The role of categorization in visual search for orientation.

Visual search for 1 target orientation is fast and virtually independent of set size if all of the distractors are of a single, different orientation. However, in the presence of distractors of several orientations, search can become inefficient and strongly dependent on set size (Exp 1). Search can be inefficient even if only 2 distractor orientations are used and even if those orientations are quite remote from the target orientation (e.g., 20° or even 40° away, Exp 2). Search for 1 orientation among heterogeneous distractor orientations becomes more efficient if the target orientation is the only item possessing a categorical attribute such as steep, shallow (Exp 3), tilted left or tilted right (Exp 4), or simply tilted (Exps 5 and 6). Orientation categories appear to be 1 of several strategies used in visual search for orientation. These serve as a compromise between the limits on parallel visual processing and the demands of a complex visual world. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reversing visual search asymmetries with conjunctions of movement and orientation.

Many theories of visual search offer general principles intended to apply to search for targets defined by any stimulus attribute. The importance of considering specific properties of different visual subsystems is demonstrated by examining search for movement–orientation conjunctions. In displays of intermingled moving and stationary stimuli, search for a salient tilted target (45° vs vertical) is easier among moving than stationary stimuli. If a finer orientation distinction is required (9° vs vertical), the reverse is true; search is easier among the stationary. This follows from the known properties of visual subsystems specialized for processing moving or stationary stimuli. It is not predicted by general theories of visual search such as guided search or similarity theory, nor by principles of Gestalt grouping. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of gravitational cues on visual search for orientation.

To determine whether nonvisual (vestibular and somatosensory) information participates in low-level orientation processing, Ss in different postural conditions (upright, supine, and sitting immobilized) searched for a target distinguishable from distractors by differences in orientation (A. Treisman's [1985] "pop-out" paradigm). Searches for vertical and horizontal targets were dramatically modified as a function of the postural position, indicating that the processing of orientation in early vision is not only retinal but integrates information from the sensory graviceptors. This visuovestibular phenomenon is interpreted in the conceptual framework of D. H. Foster and P. A. Ward's (1991) model based on local orthogonal orientation filters and T. A. Stoffregen and G. E. Riccio's (1988) dynamics of balance theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Display density influences visual search for conjunctions of movement and orientation.

J. Driver and P. McLeod (1992) reported that the ease of visual search for targets defined by a conjunction of movement and orientation was affected by an interaction between target movement and target-nontarget discriminability. When the orientation discrimination to distinguish target from nontarget was difficult, stationary targets were easier to find than moving targets. But when the orientation discrimination to distinguish target from nontarget was easy, moving targets were easier to find than stationary targets. H. J. Muller and J. Maxwell (1994) repeated the experiment but failed to find the interaction. The authors show that the difference between these results was due to the density of the visual displays used. With a high-density display, the authors replicate Driver and McLeod's result; with a low-density display, they replicate Muller and Maxwell's result. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of surface medium on visual search for orientation and size features.

By using a visual search task, this study examined the encoding of orientation and size for stimuli defined in five different surface media: luminance, color, texture, relative motion, and binocular disparity. Results indicated a spatially parallel analysis of size and orientation features for all surface media, with the possible exception of binocular disparity. The data also revealed a search rate asymmetry in the orientation task for all media: Parallel or shallow search functions were obtained for oblique targets in vertical distractors, whereas steeper serial search functions were obtained for vertical targets in oblique distractors. No consistent asymmetry was found for the large and small targets in the size task. There seemed to be common principles of coding in all these different media, suggesting either a single analysis of shape features applied to a common representation or multiple analyses, one for each surface medium, with each extracting a similar set of features. The shared coding principles may facilitate the use of redundancy across media to reduce ambiguities in the locations and shapes of contours in the visual scene. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature asymmetries in visual search: effects of display duration, target eccentricity, orientation and spatial frequency

In Experiments 1-3, we monitored search performance as a function of target eccentricity under display durations that either allowed or precluded eye movements. The display was present either until observers responded, for 104 msec, or for 62 msec. In all three experiments an orientation asymmetry emerged: observers detected a tilted target among vertical distracters more efficiently than a vertical target among vertical distracters. As target eccentricity increased, reaction times and errors augmented, and the set size effect became more pronounced, more so for vertical than tilted targets. In Experiments 4-7, the stimulus spatial properties were manipulated: spatial frequency; size; and orientation. The eccentricity effect was more pronounced for vertical than tilted targets and for high- than low-spatial frequency targets. This effect was eliminated when either the size, the size and orientation, or the size and spatial frequency were magnified (M-cortical factor). By increasing the signal-to-noise ratio, magnification reduced the extent of both asymmetries; it aided more the detection of tilted than vertical and of high- than low-spatial frequency targets. Experiments 4-7 indicate that performance improvement in the magnified conditions was due to the specific pairing of stimulus size with retinal eccentricity and not to the larger stimulus size of the magnified conditions. We conclude that stimulus size, orientation and spatial frequency influence the extent of the eccentricity effect and the efficiency of search performance.     

Cue search and comparison processes in visual search for letters.

