bluuebunny/crossref_metadata_2025_split huggingface dataset:
The relationship between spatial attention and saccades in the frontoparietal network of the monkey
Authors: Wardak Claire , Olivier Etienne , Duhamel Jean‐René 
Published: June 2011

AbstractSpatial attention bears a remarkable resemblance to saccadic eye movements from both a behavioural and a neurophysiological point of view. In this review, we examine the contributions of two cortical areas, namely the lateral intraparietal area (LIP) and frontal eye field (FEF), to saccades and attention and discuss the possible interactions between these two areas. Based on the results of electrophysiological studies and on inactivation studies performed in the macaque monkey, we propose that LIP is mainly involved in salience representation and an attentional selection mechanism that underlies saccade guidance, at least when two objects or locations are in competition in the visual environment. In contrast, we suggest that FEF is involved in coding and triggering saccadic eye movements, as well as in coding the location of attention or the attentional shifts. However, these two functions subserved by the FEF are dissociable at a neuronal level. Saccade planning and attentional selection are intimately coupled from a behavioural point of view but correspond to distinct functional operations.
Neck muscle responses evoked by transcranial magnetic stimulation of the human frontal eye fields
Authors: Goonetilleke Samanthi C. , Gribble Paul L. , Mirsattari Seyed M. , Doherty Timothy J. , Corneil Brian D. 
Published: June 2011

AbstractTranscranial magnetic stimulation (TMS) provides a non‐invasive means of investigating brain function. Whereas TMS of the human frontal eye fields (FEFs) does not induce saccades, electrical stimulation of the monkey FEF evokes eye–head gaze shifts, with neck muscle responses evoked at stimulation levels insufficient to evoke a saccade. These animal results motivated us to examine whether TMS of the FEF (TMS‐FEF) in humans evokes a neck muscle response. Subjects performed memory‐guided saccades to the left or right while TMS (two pulses at 20 Hz) was delivered on 30% of trials to the left FEF coincident with saccade instruction. As reported previously, TMS‐FEF decreased contralateral saccade reaction times. We simultaneously recorded the activity of splenius capitis (SPL) (an ipsilateral head turner). TMS‐FEF evoked a lateralized increase in the activity of the right SPL but not the left SPL, consistent with the recruitment of a contralateral head‐turning synergy. In some subjects, the evoked neck muscle response was time‐locked to stimulation, whereas in others the evoked response occurred around the time of the saccade. Importantly, evoked responses were greater when TMS was applied to the FEF engaged in contralateral saccade preparation, with even greater evoked responses preceding shorter latency saccades. These results provide new insights into both the nature of TMS and the human oculomotor system, demonstrating that TMS‐FEF engages brainstem oculomotor circuits in a manner consistent with a general role in eye–head gaze orienting. Our results also suggest that pairing neck muscle recordings with TMS‐FEF provides a novel way of assaying the covert preparation of oculomotor plans.
Neural mechanisms of saccade target selection: gated accumulator model of the visual–motor cascade
Authors: Schall Jeffrey D. , Purcell Braden A. , Heitz Richard P. , Logan Gordon D. , Palmeri Thomas J. 
Published: June 2011

AbstractWe review a new computational model developed to understand how evidence about stimulus salience in visual search is translated into a saccade command. The model uses the activity of visually responsive neurons in the frontal eye field as evidence for stimulus salience that is accumulated in a network of stochastic accumulators to produce accurate and timely saccades. We discovered that only when the input to the accumulation process was gated could the model account for the variability in search performance and predict the dynamics of movement neuron discharge rates. This union of cognitive modeling and neurophysiology indicates how the visual–motor transformation can occur, and provides a concrete mapping between neuron function and specific cognitive processes.
The search for the neural mechanisms of the set size effect
Authors: Jerde Trenton A. , Ikkai Akiko , Curtis Clayton E. 
Published: June 2011

AbstractThe set size effect in visual search refers to the linear increase in response time (RT) or decrease in accuracy as the number of distractors increases. Previous human and monkey studies have reported a correlation between set size and neural activity in the frontal eye field (FEF) and intraparietal sulcus (IPS). In a recent functional magnetic resonance imaging study, we did not observe a set size effect in the superior precentral sulcus (sPCS, thought to be the human homolog of the FEF) and IPS in an oculomotor visual search task (Ikkai et al., 2011). Our task used placeholders in the search array, along with the target and distractors, in order to equate the amount of retinal stimulation for each set size. We here attempted to reconcile these differences with the results from a follow‐up experiment in which the same oculomotor visual search task was used, but without placeholders. A strong behavioral set size effect was observed in both studies, with very similar saccadic RTs and slopes between RT and set size. However, a set size effect was now observed in the sPCS and IPS. We comment on this finding and discuss the role of these neural areas in visual search.
Split of spatial attention as predicted by a systems‐level model of visual attention
Authors: Zirnsak Marc , Beuth Frederik , Hamker Fred H. 
Published: June 2011

