Spatial context learning in visual search and change detection

Humans conduct visual search more efficiently when the same display is presented for a second time, showing learning of repeated spatial contexts. In this study, we investigate spatial context learning in two tasks: visual search and change detection. In both tasks, we ask whether subjects learn to associate the target with the entire spatial layout of a repeated display (configural learning) or with individual distractor locations (nonconfigural learning). We show that nonconfigural learning results from visual search tasks, but not from change detection tasks. Furthermore, a spatial layout acquired in visual search tasks does not enhance change detection on the same display, whereas a spatial layout acquired in change detection tasks moderately enhances visual search. We suggest that although spatial context learning occurs in multiple tasks, the content of learning is, in part, task specific.     

Strategies of flanker coprocessing in single and dual tasks

In this study, the authors used a dual-task flanker paradigm to investigate the degree to which flankers are coprocessed with the target as a function of whether flankers have to be used as stimuli for a second task. A series of experiments, in which performance in dual tasks was compared with that in single tasks, revealed that participants had a strong tendency to coprocess flankers to a large degree in dual tasks, even if this impaired performance. Coprocessing of flankers was reduced only when totally irrelevant flankers were presented at the beginning of a trial or single tasks were performed on the great majority of trials within a block. The results suggest that it was demanding to process targets and flankers serially when both had to be used for a dual task. As a consequence, target and flankers were processed in parallel, even if this was nonoptimal for target selection.     

The effects of uncertainty in error monitoring on associated ERPs

A series of experiments were conducted to address the effect of uncertainty regarding performance for predicting the likelihood of a correct-response negativity (CRN) in addition to error-related negativity (ERN). In Study 1, 18 healthy young adults completed letter discrimination tasks during single and dual attention conditions designed to manipulate response certainty. In the second study, the same participants completed easy and difficult tone discrimination tasks designed to influence stimulus certainty. In the third study, task difficulty was manipulated to produce different error rates without altering certainty. Studies 1 and 2 indicated that error and correct responses are processed more similarly when uncertainty is present (i.e., ERN approximately CRN). Furthermore, uncertainty was associated with attenuation of the ERN and enhancement of the CRN, consistent with an error detection hypothesis. Study 3 indicated that task difficulty alone does not influence the ERN or likelihood of a CRN. These results offer support for the error detection account of the ERN and establish the role of uncertainty in predicting the CRN, as postulated by .     

Distractor-response bindings in dual task scenarios

If a response is executed in reaction to a target stimulus, accompanying distractor stimuli can be integrated with and later on retrieve this response, an effect called distractor-response binding. There has been some debate as to whether S-R binding is generally influenced by attentional processes and in particular the role of attentional processes for the binding of irrelevant stimuli and responses is unclear. We therefore analyze the impact of spatial input attention while engaging central attention in an additional task. In particular, participants worked in dual task situations that induced load on central attention while the distribution of spatial attention was manipulated by varying the location of the different tasks. Distractor-response binding occurred only if both tasks were presented in the same spatial location. In contrast, binding effects within one task were prevented if spatial attention was withdrawn from the task by presenting a second task in a separate area. It is concluded that input but no central attention is required for the integration of distractor stimuli and responses. Theoretical and practical implications of these findings are discussed.     

Parallel working memory for spatial location and food-related object cues in foraging pigeons: binocular and lateralized monocular performance

During foraging, animals can increase their success by both remembering feeding sites and remembering food-related object cues. Because earlier studies have tested either the site or object memory in isolation, the aim of the present study was to evaluate how efficiently birds can utilize both memories simultaneously. Furthermore, the idea was tested that lateralization might be the principle of brain organization that allows for efficient parallel processing. Pigeons learned to search for food in a complex maze with 16 baited sites. To obtain the maximum reward they had to perform two tasks in parallel, a spatial working memory task and an object-specific working memory task. Birds performed well on this dual task but, compared with spatial working memory alone, they were impaired during the first choices of a trial (Experiment 1). When the left and the right brain hemispheres were tested separately by means of monocular occlusion (Experiment 2), object discrimination was better when birds used their right eye/left hemisphere. This was most pronounced during the first choices of a trial. On the spatial component of the task, performance on binocular trials was better than on monocular trials, but monocularly both hemispheres performed at the same level. Results show that on this dual task, discrimination of food-related object cues predominantly involved the left brain hemisphere whereas both hemispheres contributed equally to spatial performance.     

