Robust representations for faces: Evidence from visual search.

We report evidence from visual search that people can develop robust representations for highly overlearned faces. When observers searched for their own face versus the face of an unfamiliar observer, search slopes and intercepts revealed consistently faster processing of self than stranger. These processing advantages persisted even after hundreds of presentations of the unfamiliar face and even for atypical profile and upside-down views. Observers not only showed rapid asymptotic recognition of their own face as the target, but could reject their own face more quickly as the distractor. These findings suggest that robust representations for a highly overlearned face may (a) mediate rapid asymptotic visual processing, (b) require extensive experience to develop, (c) contain abstract or view-invariant information, (d) facilitate a variety of processes such as target recognition and distractor rejection, and (e) demand less attentional resources. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Goal-directed guidance of attention: Evidence from conjunctive visual search.

Conjunctive visual search is most difficult when distractor types are in equal proportions and gets easier as the proportions diverge (e.g., E. Zohary & S. Hochstein, 1989). This may reflect restriction of search to the feature shared by the target and the less-frequent distractor. Alternatively, such effects could reflect target salience, which varies with distractor ratio. In 2 experiments, 60 participants searched 64-element displays for a conjunctive target among distractors of 2 types in various proportions. Participants were correctly informed (Experiment 1) or misinformed (Experiment 2) about which distractor type would be less frequent on most trials. In both experiments, the distractor-ratio effect was significantly influenced by the information provided to participants. These findings demonstrate the efficacy of top-down information in guiding attention and show that it can be applied flexibly, weighted toward particular target features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial organization of distractors in visual search.

This paper investigates visual search in displays in which distractors are spatially grouped. The effect on detection of target position within a spatially grouped 2-dimensional display containing 2 distractor types were examined. The authors compared detection in grouped displays with detection in 2 kinds of control display, homogeneous (one distractor type) and ungrouped (2 distractor types), to determine whether detection in grouped displays would be more similar to efficient detection in homogeneous displays than to inefficient detection in ungrouped displays. Findings show relatively efficient detection in group displays. Detection of targets at the border of two regions where distractors are coherent is easier than can be predicted by models that do not take spatial organization into account. Thus, models of visual search need to incorporate effects of spatial organization in addition to bottom-up difference calculations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preemption effects in visual search: Evidence for low-level grouping.

Experiments are presented showing that visual search for Mueller-Lyer stimuli is based on complete configurations rather than component segments. Segments easily detected in isolation were difficult to detect when embedded in a configuration, indicating preemption by low-level groups. This preemption--which caused stimulus components to become inaccessible to rapid search--was an all-or-nothing effect and so could serve as a powerful test of grouping. It is shown that these effects are unlikely to be due to blurring by simple spatial filters at early visual levels. It is proposed instead that they are due to more sophisticated processes that rapidly bind contour fragments into spatially extended assemblies. These results support the view that rapid visual search cannot access the primitive elements formed at the earliest stages of visual processing; rather, it can access only higher level, more ecologically relevant structures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing nominal information during visual search.

Conducted 3 experiments to examine the processing of nominal information during a visual search. In Exp I, 6 experienced and 2 naive Ss searched for a single pre-specified target letter, and the stimulus exposure-time needed to yield a 50% (corrected for chance) level of accuracy was estimated using the parameter estimation by sequential testing procedure. Results show that the exposure-time was not influenced by the presence (in the irrelevant items) of the target's other case; this suggested that there was no obligatory accessing of nominal information during preattentive processing. In Exp II, 6 experienced Ss searched in Condition 1 for a single target which was specified as being one of a same-name pair of letters, and in Condition 2 for a target specified as one of a same-shape pair of letters. The exposure-time required for the same-name search was greater than that required for the same-shape search. In Exp III, accuracy of search was compared in the same-shape and same-name conditions with a control condition. The target in this control condition was specified as one of a pair of letters not sharing a name or any special shape. 12 Ss searched 6-item displays and 12 Ss searched 12-item displays for a pre-specified target letter. Results confirm the difference detected in Exp II, but they do not show any difference between performance in the same-name condition and in the control condition. It is suggested that some focal processing is required for the development of a sufficiently detailed level of visual representation to allow for naming. (French summary) (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial constraints on learning in visual search: Modeling contextual cuing.

