Target-tilt and vertical-hemifield asymmetries in free-scan search for 3-D targets

In this study, asymmetries in finding pictorial 3-D targets defined by their tilt and rotation in space were investigated by means of a free-scan search task. In Experiment 1, feature search for cube tilt and rotation, as assessed by a spatial forced-choice task, was slow but still exhibited a characteristic “flat” slope; it was also much faster to upward-tilted cubes and to targets located in the upper half of the search field. Faster search times for cubes and rectangular solids in the upper field, an advantage for upward-tilted cubes, and a strong interaction between target tilt and direction of lighting (upward or downward) for the rectangular solids were all demonstrated in Experiment 2. Finally, an advantage in searching for tilted cubes located in the upper half of the display was shown in Experiment 3, which used a present-absent search task. The results of this study confirm that the upper-field bias in visual search is due mainly to a biased search mechanism and not to the features of the target stimulus or to specific ecological factors.     

Effect of spatial position on visual search for 3-D objects

We examined whether the position of objects in external space affects the visual-search task associated with the tilt of 3-D objects. An array of cube-like objects was stereoscopically displayed at a distance of 4.5 m on a large screen 1.5 m above or below eye height. Subjects were required to detect a downward-tilted target among upward-tilted distractors or an upward-tilted target among downward-tilted distractors. When the stimuli consisted of shaded parallelepipeds whose upper/bottom faces were lighter than their side faces, the upward-tilted target was detected faster. This result was in accordance with the 'top-view assumption' reported in previous research. Displaying stimuli in the upper position degraded overall performance. However, when the shaded objects whose upper/bottom faces were darker than their side faces were displayed, the detection of a downward-tilted target became as efficient as that of an upward-tilted target only at the upper position. These results indicate that it is possible for the spatial position of the stimulus to promote the detection of a downward-tilted target when shading and perspective information are consistent with the viewing direction.     

A right hemispatial field advantage on a verbal free-vision task

Within a fixed time limit for each stimulus item, right handers searched, in a top-to-bottom scan and from right to left for half the subjects and from left to right for the other half, among randomly placed and oriented words for target words that rhymed with a designated sound. A right hemispatial field advantage emerged, as well as an advantage for targets above as compared to below the horizontal meridian. A lateral X vertical location interaction showed a right-side advantage only for targets below the horizontal meridian and an upper target advantage only for targets on the left. Even though the task was presented in free vision, results were highly similar to prior findings with lateralized tachistoscopic presentation of verbal stimuli.     

Effects of prime and target eccentricity on masked repetition priming

Three experiments examined the influence of briefly presented, pattern-masked prime stimuli on target word recognition at varying eccentricities. The prime was either the same word as the targets or a different word, and prime position varied horizontally from a central fixation point. The targets were either in the same location as the primes (Experiment 1A) or always centrally located (Experiments 1B and 2). In Experiment 1A, target word recognition showed a typical right visual field advantage, and priming effects diminished with increasing prime and target eccentricity. With centrally located targets, priming effects tended to be more constrained by prime location. After eye fixation location and prime visibility were controlled for (Experiment 2), a right visual field advantage for priming effects was also evident for central targets, suggesting an influence of endogenous attentional biases in masked repetition priming.     

Effects of targets embedded within words in a visual search task

Visual search performance can be negatively affected when both targets and distracters share a dimension relevant to the task. This study examined if visual search performance would be influenced by distracters that affect a dimension irrelevant from the task. In Experiment 1 within the letter string of a letter search task, target letters were embedded within a word. Experiment 2 compared targets embedded in words to targets embedded in nonwords. Experiment 3 compared targets embedded in words to a condition in which a word was present in a letter string, but the target letter, although in the letter string, was not embedded within the word. The results showed that visual search performance was negatively affected when a target appeared within a high frequency word. These results suggest that the interaction and effectiveness of distracters is not merely dependent upon common features of the target and distracters, but can be affected by word frequency (a dimension not related to the task demands).     

Use of spatial context is restricted by relative position in implicit learning

For inefficient search, target detection is faster for repeated than for regenerated layouts. This effect, calledcontextual cuing, was assumed to arise from implicit learning of local spatial relationships between targets and distractors. However, a more global influence from distractors far from the target has not been tested. In this study, the search field was divided into upper and lower halves containing a repeated and a regenerated configuration set, respectively. The positions of the two sets were or were not exchanged, meaning that their relative as well as their absolute positions were the same or different (Experiment 1). In Experiment 2, the repeated set appeared alone in either the same or the other half of the screen (same or different absolute position). The contextual cuing effect remained when only absolute position was changed, but not when both absolute and relative positions were changed. These results suggest that contextual cuing depends on relative positional information.     

