Cultural differences in attention: Eye movement evidence from a comparative visual search task.

Individual differences in visual attention have been linked to thinking style: analytic thinking (common in individualistic cultures) is thought to promote attention to detail and focus on the most important part of a scene, whereas holistic thinking (common in collectivist cultures) promotes attention to the global structure of a scene and the relationship between its parts. However, this theory is primarily based on relatively simple judgement tasks. We compared groups from Great Britain (an individualist culture) and Saudi Arabia (a collectivist culture) on a more complex comparative visual search task, using simple natural scenes. A higher overall number of fixations for Saudi participants, along with longer search times, indicated less efficient search behaviour than British participants. Furthermore, intra-group comparisons of scan-path for Saudi participants revealed less similarity than within the British group. Together, these findings suggest that there is a positive relationship between an analytic cognitive style and controlled attention.

Attentional Differences in a Driving Hazard Perception Task in Adults with Autism Spectrum Disorders.

The current study explored attentional processing of social and non-social stimuli in ASD within the context of a driving hazard perception task. Participants watched videos of road scenes and detected hazards while their eye movements were recorded. Although individuals with ASD demonstrated relatively good detection of driving hazards, they were slower to orient to hazards. Greater attentional capture in the time preceding the hazards' onset was associated with lower verbal IQ. The findings suggest that individuals with ASD may distribute and direct their attention differently when identifying driving hazards.

Safety in numbers: target prevalence affects the detection of vehicles during simulated driving.

The "low-prevalence effect" refers to the fact that observers often fail to detect rare targets (<5 % prevalence) during visual search tasks. Previous research has demonstrated robust prevalence effects in real-world tasks that employ static images, such as airport luggage screening. No published research has examined prevalence effects in dynamic tasks, such as driving. We conducted a driving simulator experiment to investigate whether target prevalence effects influence the detection of other vehicles while driving. The target vehicles were motorcycles and buses, with prevalence being manipulated both within and between subjects: Half of the subjects experienced a high prevalence of motorcycles with a low prevalence of buses, and half experienced a high prevalence of buses with a low prevalence of motorcycles. Consistent with our hypotheses, drivers detected high-prevalence targets faster than low-prevalence targets for both vehicle types. Overall, our results support the notion that increasing the prevalence of visual search targets makes them more salient, and consequently easier to detect.

On-road behaviour of younger and older novices during the first six months of driving.

Newly qualified drivers are known to have greater crash involvement than more experienced drivers, but does the on-road driving behaviour of young novices differ from that of older novices who might be expected to be more mature and to have different driving needs? Both younger and older novices were compared with experienced drivers in their behaviour driving an instrumented car on three occasions. The three drives were conducted within the novices' first few months of becoming qualified. All drivers, including both groups of novices, increased their average road speed over the three drives, and all increased their tendency to cut across the central lane marker on bends. The older novices showed some indications of becoming more cautious with experience, by doubling their headway after six months, and by increasing the number of times they glanced into their mirrors at critical points. This increased caution may be attributable to the driving experiences of the older novices, who had experienced twice the crash rate of the younger novices during their first six months of driving.

Salience of the lambs: a test of the saliency map hypothesis with pictures of emotive objects.

Humans have an ability to rapidly detect emotive stimuli. However, many emotional objects in a scene are also highly visually salient, which raises the question of how dependent the effects of emotionality are on visual saliency and whether the presence of an emotional object changes the power of a more visually salient object in attracting attention. Participants were shown a set of positive, negative, and neutral pictures and completed recall and recognition memory tests. Eye movement data revealed that visual saliency does influence eye movements, but the effect is reliably reduced when an emotional object is present. Pictures containing negative objects were recognized more accurately and recalled in greater detail, and participants fixated more on negative objects than positive or neutral ones. Initial fixations were more likely to be on emotional objects than more visually salient neutral ones, suggesting that the processing of emotional features occurs at a very early stage of perception.

Some hazards are more attractive than others: drivers of varying experience respond differently to different types of hazard.

The ability to detect hazards in video clips of driving has been inconsistently linked to driving experience and skill. One potential reason for the lack of consistency is the failure to understand the structural differences between those hazards that discriminate between safe and unsafe drivers, and those that do not. The current study used a car simulator to test drivers of differing levels of experience on approach to a series of hazards that were categorized a priori according to their underlying structure. The results showed that learner drivers took longer to fixate hazards, although they were particularly likely to miss hazards that were obscured by the environment (such as a pedestrian emerging from behind a parked truck). While drivers with a moderate amount of experience were as fast as driving instructors to look at hazards, they spent the greatest amount of time looking at them. Only instructors' ability to detect hazards early in the approach translated into differences in driving speed for certain types of hazard. The results demonstrate that drivers of varying experience respond differently to different hazards, and lay the foundations for a hazard typology.

Decisions about objects in real-world scenes are influenced by visual saliency before and during their inspection.

Evidence from eye-tracking experiments has provided mixed support for saliency map models of inspection, with the task set for the viewer accounting for some of the discrepancies between predictions and observations. In the present experiment viewers inspected pictures of road scenes with the task being to decide whether or not they would enter a highway from a junction. Road safety observations have concluded that highly visible road users are less likely to be involved in crashes, suggesting that saliency is important in real-world tasks. The saliency of a critical vehicle was varied in the present task, as was the type of vehicle and the preferred vehicle of the viewer. Decisions were influenced by saliency, with more risky decisions when low saliency motorcycles were present. Given that the vehicles were invariably inspected, this may relate to the high incidence of "looked-but-failed-to-see" crashes involving motorcycles and to prevalence effects in visual search. Eye-tracking measures indicated effects of saliency on the fixation preceding inspection of the critical vehicle (as well as effects on inspection of the vehicle itself), suggesting that high saliency can attract an early fixation. These results have implications for recommendations about the conspicuity of vulnerable road users.

