Biomedical subjects

L C Robertson

Publications and source records attributed to L C Robertson.

At least 19 recordsLinked to original sources

PubMed1996

Normal sustained effects of selective attention are absent in schizophrenic patients withdrawn from medication.

Sustained attentional deficits have been widely reported in groups of medicated schizophrenic patients, but less is known about sequential attentional processes in patients withdrawn from medication. The attentional performance of 12 medication-withdrawn schizophrenic outpatients was compared with that of 16 matched normal volunteers on a Stroop negative priming task. This task allowed examination of both within-trial and between-trial attentional effects. Compared with the volunteers, the medication-withdrawn schizophrenic patients showed normal within-trial attentional effects as measured by standard Stroop interference and facilitation. Across trials, however, the schizophrenics exhibited reduced negative priming compared with the volunteers and in some cases a complete reversal of sustained inhibitory processes. The findings suggest that a normal inhibitory tag occurred during initial selection in the patient group, but it did not influence a subsequent act of selection as was the case for the normal volunteers. Either inhibition decayed at an abnormally fast rate in the patient group or a separate facilatory tag dominated. In either case, priming effects linked to attentional selection were clearly abnormal in the medication-withdrawn patient group.

Adult↗

PubMed1996

Perceptual and attentional asymmetries in schizophrenia: further evidence for a left hemisphere deficit.

Increasing evidence suggests the presence of a lateralizing attentional deficit in schizophrenia. In the present study, 23 unmedicated patients with schizophrenia (mean age = 32.1 years) and 14 age- and sex-matched normal subjects were studied with the Global/Local Task to provide converging evidence for the presence of a left-hemisphere-associated attentional deficit in schizophrenia. This task is sensitive to the integrity of mechanisms involved in discriminating local and global elements of stimuli. Previous research has linked the discrimination of local targets to left hemispheric processes and the discrimination of global targets to right hemispheric processes. As predicted, patients were impaired in the detection of local level targets, consistent with a left hemispheric deficit. The degree of impairment correlated with the patient's level of auditory hallucinations. These results are consistent with previous studies showing an asymmetrical attentional deficit in schizophrenia and left hemispheric dysfunction. The correlation between this deficit and auditory hallucinations is consistent with a hypothesized relationship between this symptom in schizophrenia and left temporal pathology.

Adult↗

PubMed1996

Attentional persistence for features of hierarchical patterns.

Priming for perceptual wholes and parts was examined in 4 experiments involving patterns arranged in a spatial hierarchy (D. Navon, 1977). Previous studies have demonstrated "level-specific priming" across successive trials for these patterns (L. C. Robertson, R. Egly, M. R. Lamb, & L. Kerth, 1993; L. M. Ward, 1982), and studies in neuropsychology have shown an absence of this priming effect in patient groups with parietal damage (R. Rafal & L. C. Robertson, 1994). The present experiments demonstrate that level-specific priming is linked to the spatial frequency differences between global and local forms in hierarchical patterns. They also show that level-specific priming is present even when the stimulus as a whole changes location. The effects last for up to 3 s without diminution and are not affected by changes in color, polarity, or contrast. These findings are discussed as they relate to spatial attention, object perception, and memory.

Adult↗

PubMed1995

Parietal contributions to visual feature binding: evidence from a patient with bilateral lesions.

Neurophysiologists have documented the existence of multiple cortical areas responsive to different visual features. This modular organization has sparked theoretical interest in how the "binding problem" is solved. Recent data from a neurological patient (R.M.) with bilateral parietal-occipital lesions demonstrates that the binding problem is not just a hypothetical construct; it can be a practical problem, as rare as the selective inability to perceive motion or color. R.M. miscombines colors and shapes even under free viewing conditions and is unable to judge either relative or absolute visual locations. The evidence suggests that a single explanation--an inadequate spatial representation--can account for R.M.'s spatial judgment and feature-binding deficits.

Cerebral Infarction↗

PubMed1995

Covert orienting biases in scene-based reference frames: orientation priming and visual field differences.

Performance advantages for stimuli presented in the right versus the left visual field have been found in a variety of attentional tasks. Such advantages were exploited in the present set of studies to examine orientation priming and directional biases in retinotopic and scene-based spatial coordinates. The results demonstrate that directional biases occur within spatial coordinates across orientation transformations that dissociate retinotopic from scene-based visual half fields. The results are discussed concerning the representation of spatial maps in higher visual analysis, the role of spatial coordinates in guiding covert orienting, and methods of presenting stimuli in the right or left visual field to test for functional hemispheric asymmetries.

