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63
The linkage of visual motion signals.
- Visual Cognition,
, 1999
"... Recovering a reliable 3D percept from the retinal sampling of dynamic images requires the linkage of motion signals across space and time. In this paper, we review recent experimental results that enhance our understanding of the perceptual processes of motion integration, segmentation, and selecti ..."
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Recovering a reliable 3D percept from the retinal sampling of dynamic images requires the linkage of motion signals across space and time. In this paper, we review recent experimental results that enhance our understanding of the perceptual processes of motion integration, segmentation, and selection that are necessary to solve this inverse optics problem. Simple paradigms involving the presentation of moving contours are used to assess our ability to link sparse motion information. Our results indicate that human motion perception strongly depends on both primitive stimulus characteristics, such as contrast, eccentricity, and duration, as well as higher level characteristics such as feature classification and spatial configurations. Further, the perceived direction of a moving object depends little upon its familiarity. Finally, pursuit eye movements of compositional stimuli are highly correlated with perceived motion coherence. This ensemble of results is analysed within the context of current theories of motion perception.
PET reveals occipitotemporal pathway activation during elementary form perception in humans
- Visual Neuroscience
, 1998
"... To define brain regions involved in feature extraction or elementary form perception, regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) in subjects viewing two classes of achromatic textures. Textures composed of local features (e.g. extended contours and rect ..."
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To define brain regions involved in feature extraction or elementary form perception, regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) in subjects viewing two classes of achromatic textures. Textures composed of local features (e.g. extended contours and rectangular blocks) produced activation or increased rCBF along the occipitotemporal pathway relative to textures with the same mean luminance, contrast, and spatial-frequency content but lacking organized form elements or local features. Significant activation was observed in striate, extrastriate, lingual, and fusiform cortices as well as the hippocampus and brain stem. On a scan-by-scan basis, increases in rCBF shifted from the occipitotemporal visual cortices to medial temporal (hippocampus) and frontal lobes with increased exposure to only those textures containing local features. These results suggest that local feature extraction occurs throughout the occipitotemporal (ventral) pathway during extended exposure to visually salient stimuli, and may indicate the presence of similar receptive-field mechanisms in both occipital and temporal visual areas of the human brain.
For a recent review
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"... H. pylori exploits and manipulates innate and adaptive immune cell signaling pathways to establish persistent infection ..."
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H. pylori exploits and manipulates innate and adaptive immune cell signaling pathways to establish persistent infection
Visual Attention and visual awareness
"... Intuitively, vision appears an overall easy process, effortless, almost automatic, and so efficient that a simple glance at a complex scene is sufficient to produce immediate awareness of its entire structure and elements. Unfortunately, much of this is a grand illusion (O’Regan & Noe, 2001). P ..."
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Intuitively, vision appears an overall easy process, effortless, almost automatic, and so efficient that a simple glance at a complex scene is sufficient to produce immediate awareness of its entire structure and elements. Unfortunately, much of this is a grand illusion (O’Regan & Noe, 2001). Proper manipulations will reveal that many often essential aspects of the visual scene can go purely unnoticed. For example, human subjects will often fail to notice an unexpected but quite large stimulus flashed right at the center of gaze during a psychophysical experiment (a phenomenon known as “inattentional blindness”, Mack and Rock, 1998). In more natural environments, observers can fail to notice the appearance or disappearance of a large object (Fig 3.1; Rensink et al, 1997; O’Regan et al, 1999), the change in identity of the person they are conversing with (Simons and Levin, 1998), or the passage of a gorilla in the middle of a ball game (Simons and Chabris, 1999). As a group, these visual failures are referred to as “change blindness ” (Rensink, 2002). Such limitations are rarely directly experienced in real life –except as one of the main instrument of magician tricks; yet they shape much of our visual perceptions.
Tsotsos. A connectionist perspective on laterality in visual attention
, 2005
"... This paper contains a comprehensive review of attention with a significant emphasis on lateralization of function. Connectivity and computation associated with the human visual system is described in detail, and the existing body of psychophysical, neurophysiological and computational studies relati ..."