Predictive visual context facilitates visual search, a benefit termed contextual cuing (M. M. Chun & Y. Jiang, 1998). In the original task, search arrays were repeated across blocks such that the spatial configuration (context) of all of the distractors in a display predicted an embedded target location. The authors modeled existing results using a connectionist architecture and then designed new behavioral experiments to test the model's assumptions. The modeling and behavioral results indicate that learning may be restricted to the local context even when the entire configuration is predictive of target location. Local learning constrains how much guidance is produced by contextual cuing. The modeling and new data also demonstrate that local learning requires that the local context maintain its location in the overall global context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention-referenced visual representations: Evidence from impaired visual localization.

Spatial representations in the visual system were probed in 4 experiments involving A. H., a woman with a developmental deficit in localizing visual stimuli. Previous research (M. McCloskey et al., 1995) has shown that A. H.'s localization errors take the form of reflections across a central vertical or horizontal axis (e.g., a stimulus 30° to her left localized to a position 30° to her right). The present experiments demonstrate that A. H.'s errors vary systematically as a function of where her attention is focused, independent of how her eyes, head, or body are oriented, or what potential reference points are present in the visual field. These results suggest that the normal visual system constructs attention-referenced spatial representations, in which the focus of attention defines the origin of a spatial coordinate system. A more general implication is that some of the brain's spatial representations take the form of coordinate systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of selective attention during visual search.

Monitored eye movements in 8 2nd graders, 8 6th graders, and 8 college students during a search task in which Ss were given different types of information about target location before trial onset. Whereas color cues facilitated search performance in the 2 older groups, form cues were less successful in facilitating search and significantly interfered with search relative to a control condition for the 2nd graders. Both facilitation and interference effects in overall search times were related to number of fixations rather than to average fixation during a trial. (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)     

Attentional demands of processing shape in three-dimensional space: Evidence from visual search and precuing paradigms.

The hypothesis that representation of projective shape is preattentive whereas representation of objective shape in 3-dimensional space requires allocation of attention was tested in 2 visual search and 2 precuing experiments. In the visual search experiments, the slope for projective shape search was expected to approach 0 and that for objective shape search was expected to be a positive monotonic function of set size. In the precuing experiments, the effects of precuing were expected to be largely limited to the task requiring representation of objective shape. The overall pattern of results conformed to expectations. The findings are interpreted in the context of a model of shape-at-a-slant processing set out by W. Epstein and B. Lovitts (1985) and Epstein and T. Babler (1989, 1990). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye movements during parallel–serial visual search.

Two experiments (one using O and Q-like stimuli and the other using colored–oriented bars) investigated the oculomotor behavior accompanying parallel–serial visual search. Eye movements were recorded as participants searched for a target in 5- or 17-item displays. Results indicated the presence of parallel–serial search dichotomies and 2:1 ratios of negative to positive slopes in the number of saccades initiated during both search tasks. This saccade number measure also correlated highly with search times, accounting for up to 67% of the reaction time (RT) variability. Weak correlations between fixation durations and RTs suggest that this oculomotor measure may be related more to stimulus factors than to search processes. A third experiment compared free-eye and fixed-eye searches and found a small RT advantage when eye movements were prevented. Together these findings suggest that parallel–serial search dichotomies are reflected in oculomotor behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye movements during parallel-serial visual search

Two experiments (one using O and Q-like stimuli and the other using colored-oriented bars) investigated the oculomotor behavior accompanying parallel-serial visual search. Eye movements were recorded as participants searched for a target in 5- or 17-item displays. Results indicated the presence of parallel-serial search dichotomies and 2:1 ratios of negative to positive slopes in the number of saccades initiated during both search tasks. This saccade number measure also correlated highly with search times, accounting for up to 67% of the reaction time (RT) variability. Weak correlations between fixation durations and RTs suggest that this oculomotor measure may be related more to stimulus factors than to search processes. A third experiment compared free-eye and fixed-eye searches and found a small RT advantage when eye movements were prevented. Together these findings suggest that parallel-serial search dichotomies are reflected in oculomotor behavior.     

