Визуальный поиск: механизмы и особенности внимания.

Type of perceptual task requiring attention
vision in biology
Visual search is a type of perceptual task requiring attention that typically involves an active scan of the visual environment for a particular object or feature (the target) among other objects or features (the distractors). Visual search can take place with or without eye movements. The ability to consciously locate an object or target amongst a complex array of stimuli has been extensively studied over the past 40 years. Practical examples of using visual search can be seen in everyday life, such as when one is picking out a product on a supermarket shelf, when animals are searching for food among piles of leaves, when trying to find a friend in a large crowd of people, or simply when playing visual search games such as Where's Wally? Much previous literature on visual search used reaction time in order to measure the time it takes to detect the target amongst its distractors. An example of this could be a green square (the target) amongst a set of red circles (the distractors). However, reaction time measurements do not always distinguish between the role of attention and other factors: a long reaction time might be the result of difficulty directing attention to the target, or slowed decision making processes or slowed motor responses after attention is already directed to the target and the target has already been detected. Many visual search paradigms have therefore used eye movement as a means to measure the degree of attention given to stimuli. However, eyes can move independently of attention, and therefore eye movement measures do not completely capture the role of attention.

Feature search (also known as "disjunctive" or "efficient" search) is a visual search process that focuses on identifying a previously requested target amongst distractors that differ from the target by a unique visual feature such as color, shape, orientation, or size. An example of a feature search task is asking a participant to identify a white square (target) surrounded by black squares (distractors). bottom up processing, Lastly, parallel processing is the mechanism that then allows one's feature detectors to work simultaneously in identifying the target. An example of a conjunction search task is having a person identify a red X (target) amongst distractors composed of black Xs (same shape) and red Os (same color). In the early stages of processing, conjunction search utilizes bottom up processes to identify pre specified features amongst the stimuli. In many cases, top down processing affects conjunction search by eliminating stimuli that are incongruent with one's previous knowledge of the target description, which in the end allows for more efficient identification of the target.

In everyday situations, people are most commonly searching their visual fields for targets that are familiar to them. When it comes to searching for familiar stimuli, top down processing allows one to more efficiently identify targets with greater complexity than can be represented in a feature or conjunction search task. although global statistical information available in real world scenes can also help people locate target objects. While bottom up processes may come into play when identifying objects that are not as familiar to a person, overall top down processing highly influences visual searches that occur in everyday life. Familiarity can play especially critical roles when parts of objects are not visible (as when objects are partly hidden from view because they are behind other objects). Visual information from hidden parts can be recalled from long term memory and used to facilitate search for familiar objects.

It is also possible to measure the role of attention within visual search experiments by calculating the slope of reaction time over the number of distractors present. Generally, when high levels of attention are required when looking at a complex array of stimuli (conjunction search), the slope increases as reaction times increase. For simple visual search tasks (feature search), the slope decreases due to reaction times being fast and requiring less attention. However, the use of a reaction time slope to measure attention is controversial because non attentional factors can also affect reaction time slope.

There is a variety of speculation about the origin and evolution of visual search in humans. It has been shown that during visual exploration of complex natural scenes, both humans and nonhuman primates make highly stereotyped eye movements. Furthermore, chimpanzees have demonstrated improved performance in visual searches for upright human or dog faces, suggesting that visual search (particularly where the target is a face) is not peculiar to humans and that it may be a primal trait. Research has suggested that effective visual search may have developed as a necessary skill for survival, where being adept at detecting threats and identifying food was essential. The importance of evolutionarily relevant threat stimuli was demonstrated in a study by LoBue and DeLoache (2008) in which children (and adults) were able to detect snakes more rapidly than other targets amongst distractor stimuli. However, some researchers question whether evolutionarily relevant threat stimuli are detected automatically.

Over the past few decades there have been vast amounts of research into face recognition, specifying that faces endure specialized processing within a region called the fusiform face area (FFA) located in the mid fusiform gyrus in the temporal lobe. Debates are ongoing whether both faces and objects are detected and processed in different systems and whether both have category specific regions for recognition and identification. Much research to date focuses on the accuracy of the detection and the time taken to detect the face in a complex visual search array. When faces are displayed in isolation, upright faces are processed faster and more accurately than inverted faces, but this effect was observed in non face objects as well. When faces are to be detected among inverted or jumbled faces, reaction times for intact and upright faces increase as the number of distractors within the array is increased. Hence, it is argued that the 'pop out' theory defined in feature search is not applicable in the recognition of faces in such visual search paradigm. Conversely, the opposite effect has been argued and within a natural environmental scene, the 'pop out' effect of the face is significantly shown. This could be due to evolutionary developments as the need to be able to identify faces that appear threatening to the individual or group is deemed critical in the survival of the fittest. More recently, it was found that faces can be efficiently detected in a visual search paradigm, if the distracters are non face objects, however it is debated whether this apparent 'pop out' effect is driven by a high level mechanism or by low level confounding features. Furthermore, patients with developmental prosopagnosia, who have impaired face identification, generally detect faces normally, suggesting that visual search for faces is facilitated by mechanisms other than the face identification circuits of the fusiform face area. Patients with forms of dementia can also have deficits in facial recognition and the ability to recognize human emotions in the face. In a meta analysis of nineteen different studies comparing normal adults with dementia patients in their abilities to recognize facial emotions, the patients with frontotemporal dementia were seen to have a lower ability to recognize many different emotions. These patients were much less accurate than the control participants (and even in comparison with Alzheimer's patients) in recognizing negative emotions, but were not significantly impaired in recognizing happiness. Anger and disgust in particular were the most difficult for the dementia patients to recognize. Some factors such as the cross race effect can influence one's ability to recognize and remember faces.

