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Visual Features (visual + feature)
Selected AbstractsEffects of attention and arousal on early responses in striate cortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005Vahe Poghosyan Abstract Humans employ attention to facilitate perception of relevant stimuli. Visual attention can bias the selection of a location in the visual field, a whole visual object or any visual feature of an object. Attention draws on both current behavioral goals and/or the saliency of physical attributes of a stimulus, and it influences activity of different brain regions at different latencies. Attentional effect in the striate and extrastriate cortices has been the subject of intense research interest in many recent studies. The consensus emerging from them places the first attentional effects in extrastriate areas, which in turn modulate activity of V1 at later latencies. In this view attention influences activity in striate cortex some 150 ms after stimulus onset. Here we use magnetoencephalography to compare brain responses to foveally presented identical stimuli under the conditions of passive viewing, when the stimuli are irrelevant to the subject and under an active GO/NOGO task, when the stimuli are cues instructing the subject to make or inhibit movement of his/her left or right index finger. The earliest striate activity was identified 40,45 ms after stimulus onset, and it was identical in passive and active conditions. Later striate response starting at about 70 ms and reaching a peak at about 100 ms showed a strong attentional modulation. Even before the striate cortex, activity of the right inferior parietal lobule was modulated by attention, suggesting this region as a candidate for mediating attentional signals to the striate cortex. [source] Involvement of the human frontal eye field and multiple parietal areas in covert visual selection during conjunction searchEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2000Tobias Donner Abstract Searching for a target object in a cluttered visual scene requires active visual attention if the target differs from distractors not by elementary visual features but rather by a feature conjunction. We used functional magnetic resonance imaging (fMRI) in human subjects to investigate the functional neuroanatomy of attentional mechanisms employed during conjunction search. In the experimental condition, subjects searched for a target defined by a conjunction of colour and orientation. In the baseline condition, subjects searched for a uniquely coloured target, regardless of its orientation. Eye movement recordings outside the scanner verified subjects' ability to maintain fixation during search. Reaction times indicated that the experimental condition was attentionally more demanding than the baseline condition. Differential activations between conditions were therefore ascribed to top-down modulation of neural activity. The frontal eye field, the ventral precentral sulcus and the following posterior parietal regions were consistently activated: (i) the postcentral sulcus; (ii) the posterior; and (iii) the anterior part of the intraparietal sulcus; and (iv) the junction of the intraparietal with the transverse occipital sulcus. Parietal regions were spatially distinct and displayed differential amplitudes of signal increase with a maximal amplitude in the posterior intraparietal sulcus. Less consistent activation was found in the lateral fusiform gyrus. These results suggest an involvement of the human frontal eye field in covert visual selection of potential targets during search. These results also provide evidence for a subdivision of posterior parietal cortex in multiple areas participating in covert visual selection, with a major contribution of the posterior intraparietal sulcus. [source] The lateral-occipital and the inferior-frontal cortex play different roles during the naming of visually presented objectsHUMAN BRAIN MAPPING, Issue 12 2009Philippe A. Chouinard Abstract We reasoned that if an area is devoted to processing only the visual features of objects, then transcranial magnetic stimulation (TMS) applied to this area in either hemisphere would affect the naming of objects presented in contralateral but not ipsilateral space. In contrast, if an area is involved in language, then one might expect to see effects of TMS when applied over the left but not the right hemisphere, regardless whether objects are in contralateral or ipsilateral space. Our experiments reveal two important findings. First, TMS delivered to the lateral-occipital complex (LOC), a visual-form area, affected the naming of objects presented in contralateral but not ipsilateral space, independent of which hemisphere was stimulated. In two additional experiments, when participants named the color of objects or made judgments about the size of stimuli as shown physically on a computer screen, TMS over the contralateral LOC did not affect color naming but did affect the participants' ability to make size judgments. Second, TMS delivered to the left but not the right posterior inferior-frontal gyrus (pIFG) affected the naming of objects irrespective of whether objects were presented in contralateral or ipsilateral space. In a separate experiment, when participants were asked to either read or categorize words, TMS over the left but not the right pIFG affected word categorization but not word reading. On the basis of these findings, we propose that when people name visually-presented objects, LOC processes the visual form of objects while the left pIFG processes the semantics of objects. