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Closure, primarily investigated in perception, is described as the phenomenal completion of incomplete stimuli. The present study provided a brief overview of the gestalt concept of perceptual closure. Issues discussed include organizational processes in perception (based on Wertheimer's Laws of Organization in Perceptual Forms), which outlined the nature of our perceptual experience as governed by organizational processes; isomorphism (a cortical-field theory), which signified a topological correspondence between organizational processes in perception and neurophysiological processes in the brain; perceptual closure (unification of the disorganized and discrete parts of a visual presentation into a single, unified presentation); flexibility of closure (facilitates the presentation of images in optical illusions); investigation of closure (techniques used to investigate closure phenomena in perception); and the universality of closure (initially investigated in perception and extended to include other areas of psychology such as thinking and reasoning, personality, social attitudes, and problem-solving). Closure has also been investigated in poetry, music, and sports. The interest that this gestalt principle has generated suggests that it is neither restricted nor limited in its expression., Organizational Processes in Perception Gestalt psychologists maintained that all psychological phenomena were understood in terms of whole-processes, as opposed to the piecemeal, atomistic approach of the structuralist and behaviourist schools. [...]

The present study, which investigated closure and flexibility of closure as it relates to perception and inductive reasoning, was based on the assumption that closure processes, as understood in perception, were the same or similar to closure processes in inductive reasoning. The study provided an overview of research that investigated closure in perception and closure in reasoning, and identified flexibility of closure as a dynamic function inherent in Wertheimer's laws of perceptual organization. Flexibility of closure was considered a fundamental component of perception and inductive reasoning. Flexibility of closure in perception facilitated the presentation of images in the old-woman young-woman illusion, and maintained a closed image of each that was well-defined, regular, and simplistic. Flexibility of closure in inductive reasoning facilitated the incorporation of observed events that supported the premise (a statement of the relationship between the observed event and the identification of that event), and maintained as a closed unit until it became necessary to modify the premise. Flexibility of closure in perception and flexibility of closure in inductive reasoning have yet to endure the rigours of scientific investigation. In the present study, flexibility of closure in perception provided a fruitful approach to the study of optical illusions, and flexibility of closure in inductive reasoning contributed toward an understanding of the inductive reasoning process., Closure in Perception Gestalt psychology maintained that we see our world as an organized unity. For example, the world that we experience is stable, well-defined, regular, and simplistic. Wertheimer (1923/1938b), [...]

Two perspectives compete to explain how the surface form of digits affects cognitive processing of numerical magnitude; one argues for a common pathway and the other for separate pathways. This study examined the operand-related error effect in simple multiplication operations using different combinations of visually presented Arabic digits and auditorily presented Mandarin number words. The study suggested two conclusions, both consistent with the separate pathway perspective. First, the numerical surface form (Arabic digits, spoken Mandarin number words) affected retrieval. That is, surface properties were maintained as specific codes throughout processing. Second, the phonological code activated by spoken Mandarin number words interfered with activation of answers during retrieval., The same quantity can be represented using multiple surface forms (e.g., Arabic digits, written or spoken number words, Roman numerals). The degree to which surface forms affect number processing is [...]

Purpose: The purpose of this study was to determine the effects of enriching line drawings with color/texture and environmental context as a facilitator of naming speed and accuracy in older adults. Method: Twenty young and 23 older adults named high-frequency picture stimuli from the Boston Naming Test (Kaplan, Goodglass, & Weintraub, 2001) under three conditions: (a) black-and-white items, (b) colorized-texturized items, and (c) scene-primed colored items (e.g., 'hammock' preceded 1,000 ms by a backyard scene). Results: With respect to speeded naming latencies, mixed-model analyses of variance revealed that young adults did not benefit from colorization-texturization but did show scene-priming effects. In contrast, older adults failed to show facilitation effects from either colorized-texturized or scene-primed items. Moreover, older adults were consistently slower to initiate naming than were their younger counterparts across all conditions. Conclusions: Perceptual and contextual enrichment of sparse line drawings does not appear to facilitate visual confrontation naming in older adults, whereas younger adults do tend to show benefits of scene priming. We interpret these findings as generally supportive of a processing speed account of age-related object picture-naming difficulty. Key Words: aging, naming, picture, perception, response time, lexical retrieval, Older adults experience increasing word-finding difficulty with advancing age, as reflected by decreases in accuracy and increases in the amount of time needed to name items, even in the absence [...]