In 2 experiments, each with 16 college students and laboratory staff members, Ss searched 4- and 8-letter arrays for the presence of a T or an F. The position of the target was indicated by a bar marker presented at 1 of 7 stimulus onset asynchronies (SOAs): –200, –25, 50, 125, 200, 275, or 350 msec. In Exp I, SOA conditions were blocked; in Exp II, SOA conditions varied randomly from trial to trial. In both experiments array size and SOA interacted. With 8-letter arrays, reaction time (RT) increased linearly with SOA with a slope less than 1. With 4-letter arrays, RT increased with SOA but reached asymptote at the level of no-cue control RTs at the 125-msec SOA. Results support the notion that cue search and comparison processes may function concurrently. (French summary) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age and skill in visual search.

The effects of age and experience on visual-cognitive performance were examined by administering a domain-relevant visual search task and a standard letter search task to skilled and control Ss at 2 age levels (young and middle-aged adults). In the skilled task, Ss searched for a designated item within 3-item displays using images of bacteria morphology as targets and distractors. Each target was preceded by a word prime representative of bacteria morphology that was valid, invalid, or neutral with respect to the diagnostic characteristics of the target. Skilled Ss showed an age deficit in letter search performance, but the performance of the young and middle-aged skilled Ss was not different on the domain-relevant task. Valid primes produced benefits for the young and middle-aged skilled participants, whereas control Ss were unaffected by the prime manipulation. Results were consistent with the prediction that experience serves to attenuate age-related declines in visual-cognitive performance in the skilled domain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Superior visual search in autism.

Children with a diagnosis of autism and normally developing children, matched for age and general ability, were tested on a series of visual search tasks in 2 separate experiments. The children with autism performed better than the normally developing children on difficult visual search tasks,. This result occurred regardless of whether the target was uniquely defined by a single feature or a conjunction of features, as long as ceiling effects did not mask the difference. Superior visual search performance in autism can be seen as analogous to other reports of enhanced unique item detection in autism. Unique item detection in autism is discussed in the light of mechanisms proposed to be involved in normal visual search performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preattentive visual search and perceptual grouping in schizophrenia

Differentiated retinal pigment epithelial (RPE) cells in vivo express basal levels of FGF-5, a secreted member of the FGF gene family. RPE cells proliferate in response to pathological events, resulting in a transient increase in FGF-5 gene expression. The goal of this study is to identify cis-acting sequences in the FGF-5 gene promoter which upregulate FGF-5 gene expression when differentiated RPE cells enter the cell cycle and proliferate. In vitro cultures of RPE cells were transfected with various FGF-5 promoter/luciferase deletion constructs, using methods specifically optimized for proliferating and differentiated RPE cells. A proximal promoter/enhancer whose activity is not cell-context dependent was identified between FGF-5 sequences -314 and +48. In addition, a silencer element (-1256/-883) was identified in the distal region which is active only in differentiated RPE cells. When tested in a heterologous system, the same element had silencer activity in differentiated cells. Two small regions in the distal FGF-5 gene promoter, -1195/-1173 and -984/-967 were able to specifically bind to nuclear proteins from differentiated RPE cells but not from proliferating RPE cells as evidenced by gel mobility shift assays. Therefore, FGF-5 gene expression in the RPE may be regulated by the formation of differentiation-specific complexes.     

Attentional priming and visual search in pigeons.

Advance information about a target's identity improved visual search efficiency in pigeons. Experiments 1 and 2 compared information supplied by visual cues with information supplied by trial sequences. Reaction times (RTs) were lower when visual cues signaled a single target rather than two. RTs were lower (Experiment 1) or accuracy improved (Experiment 2) when a sequence of trials presented a single target rather than a mixture of 2. Experiments 3, 4, and 5 considered the selectivity of visual priming by introducing probe trials that reversed the usual cue–target relationship. RT was higher following such miscues than following the usual 1- or 2-target cuing relationships (Experiment 3); the miscuing effect persisted over variations in the target's concealment (Experiments 4 and 5), but did not occur when the target was presented alone (Experiment 4). Findings indicate that priming modifies an attentional mechanism and suggest that this effect accounts for search images. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flicker is a primitive visual attribute in visual search.

At the earliest processing stages, visual stimuli are decomposed by a set of filters tuned to specific values of such attributes as colour, orientation, and motion. These filters have been characterised both neurophysiologically and behaviourally. The single exception is the attribute of flicker that has been characterised neurophysiologically but not behaviourally. Using a visual search paradigm, the authors provide the first behavioural demonstration that flicker is indeed a primitive attribute used by the visual system in stimulus encoding. Consistent with the temporal contrast-sensitivity function, sensitivity to flicker was highest at about 10 Hz and decreased as the flicker rate was either increased or decreased. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

More than just finding color: Strategy in global visual search is shaped by learned target probabilities.