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] Learning While Babbling: Prelinguistic Object-Directed Vocalizations Indicate a Readiness to LearnINFANCY, Issue 4 2010Michael H. Goldstein Two studies illustrate the functional significance of a new category of prelinguistic vocalizing,object-directed vocalizations (ODVs),and show that these sounds are connected to learning about words and objects. Experiment 1 tested 12-month-old infants' perceptual learning of objects that elicited ODVs. Fourteen infants' vocalizations were recorded as they explored novel objects. Infants learned visual features of objects that elicited the most ODVs but not of objects that elicited the fewest vocalizations. Experiment 2 assessed the role of ODVs in learning word,object associations. Forty infants aged 11.5 months played with a novel object and received a label either contingently on an ODV or on a look alone. Only infants who received labels in response to an ODV learned the association. Taken together, the findings suggest that infants' ODVs signal a state of attention that facilitates learning. [source] Do cuckoos choose nests of great reed warblers on the basis of host egg appearance?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2007M. I. CHERRY Abstract Prevailing theory assumes cuckoos lay at random among host nests within a population, although it has been suggested that cuckoos could choose large nests and relatively active pairs within host populations. We tested the hypothesis that egg matching could be improved by cuckoos choosing nests in which host eggs more closely match their own, by assessing matching and monitoring nest fate in great reed warblers naturally or experimentally parasitized by eggs of European cuckoos. A positive correlation between cuckoo and host egg visual features suggests that cuckoos do not lay at random within a population, but choose nests and this improves egg matching: naturally parasitized cuckoo eggs were more similar to host eggs as perceived by humans and as measured by spectrophotometry. Our results suggest a hitherto overlooked step in cuckoo,host evolutionary arms races, and have nontrivial implications for the common experimental practice of artificially parasitizing clutches. [source] Vision-aided inertial navigation for pin-point landing using observations of mapped landmarksJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 5 2007Nikolas Trawny In this paper we describe an extended Kalman filter algorithm for estimating the pose and velocity of a spacecraft during entry, descent, and landing. The proposed estimator combines measurements of rotational velocity and acceleration from an inertial measurement unit (IMU) with observations of a priori mapped landmarks, such as craters or other visual features, that exist on the surface of a planet. The tight coupling of inertial sensory information with visual cues results in accurate, robust state estimates available at a high bandwidth. The dimensions of the landing uncertainty ellipses achieved by the proposed algorithm are three orders of magnitude smaller than those possible when relying exclusively on IMU integration. Extensive experimental and simulation results are presented, which demonstrate the applicability of the algorithm on real-world data and analyze the dependence of its accuracy on several system design parameters. © 2007 Wiley Periodicals, Inc. [source] Semantic visual features in content-based video retrievalPROCEEDINGS OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE & TECHNOLOGY (ELECTRONIC), Issue 1 2006Xiangming Mu A new semantic visual features (e.g., car, mountain, and fire) navigation technology is proposed to improve the effectiveness of video retrieval. Traditional temporal neighbor browsing technology allows users to navigate temporal neighbors of a selected sample frame to find additional matches, while semantic visual feature browsing enables users to navigate keyframes that have similar features to the selected sample frame. A pilot evaluation was conducted to compare the effectiveness of three video retrieval designs that support 1) temporal neighbor browsing; 2) semantic visual feature browsing; and 3) fused browsing which is a combination of both temporal neighbor and semantic visual feature browsing. Two types of searching tasks: visual centric and non-visual centric tasks were applied. Initial results indicated that the semantic visual feature browsing system was more efficient for non-visual centric tasks. [source] Ovarian maturation of wild Farfantepenaeus paulensis in relation to histological and visual changesAQUACULTURE RESEARCH, Issue 14 2003S Peixoto Abstract The present study describes the ovarian development stages of wild Farfantepenaeus paulensis (Pérez-Farfante) through the combined observation of histological and visual characteristics. Twenty-five females (61.8±2.4 g) were captured in 35,40-m deep waters off southern Brazil (27°S). The females were grouped according to the size and shape of their ovary and then killed. The colour of the fresh ovary was compared with a chromatic scale catalogue. Analysis of the histological sections of each ovary determined the morphological characteristics, size and frequency of the different oocyte types. Based on these characteristics, four distinct stages of ovarian maturation are proposed: stage I (immature), characterized by the presence of small basophilic oocytes (52.1±19.9 ,m) and ovary colour ranging from translucent to creamy; stage II (developing), with yolky oocytes (YOs) (144.2±26.1 ,m) and a light green colour; stage III (mature), presenting large YOs but with cortical rods (235.0±30.2 ,m) and an olive-brown colour; and stage IV (spent), with atretic oocytes and the same ovary colour pattern as stage I. The gonadosomatic index ranged from 1.6 (stage IV) to 13.7% (stage III) and was closely related to the different ovarian maturation stages. The observation of visual features coupled with histological characteristics was found to represent a reliable procedure to evaluate the ovarian maturation of F. paulensis. [source] | ||||||||||