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ABSTRACT: Object-substitution masking (OSM) is thought to reflect a failure of object individuation. That is, a briefly presented target surrounded by four dots is perceptually fused with the four-dot mask when the mask is visible after the target has disappeared, thereby obscuring the visibility of the target. If OSM depends on the inability to temporally segregate objects, then increasing the temporal precision of the visual system should reduce OSM. In the study reported here, we manipulated temporal precision by varying the proximity of participants' hands to visual stimuli, because stimuli in near-hand space have been found to enjoy enhanced attentional processing, and attention is known to speed visual processing. Hand placement was indeed found to affect OSM: Placing participants' hands near the visual stimuli reduced the magnitude of the masking. This finding demonstrates that object individuation can be facilitated by increasing the temporal resolution of vision via increasing the proximity of visual stimuli to the hands.
Psychological Science 04/2013; · 4.43 Impact Factor
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ABSTRACT: Object substitution masking (OSM) occurs when a sparse (e.g., four-dot), temporally trailing mask obscures the visibility of a briefly presented target. Here, we review theories of OSM: those that propose that OSM reflects the interplay between feedforward and feedback/reentrant neural processes, those that predict that feedforward processing alone gives rise to the phenomenon, and theories that focus on cognitive explanations, such as object updating. We discuss how each of these theories accommodates key findings from the OSM literature. In addition, we examine the relationship between OSM and other visual-cognitive phenomena, including object correspondence through occlusion, change blindness, metacontrast masking, backward masking, and visual short-term memory. Finally, we examine the level of processing at which OSM impairs target perception. Collectively, OSM appears to reflect the conditions under which the brain confuses two visual events for one when they are encoded with low spatiotemporal resolution, due to processing resources being otherwise occupied.
Psychonomic Bulletin & Review 02/2013; · 2.61 Impact Factor
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ABSTRACT: Although significant advances in our understanding of the cognitive and neural processes involved in conscious awareness have occurred in recent years, the precise mechanisms that support consciousness remain elusive. Examining the neural correlates associated with the moment a stimulus enters or exits conscious awareness is one way to potentially identify the neural mechanisms that give rise to consciousness. In the present study, we recorded neural activity using electroencephalography (EEG) while participants observed a bilateral shape-from-motion (SFM) display. While the display is in motion, the observer perceives an object that is immediately segregated from a noisy background. After the motion stops, the observer's experience of the object remains momentarily in awareness, before it eventually fades out of consciousness back into the noisy background. Consistent with subjective reports of perceptual experience, we observed a prominent sustained posterior contralateral negativity known as the contralateral delay activity (CDA). This activity was sustained only in conditions associated with sustained awareness. Interestingly, the amplitude of the CDA was correlated with individual differences in visual awareness, suggesting that this activity plays a significant role in the maintenance of objects in consciousness. The CDA is typically associated with visual short-term memory (VSTM), suggesting that conscious visual awareness may be mediated by the same neural and cognitive mechanisms that support VSTM. Our results demonstrate that the CDA may reflect the contents of conscious awareness, and therefore can provide a measure to track when information moves in and out of consciousness.
Psychonomic Bulletin & Review 02/2012; 19(3):429-35. · 2.61 Impact Factor
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ABSTRACT: Although significant advances in our understanding of the cognitive and neural processes involved in conscious awareness have occurred in recent years, the precise mechanisms that support consciousness remain elusive. Examining the neural correlates associated with the moment a stimulus enters or exits conscious awareness is one way to potentially identify the neural mechanisms that give rise to consciousness. In the present study, we recorded neural activity using electroencephalography (EEG) while participants observed a bilateral shape-from-motion (SFM) display. While the display is in motion, the observer perceives an object that is immediately segregated from a noisy background. After the motion stops, the observer’s experience of the object remainsmomentarily in awareness, before it eventually fades out of consciousness back into the noisy background. Consistent with subjective reports of perceptual experience, we observed a prominent sustained posterior contralateral negativity known as the
contralateral delay activity (CDA). This activity was sustained only in conditions associated with sustained awareness. Interestingly, the amplitude of the CDA was correlated with individual differences in visual awareness, suggesting that this activity plays a significant role in the maintenance of objects in consciousness. The CDA is typically associated with visual short-term memory (VSTM), suggesting that conscious visual awareness may be mediated by the same neural and cognitive mechanisms that support VSTM. Our results demonstrate that the CDA may reflect the contents of conscious awareness, and therefore can provide a measure to track when information moves in and out of consciousness.