AbstractCan we attend to multiple distinct spatial locations at the same time? According to a recent psychophysical study [J. Dubois et al. (2009)Journal of Vision, 9, 3.1–11] such a split of spatial attention might be limited to short periods of time. Following N. P. Bichot et al. [(1999)Perception & Psychophysics, 61, 403–423] subjects had to report the identity of multiple letters that were briefly presented at different locations, while two of these locations (targets) were relevant for a concurrent shape comparison task. In addition to the design used by Bichot et al. stimulus onset asynchrony between shape onset and letters was systematically varied. In general, the performance of subjects was superior at target locations. Furthermore, for short stimulus onset asynchronies, performance was simultaneously increasing at both target locations. For longer stimulus onset asynchronies, however, performance deteriorated at one of the target locations while increasing at the other target location. It was hypothesized that this dynamic deployment of attention might be caused by competitive processes in saccade‐related structures such as the frontal eye field. Here we simulated the task of Dubois et al. using a systems‐level model of attention. Our results are consistent with recent findings in the frontal eye field obtained during covert visual search, and they support the view of a transient deployment of spatial attention to multiple stimuli in the early epoch of target selection.
Investigating the role of the superior colliculus in active vision with the visual search paradigm
Authors: Shen Kelly , Valero Jerome , Day Gregory S. , Paré Martin 
Published: June 2011

AbstractWe review here both the evidence that the functional visuomotor organization of the optic tectum is conserved in the primate superior colliculus (SC) and the evidence for the linking proposition that SC discriminating activity instantiates saccade target selection. We also present new data in response to questions that arose from recent SC visual search studies. First, we observed that SC discriminating activity predicts saccade initiation when monkeys perform an unconstrained search for a target defined by either a single visual feature or a conjunction of two features. Quantitative differences between the results in these two search tasks suggest, however, that SC discriminating activity does not only reflect saccade programming. This finding concurs with visual search studies conducted in posterior parietal cortex and the idea that, during natural active vision, visual attention is shifted concomitantly with saccade programming. Second, the analysis of a large neuronal sample recorded during feature search revealed that visual neurons in the superficial layers do possess discriminating activity. In addition, the hypotheses that there are distinct types of SC neurons in the deeper layers and that they are differently involved in saccade target selection were not substantiated. Third, we found that the discriminating quality of single‐neuron activity substantially surpasses the ability of the monkeys to discriminate the target from distracters, raising the possibility that saccade target selection is a noisy process. We discuss these new findings in light of the visual search literature and the view that the SC is a visual salience map for orienting eye movements.
Full reaction time distributions reveal the complexity of neural decision‐making
Authors: Noorani Imran , Carpenter R. H. S. 
Published: June 2011

AbstractMeasurement of the stochastic distribution of reaction time or latency has become a popular technique that can potentially provide precise, quantitative information about the underlying neural decision mechanisms. However, this approach typically requires data from large numbers of individual trials, in order to enable reliable distinctions to be made between different models of decision. When data are not plentiful, an approximation to full distributional information can be provided by using a small number of quantiles instead of full distributions – often, just five are used. Although this can often be adequate when the proposed underlying model is a relatively simple one, we show here that, with more complex tasks, and correspondingly extended models, this kind of approximation can often be extremely misleading, and may hide important features of the underlying mechanisms that only full distributional analysis can reveal.
Contribution of the retino‐tectal pathway to visually guided saccades after lesion of the primary visual cortex in monkeys
Authors: Kato Rikako , Takaura Kana , Ikeda Takuro , Yoshida Masatoshi , Isa Tadashi 
Published: June 2011