In order to clarify whether the influence of color knowledge information in object recognition depends on the presence of the appropriate surface color, we designed a name-object verification task. The relationship between color and shape information provided by the name and by the object photo was manipulated in order to assess color interference independently of shape interference. We tested three different versions for each object: typically colored, black and white, and nontypically colored. The response times on the nonmatching trials were used to measure the interference between the name and the photo. We predicted that the more similar the name and the photo are, the longer it would take to respond. Overall, the color similarity effect disappeared in the black-and-white and nontypical color conditions, suggesting that the influence of color knowledge on object recognition depends on the presence of the appropriate surface color information.

How do humans use target-predictive contextual information to facilitate visual search? How are consistently paired scenic objects and positions learned and used to more efficiently guide search in familiar scenes? For example, humans can learn that a certain combination of objects may define a context for a kitchen and trigger a more efficient search for a typical object, such as a sink, in that context. The ARTSCENE Search model is developed to illustrate the neural mechanisms of such memory-based context learning and guidance and to explain challenging behavioral data on positive--negative, spatial--object, and local--distant cueing effects during visual search, as well as related neuroanatomical, neurophysiological, and neuroimaging data. The model proposes how global scene layout at a first glance rapidly forms a hypothesis about the target location. This hypothesis is then incrementally refined as a scene is scanned with saccadic eye movements. The model simulates the interactive dynamics of object and spatial contextual cueing and attention in the cortical What and Where streams starting from early visual areas through medial temporal lobe to prefrontal cortex. After learning, model dorsolateral prefrontal cortex (area 46) primes possible target locations in posterior parietal cortex based on goal-modulated percepts of spatial scene gist that are represented in parahippocampal cortex. Model ventral prefrontal cortex (area 47/12) primes possible target identities in inferior temporal cortex based on the history of viewed objects represented in perirhinal cortex. Keywords: contextual cueing, spatial attention, object recognition, visual search, scene perception DOI: 10.1037/a0020664

Five experiments examine whether the ability of emotions to influence judgments of threat extends to a very basic process inherent in threat detection: object recognition. Participants experiencing different emotions were asked to make rapid judgments about whether target individuals were holding guns or neutral objects. Results across 4 experiments supported the hypothesis that anger increases the probability that neutral objects will be misidentified as ones related to violence, but not the converse. Of import, the findings demonstrate that this bias is not a simple function of the negative valence of an emotional state, but stems from specific threat-relevant cues provided by anger. Direct manipulation of participants' expectancies for encountering guns in the environment is shown not only to remove the bias among angry individuals when set to be low but also to produce a corresponding bias among neutral participants when set to be high. A 5th study demonstrates that the bias is amenable to correction given sufficient ability. Keywords: anger, shooter bias, emotion specificity, threat detection, expectancies DOI: 10.1037/a0020665

How do infants learn to perceive the backs of objects that they see only from a limited viewpoint? Infants' 3-dimensional object completion abilities emerge in conjunction with developing motor skills--independent sitting and visual--manual exploration. Infants at 4.5 to 7.5 months of age (n = 28) were habituated to a limited-view object and tested with volumetrically complete and incomplete (hollow) versions of the same object. Parents reported infants' sitting experience, and infants' visual--manual exploration of objects was observed in a structured play session. Infants' self-sitting experience and visual--manual exploratory skills predicted looking at the novel, incomplete object on the habituation task. Further analyses revealed that self-sitting facilitated infants' visual inspection of objects while they manipulated them. The results are framed within a developmental systems approach, wherein infants' sitting skill, multimodal object exploration, and object knowledge are linked in developmental time. Keywords: perceptual development, three-dimensional object perception, exploration, object manipulation, sitting DOI: 10.1037/a0014618

