The serial process in visual search.

The conditions for serial search are described. A multiple target search methodology (Thornton & Gilden, 2007) is used to home in on the simplest target/distractor contrast that effectively mandates a serial scheduling of attentional resources. It is found that serial search is required when (a) targets and distractors are mirror twins, and (b) when the search elements lack the Gestalt property of intrinsic orientation. The finding is put into the context of Feature Integration Theory (Treisman & Gelade, 1980) that first identified the occasions of serial search to be important to object perception and understanding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the surprising salience of curvature in grouping by proximity.

The authors conducted 3 experiments to explore the roles of curvature, density, and relative proximity in the perceptual organization of ambiguous dot patterns. To this end, they developed a new family of regular dot patterns that tend to be perceptually grouped into parallel contours, dot-sampled structured grids (DSGs). DSGs are similar to the dot lattices used to study grouping by proximity, except that only one of the potential organizations is rectilinear; the others are curvilinear. The authors used the method of M. Kubovy and J. Wagemans (1995) to study grouping by proximity in DSGs. They found that in the competition between the most likely organizations, one rectilinear and the other curvilinear, the latter is more salient. This phenomenon cannot be explained by contemporary accounts of grouping by proximity or contour integration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serial deployment of attention during visual search.

This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100-150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Information-limited parallel processing in difficult heterogeneous covert visual search.

Difficult visual search is often attributed to time-limited serial attention operations, although neural computations in the early visual system are parallel. Using probabilistic search models (Dosher, Han, & Lu, 2004) and a full time-course analysis of the dynamics of covert visual search, we distinguish unlimited capacity parallel versus serial search mechanisms. Performance is measured for difficult and error-prone searches among heterogeneous background elements and for easy and accurate searches among homogeneous background elements. Contrary to the claims of time-limited serial attention, searches in heterogeneous backgrounds instead exhibited nearly identical search dynamics for display sizes up to 12 items. A review and new analyses indicate that most difficult as well as easy visual searches operate as an unlimited-capacity parallel analysis over the visual field within a single eye fixation, which suggests limitations in the availability of information, not temporal bottlenecks in analysis or comparison. Serial properties likely reflect overt attention expressed in eye movements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel Processing in Visual Search Asymmetry.

The difficulty of visual search may depend on assignment of the same visual elements as targets and distractors-search asymmetry. Easy C-in-O searches and difficult O-in-C searches are often associated with parallel and serial search, respectively. Here, the time course of visual search was measured for both tasks with speed-accuracy methods. The time courses of the 2 tasks were similar and independent of display size. New probabilistic parallel and serial search models and sophisticated-guessing variants made predictions about time course and accuracy of visual search. The probabilistic parallel model provided an excellent account of the data, but the serial model did not. Asymptotic search accuracies and display size effects were consistent with a signal-detection analysis, with lower variance encoding of Cs than Os. In the absence of eye movements, asymmetric visual search, long considered an example of serial deployment of covert attention, is qualitatively and quantitatively consistent with parallel search processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial grouping determines temporal integration.

To make sense out of a continuously changing visual world, people need to integrate features across space and time. Despite more than a century of research, the mechanisms of features integration are still a matter of debate. To examine how temporal and spatial integration interact, the authors measured the amount of temporal fusion (a measure of temporal integration) for different spatial layouts. They found that spatial grouping by proximity and similarity can completely block temporal integration. Computer simulations with a simple neural network capture these findings very well, suggesting that the proposed spatial grouping operations may occur already at an early stage of visual information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the continuity of perceptual experience: Implications for perception and attention.

When an observer views a real-world scene, some objects in the scene are partly occluded by intervening surfaces. Similarly, as the observer moves through the environment, some objects are temporarily occluded and revealed. Yet, although the retinal image is fragmented in space and time, perceptual experience is coherent and continuous. Continuity of experience is achieved by perceptual organization mechanisms, which have their effect before attention. Several experiments are described to illustrate the close interaction between perceptual organization and attention. This interaction determines the representational basis for selection, and is therefore a crucial precursor to understanding object-based mechanisms of visual selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging and perception of visual form from temporal structure.

In this study, the authors examined age-related changes in participants' ability to perceive global spatial structure defined by temporal fine structure among elements undergoing rapid, irregular change. Participants were also tested on a task involving form recognition from luminance contrast and on a task dependent on perception of 3-dimensional shape from motion. Compared with young adults, older individuals were less sensitive to spatial form defined by temporal structure. In contrast, older observers performed as well as young adults on the other two tasks that were not dependent on temporal sensitivity, ruling out nonsensory factors as the cause of the deficits on the temporal structure task. This selective deficit may reveal reduced sensitivity within the temporal impulse response of the aging visual system, a deficit that could be related to reduced effectiveness of neural inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Objects and events as determinants of parallel processing in dual tasks: Evidence from the backward compatibility effect.

