Search

Arrow signs are often used in crowded environments such as airports to direct observers’ attention to objects and areas of interest. Research with social and symbolic cues presented in isolation at fixation has suggested that social cues (such as eye gaze and pointing hands) are more effective in directing observers’ attention than symbolic cues. The present work examines whether in visual search, social cues would therefore be more effective than arrows, by asking participants to locate target objects in crowded displays that were cued by eye-gaze, pointing hands or arrow cues. Results show an advantage for arrow cues, but only for arrow cues that stand out from the surroundings. The results confirm earlier suggestions that in extrafoveal vision cue shape trumps biological relevance. Eye movements suggest that these cueing effects rely predominantly on extrafoveal perception of the cues.

Though a dynamic object, placed against stationary background, always grabs attention, opposite is not necessarily true. Hence, in this study we placed a stationary target among the dynamic distractors. We investigated whether visual detection depends on (1) set size (9, 18 or 27), (2) type of the distractor dynamics (jitter, blink, or luminance change) and (3) synchronisation (synchronized or unsynchronized distractors change). In contrast to pop-out effect of a dynamic target, the search for stationary target was serial, as the RT analysis revealed. The synchronisation of the distractor dynamic properties helped the detection especially in the larger sets. The most distracting for the target detection was illumination change of the distractors whereas the least distracting was blink.

Purpose of the present research was further examination of roles of symmetry and complexity in visual perception tasks. We tested hypothesis from perceptual economy theory, and since we used shape disruptions as one of the stimulus characteristics we could also address Luccio’s two step theory concerning perception of shape disruptions on good forms. Four experiments were conducted, visual search and simultaneous and delayed matching. Symmetry and complexity were varied, as well as set size in visual search experiment. Dependent variables were reaction time and error number. In all four experiments, symmetry had dominant effect, while significant effect of complexity was registered only in Experiment 1. However, in first three experiments interaction of symmetry and complexity was also significant. Analysis of reaction times and performance suggested that our results follow the pattern suggested by perceptual economy, i.e. that symmetry is dominant in easier tasks, while complexity was significant in most difficult task. Our results couldn’t completely support Luccio’s assumption that shape disruption is better perceived on good forms, although it can’t be completely discarded.

The main goal of the experiment was to test whether deployment ofattention could be strategically controlled. Subjects viewed five-letter arrays.Each array included a letter unique in shape (i.e. target). One of the letters ineach array (target or non-target) also differed from other letters in color orin position in relation to the array. That letter will be referred to as a featuresingleton. The probability ratio of the feature singleton being the target or anon-target letter was varied throughout three experiments. The ratios were (1)0.5 (target) : 0.5 (non-target); (2) 0.2 (target) : 0.8 (non-target); (3) 0.8 (target): 0.2 (non-target). Subjects in all three experimental conditions deployed serialprocesses, but failed to maintain complete intentional control during the courseof the search.

Laboratory of Experimental Psychology, University of Belgrade The aim of the study was the investigation of form, spatial set organization and visual attention in visual search of illusory contours. Three visual search experiments were conducted. In the first experiment, where the simple detection procedure was used, subject's task was to detect square among vertical and horizontal lines. Other experiments investigated visual search of illusory contours in four different set organizations. Introduction of set organization was the way of manipulation of target's eccentricity among other elements. Analysis showed different type of search of the regular and the illusory square figure. The search profile of the regular square proved to be parallel, while all the searches of the illusory squares remained serial. Set organization had important role in visual search of illusory contours. Regardless of serial profile, visual search was faster in cases where target figure was more salient due to the background elements organization.

Laboratory of Experimental Psychology, University of Belgrade Recent research, which was mostly focused on assessing the types of visual search of illusory contours, showed that visual search is dependent on factors like target configuration and task type. Some experimental research supports the theory of parallel search while other research supports the theory of serial search of illusory contours. The inconsistency is most likely due to the fact that various types of illusory contour configurations were used in set creation. Up to this point, our research indicated that the serial search is used in most cases. Some exceptions of search type have been proven in some modification of task type but nevertheless the search profile remained serial. In this article, we are reporting on two visual search experiments. The first experiment was an investigation of a specific feature of a Kanisza type illusory triangle, orientation. The validity of the profile defined in the first experiment was tested in our second experiment with an attempt to automatize the visual search by the multiplication of the initial experimental trials. Our results confirmed that, regardless of the number of experimental trials, the visual search profile remains serial.

Illusory contours are specific class of visual stimuli that represent stimuli configurations perceived as integral irrespective of the fact that they are given in fragmented uncompleted wholes. Due to their specific features, illusory contours gained much attention in last decade representing prototype of stimuli used in investigations focused on binding problem. On the other side, investigations of illusory contours are related to problem of the level of their visual processing. Neurophysiologic studies show that processing of illusory contours proceed relatively early, on the V2 level, on the other hand most of experimental studies claim that illusory contours are perceived with engagement of visual attention, binding their elements to whole percept. This research is focused on two experiments in which visual search of illusory contours are based on shape and orientation. The main experimental procedure evolved the task proposed by Bravo and Nakayama where instead of detection, subjects were performing identification of one among two possible targets. In the first experiment subjects detected the presence of illusory square or illusory triangle, while in the second experiment subject were detecting two different orientations of illusory triangle. The results are interpreted in terms of visual search and feature integration theory. Beside the type of visual search task, search type proved to be dependent of specific features of illusory shapes which further complicate theoretical interpretation of the level of their perception.

Though a dynamic object, placed against stationary background, always grabs attention, opposite is not necessarily true. Hence, in this study we placed a stationary target among the dynamic distractors. We investigated whether visual detection depends on (1) set size (9, 18 or 27), (2) type of the distractor dynamics (jitter, blink, or luminance change) and (3) synchronisation (synchronized or unsynchronized distractors change). In contrast to pop-out effect of a dynamic target, the search for stationary target was serial, as the RT analysis revealed. The synchronisation of the distractor dynamic properties helped the detection especially in the larger sets. The most distracting for the target detection was illumination change of the distractors whereas the least distracting was blink. [ABSTRACT FROM AUTHOR]

Microgenetic analysis was used to investigate perception of illusory contour figures which represent whole, completed forms on the basis of segmented, incomplete stimulation. The analysis provided an experimental approach to this phenomenon which was standardly investigated phenomenologically. Experimental procedure consisted of two phases: a) priming phase and b) test phase which consisted of visual search task. Two types of visual search tasks were applied: (i) classic detection, in which subjects were detecting presence or absence of the target stimuli and (ii) two-alternative forced choice, 2AFC, in which subjects performed discrimination between two concurrent targets (target A vs. target B). Variation of exposition of prim stimuli was used as an indication of the percept formation period. Concepts like early vision, visual attention and feature binding were investigated. Four experiments were conducted. Their outcome showed that (i) perception of amodal figure requires visual attention, (ii) features binding precedes spatial attention and (iii) time period of percept formation is dependent of task properties and varies between 50 - 150 ms. Some results obtained in this research could be explained by feature-integration theory (Treisman & Gelade, 1980; Treisman, 1986). Furthermore, percept formation period data comply with data acquired in Elliott & Müller's psychophysical research (1998).