Glucose availability and the electrophysiology of the human visual system

Immunoreactive parathyroid hormone-related protein (PTH-rP) was measured in simultaneously obtained cerebrospinal fluid (CSF) and plasma from 51 patients suspected of suffering from a prolapsed intervertebral disc. Endocrine or psychiatric diseases were excluded. In addition, immunoreactive parathyroid hormone (PTH) in the CSF samples was measured. Both, PTH-rP and PTH were assayed by immunoradiometric assay. The results indicate the presence of both, PTH-rP and PTH in CSF. The following concentrations (mean values +/- SD) were found: PTH-rP (pmol/l) in CSF without pleocytosis (n = 17) 0.432 +/- 0.157, with pleocytosis (n = 34) 0.654 +/- 0.675; in plasma (pmol/l) 54.1 +/- 14.632; PTH (nmol/l) in CSF without pleocytosis (n = 17) 0.454 +/- 0.099, with pleocytosis (n = 34) 0.437 +/- 0.140, and in plasma 4.272 +/- 0.794. The concentrations of both, PTH-rP and PTH, in CSF with and without pleocytosis were not significantly different. No correlation was found between PTH-rP and PTH values. The present study demonstrated PTH-rP as a normal constituent in human CSF.     

Guidance of eye movements during conjunctive visual search: The distractor-ratio effect.

The distractor-ratio effect refers to the finding that search performance in a conjunctive visual search task depends on the relative frequency of two types or subsets of distractors when the total number of items in a display is fixed. Previously, Shen, Reingold, and Pomplun (2000) examined participants' patterns of eye movements in a distractor-ratio paradigm and demonstrated that on any given trial saccadic endpoints were biased towards the smaller subset of distractors and participants flexibly switched between different subsets across trials. The current study explored the boundary conditions of this tendency to flexibly search through a smaller subset of distractors by examining the influence of several manipulations known to modulate search efficiency, including stimulus discriminability (Experiment 1), within-dimension versus cross-dimension conjunction search and distractor heterogeneity (Experiment 2). The results indicated that the flexibility of visual guidance and saccadic bias exemplified by the distractor-ratio effect is a robust phenomenon that mediates search efficiency by adapting to changes in the relative informativeness of stimulus dimensions and features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus-driven attentional capture: Evidence from equiluminant visual objects.

Previous work has shown that abrupt visual onsets capture attention. Possible mechanisms for this phenomenon include (1) luminance-change detection system and (2) a mechanism that detects the appearance of new perceptual objects. Exps 1 and 2 revealed that attention is captured in visual search by the appearance of a new perceptual object even when the object is equiluminant with its background and thus exhibits no luminance change when it appears. Exp 3 showed that a highly salient luminance increment alone is not sufficient to capture attention. These findings suggest that attentional capture is mediated by a mechanism that detects the appearance of new perceptual objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature analysis in early vision: Evidence from search asymmetries.

A series of search experiments tested detection of targets distinguished from the distractors by differences on a single dimension. Our aim was to use the pattern of search latencies to infer which features are coded automatically in early vision. For each of 12 different dimensions, one or more pairs of contrasting stimuli were tested. Each member of a pair played the role of target in one condition and the role of distractor in the other condition. Targets defined by larger values on the quantitative dimensions of length, number, and contrast, by line curvature, by misaligned orientation, and by values that deviated from a standard or prototypical color or shape were detected easily, whereas targets defined by smaller values on the quantitative dimensions, by straightness, by frame-aligned orientation, and by prototypical colors or shapes required slow and apparently serial search. We interpret the results as evidence that focused attention to single items or to groups is required to reduce background activity when the Weber fraction distinguishing the pooled feature activity with displays containing a target and with displays containing only distractors is too small to allow reliable discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging and distraction by highly familiar stimuli during visual search.