The backward-compatibility effect (BCE) is a major index of parallel processing in dual tasks and is related to the dependency of Task 1 performance on Task 2 response codes (Hommel, 1998). The results of four dual-task experiments showed that a BCE occurs when the stimuli of both tasks are included in the same visual object (Experiments 1 and 2) or belong to the same perceptual event (Experiments 3 and 4). Thus, the BCE may be modulated by factors that influence whether both task stimuli are included in the same perceptual event (objects, as studied in cognitive experiments, being special cases of events). As with objects, drawing attention to a (selected) event results in the processing of its irrelevant features and may interfere with task execution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Equivalent effects of grouping by time, voice, and location on response timing in verbal serial memory.

The grouping of list items is known to improve serial memory accuracy and constrain the nature of temporal errors. A recent study (M. T. Maybery, F. B. R. Parmentier, & D. M. Jones, 2002) showed that grouping results in a temporal organization of the participants' responses that mimics the list structure but not the timing of its presentation. Here the authors tested the prediction that the temporal grouping of responses should yield the same pattern of response time (RT) irrespective of the method of grouping at presentation. Comparing temporal, location, and voice grouping, the results show that although these methods impact on recall accuracy to varying degrees, all 3 conditions produce significant and equivalent peaks in RT at the first position of each group. The RT data were accurately simulated through a model based on ACT-R's (J. R. Anderson & M. Matessa, 1997) basic principles. Altogether, the data suggest that the temporal organization of responses in verbal serial recall results from (a) declarative knowledge about the list's structure that is independent of the perceptual means by which grouping is induced at presentation and (b) the level of activation of the items per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Are some Gestalt principles deployed more readily than others during early development? The case of lightness versus form similarity.

Four experiments investigated how readily infants achieve perceptual organization by lightness and form similarity. Infants were (a) familiarized with elements that could be organized into rows or columns on the basis of lightness or form similarity and tested with vertical versus horizontal bars depicting the familiar versus novel organization or (b) familiarized with bars and tested with elements. For lightness similarity, generalization occurred in both tasks; however, for form similarity, generalization occurred only in the elements → bars task. The findings indicate that lightness similarity is more readily deployed than form similarity and are discussed in the context of (a) whether the difference reflects speed of application or experience-based learning, (b) evidence from visual agnosic patients and the time course of application of the principles in healthy adults, and (c) development of dorsal and ventral visual processing streams. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What does visual agnosia tell us about perceptual organization and its relationship to object perception?

The authors studied 2 patients, S.M. and R.N., to examine perceptual organization and its relationship to object recognition. Both patients had normal, low-level vision and performed simple grouping operations normally but were unable to apprehend a multielement stimulus as a whole. R.N. failed to derive global structure even under optimal stimulus conditions, was less sensitive to grouping by closure, and was more impaired in object recognition than S.M. These findings suggest that perceptual organization involves a multiplicity of processes, some of which are simpler and are instantiated in lower order areas of visual cortex (e.g., collinearity). Other processes are more complex and rely on higher order visual areas (e.g., closure and shape formation). The failure to exploit these latter configural processes adversely affects object recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychosexual conflicts and defenses in visual perception.

Tachistoscopically presented stimulus material (Blacky pictures) is used to study perceptual defense and vigilance in persons with different psychosexual conflict dimensions and ego-defense preferences. It is hypothesized that when stimulus material is presented below the threshold of conscious recognition, perceptually vigilant behavior will be evoked under conditions where ego-defense mechanisms are not likely to operate, and perceptually defensive behavior will be evoked where ego-defense mechanisms are likely to operate. The vigilance and defense hypotheses are confirmed by the results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lack of flexibility in visual grouping in patients with schizophrenia.

