Дисертації з теми "Visual grouping"

Perceptual grouping plays an indispensable role on attention distribution. An example of this interaction is the impaired visual search performance when the target overlaps with a task-irrelevant salient distractor organized to a snake-like configuration by collinear bars, and when the collinear distractor is long enough (Jingling & Tseng, 2013). This phenomenon is puzzling because it is opposite to our understanding of attention capture which predicts search facilitation instead of impairment. As an attempt to fully understand the interaction between perceptual grouping and attention, the current research probed the possible neural stage of this collinear search impairment effect. In Study 1, the distractor column of the search display was split into two eyes: one eye saw a distractor with varied length (= 1, 5, or 9 bars) while the other eye saw the rest of the distractor column. When both eyes were properly fused, observers saw a search display containing a 9-bar distractor. Observers were asked to identify the orientation of a target gap that could be overlapping or non-overlapping with the distractor. It was found that search impairment was dominated by monocular collinear distractor length. In Study 2, a 9-bar distractor was shown to one eye of observers and strong flashing color patches were shown to the other eye (Continuous Flash Suppression) such that part of the distractor was suppressed from observers’ awareness. It was found that invisible collinear distractor parts enhanced search impairment, suggesting awareness of the distractor is not necessary for the effect. Results from both studies converge to suggest that the effect of collinear grouping on attention is likely to be at early visual sites like V1 where monocular information but not awareness is processed. It highlights the need to incorporate perceptual grouping into current salience-based attention models.
published_or_final_version
Psychology
Master
Master of Philosophy

According to Feature Integration Theory (Treisman & Gelade, 1980), search for a target defined by features on two different dimensions (e.g. green horizontal target among red horizontal and green vertical distractors) is conducted via serial attentive search of all items in the array. Results presented in this thesis clearly demonstrate that conjunction search is not conducted as a serial self-terminating search, and suggest that subjects selectively search a single feature set. Strong support is also provided for the role of local grouping processes in visual conjunction search. This includes evidence demonstrating: (1) that local context is an important factor in directing search toward the target, and (2) that groups of spatially adjacent homogeneous elements can be processed in parallel. These results point to the importance of spatial layout of target and distractor elements. More recent theories (e.g. Cave & Wolfe, 1990) will have to be amended in order to account for these data.

xiii, 143 p. : ill. (some col.)
The cognitive ability to group information into chunks is a well known phenomenon, however, the effects of chunking on visual representations is not well understood. Here we investigate the effects of visual chunking using Gestalt grouping principles in two tasks: visual working memory change detection and multiple object tracking. Though both these tasks have been used to study cognitive functions in the past, including object-based attention, attentional control and working memory capacity, the effect of grouping on mental representations in these tasks has not been well characterized. That is, while researches have measured effects of grouping on behavioral output in similar tasks, there are few studies of the effects of grouping on neurophysiological indices of object representations. Indeed, these current studies are the first to use event-related potentials (ERPs) to elucidate the effect of grouping on active mental representations of visual stimuli. In the visual working memory task, observers remembered either the color or orientation of pacman stimuli across a delay. We manipulated the collinearity of these objects, whether or not they formed a Kanizsa triangle figure, and measured the behavioral and electrophysiological effects. In the multiple object tracking task, a subset of identical stimuli were briefly cued as targets and then their motion was tracked by participants. We manipulated whether and which Gestalt heuristics were used to bind targets together during their motion and measured the effects on behavior and electrophysiology. In both tasks we compared the grouped to ungrouped conditions. We found that across experiments and tasks behavioral performance was enhanced in grouping conditions compared to ungrouped conditions. Furthermore, the waveforms evoked by grouped stimuli were reduced compared to waveforms produced in response to locally identical but ungrouped stimuli. These data suggest that the mental representation of visual objects may be reshaped moment-by-moment by grouping cues or task demand, giving rise to a flexible, active and dynamic yet parsimonious representation of the visual world.
Committee in charge: Edward K. Vogel, Chair; Edward Awh, Member; Ulrich Mayr, Member; Paul van Donkelaar, Outside Member

