Search tips
Search criteria

Results 1-10 (10)

Clipboard (0)

Select a Filter Below

more »
Year of Publication
Document Types
1.  Testing sensory and cognitive explanations of the antisaccade deficit in schizophrenia 
Journal of abnormal psychology  2013;122(4):1111-1120.
Recent research has suggested that people with schizophrenia (PSZ) have sensory deficits, especially in the magnocellular pathway, and this has led to the proposal that dysfunctional sensory processing may underlie higher-order cognitive deficits. Here we test the hypothesis that the antisaccade deficit in PSZ reflects dysfunctional magnocellular processing rather than impaired cognitive processing, as indexed by working memory capacity. This is a plausible hypothesis because oculomotor regions have direct magnocellular inputs, and the stimuli used in most antisaccade tasks strongly activate the magnocellular visual pathway. In the current study, we examined both prosaccade and antisaccade performance in PSZ (N = 22) and matched healthy control subjects (HCS; N = 22) with Gabor stimuli designed to preferentially activate the magnocellular pathway, the parvocellular pathway, or both pathways. We also measured working memory capacity. PSZ exhibited impaired antisaccade performance relative to HCS across stimulus types, with impairment even for stimuli that minimized magnocellular activation. Although both sensory thresholds and working memory capacity were impaired in PSZ, only working memory capacity was correlated with antisaccade accuracy, consistent with a cognitive rather than sensory origin for the antisaccade deficit.
PMCID: PMC3929125  PMID: 24364614
schizophrenia; antisaccade; working memory; magnocellular pathway; eye movements
2.  Toward the Neural Mechanisms of Reduced Working Memory Capacity in Schizophrenia 
Cerebral Cortex (New York, NY)  2012;23(7):1582-1592.
People with schizophrenia (PSZ) demonstrate reliable reductions in working memory (WM) capacity (i.e., the number of objects that can be held in memory). The present study asked whether WM impairments in PSZ can be explained by the same neural mechanisms that underlie individual differences in WM capacity among healthy individuals. Specifically, we examined event-related potentials in PSZ and healthy matched controls during a change detection task that required the storage of multiple objects in WM. The amplitude of contralateral delay activity (CDA), which correlates with WM capacity in healthy individuals, was larger in controls than in PSZ for memory loads of 3 and 5 objects, but larger in PSZ than in controls for a memory load of 1. This same pattern was found in the subgroups of PSZ and controls with an equivalent WM capacity. Moreover, the increase in CDA amplitude was correlated with individual differences in capacity in controls, but not in PSZ. These results demonstrate that WM impairment in PSZ is not associated with the same patterns of neural activity that characterize low WM capacity in healthy individuals. We propose that WM impairment in PSZ instead reflects a specific impairment in the ability to distribute attention broadly.
PMCID: PMC3673174  PMID: 22661407
CDA; event-related potentials; visual short-term memory
3.  Rapid feature-driven changes in the attentional window 
Journal of cognitive neuroscience  2013;25(7):10.1162/jocn_a_00376.
Spatial attention must adjust around an object of interest in a manner that reflects the object’s size on the retina as well as the proximity of distracting objects, a process often guided by nonspatial features. The present study used event-related potentials (ERPs) to investigate how quickly the size of this type of "attentional window" can adjust around a fixated target object defined by its color and whether this variety of attention influences the feedforward flow of subsequent information through the visual system. The task involved attending either to a circular region at fixation or to a surrounding annulus region, depending on which region contained an attended color. The region containing the attended color varied randomly from trial to trial, so the spatial distribution of attention had to be adjusted on each trial. We measured the initial sensory ERP response elicited by an irrelevant probe stimulus that appeared in one of the two regions at different times after task display onset. This allowed us to measure the amount of time required to adjust spatial attention on the basis of the location of the task-relevant feature. We found that the probe-elicited sensory response was larger when the probe occurred within the region of the attended dots, and this effect required a delay of approximately 175 ms between the onset of the task display and the onset of the probe. Thus, the window of attention is rapidly adjusted around the point of fixation in a manner that reflects the spatial extent of a task-relevant stimulus, leading to changes in the feedforward flow of subsequent information through the visual system.
PMCID: PMC3859374  PMID: 23448524
4.  Visuospatial Attention in Schizophrenia: Deficits in Broad Monitoring 
Journal of abnormal psychology  2011;121(1):119-128.
