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Visual Discrimination (visual + discrimination)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Use of multiplex real-time PCR (TaqMan) for the detection of potato viruses,

EPPO BULLETIN, Issue 3-4 2000
N. Boonham
Certain viruses affect the quality of potato tubers for either table use or processing. Visual discrimination of these viruses is problematic because of variable symptoms, but is important if proper controls are to be implemented. Work at the Central Science Laboratory has concentrated on the detection of Potato mop-top pomovirus (PMTV), Tobacco rattle tobravirus (TRV) (both associated with the disease spraing) and the tuber necrotic strain of Potato Y potyvirus (PVYNTN), the symptoms of which can often be confused with spraing. A nucleic acid-based approach has been adopted as TRV is often found as naked RNA with no associated coat protein, and accurate discrimination of PVY strains is impossible by serology. The multiplex TaqMan assay developed in this work streamlines the testing, replacing two separate tests currently used (a TRV RT-PCR and a PMTV enzyme-linked immunosorbent assay) with a single-tube assay, which has no post-PCR manipulations. The assay has been shown to be more sensitive than either of the tests which it replaces, allowing 100- and 10000-fold increases in sensitivity for TRV and PMTV detection respectively. The test reliably detected over 40 different isolates of TRV and PMTV obtained from a wide range of cultivars and locations, including samples where existing tests failed. A PCR-based method capable of discriminating strains of PVY was also developed. [source]

Cortical inhibitory circuits in eye-movement generation

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2003
Peter H. Schiller
Abstract The role inhibitory circuits play in target selection with saccadic eye movements was examined in area V1, the frontal eye fields (FEF) and the lateral intraparietal sulcus (LIP) of the Rhesus Macaque monkey by making local infusions of the GABA agonist muscimol and antagonist bicuculline. In V1, both agents greatly interfered with target selection and visual discrimination of stimuli placed into the receptive field of the affected neurons. In the FEF, bicuculline facilitated target selection without affecting visual discrimination and generated many spontaneous saccades. Muscimol in the FEF interfered with saccadic eye-movement generation. In the LIP, bicuculline was ineffective and muscimol had only a small effect. These findings suggest that in the FEF GABAergic inhibitory circuits play a central role in eye-movement generation whereas in V1 these circuits are essential for visual analysis. Inhibitory circuits in the LIP do not appear to play a central role in target selection and in visual discrimination. [source]

Impairments in visual discrimination after perirhinal cortex lesions: testing ,declarative' vs. ,perceptual-mnemonic' views of perirhinal cortex function

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2003
Timothy J. Bussey
Abstract Two experiments tested the predictions of ,declarative' vs. ,perceptual-mnemonic' views of perirhinal cortex function. The former view predicts that perirhinal cortex lesions should impair rapidly learned, but not more slowly learned, visual discriminations, whereas the latter view predicts that impairments should be related not to speed of learning but to perceptual factors. It was found that monkeys with perirhinal cortex lesions were impaired in the acquisition and performance of slowly learned, perceptually difficult greyscale picture discriminations, but were not impaired in the acquisition of rapidly learned, perceptually easier discriminations. In addition, these same monkeys were not impaired in the acquisition or performance of difficult colour or size discriminations, indicating that the observed pattern of impairments was not due to ceiling effects or difficulty per se. These findings, taken together, are consistent with the ,perceptual-mnemonic' view that the perirhinal cortex is involved in both perception and memory, but are not consistent with the ,declarative' view that the perirhinal cortex is important exclusively for declarative memory, having little or no role in perception. Moreover, the results are consistent with the more specific proposal that the perirhinal cortex contributes to the solution of complex visual discriminations with a high degree of ,feature ambiguity', a property of visual discrimination problems that can emerge when features of an object are rewarded when part of one object, but not when part of another. These and other recent findings suggest the need for a revision of prevailing views regarding the neural organization of perception and memory. [source]