Frames of reference for the light-from-above prior in visual search and shape judgements

Faced with highly complex and ambiguous visual input, human observers must rely on prior knowledge and assumptions to efficiently determine the structure of their surroundings. One of these assumptions is the 'light-from-above' prior. In the absence of explicit light-source information, the visual system assumes that the light-source is roughly overhead. A simple, low-cost strategy would place this 'light-from-above' prior in a retinal frame of reference. A more complex, but optimal strategy would be to assume that the light-source is gravitationally up, and compensate for observer orientation. Evidence to support one or other strategy from psychophysics and neurophysiology has been mixed. This paper pits the gravitational and retinal frames against each other in two different visual tasks that relate to the light-from-above prior. In the first task, observers had to report the presence or absence of a target where distractors and target were defined purely by shading. In the second task, observers made explicit shape judgements of similar stimuli. The orientation of the stimuli varied across trials and the observer's head was fixed at 0, +/-45 or +/-60 degrees . In both tasks the retinal frame of reference dominated. Visual search behaviour with shape-from-shading stimuli (SFS) was modulated purely by stimulus orientation relative to the retina. However, the gravitational frame of reference had a significant effect on shape judgements, with a 30% correction for observer orientation. In other words, shading information is processed quite differently depending on the demands of the current task. When a 'quick and dirty' representation is required to drive fast, efficient search, that is what the visual system provides. In contrast, when the task is to explicitly estimate shape, extra processing to compensate for head orientation precedes the perceptual judgment. These results are consistent with current neurophysiological data on SFS if we re-frame compensation for observer orientation as a cue-combination problem.     

Inhibition of return in a discrimination task

Inhibition of return (IOR) refers to a bias against returning visual attention to a location that has been recently attended. Although IOR has been demonstrated in a wide range of detection tasks, it has not been reliably shown in discrimination tasks. The results of the present experiment, in which eye movement responses and a cue-target procedure were used, indicate that IOR can exist in a discrimination task. Moreover, the results indicate that the amount of IOR in the discrimination task was approximately equal to that found in the detection task. The results suggest that IOR will be obtained in a discrimination task if the prior allocation of attention does not yield any useful information concerning the forthcoming discrimination judgment.     

Improving accuracy in an error detection task via task sequence

The intent of this study was to determine whether performance on an error detection task and a series of cognitive search and memory tasks would be affected if performed serially. Fifty-six participants were assigned into two experimental groups, defined by whether they performed the error detection task or the cognitive tasks first. Measures of hit rates and false alarms were taken for the error detection task, and the perceived workload of both tasks was measured immediately following completion. In the group that did the cognitive tasks first, a significant relationship between perceptions of mental demand on the cognitive tasks and subsequent performance on the error detection task was found. Also, false alarms in error detection were correlated with perceptions of time pressure and frustration measured after the error detection task. These results suggest that a mentally demanding initial task may facilitate performance in a subsequent cognitively-based task. Parts of this paper were presented at the American Psychological Society's annual convention in Atlanta, GA in June 2003. The author thanks Abbie Woodruff and Brandon Corbin for their work on the original presentation and their help in data collection, and Blaine Browne for helpful editorial comments.     

Improving accuracy in an error detection task via task sequence

The intent of this study was to determine whether performance on an error detection task and a series of cognitive search and memory tasks would be affected if performed serially. Fifty-six participants were assigned into two experimental groups, defined by whether they performed the error detection task or the cognitive tasks first. Measures of hit rates and false alarms were taken for the error detection task, and the perceived workload of both tasks was measured immediately following completion. In the group that did the cognitive tasks first, a significant relationship between perceptions of mental demand on the cognitive tasks and subsequent performance on the error detection task was found. Also, false alarms in error detection were correlated with perceptions of time pressure and frustration measured after the error detection task. These results suggest that a mentally demanding initial task may facilitate performance in a subsequent cognitively-based task. Parts of this paper were presented at the American Psychological Society's annual convention in Atlanta, GA in June 2003. The author thanks Abbie Woodruff and Brandon Corbin for their work on the original presentation and their help in data collection, and Blaine Browne for helpful editorial comments.     

Perceptual expertise improves category detection in natural scenes

There is much debate about how detection, categorization, and within-category identification relate to one another during object recognition. Whether these tasks rely on partially shared perceptual mechanisms may be determined by testing whether training on one of these tasks facilitates performance on another. In the present study we asked whether expertise in discriminating objects improves the detection of these objects in naturalistic scenes. Self-proclaimed car experts (N = 34) performed a car discrimination task to establish their level of expertise, followed by a visual search task where they were asked to detect cars and people in hundreds of photographs of natural scenes. Results revealed that expertise in discriminating cars was strongly correlated with car detection accuracy. This effect was specific to objects of expertise, as there was no influence of car expertise on person detection. These results indicate a close link between object discrimination and object detection performance, which we interpret as reflecting partially shared perceptual mechanisms and neural representations underlying these tasks: the increased sensitivity of the visual system for objects of expertise – as a result of extensive discrimination training – may benefit both the discrimination and the detection of these objects. Alternative interpretations are also discussed.     