The study attempted to distinguish automatic grouping processes from top-down processes in a visual perceptual task in 30 patients with schizophrenia and 30 matched controls. Participants decided whether 7 figures were all different or whether 2 adjacent figures were identical. The distance between figures was manipulated to produce 3 separated pairs of figures, the targets belonging to either the same pair (within-group trials) or different pairs (between-groups trials). As controls, patients benefited from proximity for grouping. Top-down processes were explored by manipulating the proportion of within-group and between-groups trials in 3 experimental blocks. In patients, response times (RTs) decreased for within-group trials when within-group trials were more frequent, indicating that performance was correctly adapted to the type of block. Unlike controls, however, this RT decrease was not accompanied by a cost for between-groups trials. Ocular movement recordings revealed that controls were able to focus on between-groups regions selectively when between-groups trials were more frequent, whereas patients were unable to do so. The authors suggest that top-down processes allowing the construction of a selective representation of between-groups regions are impaired in patients with schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serial and parallel attentive visual searches: Evidence from cumulative distribution functions of response times.

Participants searched a visual display for a target among distractors. Each of 3 experiments tested a condition proposed to require attention and for which certain models propose a serial search. Serial versus parallel processing was tested by examining effects on response time means and cumulative distribution functions. In 2 conditions, the results suggested parallel rather than serial processing, even though the tasks produced significant set-size effects. Serial processing was produced only in a condition with a difficult discrimination and a very large set-size effect. The results support C. Bundesen's (1990) claim that an extreme set-size effect leads to serial processing. Implications for parallel models of visual selection are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age-related changes in selective attention and perceptual load during visual search.

Three visual search experiments were conducted to test the hypothesis that age differences in selective attention vary as a function of perceptual load (E. A. Maylor & N. Lavie, 1998). Under resource-limited conditions (Experiments 1 and 2), the distraction from irrelevant display items generally decreased as display size (perceptual load) increased. This perceptual load effect was similar for younger and older adults, contrary to the findings of Maylor and Lavie. Distraction at low perceptual loads appeared to reflect both general and specific inhibitory mechanisms. Under more data-limited conditions (Experiment 3), an age-related decline in selective attention was evident, but the age difference was not attributable to capacity limitations as predicted by the perceptual load theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal integration between visual images and visual percepts.

Using a temporal integration task, subjects in 5 experiments were expected to combine information from temporally separated visual presentations. Evidence from these experiments indicated that perceptual information can be integrated with previously generated and currently maintained visual images to form a representation that contains information from each source. Properties and limitations of this integration process were also explored, including the time required to generated the image, the speed at which percepts were integrated with images, and the capacity of the representation. Implications for theories of visual processing and memory are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Online response preparation in a rapid serial visual search task.

Online response preparation was assessed in a visual search task using rapid serial visual presentation. In each trial, a series of letters was presented sequentially, and participants were instructed to make a target-present response if a prespecified target letter was presented or a target-absent response if it was not. Measurements of response preparation using both probe reaction time and the lateralized readiness potential indicated that preparation of the target-absent response increased near the end of the sequence. Most of the increase appeared to be due to direct priming of the target-absent response by nontarget letters, but part was due to the increased conditional probability of this response near the end of the sequence. These results extend previous studies of response preparation by showing online response preparation during a temporally extended reaction time task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel processing in face perception.

The authors examined face perception models with regard to the functional and temporal organization of facial identity and expression analysis. Participants performed a manual 2-choice go/no-go task to classify faces, where response hand depended on facial familiarity (famous vs. unfamiliar) and response execution depended on facial expression (happy vs. angry). Behavioral and electrophysiological markers of information processing—in particular, the lateralized readiness potential (LRP)—were recorded to assess the time course of facial identity and expression processing. The duration of facial identity and expression processes was manipulated in separate experiments, which allowed testing the differential predictions of alternative face perception models. Together, the reaction time and LRP findings indicate a parallel architecture of facial identity and expression analysis in which the analysis of facial expression relies on information about identity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Edge-region grouping in figure-ground organization and depth perception.

Edge-region grouping (ERG) is proposed as a unifying and previously unrecognized class of relational information that influences figure-ground organization and perceived depth across an edge. ERG occurs when the edge between two regions is differentially grouped with one region based on classic principles of similarity grouping. The ERG hypothesis predicts that the grouped side will tend to be perceived as the closer, figural region. Six experiments are reported that test the predictions of the ERG hypothesis for 6 similarity-based factors: common fate, blur similarity, color similarity, orientation similarity, proximity, and flicker synchrony. All 6 factors produce the predicted effects, although to different degrees. In a 7th experiment, the strengths of these figural/depth effects were found to correlate highly with the strength of explicit grouping ratings of the same visual displays. The relations of ERG to prior results in the literature are discussed, and possible reasons for ERG-based figural/depth effects are considered. We argue that grouping processes mediate at least some of the effects we report here, although ecological explanations are also likely to be relevant in the majority of cases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)