Adult↗

PubMed1994

Attentional asymmetry in schizophrenia: the role of illness subtype and symptomatology.

1. Patients with undifferentiated and paranoid schizophrenia, and normal controls were compared using 2 versions of the covert orienting of attention procedure which evaluate exogenous (automatic) and endogenous (controlled) cuing mechanisms. 2. For both tasks, attentional performance varied with illness subtype, but in different ways. 3. On measures of automatic orienting undifferentiated patients showed evidence consistent with a mild right visual field deficit, while paranoid showed a reduction of inhibition-of-return, a mechanism which biases against returning to previously attended locations. 4. On measures of controlled orienting only the undifferentiated group showed the asymmetry of costs which has been the emphasis of most previous studies. The pattern of cost asymmetry was similar to that previously associated with prominent negative symptoms. Additionally, the magnitude of cost asymmetry correlated positively with negative symptoms in the overall patient group. 5. These findings show that systematically considering cue type and symptomatology are critical in interpreting varying patterns of performance by different groups of patients with schizophrenia on the covert orienting procedure. The implications of these findings for understanding the psychopathology of attention in schizophrenia and its neurobiological substrates are discussed.

Adult↗

PubMed1993

Abnormal processing of irrelevant information in schizophrenia: the role of illness subtype.

In a study using a trial by trial version of the Stroop color naming task, we previously found that unmedicated patients with schizophrenia show a pattern of abnormal performance characterized by increased facilitation (speeding) of color-naming, color-congruent words but normal amounts of interference (slowing) of color-naming, color-incongruent words (Carter et al., 1992). Since a similar finding had recently been reported in patients with Parkinson's disease, we suggested that this finding was consistent with hypotheses about the neurobiological substrates of cognitive impairment that draw upon parallel patterns of cognitive performance in the two illnesses. We now report results from an enlarged group of unmedicated patients with schizophrenia that extend our original finding by allowing us to evaluate the role of illness subtype in abnormal performance on the Stroop task. We found that patients with the undifferentiated subtype of the disorder account for the increased Stroop facilitation effect. Patients with the paranoid subtype show their own pattern of abnormal performance, with normal amounts of facilitation and increased interference. These findings are consistent with the results of other studies which suggest that illness subtype is an important source of variability in studies of cognitive functioning in schizophrenia.

Adult↗

PubMed1993

Spatial attention and cuing to global and local levels of hierarchical structure.

Five experiments investigated the role of attention in identifying global and local targets in hierarchically structured patterns. Hierarchical patterns were presented at a variable stimulus onset asynchrony (SOA) either after a cue (4 arrows or shaded boxes) or after no cue. Targets occurred at the cued level 80% of the time and at the uncued level 20%. On uncued trials, target level probability was .5. Global cues produced benefits for both global and local targets over SOA on cued trials. Local cues produced benefits only for local targets. For uncued trials, responses favored local targets overall when interspersed with locally cued trials but favored global targets when interspersed with globally cued trials. The role of an attentional window and discrete distribution of attention over global and local levels of hierarchical patterns are discussed.

Adult↗

PubMed1993

Cognitive neuropsychology is more than single-case studies.

S. M. Sokol et al. (1991) claim that "The Cognitive Neuropsychology Approach" (p. 355) is limited to the single-case study design. The present article takes issue with this claim. Contrary to the beliefs of Sokol et al., we argue (a) that cognitive modularity is best studied by group design, (b) that the possibility of neural reorganization in patients should be tested through converging evidence from different populations using various methods, and (c) that cognitive neuropsychology can benefit from being a part of cognitive neuroscience where both neural and cognitive mechanisms underlying normal cognition are relevant.

Bias↗

PubMed1993

Speed of memory scanning is not affected in early HIV-1 infection.

Thirty-seven nondemented HIV-seropositive and 17 seronegative control subjects were administered the Sternberg speed of memory scanning task, a procedure frequently employed to study mental slowing in patients with subcortical dementing disorders. Experimental and control subjects did not differ in speed of memory scanning, as indexed by the slopes of set size-reaction time functions, nor on mean 0-intercepts for the RT functions, which index stimulus detection and motor response time. Intercept values were significantly greater for subjects with a positive alcohol abuse history and for subjects with greater self-reported depression, but slopes were not significantly correlated with substance abuse history or psychological distress. Cognitive slowing in early HIV-1 infection is not a nonspecific effect observed across all measures of information processing speed. Underlying component functions measured must be carefully considered when selecting reaction time tasks for study with HIV-seropositive subjects. The term "subcortical" dementia may be too general a descriptor, and RT task performance may provide an alternative basis for classification of dementia types.