Research indicates that performance in conjunctive visual search tasks significantly improves during childhood and declines in later life. More specifically, young adults have been shown to have faster reaction times on conjunctive visual search tasks than both children and older adults, but their reaction times were similar for feature visual search tasks. eye movement ability, ability of attentional focal movement, and the ability to divide visual attention among multiple objects. Studies have suggested similar mechanisms in the difficulty for older adults, such as age related optical changes that influence peripheral acuity, the ability to move attention over the visual field, the ability to disengage attention, and the ability to ignore distractors. A study by Lorenzo López et al. (2008) provides neurological evidence for the fact that older adults have slower reaction times during conjunctive searches compared to young adults. Event related potentials (ERPs) showed longer latencies and lower amplitudes in older subjects than young adults at the P3 component, which is related to activity of the parietal lobes. This suggests the involvement of the parietal lobe function with an age related decline in the speed of visual search tasks. Results also showed that older adults, when compared to young adults, had significantly less activity in the anterior cingulate cortex and many limbic and occipitotemporal regions that are involved in performing visual search tasks.

Research has found that people with Alzheimer's disease (AD) are significantly impaired overall in visual search tasks. People with AD manifest enhanced spatial cueing, but this benefit is only obtained for cues with high spatial precision. Abnormal visual attention may underlie certain visuospatial difficulties in patients with (AD). People with AD have hypometabolism and neuropathology in the parietal cortex, and given the role of parietal function for visual attention, patients with AD may have hemispatial neglect, which may result in difficulty with disengaging attention in visual search. An experiment conducted by Tales et al. (2000) In those studies, evidence was found of impairment in PD patients on the "pop out" task, but no evidence was found on the impairment of the conjunction task. As discussed, AD patients show the exact opposite of these results: normal performance was seen on the "pop out" task, but impairment was found on the conjunction task. This double dissociation provides evidence that PD and AD affect the visual pathway in different ways, and that the pop out task and the conjunction task are differentially processed within that pathway.

Studies have consistently shown that autistic individuals performed better and with lower reaction times in feature and conjunctive visual search tasks than matched controls without autism. Several explanations for these observations have been suggested. One possibility is that people with autism have enhanced perceptual capacity. Second, autistic individuals show superior performance in discrimination tasks between similar stimuli and therefore may have an enhanced ability to differentiate between items in the visual search display. A third suggestion is that autistic individuals may have stronger top down target excitation processing and stronger distractor inhibition processing than controls. Autistic children showed superior search efficiency and increased neural activation patterns in the frontal, parietal, and occipital lobes when compared to the typically developing children. Thus, autistic individuals' superior performance on visual search tasks may be due to enhanced discrimination of items on the display, which is associated with occipital activity, and increased top down shifts of visual attention, which is associated with the frontal and parietal areas.

In the past decade, there has been extensive research into how companies can maximise sales using psychological techniques derived from visual search to determine how products should be positioned on shelves. Pieters and Warlop (1999) used eye tracking devices to assess saccades and fixations of consumers while they visually scanned/searched an array of products on a supermarket shelf. Their research suggests that consumers specifically direct their attention to products with eye catching properties such as shape, colour or brand name. This effect is due to a pressured visual search where eye movements accelerate and saccades minimise, thus resulting in the consumer's quickly choosing a product with a 'pop out' effect. This study suggests that efficient search is primarily used, concluding that consumers do not focus on items that share very similar features. The more distinct or maximally visually different a product is from surrounding products, the more likely the consumer is to notice it. Janiszewski (1998) discussed two types of consumer search. One search type is goal directed search taking place when somebody uses stored knowledge of the product in order to make a purchase choice. The second is exploratory search. This occurs when the consumer has minimal previous knowledge about how to choose a product. It was found that for exploratory search, individuals would pay less attention to products that were placed in visually competitive areas such as the middle of the shelf at an optimal viewing height. This was primarily due to the competition in attention meaning that less information was maintained in visual working memory for these products.