Searching for threat

In a series of experiments, a visual search task was used to test the idea that biologically relevant threatening stimuli might be recognized very quickly or capture visuo-spatial attention. In Experiment 1, there was evidence for both faster detection and faster search rates for threatening animals than for plants. However, examination of the basis of this effect in Experiment 2 showed that it was not due to threat per se, as detection and search rate advantages were found for pleasant rather than threatening animals compared to plants. In Experiment 3, participants searched for the plants and pleasant and threatening animals used in Experiments 1 and 2, among a fixed heterogeneous selection of non-target items. There was no search rate or detection advantage for threatening animals compared to pleasant animals or plants. The same targets and non-targets as those used in Experiment 3 were also used in Experiment 4. In Experiment 4, participants searched for targets that were presented either close to or distant from an initial fixation point. There was no evidence for a "threat" detection advantage either close to or distant from the cross. Finally, an experiment was conducted in which target categories (fruit, flowers, and animals) were not pre-specified prior to each trial block. There were no differences in reaction times to detect pleasant animals, threatening animals, or fruit. We conclude that the visual search paradigm does not readily reveal any biases that might exist for threatening stimuli in the general population.     

Target location probability effects in visual search: an effect of sequential dependencies

Target location probability was manipulated in a visual search task. When the target was twice as likely to appear on 1 side of the display as the other, manual button-press response times were faster (Experiment 1A) and first saccades were more frequently directed (Experiment 1B) to the more probable locations. When the target appeared with equal probability at each location in this search task, performance benefited from repetition of target location in the preceding trials (Experiment 2). When the trial sequence was constrained so that target location did not repeat within a series of 4 trials, there was no longer an advantage for more probable locations (Experiment 3). The authors conclude that the search benefits for more probable locations resulted from short-term target location repetitions.     

Face processing is enhanced in the left and upper visual hemi-fields

We tested whether two known hemi-field asymmetries would affect visual search with face stimuli. Holistic processing of spatial configurations is better in the left hemi-field, reflecting a right hemisphere specialization, and object recognition is better in the upper visual field, reflecting stronger projections into the ventral stream. Faces tap into holistic processing and object recognition at the same time, which predicts better performance in the left and upper hemi-field, respectively. In the first experiment, participants had to detect a face with a gaze direction different from the remaining faces. Participants were faster to respond when targets were presented in the left and upper hemi-field. The same pattern of results was observed when only the eye region was presented. In the second experiment, we turned the faces upside-down, which eliminated the typical spatial configuration of faces. The left hemi-field advantage disappeared, showing that it is related to holistic processing of faces, whereas the upper hemi-field advantage related to object recognition persisted. Finally, we made the search task easier by asking observers to search for a face with open among closed eyes or vice versa. The easy search task eliminated the need for complex object recognition and, accordingly, the advantage of the upper visual field disappeared. Similarly, the left hemi-field advantage was attenuated. In sum, our findings show that both horizontal and vertical asymmetries affect the search for faces and can be selectively suppressed by changing characteristics of the stimuli.     

The reconfiguration of task set has no effect on the efficiency of feature search

In this study, we investigated whether or not the reconfiguration of a set task could modulate the efficiency of feature search. In Experiment 1, target set size was manipulated. The results revealed that enumerating targets defined by color yields a much steeper slope when executed simultaneously with a discrimination task than when done singly. However, when distractor set size was manipulated, there was no significant difference in the efficiency of individualizing targets from distractors between the two task conditions, no matter whetherthe search was guided by bottom-up information (Experiment 2) or top-down information (Experiment 3). Drawing upon these results, the authors propose that (1) an additional task can impair the efficiency of enumeration, resulting in a steep slope of counting even when target set size is quite small, and (2) in feature search, the visual system first reconfigures the task set to match the input feature information and then detects the targets with an optimal efficiency, which does not support the theory proposed by Di Lollo, Kawahara, Zuvic, and Visser (2001; Di Lollo, Smilek, Kawahara, & Ghorashi, 2005).     