P. Rabbitt's (1965, 1968) theory regarding age-related changes in cognition proposes that aging is accompanied by a decreased ability to ignore irrelevant information (perceptual noise). The present experiment examined age differences in the extent to which highly familiar stimuli used as perceptual noise could disrupt visual search performance. On Days 1–4, 10 Ss aged 19–27 yrs and 10 Ss aged 63–77 yrs performed a search task with specific, unchanging sets of target and nontarget stimuli (letters). Performance on a subsequent search task (Day 5) was disrupted when these familiar stimuli appeared as noise items in the displays, as compared with trials on which only new, unpracticed stimuli were used. The magnitude of the distraction associated with the familiar stimuli on Day 5 was equivalent for the 2 age groups. However, age differences in Day 5 search performance increased as more items in the simulus display required inspection. Age differences were thus influenced more by the requirement to attend to relevant information than by distraction from irrelevant information. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flexible feature-based inhibition in visual search mediates magnified impairments of selection: Evidence from carry-over effects under dynamic preview-search conditions.

Evidence for inhibitory processes in visual search comes from studies using preview conditions, where responses to new targets are delayed if they carry a featural attribute belonging to the old distractor items that are currently being ignored—the negative carry-over effect (Braithwaite, Humphreys, & Hodsoll, 2003). We examined whether inhibition was applied in the same manner across different types of displays or whether the inhibitory weighting applied to different features varied with their utility for the search task. To test this, we present the first empirical investigation of negative carry-over effects under the ecologically valid conditions of dynamic visual search. Experiment 1 investigated preview search using dynamic moving and static displays. Detection was very poor when new targets carried the color of the old distractors, and this negative carry-over effect was significantly exaggerated with moving, compared with static, displays. Experiments 2a and 2b demonstrated that this effect could not be attributed to an increased role of preattentive grouping between new and old items for dynamic displays. Collectively, the findings suggest that feature-based inhibition contributes strongly to preview search through dynamic displays, and this leads to an amplified attentional blindness to new targets. The data specifically indicate that inhibitory processes in search differentially weight color and location in moving and static displays, and that feature-based inhibition may underlie many instances of sustained inattentional blindness in everyday life. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The temporal dynamics of visual search: Evidence for parallel processing in feature and conjunction searches.

Feature and conjunction searches have been argued to delineate parallel and serial operations in visual processing. The authors evaluated this claim by examining the temporal dynamics of the detection of features and conjunctions. The 1st experiment used a reaction time (RT) task to replicate standard mean RT patterns and to examine the shapes of the RT distributions. The 2nd experiment used the response-signal speed-accuracy trade-off (SAT) procedure to measure discrimination (asymptotic detection accuracy) and detection speed (processing dynamics). Set size affected discrimination in both feature and conjunction searches but affected detection speed only in the latter. Fits of models to the SAT data that included a serial component overpredicted the magnitude of the observed dynamics differences. The authors concluded that both features and conjunctions are detected in parallel. Implications for the role of attention in visual processing are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention accesses multiple reference frames: Evidence from visual neglect.

Research with normal participants has demonstrated that mechanisms of selective attention can simultaneously gain access to internal representations of spatial information defined with respect to both location- and object-based frames of reference. The present study demonstrates that patients with unilateral spatial neglect following a right-hemisphere lesion are poorer at detecting information on the contralateral left side in both location- and object-based spatial coordinates simultaneously. Moreover, the extent of the neglect is modulated by the probability of a target's appearing in either reference frame; as the probability of sampling a target in a particular frame of reference increases, so does the severity of neglect in that frame. These findings suggest that attention can be flexibly and strategically assigned to a reference frame depending on the contingencies of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)