Perceptual systems often force systematically biased interpretations upon sensory input. These interpretations are obligatory, inaccessible to conscious control, and prevent observers from perceiving alternative percepts. Here we report a similarly impenetrable phenomenon in the domain of language, where the syntactic system prevents listeners from detecting a simple perceptual pattern. Healthy human adults listened to three-word sequences conforming to patterns readily learned even by honeybees, rats, and sleeping human neonates. Specifically, sequences either started or ended with two words from the same syntactic category (e.g., noun--noun--verb or verb--verb--noun). Although participants readily processed the categories and learned repetition patterns over nonsyntactic categories (e.g., animal--animal--clothes), they failed to learn the repetition pattern over syntactic categories, even when explicitly instructed to look for it. Further experiments revealed that participants successfully learned the repetition patterns only when they were consistent with syntactically possible structures, irrespective of whether these structures were attested in English or in other languages unknown to the participants. When the repetition patterns did not match such syntactically possible structures, participants failed to learn them. Our results suggest that when human adults hear a string of nouns and verbs, their syntactic system obligatorily attempts an interpretation (e.g., in terms of subjects, objects, and predicates). As a result, subjects fail to perceive the simpler pattern of repetitions--a form of syntax-induced pattern deafness that is reminiscent of how other perceptual systems force specific interpretations upon sensory input. illusions | language acquisition | modularity | perception | syntax doi/10.1073/pnas.0908963106

In two experiments, we investigated the activation of perceptual representations of referent objects during word processing. In both experiments, participants learned to associate pictures of novel three-dimensional objects with pseudowords. They subsequently performed a recognition task (Experiment 1) or a naming task (Experiment 2) on the object names while being primed with different types of visual stimuli. Only the stimuli that the participants had encountered as referent objects during the training phase facilitated recognition or naming responses. New stimuli did not facilitate the processing of object names, even if they matched a schematic or prototypical representation of the referent object that the participants might have abstracted during word--referent learning. These results suggest that words learned by way of examples of referent objects are associated with experiential traces of encounters with these objects. doi: 10.3758/MC.37.8.1187

A sequential matching task was used to compare how the difficulty of shape discrimination influences the achievement of object constancy for depth rotations across haptic and visual object recognition. Stimuli were nameable, 3-dimensional plastic models of familiar objects (e.g., bed, chair) and morphs midway between these endpoint shapes (e.g., a bed--chair morph). The 2 objects presented on a trial were either both placed at the same orientation or were rotated by 90[degrees] relative to each other. Discrimination difficulty was increased by presenting more similarly shaped objects on mismatch trials (easy: bed, then lizard: medium: bed, then chair: hard: bed, then bed--chair morph). For within-modal visual matching, orientation changes were most disruptive when shape discrimination was hardest. This interaction for 3-dimensional objects replicated the interaction reported in earlier studies presenting 2-dimensional pictures of the same objects (Lawson & Bulthoff, 2008). In contrast, orientation changes and discrimination difficulty had additive effects on within-modal haptic and cross-modal visual-to-haptic matching, whereas cross-modal haptic-to-visual matching was orientation invariant. These results suggest that the cause of orientation sensitivity may differ for visual and haptic object recognition. Keywords: visual, haptic, object recognition, depth rotation, object constancy

Object images are identified more efficiently after prior exposure. Here, the authors investigated shape representations supporting object priming. The dependent measure in all experiments was the minimum exposure duration required to correctly identify an object image in a rapid serial visual presentation stream. Priming was defined as the change in minimum exposure duration for identification as a function of prior exposure to an object. Experiment 1 demonstrated that this dependent measure yielded an estimate of predominantly visual priming (i.e., free of name and concept priming). Experiments 2 and 3 demonstrated that although priming was sensitive to orientation, visual priming was relatively invariant with image inversion (i.e., an image visually primed its inverted counterpart approximately as much as it primed itself). Experiment 4 demonstrated a similar dissociation with images rotated 90[degrees] off the upright. In all experiments, the difference in the magnitude of priming for identical or rotated--inverted priming conditions was marginal or nonexistent. These results suggest that visual representations that support priming can be relatively insensitive to picture-plane manipulations, although these manipulations have a substantial effect on object identification. Keywords: priming, object recognition, implicit memory, rapid serial visual presentation, viewpoint-independent