AbstractPrevious reports on ‘blindsight’ have shown that some patients with lesions of the primary visual cortex (V1) could localize visual targets in their scotoma with hand and/or eye movements without visual awareness. A role of the retino‐tectal pathway on residual vision has been proposed but the direct evidence for this still remains sparse. To examine this possibility, we inactivated the superior colliculus (SC) of unilateral V1‐lesioned monkeys using microinjections of muscimol, and analysed the effects on visually guided saccades. Following muscimol injections into the contralesional SC, the monkeys performed the visually guided saccade task with relatively minor deficits. The effects of ipsilesional SC inactivation were more severe. After injections, the monkeys failed to localize the target within the visual field represented at the injection site on the SC map. The effects of ipsilesional SC inactivation may result from sensory deficits, motor deficits or a combination of both. To examine these possibilities, we tested the effects of SC inactivation on the motor system by investigating spontaneous saccades. After inactivation of the ipsilesional SC, spontaneous saccades toward the injection site were not abolished, suggesting that impairment of visually guided saccades following inactivation of the ipsilesional SC could not be explained solely by a motor deficit and was primarily due to a visual deficit, presumably by interfering with processing in the superficial layer. We conclude that the retino‐tectal pathway plays an essential role in residual vision after V1 lesion. The results suggest that this pathway may be involved in mediating unconscious vision in blindsight patients.
Identifying Discontinuities in Trend Surfaces Using Bilateral Kernel Regression
Authors: Brunsdon Chris 
Published: June 2011

AbstractFollowing a brief review of the kernel regression approach to estimating surface models of the form z=f(x,y) +ε, this article will consider the situation where f is not a continuous surface function, and in particular where the discontinuities take the form of one‐dimensional breaks in the surface, and are not specified a priori. This form of model is particularly useful when visualizing some social and economic data where very rapid changes in geographical characteristics may occur – such as crime rates or house prices. The article briefly reviews approaches to this problem and proposes a novel approach (Bilateral Kernel Regression) adapting an algorithm from the field field of image processing (Bilateral Filtering), giving example analyses of synthetic and real‐world data. Techniques for enhancing the basic algorithm are also considered.
Spatially Clustered Associations in Health Related Geospatial Data
Authors: Leibovici Didier G. , Bastin Lucy , Anand Suchith , Hobona Gobe , Jackson Mike 
Published: June 2011

AbstractOverlaying maps using a desktop GIS is often the first step of a multivariate spatial analysis. The potential of this operation has increased considerably as data sources and Web services to manipulate them are becoming widely available via the Internet. Standards from the OGC enable such geospatial ‘mashups’ to be seamless and user driven, involving discovery of thematic data. The user is naturally inclined to look for spatial clusters and ‘correlation’ of outcomes. Using classical cluster detection scan methods to identify multivariate associations can be problematic in this context, because of a lack of control on or knowledge about background populations. For public health and epidemiological mapping, this limiting factor can be critical but often the focus is on spatial identification of risk factors associated with health or clinical status. In this article we point out that this association itself can ensure some control on underlying populations, and develop an exploratory scan statistic framework for multivariate associations. Inference using statistical map methodologies can be used to test the clustered associations. The approach is illustrated with a hypothetical data example and an epidemiological study on community MRSA. Scenarios of potential use for online mashups are introduced but full implementation is left for further research.
Location Intelligence: An Innovative Approach to Business Location Decision‐making
Authors: Weber Patrick , Chapman Dave 
Published: June 2011

AbstractAs one of the leading ‘world cities’, London is particularly reliant on sources of foreign direct investment (FDI). In the face of increasing global competition and a difficult economic climate, the capital must compete effectively to encourage and support such investors. Through a collaborative study with London's official FDI promotion agency, Think London, the need for a coherent framework for data, methodologies and tools to inform business location decision‐making became apparent. This article discusses the development of a rich environment to explore, compare and rank London's business neighbourhoods. This is achieved through the development and evaluation of a model for location‐based decision support. First, we discuss the development of a geo‐business classification for London which draws upon methods and practices common in geodemographic neighbourhood classification. A geo‐business classification is developed, encapsulating relevant location variables using Principal Components Analysis into a set of composite area profiles. Second, we discuss the implementation of an appropriate Multi‐Criteria Decision Making methodology, in this case Analytical Hierarchy Process (AHP), enabling the aggregation of the geo‐business classification and decision‐makers' preferences into discrete decision alternatives. Finally, we present the results of the integration of both data and model through the development and evaluation of a web‐based prototype.
Exploring the Historical Determinants of Urban Growth Patterns through Cellular Automata
Authors: Stanilov Kiril , Batty Michael 
Published: June 2011

AbstractWe have adapted METRONAMICA, an established cellular automata (CA) modelling system, to simulate the historical growth of a section of a large world city. Our model is tuned to reflect the morphology of land use patterns more accurately than traditional CA models, which abstract those patterns to more aggregate spatial scales. We explore the spatial determinants of land use patterns with detailed empirical data, documenting the historical growth of West London at an unusually high level of spatial and temporal resolution. The results of the study provide support for our considered speculations: (1) that the spatial relationships between land uses and the physical environment are remarkably consistent through time, showing little variation relative to changes in historical context; and (2) that these relationships constitute a basic code for urban growth which determines the spatial signature of land development in a given metropolitan area.
Street‐level Spatial Scan Statistic and STAC for Analysing Street Crime Concentrations
Authors: Shiode Shino 
Published: June 2011