Acquired Immunodeficiency Syndrome↗

PubMed1993

Bionomics of Anopheles quadrimaculatus and Culex erraticus (Diptera: Culicidae) in the Falls Lake basin, North Carolina: seasonal changes in abundance and gonotrophic status, and host-feeding patterns.

Larval and adult Anopheles quadrimaculatus Say (sensu lato) and Culex erraticus (Dyar & Knab) were collected at Falls of the Neuse Lake (Falls Lake) in North Carolina from May 1985 to December 1986. Adult mosquitoes were aspirated weekly from shelters in woodlands adjacent to larval sampling sites. An. quadrimaculatus and Cx. erraticus comprised > 95% of the total number of mosquitoes collected. An. quadrimaculatus adults exhibited vernal and autumnal peaks of abundance during both years. Cx. erraticus adults exhibited several peaks of abundance in summer and early fall of both years. An. quadrimaculatus initiated blood feeding in May and April 1985 and 1986, respectively. Only unfed females were found in late fall and winter. Cx. erraticus initiated blood feeding earlier than An. quadrimaculatus. In 1985, approximately 25% of the females in the first collection in May contained a blood meal, whereas in 1986, approximately 10% of the females in the first collection in April were blood fed. Females of both species ceased blood feeding in late fall. Larvae were sampled on a weekly basis from lake edge, flood plain, and creek edge habitats. Generally, An. quadrimaculatus larvae were most abundant in lake edge and flood plain habitats, whereas Cx. erraticus larvae were most abundant in the creek edge habitat. The population dynamics of An. quadrimaculatus were associated with seasonal changes in the level of Falls Lake. In 1985 and 1986, the level of Falls Lake gradually declined from May to mid-August until heavy rainfall caused a 1-m rise in lake level. Populations of An. quadrimaculatus larvae and adults increased significantly following the rise in the level of Falls Lake. In contrast, the abundance of larval and adult Cx. erraticus decreased with rising lake levels in late August. Water level management should be an effective method for controlling populations of An. quadrimaculatus but not for Cx. erraticus. Blood-fed mosquitoes were tested to identify bloodmeal hosts using both capillary precipitin and enzyme-linked immunosorbent assays. An. quadrimaculatus (n = 941) predominantly (99%) fed on mammals, principally white-tailed deer and horses. Cx. erraticus (n = 348) exhibited an opportunistic host-feeding pattern; blood meals were taken from mammalian (49%), reptile or amphibian (20%), and avian (31%) hosts.

Animals↗

PubMed1992

Attentional asymmetry in schizophrenia: controlled and automatic processes.

Two versions of Posner's covert orienting task were administered to 14 drug-free schizophrenic patients and 12 normal controls. In the schizophrenic subjects, automatic orienting to exogenous cues in the right visual field was impaired. However, this lateralizing general deficit was not present when the schizophrenics were able to direct attention effortfully in the second version of the task using endogenous cues. These findings support the hypothesis that there is a deficit in left hemispheric mechanisms mediating visual spatial attention in schizophrenia. However, when schizophrenics are given the opportunity to use an attentional strategy they are able to partially overcome this lateralized processing deficit.

Attention↗

PubMed1992

Abnormal processing of irrelevant information in chronic schizophrenia: selective enhancement of Stroop facilitation.

Thirteen medication-free chronic schizophrenic patients and 11 normal control subjects were administered a trial by trial version of the Stroop Color Naming Task which evaluated separately the processes of interference and facilitation. There was no difference between the groups in the amount of interference to naming the colors of color-incongruent words. However, patients with schizophrenia showed significantly greater speed in naming the colors of color-congruent words when compared with control subjects. Thus, facilitation on the Stroop Task appears to be selectively enhanced in schizophrenia. Similar findings have been recently observed in patients with Parkinson's disease. This result may indicate a selective disruption of an automatic inhibitory process in this patient group and is consistent with the hypothesis that a deficit in mesocortical dopamine projections to the frontal cortex underlies some of the cognitive deficits of chronic schizophrenia.