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This paper contains a comprehensive review of attention with a significant emphasis on lateralization of function. Connectivity and computation associated with the human visual system is described in detail, and the existing body of psychophysical, neurophysiological and computational studies relating to attention is summarized. This provides the foundation for the later chapters which describe the nature of communication between hemispheres, and the relative efficiency with which each hemisphere handles different attentive and visuospatial tasks. Finally, we outline some
Modeling Parietal-Premotor Interactions inPrimate Control of Grasping
"... Visual information is processed in posterior parietal cortex for the hypothesized purpose of extracting a variety of affordances for the generation of motor behavior. The term affordance is used to mean that visual cues are mapped directly to parameters that are relevant for motor interaction. In th ..."
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Visual information is processed in posterior parietal cortex for the hypothesized purpose of extracting a variety of affordances for the generation of motor behavior. The term affordance is used to mean that visual cues are mapped directly to parameters that are relevant for motor interaction. In this paper, we present the FARS model of the cortical involvement in grasping, a model which focuses on the interaction between anterior intra-parietal area (AIP) and premotor area F5. The model represents the role of other intra-parietal areas, working in concert with inferotemporal cortex and F5, to provide AIP with a full range of information from which affordances may be derived. The model also suggests how task information and other constraints may resolve the action opportunities provided Fagg & Arbib: Parietal-Premotor Interactions in the Control of Grasping March, 1998 2 by multiple affordances. Our model demonstrates not only that posterior parietal cortex is a network of interacting subsystems, but also that it functions through a pattern of "cooperative computation " with a multiplicity of other brain regions. Finally, through the use of several novel tasks, the model allows us to make specific predictions regarding neural firing patterns at both the single unit and population levels, which aids in our further understanding of information encoding in these brain regions.
MEG studies of visual processing
- In: Zani, A., Proverbio, A. M. (Eds.), Cognitive Electrophysiology of Mind and
, 2002
"... Numerous magnetoencephalographic (MEG) investigations of the functional organization of the human visual system have been conducted since 1968, when ..."
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Numerous magnetoencephalographic (MEG) investigations of the functional organization of the human visual system have been conducted since 1968, when
Received Day Month Year Revised Day Month Year
, 2009
"... The topic of vision-based grasping is being widely studied using various techniques and with different goals in humans and in other primates. The fundamental related findings are reviewed in this paper, with the aim of providing researchers from different fields, including intelligent robotics and n ..."
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The topic of vision-based grasping is being widely studied using various techniques and with different goals in humans and in other primates. The fundamental related findings are reviewed in this paper, with the aim of providing researchers from different fields, including intelligent robotics and neural computation, a comprehensive but accessible view on the subject. A detailed description of the principal sensorimotor processes and the brain areas involved in them is provided following a functional perspective, in order to make this survey especially useful for computational modeling and bio-inspired robotic applications.
COMMENTARY EVIDENCE FOR COVERT ATTENTION swr I 'CHING FROM EYE-MOVEMENTS. REPLY TO COMMEN~IARIES ON LIECI4TY ET AL., 20031
, 2003
"... We argue that our research objectives in Liechty, Pieters, and Wedel (2003) are to provide general-izable insights into covert visual attention to complex, mullimodal stimuli n their natural context, through inverse inference from eye-movement data. We discuss the most imporlant issues raised by Fen ..."
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We argue that our research objectives in Liechty, Pieters, and Wedel (2003) are to provide general-izable insights into covert visual attention to complex, mullimodal stimuli n their natural context, through inverse inference from eye-movement data. We discuss the most imporlant issues raised by Feng (2003) and Reichle and Nelson (2003), in particular the task definition, inclusion of ad features, object-based versus pace-based attention and the evidence for the where and whal streams. Key words: covert visual attention, space based attention, object based attention, where and what stream, scan paths, hidden Markov model, print advertising. 1. Inverse Inference on Visual Attention Our research objectives in Liechty, Pieters, and Wedel (2003) are to provide generaliz-able insights into covert visual ttention to complex, multimodal stimuli n their natural context, through inverse inference from eye-movement data. We find that patterns of saccades are indica-tive of such covert attention states, and our study yields evidence that people exhibit a sequence of rapid switches between local and global covert states of visual attention. During a typical stim-ulus exposure, there tend to be about hree of those switches on average, while subjects almost always start in the local and typically end in the global state; where the local state lasts around 1.1