Visual search in a forced-choice paradigm

The processing of visual information was investigated in the context of two visual search tasks. The first was a forced-choice task in which one of two alternative letters appeared in a visual display of from one to five letters. The second task included trials on which neither of the two alternatives was present in the display. Search rates were estimated from the slopes of best linear fits to response latencies plotted as a function of the number of items in the visual display. These rates were found to be much slower than those estimated in yes-no search tasks. This result was interpreted as indicating that the processes underlying visual search in yes-no and forced-choice tasks are not the same.     

双重作业的颜色编码方式对作业绩效的影响

研究探讨了不同颜色编码方式对双重任务操作绩效的影响。实验结果证明：若采用同类颜色编码方式,同时操作的两种作业就会产生结构限制,降低双重任务操作绩效;相反,若采用异常颜色编码方式,将有效地减少双重任务操作的结构限制,使双重任务的操作绩效得到提高。     

System reconfiguration, not resource depletion, determines the efficiency of visual search

We examined two theories of visual search: resource depletion, grounded in a static, built-in brain architecture, with attention seen as a limited depletable resource, and system reconfiguration, in which the visual system is dynamically reconfigured from moment to moment so as to optimize performance on the task at hand. In a dual-task paradigm, a search display was preceded by a visual discrimination task and was followed, after a stimulus onset asynchrony (SOA) governed by a staircase procedure, by a pattern mask. Search efficiency, as indexed by the slope of the function relating critical SOA to number of distractors, was impaired under dual-task conditions for tasks that were performed efficiently (shallow search slope) when done singly, but not for tasks performed inefficiently (steep slope) when done singly. These results are consistent with system reconfiguration, but not with resource depletion, models and point to a dynamic, rather than a static, architecture of the visual system.     

On the strategic modulation of the time course of facilitation and inhibition of return

In studies of exogenous attentional orienting, response times for targets at previously cued locations are often longer than those for targets at previously uncued locations. This effect is known widely as inhibition of return (IOR). There has been debate as to whether IOR can be observed in discrimination as well as detection tasks. The experiments reported here confirm that IOR can be observed when target discrimination is required and that the cue-target interval at which IOR is observed is often longer in discrimination than in detection tasks. The results also demonstrate that the later emergence of IOR is related to perceptual discrimination rather than to response selection differences between discrimination and detection tasks. More difficult discrimination tasks lengthen the SOA at which IOR emerges. In contrast, increasing task difficulty by adding a distractor to the location opposite the target shortens the SOA at which IOR emerges. Together, the results reveal an adaptive interaction between exogenous and endogenous attentional systems, in which the action of the orienting (exogenous) system is modulated endogenously in accord with task demands.     

Rapid discrimination of McCollough effects.

The McCollough effect is a colour aftereffect that is contingent on pattern orientation. Three experiments were conducted to establish whether such aftereffect colours could serve as a basis for discrimination in several rapid discrimination tasks. In the first experiment it was investigated whether aftereffect colours could act like a simple 'feature' in a visual search task involving a difficult orientation discrimination. Without McCollough adaptation, the time taken to detect a 'target' among 'distractors' increased substantially as the number of distractors increased. With adaptation, detection time was essentially independent of the number of distractors, indicating that the nature of the task changed from a difficult orientation discrimination to a simple discrimination based on differences in aftereffect colours. The second and third experiments employed a difficult four-alternative forced-choice procedure in which subjects were required to discriminate a monochromatic patch of square-wave grating oriented at 45 degrees from three others oriented at 135 degrees (and vice versa). The gratings were presented very briefly (67-333 ms) followed by a 500 ms mask. Subjects performed the task with and without McCollough adaptation. Performance was strikingly better after adaptation: colour aftereffects could be used to make the discrimination even at exposure durations as short as 67 ms. The third experiment demonstrated that this enhanced performance was indeed due to perceived colour differences (rather than a possible contrast difference). The results of the three experiments are discussed in relation to proposals about the locus of the McCollough effect.     