Psychonomic Bulletin & Review 02/2012; · 2.61 Impact Factor
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ABSTRACT: When faced with maintaining multiple objects in visual working memory, item information must be bound to the correct object in order to be correctly recalled. Sometimes, however, binding errors occur, and participants report the feature (e.g., color) of an unprobed, non-target item. In the present study, we examine whether the configuration of sample stimuli affects the proportion of these binding errors. The results demonstrate that participants mistakenly report the identity of the unprobed item (i.e., they make a non-target response) when sample items are presented close together in space, suggesting that binding errors can increase independent of increases in memory load. Moreover, the proportion of these non-target responses is linearly related to the distance between sample items, suggesting that these errors are spatially specific. Finally, presenting sample items sequentially decreases non-target responses, suggesting that reducing competition between sample stimuli reduces the number of binding errors. Importantly, these effects all occurred without increases in the amount of error in the memory representation. These results suggest that competition during encoding can account for some of the binding errors made during VWM recall.
Journal of Vision 01/2012; 12(4). · 3.38 Impact Factor
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ABSTRACT: Visual short-term memory (VSTM) is a capacity limited resource, which is consistently estimated to hold about four visual items at a time. There is, however, debate in the literature about what constitutes an "item" and how resources are allocated within VSTM. Some research suggests information is stored in VSTM as discrete objects; however, there is also evidence suggesting that within-object features alter VSTM performance. The present study addresses the question of whether VSTM load effects reflect the number of discrete objects and/or the number of within-object features. An electrophysiological correlate of VSTM--the contralateral delay activity (CDA)--was measured while participants performed a lateralized change-detection task, in which to-be-remembered items varied in the number of features and locations. Each trial contained either a solitary simple feature (shape, color, or orientation) or one of two multifeature arrays: three features presented at three separate locations or three features bound at one location. While presenting multiple features--regardless of whether they are at discrete locations or bound within a single object--resulted in greater CDA amplitude relative to a solitary feature, there was a dissociation in the distribution of activity between the two multifeature conditions, such that the CDA at site P1/P2 was sensitive to the number of discrete objects, while activity at P7/P8 was most enhanced when multiple features were bound in one object. The findings demonstrate the inhomogeneity of the CDA and suggest this electrophysiological marker may reflect both discrete object individuation/separation and flexible feature-feature binding in VSTM.
Journal of Vision 01/2012; 12(8):14. · 3.38 Impact Factor
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ABSTRACT: In four experiments we assessed whether visual working memory (VWM) maintains a record of previously processed visual information, allowing old information to be inhibited, and new information to be prioritized. Specifically, we evaluated whether VWM contributes to the inhibition (i.e., visual marking) of previewed distractors in a preview search. We evaluated this proposal by testing three predictions. First, Experiments 1 and 2 demonstrate that preview inhibition is more effective when the number of previewed distractors is below VWM capacity than above; an effect that can only be observed at small preview set sizes (Experiment 2A) and when observers are allowed to move their eyes freely (Experiment 2B). Second, Experiment 3 shows that, when quantified as the number of inhibited distractors, the magnitude of the preview effect is stable across different search difficulties. Third, Experiment 4 demonstrates that individual differences in preview inhibition are correlated with individual differences in VWM capacity. These findings provide converging evidence that VWM supports the inhibition of previewed distractors. More generally, these findings demonstrate how VWM contributes to the efficiency of human visual information processing--VWM prioritizes new information by inhibiting old information from being reselected for attention.