Though nonhuman animals lack anything like a set of grammatical structures in their natural vocalizations, studies now suggest that at least some animals can extract patterns from a structured input that appear abstract and rule-like. The authors continue this line of research by adding three new methodological contributions, specifically, tests of (1) a free-ranging animal population (as opposed to captive laboratory subjects), (2) a new taxonomic group (i.e., Old World monkeys: rhesus macaques, Macaca mulatta), and (3), the presentation of artificially sequenced strings of species-specific vocalizations (as opposed to artificial symbols or speech stimuli). Specifically, the authors created artificial strings of rhesus vocalizations in the pattern notated as AAB (i.e., two identical calls [AA] followed by a different one [B]) or ABB. Following habituation to AAB strings, rhesus monkeys showed significantly more orienting responses to novel ABB strings than to novel AAB strings. Further, following habituation to an ABB pattern, rhesus responded more in test trials to AAB than ABB. These results, combined with other parallel studies, suggest that animals can extract an identity relationship from an artificial sequence of sounds, and can do so even though the tokens are species-specific vocalizations that are never produced in this sequence. Keywords: Pattern recognition, identity, abstract rules, language evolution, nonhuman primates, rhesus monkeys

Perception of floor projected moving geometric shapes was examined in the context of the Situated Multimedia Arts Learning Laboratory (SMALLab), an immersive, mixed-reality learning environment. As predicted, the projected destinations of shapes which retreated in depth (proximal origin) were judged significantly less accurately than those that approached (distal origin). Participants maintained similar magnitudes of error throughout the session, and no effect of practice was observed. Shape perception in an immersive multimedia environment is comparable to the real world. One may conclude that systematic exploration of basic psychological phenomena in novel mediated environments is integral to an understanding of human behavior in novel human-computer interaction architectures.

Do all components of a sign contribute equally to its recognition? In the present study, misperceptions in the sign-spotting task (based on the word-spotting task; Cutler & Norris, 1988) were analyzed to address this question. Three groups of deaf signers of British Sign Language (BSL) with different ages of acquisition (AoA) saw BSL signs combined with nonsense signs, along with combinations of two nonsense signs. They were asked to spot real signs and report what they had spotted. We will present an analysis of false alarms to the nonsense-sign combinations--that is, misperceptions of nonsense signs as real signs (cf. van Ooijen, 1996). Participants modified the movement and handshape parameters more than the location parameter. Within this pattern, however, there were differences as a function of AoA. These results show that the theoretical distinctions between form-based parameters in sign-language models have consequences for online processing. Vowels and consonants have different roles in speech recognition; similarly, it appears that movement, handshape, and location parameters contribute differentially to sign recognition.

In three experiments, we explored the basis of adults' judgments of individual object persistence through transformation. Participants watched scenarios in which an object underwent a transformation into an object belonging to the same or a different basic-level kind. Participants were queried about the object's persistence through the transformation as an individual (indexed by its proper name) and as a member of the original kind (indexed by its basic-level count noun in Experiments 1 and 2, or by its superordinate-level noun in Experiment 3). In all experiments, participants rated objects that were altered in a way that maintained basic-level kind to be less likely to retain their proper name than those that were altered in a way that changed basic-level kind. These findings suggest that shared basic-level kind membership serves as a dimension of similarity over which objects' unique individual identities are highlighted. We discuss the implications of the results for existing theoretical accounts of adults' judgments of individual object persistence.

Two event-related potential (ERP) experiments were used to examine the representation of object feature information and background knowledge in semantic memory. Participants were trained on novel object categories with three features and were tested with new exemplars that were complete or were missing one to two features that were essential or nonessential to object function. In both a category membership judgment task (Experiment 1) and a parts detection task (Experiment 2), the N400, a functionally specific measure of semantic access, was graded with feature number but was insensitive to knowledge-based feature importance. A separable ERP effect related to knowledge was seen in Experiment 1 as an enhanced frontocentral negativity (beginning ~300 msec) to exemplars missing a nonessential versus an essential feature, but this effect did not manifest when background knowledge was less task relevant (Experiment 2). Thus, similarity-and knowledge-based effects are separable, and the locus of knowledge effects varies with task demands but does not seem to arise from facilitated semantic access.