Adult↗

PubMed1992

Performance of patients with early HIV-1 infection on the Stroop Task.

HIV-seropositive and seronegative control subjects performed a standard paper-and-pencil version and an experimental reaction time version of the Stroop Color-Word Naming Task. Results indicated that both symptomatic and asymptomatic HIV-positive subjects showed an exaggerated Stroop effect compared to controls, but this increase was only apparent on the RT version of the task. Analysis of components of the effect indicated that HIV-positive subjects showed increased inhibition compared to controls but normal facilitation. These results suggest that HIV-related cognitive slowing has an attentional component, most likely involving controlled processes. In addition, these results emphasize the utility and sensitivity of RT measures in the study of early HIV-1 infection.

AIDS Dementia Complex↗

PubMed1992

Decision-making speed in HIV-1 infection: a preliminary report.

OBJECTIVES: To test the efficacy of reaction time measures derived from cognitive psychology as measures of subclinical cognitive slowing in individuals with HIV-1 infection. DESIGN: Cognitive slowing is the primary deficit in AIDS dementia. One measure of cognitive slowing is decision-making speed, the discrepancy between simple and choice reaction times, which represents an index of central information processing time. METHODS: Nineteen HIV-seropositive and 13 control subjects performed a detection and decision task in a reaction time procedure. All subjects were administered measures of simple and choice reaction time, a control measure of rate of verbal encoding, and measures of psychological distress. RESULTS: Compared with controls, both symptomatic and asymptomatic HIV-seropositive subjects had significantly longer decision times, but performed the control task of rate of encoding normally. Simple reaction times correlated significantly with depression scores, but choice reaction times were unrelated to psychological distress. CONCLUSIONS: The results support mental slowing as the initial cognitive disturbance of HIV-1 infection and emphasize potential use of reaction times as markers of central nervous system involvement in HIV-1 infection.

Adult↗

PubMed1992

Spatial attention in HIV-1 infection: a preliminary report.

In a preliminary study, 30 nondemented human immunodeficiency virus (HIV-1) seropositive subjects without acquired immunodeficiency syndrome and 14 seronegative controls performed a reaction time measure of spatial attention. Compared with controls, seropositive asymptomatic subjects showed normal facilitation of reaction time at short cue-target intervals when attention was precued, but symptomatic subjects were impaired. However, asymptomatic subjects showed no evidence of normal inhibition of attention at the cued location at longer cue-target intervals, suggesting possible subtler spatial attentional deficits in this group. Cognitive slowing in HIV-1 infection may have an attentional component, with possible involvement of both automatic and controlled processes.

AIDS Dementia Complex↗

PubMed1991

Neuropsychological contributions to theories of part/whole organization.

Recent evidence from neuropsychology has proven useful in defining neural and cognitive subsystems involved in certain cognitive processes such as spatial attention (Posner, Walker, Friedrich, & Rafal, 1984) and imagery (Farah, 1988; Kosslyn, 1986). In this article we discuss neuropsychological evidence that suggests a modular system is responsible for the organization of parts and wholes by the visual system. We review both normal and neuropsychological evidence that suggest that hierarchical organization of objects within objects involves the coordination of at least four separate subsystems, one that emphasizes the global properties of a figure (association with right posterior superior temporal-parietal regions), one that emphasizes the local properties of a figure (associated with left posterior superior temporal-parietal regions), one that controls the distribution of attentional resources to these subsystems (associated with right or left lateral parietal lobe), and one that interconnects global and local properties and relies on the integrity of posterior temporal-temporal pathways.

Attention↗

PubMed1991

Normal global-local analysis in patients with dorsolateral frontal lobe lesions.

The role of prefrontal cortex in the analysis of global and local levels of a visual stimulus was assessed by measuring reaction time to identify a target at one level or the other. Unlike patients with temporal-parietal lesions (STG), there were no global-local performance deficits in right or left prefrontal groups (RFL or LFL). Reallocation of attention to global and local levels was measured by examining changes in performance when the probability of a target appearing at one level or the other varied. While patients with lateral parietal lesions (IPL) have been shown to have deficits in these conditions, both RFL and LFL showed normal changes in performance. In sum, the performance of prefrontal groups differed from both IPL and STG groups but not from normal controls. These results strengthen previous arguments that posterior association cortex is crucial in responding to global and local levels of a pattern.

Adult↗