The organization of visual object representations: a connectionist model of effects of lesions in perirhinal cortex

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002
Timothy J. Bussey
Abstract We have developed a simple connectionist model based on the idea that perirhinal cortex has properties similar to other regions in the ventral visual stream, or ,what' pathway. The model is based on the assumption that representations in the ventral visual stream are organized hierarchically, such that representations of simple features of objects are stored in caudal regions of the ventral visual stream, and representations of the conjunctions of these features are stored in more rostral regions. We propose that a function of these feature conjunction representations is to help to resolve ,feature ambiguity', a property of visual discrimination problems that can emerge when features of an object predict a given outcome (e.g. reward) when part of one object, but predict a different outcome when part of another object. Several recently reported effects of lesions of perirhinal cortex in monkeys have provided key insights into the functions of this region. In the present study these effects were simulated by comparing the performance of connectionist networks before and after removal of a layer of units corresponding to perirhinal cortex. The results of these simulations suggest that effects of lesions in perirhinal cortex on visual discrimination may be due not to the impairment of a specific type of learning or memory, such as declarative or procedural, but to compromising the representations of visual stimuli. Furthermore, we propose that attempting to classify perirhinal cortex function as either ,perceptual' or ,mnemonic' may be misguided, as it seems unlikely that these broad constructs will map neatly onto anatomically defined regions of the brain. [source]

Alcohol intoxication effects on visual perception: An fMRI study

HUMAN BRAIN MAPPING, Issue 1 2004
Vince D. Calhoun
Abstract We examined the effects of two doses of alcohol (EtOH) on functional magnetic resonance imaging (fMRI) activation during a visual perception task. The Motor-Free Visual Perception Test,Revised (MVPT-R) provides measures of overall visual perceptual processing ability. It incorporates different cognitive elements including visual discrimination, spatial relationships, and mental rotation. We used the MVPT-R to study brain activation patterns in healthy controls (1) sober, and (2) at two doses of alcohol intoxication with event-related fMRI. The fMRI data were analyzed using a general linear model approach based upon a model of the time course and a hemodynamic response estimate. Additionally, a correlation analysis was performed to examine dose-dependent amplitude changes. With regard to alcohol-free task-related brain activation, we replicate our previous finding in which SPM group analysis revealed robust activation in visual and visual association areas, frontal eye field (FEF)/dorsolateral prefrontal cortex (DLPFC), and the supplemental motor area (SMA). Consistent with a previous study of EtOH and visual stimulation, EtOH resulted in a dose-dependent decrease in activation amplitude over much of the visual perception network and in a decrease in the maximum contrast-to-noise ratio (in the lingual gyrus). Despite only modest behavior changes (in the expected direction), significant dose-dependent activation increases were observed in insula, DLPFC, and precentral regions, whereas dose-dependent activation decreases were observed in anterior and posterior cingulate, precuneus, and middle frontal areas. Some areas (FEF/DLPFC/SMA) became more diffusely activated (i.e., increased in spatial extent) at the higher dose. Alcohol, thus, appears to have both global and local effects upon the neural correlates of the MVPT-R task, some of which are dose dependent. Hum. Brain Mapping 21:15,26, 2004. © 2003 Wiley-Liss, Inc. [source]

The distribution of circularly polarized light reflection in the Scarabaeoidea (Coleoptera)

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2010
J. DAVID PYE fls
The light reflected from many scarab beetles is strongly circularly polarized, a phenomenon that may be unique in nature. Approximately 1500 genera and more than 19 000 species/subspecies of scarab beetles (Scarabaeoidea) in the collection of the Natural History Museum, London, were surveyed with circularly polarizing filters to assess how widespread this effect is and how it relates to colour patterns in the individuals concerned. Over 1100 measurements were made of the strength of the circular polarization, in some cases registering 97%. Circular polarization had been previously described from five subfamilies of Scarabaeidae and, in the present study, was found in three further subfamilies: Phaenomeridinae, Dynastinae and Euchirinae, as well as in the subfamily Ceratocanthinae of the family Hybosoridae, comprising the first records outside the Scarabaeidae. The results may have implications for the taxonomy of the group, for visual discrimination, and for the behaviour of the species themselves. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 585,596. [source]