In the possible/impossible object decision test, priming has consistently been found for structurally possible, but not impossible, objects, leading Schacter, Cooper, and Delaney (1990) to suggest that priming relies on a system that represents the global 3-D structure of objects. Using a modified design with matching objects to control for the influence of episodic memory, Ratcliff and McKoon (1995) and Williams and Tart (1997) found negative priming for impossible objects (i.e., lower performance for old than for new items). Both teams argued that priming derives from (1) episodic memory for object features and (2) bias to respond 'possible' to encoded objects or their possible parts. The present study applied the matched-objects design to the original Schacter and Cooper stimuli--same possible objects and matching impossible figures--with minimal procedural variation. The data from Experiment I only partially supported the bias models and suggested that priming was mediated by both local and global structural descriptions. Experiment 2 showed that negative priming for impossible objects derived from the structural properties of these objects, not from the influence of episodic memory on task performance. Supplemental materials for this study may be downloaded from mc.psychonomic-journals .org/content/supplemental.

The authors describe a new visual illusion first discovered in a natural setting. A cyclist riding beside a pair of sagging chains that connect fence posts appears to move up and down with the chains. In this illusion, a static shape (the chains) affects the perception of a moving shape (the bicycle), and this influence involves assimilation (averaging) rather than opposition (differentiation). These features distinguish the illusion from illusions of motion capture and induced motion. The authors take this bicycle illusion into the laboratory and report 4 findings: Naive viewers experience the illusion when discriminating horizontal from sinusoidal motion of a disc in the context of stationary curved lines; the illusion shifts from motion assimilation to motion opposition as the visual size of the display is increased; the assimilation and opposition illusions are dissociated by variations in luminance contrast of the stationary lines and the moving disc; and the illusion does not occur when simply comparing two stationary objects at different locations along the curved lines. The bicycle illusion provides a unique opportunity for studying the interactions between shape and motion perception. Keywords: motion and shape perception, motion assimilation, visual illusion

This study investigated the effects of dispersion, color, and rotation of figures on recognition under varied exposure times. A total of 30 women and 15 men, Taiwanese college students ages 18 to 20 years (M = 19.1, SD = 1.2), participated. Subjects were to recognize a target figure and respond with its location in each stimulus by pressing a mouse button. Analysis showed that the effect of rotation on accuracy was significant. Accuracy for the rotation of 180[degrees] was greater than those for 60[degrees] and 300[degrees]. Exposure time also significantly influenced accuracy. The accuracy was greater for 2 and 3 sec. than for 1 sec. No significant effects on accuracy were associated with dispersion and color, and neither had any interactive effect on accuracy. Dispersion significantly affected the response time as response time for dispersion under 0.4 and 0.5 conditions were shorter than those under 0.2 and 0.3 conditions. Significantly less response time was needed for rotation of 180[degrees] than for 60[degrees] and 300[degrees] conditions. Response time was longer for red figures than for blue, green, and yellow figures. No significant effect on response time was associated with duration of exposure. Two interactive two-way effects were found: dispersion x color of figure and dispersion x rotation. Implications for figure or icon design are discussed.

Object identification in perceptual tests may include constituents of mental rotation. A matching-to-sample task was conducted with same or different objects to look for evidence of rotation. Elementary schoolchildren (6 to 8 years old) in Grades 1 to 4 (N=264) participated, using the inclined Flags Test and the Water Level Test to ensure that children can use kinematic imagery for the Flags Test even if they used static imagery for the Water Level Test. Performance on the inclined Flags Test varied by age group. Use of implicit mental rotation of the inclined object was inferred in recognition. Also, children at the pre-operational stage showed a rotational effect, i.e., they could transform the object by turning it, thereby confirming kinematic imagery is used from age 6. As a consequence, solving both rotation tasks may require not only recognition of object frames but also objects internal to the frame.