Although selective attention is thought to be impaired in people with schizophrenia (PSZ), prior research has found no deficit in the ability to select 1 location and withdraw attention from another. PSZ and healthy control subjects (HCS) performed a stimulus detection task in which 1, 2, or all 4 peripheral target locations were cued. When 1 or 2 locations were cued, both PSZ and HCS responded faster when the target appeared at a cued than uncued location. However, increases in the number of validly cued locations had much more deleterious effects on performance for PSZ than HCS, especially for targets of low contrast whose detection was more dependent on attention. PSZ also responded more slowly in trials with 4 cued locations relative to trials with 1 or 2 invalidly cued locations. Thus, visuospatial attention deficits in schizophrenia arise when broad monitoring is required rather than when attention must be focused narrowly.
PMCID: PMC3465689  PMID: 21604825
5.  The role of magnocellular signals in oculomotor attentional capture 
Journal of vision  2011;11(13):10.1167/11.13.11 11.
While it is known that salient distractors often capture covert and overt attention, it is unclear whether salience signals that stem from magnocellular visual input have a more dominant role in oculomotor capture than those that result from parvocellular input. Because of the direct anatomical connections between the magnocellular pathway and the superior colliculus, salience signals generated from the magnocellular pathway may produce greater oculomotor capture than those from the parvocellular pathway, which could be potentially harder to overcome with “top-down”, goal-directed guidance. Although previous research has addressed this with regard to magnocellular transients, in the current research we investigated whether a static singleton distractor defined along a dimension visible to the magnocellular pathway would also produce enhanced oculomotor capture. In two experiments, we addressed this possibility by comparing a parvo-biased singleton condition, in which the distractor was defined by isoluminant chromatic color contrast, with a magno+parvo singleton condition, in which the distractor also differed in luminance from the surrounding objects. In both experiments, magno+parvo singletons elicited faster eye movements than parvo-only singletons, presumably reflecting faster information transmission in the magnocellular pathway, but magno+parvo singletons were not significantly more likely to produce oculomotor capture. Thus, although magnocellular salience signals are available more rapidly, they have no sizable advantage over parvocellular salience signals in controlling oculomotor orienting when all stimuli have a common onset.
PMCID: PMC3218571  PMID: 22076486
6.  The relationship between working memory capacity and broad measures of cognitive ability in healthy adults and people with schizophrenia 
Neuropsychology  2013;27(2):220-229.
Working memory (WM) capacity, typically measured with cognitively complex span tasks, is correlated with higher-order cognitive abilities in healthy adults. The goals of the present study were to determine: 1) if a more focused measure of visual WM storage capacity would show similar higher-order ability correlations in healthy adults and in people with schizophrenia (PSZ) thereby demonstrating the importance of simple storage capacity, 2) determine if the illness alters the pattern of correlations across cognitive domains, and, 3) evaluate whether between-group differences in WM capacity could account for the generalized cognitive impairment in PSZ.
Ninety-nine PSZ and 77 healthy controls (HCs) completed a visual WM change localization task, the Wechsler Abbreviated Scale of Intelligence (WASI) and the MATRICS Consensus Cognitive Battery (MCCB).
PSZ performed more poorly than HC on all cognitive measures. The between-group effect size for WM capacity was large (d = 1.11). WM robustly correlated with WASI and MCCB performance with no significant differences in the magnitude or pattern of correlations across groups. When the groups were pooled, WM capacity correlated at r=0.68 with MCCB composite score and at r=0.56 with WASI estimated Full Scale IQ. WM capacity accounted for approximately 40% of the between-group variance across the WASI and MCCB.
A simple measure of WM storage capacity is robustly associated with the higher-order cognitive abilities assessed by the WASI and MCCB in both HC and PSZ. WM capacity reduction may be a critical determinant of the general cognitive impairment in PSZ.
PMCID: PMC3746349  PMID: 23527650
working memory; schizophrenia; intelligence
7.  Response Activation Impairments in Schizophrenia: Evidence from the Lateralized Readiness Potential 
Psychophysiology  2011;49(1):73-84.
Previous research has demonstrated deficits in pre-response motor activity in schizophrenia, as evidenced by a reduced lateralized readiness potential (LRP). The LRP deficit could be due to increased activation of the incorrect response (e.g., failure to suppress competition) or to reduced activation of the correct response (e.g., a low-level impairment in response preparation). To distinguish these possibilities, we asked whether the LRP impairment is increased under conditions of strong response competition. We manipulated the compatibility of stimulus-response mappings (Experiment 1) and the compatibility of the target with flankers (Experiment 2). In both experiments, the patient LRP was reduced as much under conditions of low response competition as under high competition. These results are incompatible with a failure of patients to suppress competition and are instead consistent with a deficit in activating the correct response.