Visual search asymmetry for viewing direction

In visual search experiments, we examined the existence of a search asymmetry for the direction with which three-dimensional objects are viewed. It was found that an upward-tilted target object among downward-tilted distracting objects was detected faster than when the orientation of target and distractors was reversed. This indicates that the early visual process regards objects tilted downward with respect to the observer as the situation that is more likely to be encountered. That is, the system is set up to expect to see the tops of these objects. We also found a visual field anisotropy, in that the asymmetry was more pronounced in the lower visual field. These findings are consistent with the idea that the tops of objects are usually situated in the lower visual field and less often in the upper field. Examination of the conditions under which the asymmetry and the anisotropy occur demonstrated the importance of the three-dimensional nature of the stimulus objects. Early visual processing thus makes use of heuristics that take into account specific relationships between the relative locations in space of the observer and 3-D objects.     

Similarity modulates the face-capturing effect in change detection

We investigated whether similarity among faces could modulate the face-capturing effect in change detection. In Experiment 1, a singleton search task was used to demonstrate that a face stimulus captures attention and the odd-one-out hypothesis cannot account for the results. Searching for a face target was faster than searching for a nonface target no matter whether distractor–distractor similarity was low or high. The fast search, however, did not lead to a face-detection advantage in Experiment 2 when the pre- and postchange faces were highly similar. When participants in Experiment 3 had to divide their attention between two faces in stimulus displays for change detection, detection performance was worse than performance in detecting nonface changes. The face-capturing effect alone is insufficient to produce the face-detection advantage. Face processing is efficient but its effect on performance depends on the stimulus–task context.     

Feature-based control of attention: evidence for two forms of dimension weighting.

In three experiments, I examined whether prior knowledge of a target feature dimension is useful for guiding spatial attention to the target in a variety of tasks: visual search (Experiments 1A and 1B), texture segregation (Experiment 2), and visual enumeration (Experiment 3). Experiment 1A used a simple search task and found that reaction times for blocks in which a target was defined within a single feature dimension were shorter than those for blocks in which a target was defined across dimensions (within-dimension facilitation: WDF). Intertrial facilitation (ITF; Müller, Heller, & Ziegler, 1995), a dimension-based priming effect from one trial to the immediately following one, was also observed. Both WDF and ITF disappeared when the same stimuli were used under a compound search task (Experiment 1B), in which participants responded to an attribute of the target in a feature dimension different from its defining dimensions. Experiments 2 and 3 showed that WDF and ITF are not necessarily contingent upon each other: In a texture discrimination task, only WDF was found; in an enumeration task for six or seven targets, only ITF was found. These results show that the two forms of dimension weighting, WDF and ITF, are mediated by different mechanisms. WDF was eliminated when focal attention to targets was required, suggesting that feature-based modulation is limited as a source for controlling spatial attention (Kumada, 1999). ITF was correlated with type of response, suggesting dimension-specific response mechanisms (Cohen & Shoup, 1997).     

Feature-based control of attention: Evidence for two forms of dimension weighting

In three experiments, I examined whether prior knowledge of a target feature dimension is useful for guiding spatial attention to the target in a variety of tasks: visual search (Experiments 1A and 1B), texture segregation (Experiment 2), and visual enumeration (Experiment 3). Experiment 1A used a simple search task and found that reaction times for blocks in which a target was defined within a single feature dimension were shorter than those for blocks in which a target was defined across dimensions (within-dimension facilitation; WDF). Intertrial facilitation (ITF; Müller, Heller, & Ziegler, 1995), a dimension-based priming effect from one trial to the immediately following one, was also observed. Both WDF and ITF disappeared when the same stimuli were used under a compound search task (Experiment 1B), in which participants responded to an attribute of the target in a feature dimension different from its defining dimensions. Experiments 2 and 3 showed that WDF and ITF are not necessarily contingent upon each other: In a texture discrimination task, only WDF was found; in an enumeration task for six or seven targets, only ITF was found. These results show that the two forms of dimension weighting, WDF and ITF, are mediated by different mechanisms. WDF was eliminated when focal attention to targets was required, suggesting that feature-based modulation is limited as a source for controlling spatial attention (Kumada, 1999). ITF was correlated with type of response, suggesting dimension-specific response mechanisms (Cohen & Shoup, 1997).     

Memory processes in multiple-target visual search

Gibson, Li, Skow, Brown, and Cooke (Psychological Science, 11, 324-327, 2000) had participants carry out a search task in which they were required to detect the presence of one or two targets. In order to successfully perform such a multiple-target visual search task, participants had to remember the location of the first target while searching for the second target. In two experiments we investigated the cost of remembering this target location. In Experiment 1, we compared performance on the Gibson et al. task with performance on a more conventional present-absent search task. The comparison suggests a substantial performance cost as measured by reaction time, number of fixations and slope of the search functions. In Experiment 2, we looked in detail at refixations of distractors, which are a direct measure of attentional deployment. We demonstrated that the cost in this multiple-target visual search task was due to an increased number of refixations on previously visited distractors. Such refixations were present right from the start of the search. This change in search behaviour may be caused by the necessity of having to remember a target-allocating memory for the upcoming target may consume memory capacity that may otherwise be available for the tagging of distractors. These results support the notion of limited capacity memory processes in search.     