Two experiments were conducted with younger and older speakers. In Experiment 1, participants named single objects that were intact or visually degraded, while hearing distractor words that were phonologically related or unrelated to the object name. In both younger and older participants naming latencies were shorter for intact than for degraded objects and shorter when related than when unrelated distractors were presented. In Experiment 2, the single objects were replaced by object triplets, with the distractors being phonologically related to the first object's name. Naming latencies and gaze durations for the first object showed degradation and relatedness effects that were similar to those in single-object naming. Older participants were slower than younger participants when naming single objects and dower and less fluent on the second but not the first object when naming object triplets. The results of these experiments indicate that both younger and older speakers plan object names sequentially, but that older speakers use this planning strategy less efficiently.

A series of experiments provided converging support for the hypothesis that action preparation biases selective attention to action-congruent object features. When visual transients are masked in so-called change-blindness scenes, viewers are blind to substantial changes between 2 otherwise identical pictures that flick back and forth. The authors report data in which participants planned a grasp prior to the onset of a change-blindness scene in which 1 of 12 objects changed identity. Change blindness was substantially reduced for grasp-congruent objects (e.g., planning a whole-hand grasp reduced change blindness to a changing apple). A series of follow-up experiments ruled out an alternative explanation that this reduction had resulted from a labeling or strategizing of responses and provided converging support that the effect genuinely arose from grasp planning. Keywords: motor-visual priming, visual attention, object affordances, change blindness

This study addressed the view that object superiority depends on the informativeness or task relevance of particular contexts. It was hypothesized that target search is facilitated to the extent that global properties of a complex stimulus provide informative cues to target location. Results of Experiments 1 and 2 showed that when the target appeared at variable relative positions it was identified better in a coherent context than in an incoherent one. Because the coherent context was presumed to contain informative global cues to location, the results confirmed the hypothesis. Experiment 2 also indicated that when only informative local properties were available, search was facilitated, albeit to a lesser extent than when global properties were available. Overall, the results extend the informativeness view of object superiority effects.

Visual attention research has revealed that attentional allocation can occur in space- and/or object-based coordinates. Using the direct and elegant design of R. Egly, J. Driver, and R. Rafal (1994), the present experiments tested whether space- and object-based inhibition of return (IOR) emerge under similar time courses. The experiments were capable of isolating both space- and object-based effects induced by peripheral and back-to-center cues. The results generally support the contention that spatially nonpredictive cues are effective in producing space-based IOR at a variety of stimulus onset asynchronies (SOAs) and under a variety of stimulus conditions. Whether facilitatory or inhibitory in direction, the object-based effects occurred over a very different time course than did the space-based effects. Reliable object-based IOR was only found under limited conditions and was tied to the time since the most recent cue (peripheral or central). The finding that object-based effects are generally determined by SOA from the most recent cue may help to resolve discrepancies in the IOR literature. These findings also have implications for the search facilitator role that IOR is purported to play in the guidance of visual attention. Keywords: attention, cues, space perception

This research comparatively assessed grouping mechanisms of humans (n = 8) and baboons (n = 8) in an illusory task that employs configurations of target and surrounding circles arranged to induce the Ebbinghaus (Titchener) illusion. Analyses of response behaviors and points of subjective equality demonstrated that only humans misjudged the central target size under the influence of the Ebbinghaus illusion, whereas baboons expressed a more veridical perception of target sizes. It is argued that humans adopted a global mode of stimulus processing of the illusory figure in our task that has favored the illusion. By contrast, a strong local mode of stimulus processing with attention restricted to the target must have prevented illusory effects in baboons. These findings suggest that monkeys and humans have evolved modes of object recognition that do not similarly rely on the same gestalt principles. Keywords: baboon, Ebbinghaus illusion, Titchener illusion, global-local precedence, visual cognition

We evaluated the impact of visual similarity and action similarity on visual object identification. We taught participants to associate novel objects with nonword labels and verified that in memory visually similar objects were confused more often than visually dissimilar objects. We then taught participants to associate novel actions with nonword labels and verified that similar actions were confused more often than dissimilar actions. We then paired specific objects with specific actions. Visually similar objects paired with similar actions were confused more often in memory than when these same objects were paired with dissimilar actions. Hence the actions associated with objects served to increase or decrease their separation in memory space, and influenced the ease with which these objects could be identified. These experiments ultimately demonstrated that when identifying stationary objects, the memory of how these object were used dramatieaUy influenced the ability to identify these objects.