Journal of Experimental Psychology Human Perception & Performance 10/2011; 38(3):643-63. · 3.06 Impact Factor
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ABSTRACT: Visual working memory (VWM) is a capacity-limited cognitive resource that plays an important role in complex cognitive behaviors. Recent studies indicate that regions subserving VWM may play a role in the perception and recognition of visual objects, suggesting that conscious object perception may depend on the same cognitive and neural architecture that supports the maintenance of visual object information. In the present study, we examined this question by testing object processing under a concurrent VWM load. Under a high VWM load, recognition was impaired for objects presented in the left visual field, in particular when two objects were presented simultaneously. Multivariate fMRI revealed that two independent but partially overlapping networks of brain regions contribute to object recognition. The first network consisted of regions involved in VWM encoding and maintenance. Importantly, these regions were also sensitive to object load. The second network comprised regions of the ventral temporal lobes traditionally associated with object recognition. Importantly, activation in both networks predicted object recognition performance. These results indicate that information processing in regions that mediate VWM may be critical to conscious visual perception. Moreover, the observation of a hemifield asymmetry in object recognition performance has important theoretical and clinical significance for the study of visual neglect.
Journal of Cognitive Neuroscience 03/2011; 23(10):2968-82. · 5.18 Impact Factor
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ABSTRACT: When multiple stimuli are concurrently displayed in the visual field, they must compete for neural representation at the processing expense of their contemporaries. This biased competition is thought to begin as early as primary visual cortex, and can be driven by salient low-level stimulus features. Stimuli important for an organism's survival, such as facial expressions signaling environmental threat, might be similarly prioritized at this early stage of visual processing. In the present study, we used ERP recordings from striate cortex to examine whether fear expressions can bias the competition for neural representation at the earliest stage of retinotopic visuo-cortical processing when in direct competition with concurrently presented visual information of neutral valence. We found that within 50 msec after stimulus onset, information processing in primary visual cortex is biased in favor of perceptual representations of fear at the expense of competing visual information (Experiment 1). Additional experiments confirmed that the facial display's emotional content rather than low-level features is responsible for this prioritization in V1 (Experiment 2), and that this competition is reliant on a face's upright canonical orientation (Experiment 3). These results suggest that complex stimuli important for an organism's survival can indeed be prioritized at the earliest stage of cortical processing at the expense of competing information, with competition possibly beginning before encoding in V1.
Journal of Cognitive Neuroscience 01/2011; 23(11):3410-8. · 5.18 Impact Factor
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ABSTRACT: Humans map timewords such as “yesterday” or “future” onto a mental timeline that holds temporally earlier events on the left side of space and temporally later events on the right side. The perception of time and spatial mapping both are partially subserved by right temporo-parietal brain regions. We tested stroke patients with right-hemisphere lesions on a spatio-temporal cueing task to see whether spatial associations of noninformative temporal cues would elicit the same cognitive deficits as do typical stimulus-driven exogenous cues. While our right brain-damaged patients were able to maintain a mental timeline with words referring to the past sitting to the left and words referring to the future sitting to the right, we also observed that the typical deficit in disengaging from incongruently cued locations persists for noninformative cues that are mapped onto a mental spatial continuum.
Cognitive neuroscience 12/2010; 1(4):289-295. · 0.77 Impact Factor
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ABSTRACT: Attentional capture can be contingent on attentional control settings (ACSs), such that peripheral cues influence processing for a subsequent target only when they share a critical feature with the target. Our previous demonstration that two ACSs from within the same feature category can be maintained simultaneously allows us to investigate the processing stage at which such ACSs are implemented. We compared the relative efficacy of ACSs from two different feature categories (shape and color) that are associated with different levels within the visual processing hierarchy. Participants were instructed to respond to one of two colors at one location and one of two shapes at another location, while ignoring the nontarget color and shape. We observed that spatial capture was modulated by whether the cues fit an ACS, with slightly greater contingent capture effects for ACSs defined by color than by shape. Thus, two ACSs from different feature sets (color and shape) can be maintained in parallel, although effectiveness of the control set varied with the type of feature.