In 2 experiments, eye movements were examined during searches in which elements were grouped into four 9-item clusters. The target (a red or blue T) was known in advance, and each cluster contained different numbers of target-color elements. Rather than color composition of a cluster invariantly guiding the order of search though clusters, the use of color was determined by the probability that the target would appear in a cluster of a certain color type: When the target was equally likely to be in any cluster containing the target color, fixations were directed to those clusters approximately equally, but when targets were more likely to appear in clusters with more target-color items, those clusters were likely to be fixated sooner. (The target probabilities guided search without explicit instruction.) Once fixated, the time spent within a cluster depended on the number of target-color elements, consistent with a search of only those elements. Thus, between-cluster search was influenced by global target probabilities signaled by amount of color or color ratios, whereas within-cluster search was directly driven by presence of the target color. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamic prototypicality effects in visual search.

In recent studies, researchers have discovered a larger neural activation for stimuli that are more extreme exemplars of their stimulus class, compared with stimuli that are more prototypical. This has been shown for faces as well as for familiar and novel shape classes. We used a visual search task to look for a behavioral correlate of these findings regarding both simple geometrical shapes and more complex, novel shape classes. The latter stimulus set enabled us to control for the physical properties of the shapes, establishing that the effects are solely due to the positions of the particular stimuli in a particular shape space (i.e., more extreme versus more central in shape space) and not to specific shape features. The results indicate that finding an atypical instance of a shape class among more prototypical ones is easier and faster than the other way around. The prototypical status of a shape in our experiment could change very quickly, that is, within minutes, depending on the subset of shapes that was shown to the participants. Manipulating the degree of familiarity toward the shapes by selectively increasing familiarity for the extreme shapes did not influence our results. In general, we show that the prototypical status of a stimulus in visual search is a highly dynamic property, depending on the distribution of stimuli within a shape space but not on familiarity with the prototype. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Category effects in temporal visual search.

When subjects identify a target during rapid serial visual presentation (RSVP), they show a reduced ability to detect a subsequent probe stimulus relative to when they ignore the target. The present study demonstrated an effect of target/probe categorical relation upon this probe detection deficit (attentional blink). Experiment 1 used letters for both target and probe, replicating the general methods and results of Raymond, Shapiro, and Arnell (1992). Experiment 2 varied target/probe categorical relation via instructional set: The target was referred to as the letter 'oh', whereas for other subjects it was referred to as the number 'zero.' Treating O as a number attenuated the probe detection deficit. This different-category attenuation was confirmed in Experiment 3 where the target was a letter and the probe was a number. The observed category effect suggests that the probe detection deficit in RSVP may map a time course from spreading intra-category inhibition following temporal target selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel coding of conjunctions in visual search

The microtubule associated protein tau is the main structural component of paired helical filaments (PHFs), aberrant polymers found intracellularly in neurons of brains with the Alzheimer's disease. Glycation is one of the posttranslational modifications that has been found in tau from PHFs, but not in normal brain tau. Studies were carried out with purified tau protein subjected to chemical modifications, in order to further investigate the mechanisms of tau self-association into PHFs. Tau was subjected to modifications affecting reactive lysyl residues, e.g., carbamoylation with potassium cyanate and glycation reaction with glucose. The effects of these modifications to produce functional alterations in tau capacity to bind brain tubulin and to induce microtubule assembly were investigated. Chemically-modified tau and tau of Alzheimer's type exhibited a similar microtubule interaction behavior as analysed by overlay assays, but those were different than normal tau controls. On the other hand, studies of the microtubule assembly kinetics indicated that the reported tau modifications resulted in a loss of its capacity to promote microtubule assembly from purified tubulin preparations. The data on the differences in the electrophoretic profiles, Western blots and the overlay patterns, along with those on the microtubule polymerisation of normal brain tau as compared with both modified and Alzheimer's tau, suggest changes in the functional behavior of this protein as a result of its structural modifications. These studies were complemented with an immunogold analysis at the electron microscope level, which indicated that the modified tau did not incorporate into assembled microtubules. These findings, combined with the results on tau chemical modifications suggest that the reactive lysine residues within functional domains on tau, e.g., those of the repetitive binding motifs, were affected by these modifications. Furthermore, these observations provide new clues to understand the anomalous interactions of tau in Alzheimer's disease.     

Perceptual encoding efficiency in visual search.

The authors present 10 experiments that challenge some central assumptions of the dominant theories of visual search. Their results reveal that the complexity (or redundancy) of nontarget items is a crucial but overlooked determinant of search efficiency. The authors offer a new theoretical outline that emphasizes the importance of nontarget encoding efficiency, and they test this proposal using dot pattern stimuli adapted from W. R. Garner and D. E. Clement (1963). The results provide converging support for the importance of nontarget encoding efficiency in accounting for visual search performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Location-specific target expectancies in visual search.

Observers searched for local target letters in global letter configurations. Different targets appeared with different frequencies in the different locations of the configurations. Experiment 1 showed that in each location, the target that was presented there more frequently was detected faster. Experiment 2 indicated that this location-specific target probability effect was due to perceptual facilitation and that facilitation was not restricted to letters but could be generalized to nonletter stimuli. Experiments 3 and 4 showed that the location distribution of targets could be acquired for 2 global configurations concurrently and that facilitation referred to locations within the configurations, not to screen locations. The results indicate a general sensitivity of the visual system for the location of details in global configurations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)