Recent work by Amso and Johnson (Developmental Psychology, 42(6), 1236-1245, 2006) implicates the role of visual selective attention in the development of perceptual completion during early infancy. In the current […]

Peptidoglycan recognition proteins (PGRPs) are highly conserved pattern-recognition molecules of the innate immune system that bind bacterial peptidoglycans (PGNs), which are polymers of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by short peptide stems. Human PRGPs are bactericidal against pathogenic and nonpathogenic Gram-positive bacteria, but not normal flora bacteria. Like certain glycopeptide antibiotics (e.g., vancomycin), PGRPs kill bacteria by directly interacting with their cell wall PGN, thereby interfering with PGN maturation. To better understand the bactericidal mechanism of PGRPs, we determined the crystal structure of the C-terminal PGN-binding domain of human PGRP-I[beta] in complex with NAGNAM-L-Ala-[gamma]-D-Glu-D-Lys-D-Ala-D-Ala, a synthetic glycopeptide comprising a complete PGN repeat. This structure, in conjunction with the previously reported NMR structure of a dimeric PGN fragment, permitted identification of major conformational differences between free and PGRP-bound PGN with respect to the relative orientation of saccharide and peptide moieties. These differences provided structural insights into the bactericidal mechanism of human PGRPs. On the basis of molecular modeling, we propose that these proteins disrupt cell wall maturation not only by sterically encumbering access of biosynthetic enzymes to the nascent PGN chains, but also by locking PGN into a conformation that prevents formation of cross-links between peptide stems in the growing cell wall, bacteria | cell wall | crystal structure | innate immunity

The surface myoelectric signal (MES) has been used as an input to controllers for powered prostheses for many years. As a result of recent technological advances it is reasonable to assume that there will soon be implantable myoelectric sensors which will enable the internal MES to be used as input to these controllers. An internal MES measurement should have less muscular crosstalk allowing for more independent control sites. However, it remains unclear if this benefit outweighs the loss of the more global information contained in the surface MES. This paper compares the classification accuracy of six pattern recognition-based myoelectric controllers which use multi-channel surface MES as inputs to the same controllers which use multi-channel intramuscular MES as inputs. An experiment was designed during which surface and intramuscular MES were collected simultaneously for 10 different classes of isometric contraction. There was no significant difference in classification accuracy as a result of using the intramuscular MES measurement technique when compared to the surface MES measurement technique. Impressive classification accuracy (97 %) could be achieved by optimally selecting only three channels of surface MES. Index Terms--Classification, EMG, intramuscular, myoelectric, pattern recognition, prostheses.

Primates are remarkably good at recognizing objects. The level of performance of their visual system and its robustness to image degradations still surpasses the best computer vision systems despite decades of engineering effort. In particular, the high accuracy of primates in ultra rapid object categorization and rapid serial visual presentation tasks is remarkable. Given the number of processing stages involved and typical neural latencies, such rapid visual processing is likely to be mostly feedforward. Here we show that a specific implementation of a class of feedforward theories of object recognition (that extend the Hubel and Wiesel simple-tocomplex cell hierarchy and account for many anatomical and physiological constraints) can predict the level and the pattern of performance achieved by humans on a rapid masked animal vs. non-animal categorization task. object recognition | computational model | visual cortex | natural scenes | preattentive vision

Recent research indicates that by 4.5 months, infants use shape and size information as the basis for individuating objects but that it is not until 11.5 months that they use color information for this purpose. The present experiments investigated the extent to which infants' sensitivity to color information could be increased through select experiences. Five experiments were conducted with 10.5- and 9.5-month-olds. The results revealed that multimodal (visual and tactile), but not unimodal (visual only), exploration of the objects prior to the individuation task increased 10.5-month-olds' sensitivity to color differences. These results suggest that multisensory experience with objects facilitates infants' use of color information when individuating objects. In contrast, 9.5-month-olds did not benefit from the multisensory procedure; possible explanations for this finding are explored. Together, these results reveal how an everyday experience--combined visual and tactile exploration of objects--can promote infants' use of color information as the basis for individuating objects. More broadly, these results shed light on the nature of infants' object representations and the cognitive mechanisms that support infants' changing sensitivity to color differences. Keywords: object individuation, color, infant cognition, multimodal processing