Il presente lavoro è motivato dal problema della constituzione di unità percettive a livello della corteccia visiva primaria V1. Si studia dettagliatamente il modello geometrico di Citti-Sarti con particolare attenzione alla modellazione di fenomeni di associazione visiva. Viene studiato nel dettaglio un modello di connettività. Il contributo originale risiede nell'adattamento del metodo delle diffusion maps, recentemente introdotto da Coifman e Lafon, alla geometria subriemanniana della corteccia visiva. Vengono utilizzati strumenti di teoria del potenziale, teoria spettrale, analisi armonica in gruppi di Lie per l'approssimazione delle autofunzioni dell'operatore del calore sul gruppo dei moti rigidi del piano. Le autofunzioni sono utilizzate per l'estrazione di unità percettive nello stimolo visivo. Sono presentate prove sperimentali e originali delle capacità performanti del metodo.

Objective: The goal of this research was to determine whether alternate-line shading (zebra-striping) of grid-based displays affects the strategy (i.e., “visual flow”) and efficiency of serial search. Background: Grids, matrices, and tables are commonly used to organize information. A number of design techniques and psychological principles are relevant to how viewers’ eyes can be guided through such visual works. One common technique for grids, “zebra-striping,” is intended to guide eyes through the design, or “create visual flow” by alternating shaded and unshaded rows or columns. Method: 13 participants completed a visual serial search task. The target was embedded in a grid that had 1) no shading, 2) shading of alternating rows, or 3) shading of alternating columns. Response times and error rates were analyzed to determine search strategy and efficiency. Results: Our analysis found evidence supporting a weak effect of shading on search strategy. The direction of shading had an impact on which parts of the grid were responded to most rapidly. However, a left-to-right reading bias and middle-to-outside edge effect were also found. Overall performance was reliably better when the grid had no shading. Exploratory analyses suggest individual differences may be a factor. Conclusion: Shading seems to create visual flow that is relatively weak compared to search strategies related to the edge effect or left-to-right reading biases. In general, however, the presence of any type of shading reduced search performance. Application: Designers creating a grid-based display should not automatically assume that shading will change viewers search strategies. Furthermore, although strategic shading may be useful for tasks other than that studied here, our current data indicate that shading can actually be detrimental to visual search for complex (i.e., conjunctive) targets.

Syftet med denna uppsats är att identifiera den mest effektiva egenskapen av en text eller sida för att uppnå visuell hierarki, som är ett verktyg för att få det önskade flödet av uppmärksamhet i en sida eller webbsida genom att ge vissa element en viss vikt i kontrast, storlek och placering. Vi vill ge en möjlighet för vidare forskning snarare än att ge en slutsats som ger ett slutgiltigt svar på frågeställningarna. Det finns fler sätt att manipulera text för att uppnå önskad visuell hierarki men vi valde de vanligaste. Detta arbete är baserat på ett experiment som görs på 50 deltagare med ett onlinefrågeformulär och tre självgjorda bilder där vi kan utvärdera resultaten, jämföra dem med andra teorier och beräkna den mest effektiva uppmärksamhetsgivaren. Vi har också utvecklat en hypotes om vad resultatet kommer att visa. Vår studie föreslår att kontrasten i färg kan vara den viktigaste faktorn för att uppnå och upprätthålla visuell hierarki.
The purpose of this paper is to identify the most effective property of a text or a page to achieve visual hierarchy, which is a tool for getting the desired flow of attention in a page or a web page by giving certain elements a degree of weight in contrast, size and positioning.We want to give an opportunity for further research rather than an absolute conclusion of how it really is. There are more ways to manipulate text to achieve the desired visual hierarchy but we choose the most common. This paper is based on an experiment involving 50 participants with an online questionnaire and three self-made pictures where we will evaluate the results, compare them with other theories and calculate the most effective enhancer of attention. We have also developed a hypothesis on what the results will show. Our study proposes that contrast in color might be the most important factor to achieve and maintain visual hierarchy.