Attention Perception & Psychophysics 10/2010; 72(7):1730-5. · 2.04 Impact Factor
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ABSTRACT: There is now substantial evidence that during visual search, previously searched distractors are stored in memory to prevent them from being reselected. Studies examining which memory resources are involved in this process have indicated that while a concurrent spatial working memory task does affect search slopes, depleting visual working memory (VWM) resources does not. In the present study, we confirm that VWM load indeed has no effect on the search slope; however, there is an increase in overall reaction times that is directly related to the number of items held in VWM. Importantly, this effect on search time increases proportionally with the memory load until the capacity of VWM is reached. Furthermore, the search task interfered with the number of items stored in VWM during the concurrent change-detection task. These findings suggest that VWM plays a role in the inhibition of previously searched distractors.
Quarterly journal of experimental psychology (2006) 08/2010; 63(8):1457-66. · 1.96 Impact Factor
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ABSTRACT: When one is responding to targets containing a specific feature, non-predictive peripheral cues that share this feature lead to faster responses to the target, while cues that do not contain the target feature effectively are ignored, providing evidence for the role of attentional control settings (ACSs) in the contingent capture hypothesis. It is unclear, however, at what stage of processing multiple ACSs are implemented. We took advantage of the excellent temporal resolution of electroencephalography to demonstrate that the maintenance of multiple ACSs influences later stages of attentional selection rather than providing an early attentional filter. N2pc analyses for cues and targets revealed a similar degree of spatial capture for any peripheral cue, regardless of control settings, with target P3s reflecting the application of the ACS color contingencies.
Cognitive Neuroscience. 06/2010; 1(2):102-110.
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ABSTRACT: When a unique stimulus is embedded in an otherwise homogenous display, it is thought to "pop-out" due to its relative increase in salience. We investigated whether the visual system has the ability to equally prioritize multiple salient pop-out items competing for awareness or whether this early stage of visual processing is constrained by capacity limits. We used signal detection (d') methods to determine if sensitivity to a salient pop-out item decreases as function of the number of total salient items present in the visual display. Participants engaged in a signal detection task where they had to report the presence or absence of a simple display change that involved either a pop-out or a non-salient distractor stimulus. Results across four experiments consistently showed that sensitivity to changes involving pop-out stimuli was significantly reduced after more than one of these items was present in the visual array. Results are discussed in terms of neural models of visual encoding and other known capacity limits during visual processing.
Journal of Vision 01/2010; 10(2):14.1-12. · 3.38 Impact Factor
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ABSTRACT: Although limited in capacity, visual working memory (VWM) plays an important role in many aspects of visually-guided behavior. Recent experiments have demonstrated an electrophysiological marker of VWM encoding and maintenance, the contralateral delay activity (CDA), which has been shown in multiple tasks that have both explicit and implicit memory demands. Here, we investigate whether the CDA is evident during visual search, a thoroughly-researched task that is a hallmark of visual attention but has no explicit memory requirements.
The results demonstrate that the CDA is present during a lateralized search task, and that it is similar in amplitude to the CDA observed in a change-detection task, but peaks slightly later. The changes in CDA amplitude during search were strongly correlated with VWM capacity, as well as with search efficiency. These results were paralleled by behavioral findings showing a strong correlation between VWM capacity and search efficiency.
We conclude that the activity observed during visual search was generated by the same neural resources that subserve VWM, and that this activity reflects the maintenance of previously searched distractors.
PLoS ONE 01/2009; 4(11):e8042. · 4.09 Impact Factor
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ABSTRACT: If some of the distractors in a visual search task are previewed prior to the presentation of the remaining distractors and the target, search time is reduced relative to when all of the items are displayed simultaneously. Here, we tested whether the ability to preferentially search new items during such a preview search is limited. We confirmed previous studies: The proportion of fixations on old items was significantly less than chance. However, the probability of fixating old locations was negatively affected by increasing the number of previewed distractors, suggesting that inhibition is limited to a small number of old items. Furthermore, the ability to inhibit old locations was limited to the first four fixations, indicating that by the fifth fixation, the resources required to sustain inhibition had been depleted. Together, these findings suggest that inhibition of old items in a preview search is a top-down mediated process dependent on capacity-limited cognitive resources.