These experiments explored the role of prior experience in 12- to 18-month-old infants' tool-directed actions. In Experiment 1, infants' use of a familiar tool (spoon) to accomplish a novel task (turning on lights inside a box) was examined. Infants tended to grasp the spoon by its handle even when doing so and made solving the task impossible (the bowl did not fit through the hole in the box, but the handle did) and even though the experimenter demonstrated a bowl-grasp. In contrast, infants used a novel tool flexibly and grasped both sides equally often. In Experiment 2, infants received training using the novel tool for a particular function; 3 groups of infants were trained to use the tool differently. Later, infants' performance was facilitated on tasks that required infants to grasp the part of the tool they were trained to grasp. The results suggest that (a) infants' prior experiences with tools are important to understanding subsequent tool use, and (b) rather than learning about tool function (e.g., hammering), infants learn about which part of the tool is meant to be held, at least early in their exposure to a novel tool. Keywords: tool use, infancy, object knowledge, spoons, handles

In this paper, we introduce a new skeleton pruning method based on contour partitioning. Any contour partition can be used, but the partitions obtained by Discrete Curve Evolution (DCE) yield excellent results. The theoretical properties and the experiments presented demonstrate that obtained skeletons are in accord with human visual perception and stable, even in the presence of significant noise and shape variations, and have the same topology as the original skeletons. In particular, we have proven that the proposed approach never produces spurious branches, which are common when using the known skeleton pruning methods. Moreover, the proposed pruning method does not displace the skeleton points. Consequently, all skeleton points are centers of maximal disks. Again, many existing methods displace skeleton points in order to produces pruned skeletons. Index Terms--Skeleton, skeleton pruning, contour partition, discrete curve evolution.

Accurate identification of cerebral palsy (CP) gait is important for diagnosis as well as for proper evaluation of the treatment outcomes. This paper explores the use of support vector machines (SVM) for automated detection and classification of children with CP using two basic temporal-spatial gait parameters (stride length and cadence) as input features. Application of the SVM method to a children's dataset (68 normal healthy and 88 with spastic diplegia form of CP) and testing on tenfold cross-validation scheme demonstrated that an SVM classifier was able to classify the children groups with an overall accuracy of 83.33% [sensitivity 82.95%, specificity 83.82%, area under the receiver operating curve (AUC-ROC = 0.88)]. Classification accuracy improved significantly when the gait parameters were normalized by the individual leg length and age, leading to an overall accuracy of 96.80% (sensitivity 94.32%, specificity 100%, AUC-ROC area=0.9924). This accuracy result was, respectively, 3.21% and 1.93% higher when compared to an linear discriminant analysis and an multilayer-perceptron-based classifier. SVM classifier also attains considerably higher ROC area than the other two classifiers. Among the four SVM kernel functions (linear, polynomial, radial basis, and analysis of variance spline) studied, the polynomial and radial basis kernel performed comparably and outperformed the others. Classifier's performance as functions of regularization and kernel parameters was also investigated. The enhanced classification accuracy of the SVM using only two easily obtainable basic gait parameters makes it attractive for identifying CP children as well as for evaluating the effectiveness of various treatment methods and rehabilitation techniques. Index Terms--Cerebral palsy, classification, gait, neural networks, support vector machines.

A basic problem of visual perception is how human beings recognize objects after spatial transformations. Three central classes of findings have to be accounted for: (a) Recognition performance varies systematically with orientation, size, and position; (b) recognition latencies are sequentially additive, suggesting analogue transformation processes: and (c) orientation and size congruency effects indicate that recognition involves the adjustment of a reference frame. All 3 classes of findings can be explained by a transformational framework of recognition: Recognition is achieved by an analogue transformation of a perceptual coordinate system that aligns memory and input representations. Coordinate transformations can be implemented neurocomputationally by gain (amplitude) modulation and may be regarded as a general processing principle of the visual cortex. Keywords: alignment, coordinate transformations, gain modulation, object recognition, reference frames