You detect while I search: examining visual search efficiency in a joint search task

Numerous factors impact attentional allocation, with behaviour being strongly influenced by the interaction between individual intent and our visual environment. Traditionally, visual search efficiency has been studied under solo search conditions. Here, we propose a novel joint search paradigm where one individual controls the visual input available to another individual via a gaze contingent window (e.g., Participant 1 controls the window with their eye movements and Participant 2 – in an adjoining room – sees only stimuli that Participant 1 is fixating and responds to the target accordingly). Pairs of participants completed three blocks of a detection task that required them to: (1) search and detect the target individually, (2) search the display while their partner performed the detection task, or (3) detect while their partner searched. Search was most accurate when the person detecting was doing so for the second time while the person controlling the visual input was doing so for the first time, even when compared to participants with advanced solo or joint task experience (Experiments 2 and 3). Through surrendering control of one’s search strategy, we posit that there is a benefit of a reduced working memory load for the detector resulting in more accurate search. This paradigm creates a counterintuitive speed/accuracy trade-off which combines the heightened ability that comes from task experience (discrimination task) with the slower performance times associated with a novel task (the initial search) to create a potentially more efficient method of visual search.     

Rapid discrimination of visual patterns in children and adults

Rapid visual discrimination in children (9 to 11 yr.) and adults was investigated using two tasks in which the subject had to search for a target pattern embedded in 35 background patterns. The time available for inspecting the search arrays was altered by varying the stimulus duration. In one task, there was a large difference in the feature or 'texton' content of patterns between the target and the background; in the other, this difference was small. In the first task, the children could detect the target pattern in a briefly flashed search array with high accuracy, because the target 'popped out' perceptually from the array, but in the second task the same detection rate was not reached until the stimulus duration was much longer, since a serial searching strategy was required. Results achieved by children and adults were similar. It seems that serial visual search is as efficient in children as in adults.     

Task-dependent costs in processing two simultaneous auditory stimuli

A listener presented with two speech signals must at times sacrifice the processing of one signal in order to understand the other. This study was designed to distinguish costs related to interference from a second signal (selective attention) from costs related to performing two tasks simultaneously (divided attention). Listeners presented with two processed speech-in-noise stimuli, one to each ear, either (1) identified keywords in both or (2) identified keywords in one and detected the presence of speech in the other. Listeners either knew which ear to report in advance (single task) or were cued afterward (partial-report dual task). When the dual task required two identification judgments, performance suffered relative to the single-task condition (as measured by percent correct judgments). Two different tasks (identification for one stimulus and detection for the other) resulted in much smaller reductions in performance when the cue came afterward. We concluded that the degree to which listeners can simultaneously process dichotic speech stimuli seems to depend not only on the amount of interference between the two stimuli, but also on whether there is competition for limited processing resources. We suggest several specific hypotheses as to the structural mechanisms that could constitute these limited resources.     

Responding to the direction of the eyes: In search of the masked gaze-cueing effect

Recent studies have demonstrated that masked gaze cues can produce a cueing effect. Those studies, however, all utilized a localization task and, hence, are ambiguous with respect to whether the previously observed masked gaze-cueing effect reflects the orienting of attention or the preparation of a motor response. The aim of the present study was to investigate this issue by determining whether masked gaze cues can modulate responses in detection and discrimination tasks, both of which isolate spatial attention from response priming. First, we found a gaze-cueing effect for unmasked cues in detection, discrimination, and localization tasks, which suggests that the gaze-cueing effect for visible cues is not task dependent. Second, and in contrast, we found a gaze-cueing effect for masked cues in a localization task, but not in detection or discrimination tasks, which suggests that the gaze-cueing effect for masked cues is task dependent. Therefore, the present study shows that the masked gaze-cueing effect is attributed to response priming, as opposed to the orienting of spatial attention.     

Inhibition of return using discrimination of location

The present study investigated "inhibition of return" which refers to increased response latency when the target in a location discrimination task appears in the same location on consecutive trials. Location discrimination tasks were performed by 28 university students (19-21 years of age) in two experiments. In Exp. 1 the task was to press a left or right button in response to a stimulus displayed on a computer screen. The first condition manipulated stimulus-response compatibility which resulted in changing the inhibition of return. Inhibition of return was stronger when the condition was stimulus-response incompatibility. This result shows that inhibition of return functions strongly under incompatible conditions. A second condition required performance of dual tasks in Exp. 2. Again, changes in inhibition of return were seen. These results show that inhibition of return functions strongly under both dual task and incompatible conditions. Inhibition of return was interpreted as functioning strongly when the task was more difficult.