PMCID: PMC3240710  PMID: 22091661
8.  Control of Working Memory Content in Schizophrenia 
Schizophrenia Research  2011;134(1):70-75.
People with schizophrenia (PSZ) exhibit signs of reduced working memory (WM) capacity. However, this may reflect an impairment in managing its content, e.g. preventing irrelevant information from taking up available storage space, rather than a true capacity reduction. We tested the ability to eliminate and update WM content in 38 PSZ and 30 healthy control subjects (HCS). Images of real-world objects were presented consecutively, and a tone cued the item most likely to be tested for memory. On half the trials, randomly intermixed, a second tone occurred. Participants were informed that the item cued by the second tone was now the most likely to be tested, and the item cued by the first tone now the least likely, providing incentive to eliminate the first cued item from WM. Both HCS and PSZ displayed a robust performance advantage for cued items. Unexpectedly, PSZ more efficiently removed the no-longer-essential item from WM than HCS. The magnitude of the WM clearance of this first cued item correlated with memory performance for the newly prioritized second cued item in PSZ, indicating that it was adaptive. However, WM clearance was not associated with WM capacity, ruling out the need to budget limited resources as an explanation for greater clearance in PSZ. A robust correlation between WM clearance and poverty of speech in PSZ instead suggests that the propensity to rapidly clear non-essential information and minimize the number of items in WM may be the reflection of a negative symptom trait. This finding may reflect a more general tendency of PSZ to focus processing more narrowly than HCS.
PMCID: PMC3275350  PMID: 22079944
schizophrenia; working memory; clearance; updating; capacity; alogia
9.  Failure of Schizophrenia Patients to Overcome Salient Distractors During Working Memory Encoding 
Biological psychiatry  2010;68(7):603-609.
Prior demonstrations of impaired attentional control in schizophrenia focused on conditions in which top-down control is needed to overcome prepotent response tendencies. Attentional control over stimulus processing has received little investigation. Here we test whether attentional control is impaired during working memory encoding when salient distractors compete with less salient task-relevant stimuli.
Patients with schizophrenia (n=28) and healthy controls (HC, n=25) performed a visuospatial working memory paradigm in which half of the to-be-encoded stimuli flickered to increase their salience. After a 2-s delay, stimuli reappeared and participants had to decide whether or not a probed item had shifted location.
In the Unbiased condition where flickering and non-flickering stimuli were equally likely to be probed, both groups displayed a trend towards better mesmory for the flickering items. In the Flicker-bias condition in which the flickering stimuli were likely to be probed, both groups displayed a robust selection advantage for the flickering items. However, in the Nonflicker-bias condition in which the non-flickering stimuli were likely to be probed, only HC showed selection of the non-flickering items. Patients displayed a trend toward preferential memory for the flickering items, as in the unbiased condition.
Both groups were able to select salient over non-salient stimuli, but patients with schizophrenia were unable to select non-salient over salient stimuli, consistent with impairment in the effortful control of attention. These findings demonstrate the generality of top-down control failure in schizophrenia in the face of bottom-up competition from salient stimuli as with prepotent response tendencies.
PMCID: PMC2942999  PMID: 20570242
schizophrenia; selective attention; distraction; bottom-up; top-down; working memory
10.  Why Salience is Not Enough: Reflections on Top-Down Selection in Vision 
Acta psychologica  2010;135(2):130-132.
The target article represents a distillation of nearly 20 years of work dedicated to the analysis of visual selection. Throughout these years, Jan Theeuwes and his colleagues have been enormously productive in their development of a particular view of visual selection, one that emphasizes the role of bottom-up processes. This work has been very influential, as there is substantial merit to many aspects of this research. However, this endeavor has also been provocative—the reaction to this work has resulted in a large body of research that emphasizes the role of top-down processes. Here we highlight recent work not covered in Theeuwes’s review and discuss how this literature may not be compatible with Theeuwes’s theoretical perspective. In our view this ongoing debate has been one of the most interesting and productive in the field. One can only hope that in time the ultimate result will be a complete understanding of how visual selection actually works.
PMCID: PMC2948621  PMID: 20580341

Results 1-10 (10)