AbstractThis study develops new types of hotspot detection methods to describe the micro‐space variation of the locations of crime incidents at the street level. It expands on two of the most widely used hotspot detection methods, Spatial and Temporal Analysis of Crime and Spatial Scan Statistic, and applies them to the analysis of the network space. The study first describes the conceptual and the methodological framework of the new methods followed by analyses using: (1) a simulated distribution of points along the street network; and (2) real street‐crime incident data. The simulation study using simulated point distributions confirms that the proposed methods is more accurate, stable and sensitive in detecting street‐level hotspots than their conventional counterparts are. The empirical analysis with real crime data focuses on the distribution of the drug markets and robberies in downtown Buffalo, NY in 1995 and 1996. The drug markets are found to form hotspots that are dense, compact and stable whereas hotspots of the robberies are observed more thinly across a wider area. The study also reveals that the location of the highest risk remains on the same spot over time for both types of crimes, indicating the presence of hotbeds which requires further attention.
How fast is a cow? Cross‐Scale Analysis of Movement Data
Authors: Laube Patrick , Purves Ross S. 
Published: June 2011

AbstractData representing the trajectories of moving point objects are becoming increasingly ubiquitous in GIScience, and are the focus of much methodological research aimed at extracting patterns and meaning describing the underlying phenomena. However, current research within GIScience in this area has largely ignored issues related to scale and granularity – in other words how much are the patterns that we see a function of the size of the looking glass that we apply? In this article we investigate the implications of varying the temporal scale at which three movement parameters, speed, sinuosity and turning angle are derived, and explore the relationship between this temporal scale and uncertainty in the individual data points making up a trajectory. A very rich dataset, representing the movement of 10 cows over some two days every 0.25 s is investigated. Our cross‐scale analysis shows firstly, that movement parameters for all 10 cows are broadly similar over a range of scales when the data are segmented to remove quasi‐static subtrajectories. However, by exploring realistic values of GPS uncertainty using Monte Carlo Simulation, it becomes apparent that fine scale measurement of all movement parameters is masked by uncertainties, and that we can only make meaningful statements about movement when we take these uncertainties into account.
Using Participatory Computer Simulation to Explore the Process of Urban Evolution
Authors: Dearden Joel , Wilson Alan 
Published: June 2011

AbstractWhen planners intervene in urban systems they seek in part to generate a positive response from those parts of a city outside of their control, namely the private market and private individuals. This response is difficult to predict due to the fact that the city is a nonlinear system of organized complexity. Models of cities which seek to explain this response are necessarily complicated and dynamic. Where an analytical solution is not possible we turn to computer simulation and interactive visualization in order to understand their output. Allowing human participation in such simulations provides a sandbox in which to experiment with the dynamic behaviour of an urban model and play a part in its evolution. Two possible options for structuring this participation are: (1) toy retail systems, which allow unconstrained experimentation, and (2) games, which impose rules and involve role‐play and competition. To explore these ideas we construct a toy retail system and a two‐player retail game, both of which are derived from an existing agent‐based retail model. We explore the application of these systems to the metropolitan county of South Yorkshire in the UK.
Automatic Classification of Retail Spaces from a Large Scale Topographic Database
Authors: Mackaness William A , Chaudhry Omair Z 
Published: June 2011

AbstractThere is considerable interest in understanding the distribution patterns of different types of retail space, over time, and doing so at a national scale. Yet a lack of suitable data, coupled with poor classification schemas, has stymied efforts to create such a national perspective. This research reports on metrics and classification methodologies that have been applied to large scale topographic data, that afford a systematic classification of certain retail spaces potentially at the national coverage. By analysing the form, composition, extent and patterns of buildings within retail spaces, together with their degree of centrality and levels of access, we demonstrate that it is possible to classify different types of retail space. The research illustrates the utility of fine scale topographic data beyond mere mapping. The article compares three methodologies used for classification (Boolean, fuzzy logic and Bayesian modelling) and evaluates them through comparison with known locations of various retail types as a way of assessing the validity of these approaches. The quality of the results are good, though the work highlights the inconsistency in definitions that currently exist – reflecting, as much as anything, the shifting sands of definitions of various retail spaces that ebb and flow according to consumer needs, and the ambitions of urban planners.