Impairments in visual discrimination after perirhinal cortex lesions: testing ,declarative' vs. ,perceptual-mnemonic' views of perirhinal cortex function

Perirhinal cortex resolves feature ambiguity in complex visual discriminations

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2002
Timothy J. Bussey
Abstract The present experiment tested predictions of a ,perceptual,mnemonic/feature conjunction' (PMFC) model of perirhinal cortex function. The model predicts that lesions of perirhinal cortex should disrupt complex visual discriminations with a high degree of ,feature ambiguity', a property of visual discrimination problems that can emerge when features of an object are rewarded when they are part of one object, but not when part of another. As feature ambiguity is thought to be the critical factor, such effects should be independent of the number of objects to be discriminated. This was tested directly, by assessing performance of control monkeys and monkeys with aspiration lesions of perirhinal cortex on a series of concurrent discriminations in which the number of object pairs was held constant, but the degree of feature ambiguity was varied systematically. Monkeys were tested in three conditions: Maximum Feature Ambiguity, in which all features were explicitly ambiguous (AB+, CD+, BC,, AD,; the biconditional problem); Minimum Feature Ambiguity, in which no features were explicitly ambiguous (AB+, CD+, EF,, GH,); and Intermediate Feature Ambiguity, in which half the features were explicitly ambiguous (AB+, CD+, CE,, AF,). The pattern of results closely matched that predicted by simulations using a connectionist network: monkeys with perirhinal cortex lesions were unimpaired in the Minimum Feature Ambiguity condition, mildly impaired in the Intermediate Feature Ambiguity condition and severely impaired in the Maximum Feature Ambiguity condition. These results confirm the predictions of the PMFC model, and force a reconsideration of prevailing views regarding perirhinal cortex function. [source]

Learning associations between places and visual cues without learning to navigate: Neither fornix nor entorhinal cortex is required

HIPPOCAMPUS, Issue 4 2003
E.A. Gaffan
Abstract Rats with fornix transection, or with cytotoxic retrohippocampal lesions that removed entorhinal cortex plus ventral subiculum, performed a task that permits incidental learning about either allocentric (Allo) or egocentric (Ego) spatial cues without the need to navigate by them. Rats learned eight visual discriminations among computer-displayed scenes in a Y-maze, using the constant-negative paradigm. Every discrimination problem included two familiar scenes (constants) and many less familiar scenes (variables). On each trial, the rats chose between a constant and a variable scene, with the choice of the variable rewarded. In six problems, the two constant scenes had correlated spatial properties, either Allo (each constant appeared always in the same maze arm) or Ego (each constant always appeared in a fixed direction from the start arm) or both (Allo + Ego). In two No-Cue (NC) problems, the two constants appeared in randomly determined arms and directions. Intact rats learn problems with an added Allo or Ego cue faster than NC problems; this facilitation provides indirect evidence that they learn the associations between scenes and spatial cues, even though that is not required for problem solution. Fornix and retrohippocampal-lesioned groups learned NC problems at a similar rate to sham-operated controls and showed as much facilitation of learning by added spatial cues as did the controls; therefore, both lesion groups must have encoded the spatial cues and have incidentally learned their associations with particular constant scenes. Similar facilitation was seen in subgroups that had short or long prior experience with the apparatus and task. Therefore, neither major hippocampal input,output system is crucial for learning about allocentric or egocentric cues in this paradigm, which does not require rats to control their choices or navigation directly by spatial cues. Hippocampus 2003;13:445,460. © 2003 Wiley-Liss, Inc. [source]