The report describes a recognition system called GROPER, which performs grouping by using distance and relative orientation constraints that estimate the likelihood of different edges in an image coming from the same object. The thesis presents both a theoretical analysis of the grouping problem and a practical implementation of a grouping system. GROPER also uses an indexing module to allow it to make use of knowledge of different objects, any of which might appear in an image. We test GROPER by comparing it to a similar recognition system that does not use grouping.

碩士
國立雲林科技大學
工業設計系碩士班
94
The perceptual system of humans to the real world can be broadly classified as “holistic” and “partial” processing. The “holistic” means the object figure upon which the visual sensor will focus while the “partial” means the background that surrounds the main figure. The salience of the object is decided by the stimulus contrast between figure and ground. According to the Gestalt theory, the structure of visual system is mainly decided by the holistic processing rather than the partial processing. This study, based on the grouping theory of Gestalt psychology, will investigate the performance of object identification and target searching. The experiments will focus on the interaction between “shapes of good form”、“low of proximity” and “low of similarity” to different position of object for the performance of target searching, and use the touch screen to show the target figure and select it immediately from the screen. We make use of the compare of reaction time to find out the efficiency of target searching, and know the difference and the influence between both sexes. The results are described as the following: 1.When the subjects search the target figures, they will bear on features of different level changing in the three perceptual theory of Gestalt. 2.The feature variation of figure is more outstanding than the feature variation of ground. Besides, feature variations show different attention and influence level on each other. 3.Subjects will rest on their left or right handed to the tendency of the searching mode.

碩士
國立臺灣海洋大學
資訊工程學系
95
This paper presents an object-based image retrieval using a method based on perceptual grouping of image regions using the modified generalized Hough transform. The effectiveness of region-based representation for content-based image retrieval is extensively studied in the literature. One common weakness of the region-based approaches is that the homogeneous image regions have little correspondence to the semantic image concepts, thus, the retrieval results of region-based approaches in terms of regions’ low-level visual features are far from satisfactory. It is desirable and yet remains as a challenge for querying multimedia data by finding an object inside a target image. Given an object model, an added difficulty is that the object might be translated, rotated, and scaled inside a target image. Object segmentation and recognition is the primary step of computer vision for applying to image retrieval of higher-level image analysis. However, automatic segmentation and recognition of objects via object models is a difficult task without a priori knowledge about the shape of objects. Instead of segmentation and detailed object representation, the objective of this research is to develop and apply computer vision methods that explore the structure of an image object by perceptual grouping of image regions to retrieve images from a database. A voting scheme based on generalized Hough transform is proposed to provide object search method, which is invariant to the translation, rotation, scaling of image data, and hence, invariant to orientation and position. Computer simulation results show that the proposed method gives good performance in terms of retrieval accuracy and robustness.

What exactly are the "parts" that make up the whole object, and how and when do they group? The answer that is proposed hinges on Emergent Features: features that materialize from the configuration which make the object more discriminable from other objects. EFs are not possessed by any individual part and are processed as or more quickly than are the properties of the parts. The present experiments focus on visual discrimination of two-line configurations in an odd-quadrant task. RT data were obtained and compared with a prediction based on the number of EF differences in the odd quadrant (the higher the number of EF differences, the faster the discrimination was predicted). The results suggest that the EFs most responsible for the variations in RT might be lateral endpoint offset, intersections, parallelism, connectivity, number of terminators, and pixel count. Future directions include investigating the individual contributions and salience of EFs.