Perception & Psychophysics 12/2008; 70(8):1552-7. · 1.37 Impact Factor
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ABSTRACT: Exposure to prisms has long been used to explore the control of visually guided actions primarily because adaptation requires the recalibration of misaligned reference frames due to perturbed visual input (i.e. eye-in-head and hand-centered reference frames must be realigned). To date, the only neuroimaging study to explore the direct effects of prisms on pointing used positron emission tomography and found increased activation only in right parietal cortex. We used event-related functional MRI to examine the effects of prisms on visuomanual pointing. Results demonstrated changes in activity in the anterior cingulate, the anterior intraparietal region and in a medial region of the right cerebellum. Specifically, activity in these regions was higher for the first few pointing trials made while viewing targets through prisms when directly contrasted to the last few trials. These results highlight that a more extensive network of cortical and cerebellar regions is involved in recalibrating visuomotor commands in the face of perturbed visual input.
European Journal of Neuroscience 11/2008; 28(8):1696-704. · 3.63 Impact Factor
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ABSTRACT: Previous research has demonstrated that, in addition to ventral stream processing of object form, manipulable objects are represented functionally in the dorsal stream. Here, we demonstrate how the two streams interact via attentional selection and consolidation such that objects whose form fits the function of a previously seen object, such as a tool, benefit from attentional enhancements due to the action affordance of the tool. Using the attentional blink (AB) paradigm and event-related potentials (ERPs), we tested whether providing an action relationship between two objects appearing closely together in time counteracts the typical decrement observed for processing of the second item. We used images (experiments 1a and 2) and names (experiment 1b) of common tools, objects that can be acted upon by those tools, and unrelated objects. We found that pictorial presentation of a tool and its action counterpart results in a diminished attentional blink as well as enhanced attentional selection seen as a larger P3, relative to tools and unrelated objects, and that this attentional enhancement is not driven by semantic associations. This means that the action affordance instantiated by the perception of a tool will reduce the functional blindness normally observed when two targets are presented too closely in time, specifically when the physical properties of the tool that elicit an action affordance are perceived.
Neuropsychologia 08/2008; 47(6):1600-8. · 3.64 Impact Factor
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ABSTRACT: The three experiments presented in the paper examine visual prior entry (determining which of two stimuli appeared first) and prior exit (determining which of two stimuli disappeared first) effects with a temporal order judgment (TOJ) task. In addition to using onset and offset targets, the preceding cues also consisted of either onset or offset stimuli. Typical, and equivalent, prior entry effects were found when either onset or offset cues preceded the onset targets. Unexpectedly large prior exit effects where found with the offset targets, with offset cues producing greater capture effects than onset cues. These findings are consistent with the notion that more attention is allocated to searching the visual field when targets are more difficult to find. In addition, the results indicate that attentional control settings may be more likely to occur with more difficult searches. In addition, these findings demonstrate that TOJ tasks provide extremely precise measures of the allocation of attention and are very sensitive to a range of task manipulations.
Psychological Research 08/2008; 72(4):443-50. · 2.47 Impact Factor
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ABSTRACT: When non-informative peripheral cues precede a target defined by a specific feature, cues that share the critical feature will capture attention while cues that do not will be effectively ignored. We tested whether different attentional control sets can be simultaneously maintained over distinct regions of space. Participants were instructed to respond only to specific colored targets at specific locations. Most trials included non-predictive cues whose location and/or color were either congruent or incongruent with the spatial and/or color properties of the impending target. We observed contingent capture only for cues that were consistent with the attentional control set applied to that region of space. This is the first demonstration that separate attentional control sets can be simultaneously maintained at distinct spatial locations, with implications for the flexibility of endogenous control over automatic attentional orienting.
Cognition 05/2008; 107(1):295-303. · 3.16 Impact Factor