Prevalence-based decisions undermine visual search

In visual search, observers make decisions about the presence or absence of a target based on their perception of a target during search. The present study investigated whether decisions can be based on observers’ expectation rather than perception of a target. In Experiment 1, participants were allowed to make target-present responses by clicking on the target or, if the target was not perceived, a target-present button. Participants used the target-present button option more frequently in difficult search trials and when target prevalence was high. Experiment 2 and 3 employed a difficult search task that encouraged the use of prevalence-based decisions. Target presence was reported faster when target prevalence was high, indicating that decisions were, in part, cognitive, and not strictly perceptual. A similar pattern of responses were made even when no targets appeared in the search (Experiment 3). The implication of these prevalence-based decisions for visual search models is discussed.     

Conflict-induced perceptual filtering

In a variety of conflict paradigms, target and distractor stimuli are defined in terms of perceptual features. Interference evoked by distractor stimuli tends to be reduced when the ratio of congruent to incongruent trials is decreased, suggesting conflict-induced perceptual filtering (i.e., adjusting the processing weights assigned to stimuli associated with the target and with the distractor features). In search of evidence for such a mechanism, we administered a flanker task, in which targets and distractors were defined in terms of stimulus location (Experiment 1) or color (Experiment 2). The efficiency of processing stimuli associated with target and distractor features was assessed in intermixed trials of a visual search task, in which a target had to be detected irrespective of these features. In both experiments search times were shorter for stimuli associated with the target feature than with the distractor feature of the flanker task. This effect was increased under conditions of a reduced congruent/incongruent ratio, thereby providing evidence for conflict-dependent perceptual filtering.     

自我面孔对空间注意的调控：来自Posner空间线索范式的证据

利用Posner的空间线索范式,三个实验意在探寻自我面孔作为特殊的刺激对空间注意的调控作用。在实验一中,自我或者熟悉的面孔作为内源性线索出现在视野中央,通过朝左或者朝右来提示目标出现的位置。在实验二（小图）和实验三（大图）中,自我或熟悉的面孔与目标同时呈现,作为与任务无关的刺激出现在视野的左侧或右侧。实验一的结果发现,与熟悉的面孔相比较,自我面孔产生了更大的提示效应。这意味着当自我面孔与任务相关时,对提示位置易化优于熟悉的面孔。与之相反的是,在实验二和实验三中,自我面孔和熟悉的面孔同样捕获目标位置的空间注意。然而,研究并没有发现自我面孔与熟悉面孔在捕获注意上的差异。这一结果也许暗示着在注意捕获的过程中,面孔效应足够大而掩盖了自我效应的出现。这些发现表明自我面孔之所以是具有特殊性的刺激不仅受感知过程的影响,还依赖于与任务的关系。     

空间工作记忆负载对真实场景情境提示效应的影响

重复的画面布局能够促进观察者对目标项的搜索 (情境提示效应)。本研究采用双任务范式,分别在视觉搜索任务的学习阶段 (实验2a) 和测验阶段 (实验2b) 加入空间工作记忆任务, 并与单任务基线 (实验1)进行比较, 考察空间工作记忆负载对真实场景搜索中情境线索学习和情境提示效应表达的影响。结果发现: 空间负载会增大学习阶段的情境提示效应量, 同时削弱测验阶段的情境提示效应量, 而不影响情境线索的外显提取。由此可见, 真实场景中情境线索的学习和提示效应的表达均会受到有限的工作记忆资源的影响, 但情境线索提取的外显性不变。     

Searching through the hierarchy: How level of target categorization affects visual search

Does the same basic-level advantage commonly observed in the categorization literature also hold for targets in a search task? We answered this question by first conducting a category verification task to define a set of categories showing a standard basic-level advantage, which we then used as stimuli in a search experiment. Participants were cued with a picture preview of the target or its category name at either superordinate, basic, or subordinate levels, then shown a target-present/absent search display. Although search guidance and target verification was best using pictorial cues, the effectiveness of the categorical cues depended on the hierarchical level. Search guidance was best for the specific subordinate-level cues, whereas target verification showed a standard basic-level advantage. These findings demonstrate different hierarchical advantages for guidance and verification in categorical search. We interpret these results as evidence for a common target representation underlying categorical search guidance and verification.