The effect of display visual angle on span of apprehension (SOA) task performance was investigated in patients with schizophrenia and nonpsychiatric individuals. Narrow and wide visual-angle presentations of 3- and 10-letter arrays were compared. Detection rates were significantly higher with narrow than wide visual angle for nonpsychiatric individuals; the performance of those with schizophrenia was stable across visual-angle conditions. Patients with schizophrenia were best discriminated from nonpsychiatric individuals in the narrow-angle, 10-letter condition. Scanpath analyses, which were based on the pattern of detection rates across different target quadrant locations, suggested that the patients with schizophrenia used a similar number and path of covert scan moves as did the controls. Hypotheses are discussed regarding which of the multiple cognitive processes tapped by the SOA task may be impaired in schizophrenia.
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Subgroups of patients with schizophrenia were examined in relation to repetition and semantic priming under conditions in which the prime stimulus was to be either attended to or ignored (unattended). Attended conditions normally would produce positive priming; and unattended conditions, negative priming (i.e., a delayed reaction resulting from inhibition of target information previously presented as to-be-ignored stimulus). Cluster analysis of participants' ratings on the Schedule for the Assessment of Positive Symptoms and the Schedule for the Assessment of Negative Symptoms revealed three subgroups that aligned broadly previous research citing with disorganization, reality distortion, and psychomotor poverty syndromes, and a fourth episodic subgroup. The Disorganization, Reality Distortion, and Episodic subgroups were associated with reduced, indeed reversed, negative priming in unattended priming conditions, whereas the Psychomotor Poverty subgroup exhibited the usual negative priming effect. Participants in the former three subgroups also exhibited reversed positive priming for the repetition condition, while the Psychomotor Poverty group displayed the expected positive priming effect. These results indicate that weakening of inhibitory processes may underlie both the reality distortion and disorganization dimensions of positive schizophrenic symptomatology, including the latent presence of these symptoms. In contrast, negative symptoms contributing to the psychomotor poverty dimension of schizophrenia are not linked to reduced inhibition. The association of positive symptom subgroups with reversed positive priming suggested that, for these participants, stimuli and task differences have an impact on the preattentive activation of information underlying such priming. It is proposed that a "reduced inhibition" model of schizophrenic symptomatology may need to be extended to account for influences on preattentive processing.
Article
The experimental situation of concern is one in which a visual display comprising a number of discrete elements, in the present study randomly selected consonants, is presented tachistoscopically for an interval short enough to permit only a single fixation. Questions of primary interest are: (i) How much information in the display is reflected in selective responses by the subject; and (ii) is the information associated with individual elements of the display processed simultaneously or serially? Evidence bearing on the first question was obtained, firstly, by the classical procedure of verbal report, and secondly, by a discrimination procedure in which the subject was required to indicate only which member of a predesignated pair of elements was present in each display. (H. A. Taylor collaborated in these experiments.) Results from the second method yield estimates of transmitted information significantly larger than those from the first and agree quantitatively with those reported earlier by G. Sperling for a sampling procedure. Relative to the second question, a simultaneous sampling model, derived from statistical learning theory, can be rejected. A model assuming serial sampling of the display elements with random stopping provides a relatively good account of the data. When the estimate of the number of elements processed is plotted versus number of elements in the display, the curve yielded by the report procedure levels off beyond 5 to 6 elements while the curve for the detection procedure continues to rise. This disparity poses special problems for theories of retention loss following stimulation and immediate response.
  • Miller S.
  • Granholm E.