In order to understand how the neural system encodes and processes information, research has focused on the study of neural representations of simple stimuli, paying no particular attention to it's temporal structure, with the assumption that a deeper understanding of how the neural system processes simpli fied stimuli will lead to an understanding of how the brain functions as a whole [1]. However, time is intrinsically bound to neural processing as all sensory, motor, and cognitive processes are inherently dynamic. Despite the importance of neural and stimulus dynamics, little is known of how the neural system represents rich spatio-temporal stimulus, which ultimately link the neural system to a continuously changing environment. The purpose of this thesis is to understand whether and how temporally-structured neural activity modulates the processing of information within the brain, proposing in turn that, the precise interaction between the spatio-temporal structure of the stimulus and the neural system is particularly relevant, particularly when considering the ongoing plasticity mechanisms which allow the neural system to learn from experience. In order to answer these questions, three studies were conducted. First, we studied the impact of spiking temporal structure on a single neuron spiking response, and explored in which way the functional connections to pre-synaptic neurons are modulated through adaptation. Our results suggest that, in a generic spiking neuron, the temporal structure of pre-synaptic excitatory and inhibitory neurons modulate both the spiking response of that same neuron and, most importantly, the speed and strength of learning. In the second, we present a generic model of a spiking neural network that processes rich spatio-temporal stimuli, and explored whether the processing of stimulus within the network is modulated due to the interaction with an external dynamical system (i.e. extracellular media), as well as several plasticity mechanisms. Our results indicate that the memory capacity, that re ects a dynamic short-term memory of incoming stimuli, can be extended on the presence of plasticity and through the interaction with an external dynamical system, while maintaining the network dynamics in a regime suitable for information processing. Finally, we characterized cortical signals of human subjects (electroencephalography, EEG) associated to a visual categorization task. Among other aspects, we studied whether changes in the dynamics of the stimulus leads to a changes in the neural processing at the cortical level, and introduced the relevance of large-scale integration for cognitive processing. Our results suggest that the dynamic synchronization across distributed cortical areas is stimulus specific and specifically linked to perceptual grouping. Taken together, the results presented here suggest that the temporal structure of the stimulus modulates how the neural system encodes and processes information within single neurons, network of neurons and cortical areas. In particular, the results indicate that timing modulates single neuron connectivity structures, the memory capability of networks of neurons, and the cortical representation of a visual stimuli. While the learning of invariant representations remains as the best framework to account for a number of neural processes (e.g. long-term memory [2]), the reported studies seem to provide support the idea that, at least to some extent, the neural system functions in a non-stationary fashion, where the processing of information is modulated by the stimulus dynamics itself. Altogether, this thesis highlights the relevance of understanding adaptive processes and their interaction with the temporal structure of the stimulus, arguing that a further understanding how the neural system processes dynamic stimuli is crucial for the further understanding of neural processing itself, and any theory that aims to understand neural processing should consider the processing of dynamic signals. 1. Frankish, K., and Ramsey, W. The Cambridge Handbook of Cognitive Science. Cambridge University Press, 2012. // 2. McGaugh, J. L. Memory{a Century of Consolidation. Science 287, 5451 (Jan. 2000), 248{251.

In the brain, every cortical inter-area feedforward projection shares a reciprocal feedback connection. Despite its pervasive nature in the brain, our understanding of the functional role of neural feedback in form perception remains incomplete, particularly in behaving animals. This problem is addressed in humans with a novel form completion paradigm. Seven subjects (5 female) had their EEG waveforms analysed using three linear models showing non-significant differences between stimulus conditions designed to produce differences by manipulating neural feedback to V1. Two of these subjects (one female), in addition to EEG waveforms, had combined magnetic resonance imaging (MRI) and functional MRI (fMRI) cortical maps that allowed anatomically close areas such as V1 and V2 to have their signals decomposed and neural feedback inferred. Differences between stimulus conditions arose once signals had been divided into V1 and V2. Significant differences (p < .05) for one subject in V1 and V2 suggests cortical interactions at 100ms and 350ms. This suggests the form completion paradigm has utility at investigating the influence of the V2 far receptive field surround on V1, given future given signal to noise issues are resolved.