Encoding time and signs exposure time in the representation of diagrammatic deontic meanings.

It has been proposed that prohibition and obligation be represented in different ways in reasoning with deontic information (Bucciarelli & Johnson-Laird, 2005). Obligations are salient in permissible situations and prohibitions in impermissible situations. In some specific cases, differential initial representations are also consistently predicted from the comprehension of negations, if prohibition is considered as the negation of an obligation. Three experiments evaluate whether traffic signs of prohibition and obligation speed up the response time to the proposed direction represented and whether this advantage remains when people have more time to think. When making judgements about the manoeuvre performed by a vehicle, participants' response times are consistent with the predicted representation when they have a short time (i.e., 300ms) to understand the premise. In this case they represent what is permissible by obligatory signs and also what is impermissible by prohibitory signs. However, if they have more time (i.e., 1000 ms) to understand the premise, they still represent what is permissible by obligatory signs but they seem to change their initial representations to what is permissible by prohibitory signs.

Modeling eye movements in visual agnosia with a saliency map approach: bottom-up guidance or top-down strategy?

Two recent papers (Foulsham, Barton, Kingstone, Dewhurst, & Underwood, 2009; Mannan, Kennard, & Husain, 2009) report that neuropsychological patients with a profound object recognition problem (visual agnosic subjects) show differences from healthy observers in the way their eye movements are controlled when looking at images. The interpretation of these papers is that eye movements can be modeled as the selection of points on a saliency map, and that agnosic subjects show an increased reliance on visual saliency, i.e., brightness and contrast in low-level stimulus features. Here we review this approach and present new data from our own experiments with an agnosic patient that quantifies the relationship between saliency and fixation location. In addition, we consider whether the perceptual difficulties of individual patients might be modeled by selectively weighting the different features involved in a saliency map. Our data indicate that saliency is not always a good predictor of fixation in agnosia: even for our agnosic subject, as for normal observers, the saliency-fixation relationship varied as a function of the task. This means that top-down processes still have a significant effect on the earliest stages of scanning in the setting of visual agnosia, indicating severe limitations for the saliency map model. Top-down, active strategies-which are the hallmark of our human visual system-play a vital role in eye movement control, whether we know what we are looking at or not.

Visual strategies used for time-to-arrival judgments in driving.

To investigate the sources of visual information that are involved in the anticipation of collisions we recorded eye movements while participants made relative timing judgments about approaching vehicles at a junction. The avoidance of collisions is a critical aspect in driving, particularly where cars enter a line of traffic from a side road, and the present study required judgments about animations in a virtual driving environment. In two experiments we investigated the effects of (i) the angle of approach of the vehicle and the type of path (straight or curved) of the observer, and (ii) the speed of both the observer and the approaching car. Relative timing judgments depend on the angle of approach of the other vehicle (judgments are more accurate for perpendicular than for obtuse angles). Eye-movement analysis shows that visual strategies in relative timing judgments are characterised by saccadic eye movements back and forth between the approaching car and the road ahead, particularly the side line which may serve as a spatial reference point. Results suggest that observers use the distance of the car from this reference point for their timing judgments.

The potency of people in pictures: evidence from sequences of eye fixations.

Does the presence of people in a natural scene affect the way that we inspect that picture? Previous research suggests that we have a natural tendency to look at the social information before other items in a scene. There is also evidence that accuracy of visual memory and the way we move our eyes are related. This experiment investigated whether eye movements differed when participants correctly and incorrectly identified stimuli at recognition, and how this is affected by the presence of people. Eye movements were recorded from 15 participants while they inspected photographs at encoding and during a recognition memory test. Half of the pictures contained people and half did not. The presence of people increased recognition accuracy and affected average fixation duration and average saccadic amplitude. Accuracy was not affected by the size of the Region of Interest (RoI), the number of people in the picture, or the distance of the person from the center. Analyses of the order and pattern of fixations showed a high similarity between encoding and recognition in all conditions, but the lack of relationship between string similarity and recognition accuracy challenges the idea that the reproduction of eye movements alone is enough to create a memory advantage.

Brief report: driving hazard perception in autism.

This study investigated whether individuals with ASD (autistic spectrum disorders) are able to identify driving hazards, given their difficulties processing social information, Klin et al. (Archives of General Psychiatry 59: 809-816, 2002). Twenty-three adult males with ASD and 21 comparison participants viewed 10 video clips containing driving hazards. In half of the clips the source of the hazard was a visible person (social); in the other half the source was a car (non-social). Participants with ASD identified fewer social hazards than the comparison participants (U = 163.00, N = 44, p < .05) but not non-social. Participants with ASD were also slower to respond than comparison participants, F(1,40) = 4.93, p < .05. This suggests that, although people with ASD can perceive driving hazards they may have specific difficulty identifying them if they involve a person.

Fixation and saliency during search of natural scenes: the case of visual agnosia.

Models of eye movement control in natural scenes often distinguish between stimulus-driven processes (which guide the eyes to visually salient regions) and those based on task and object knowledge (which depend on expectations or identification of objects and scene gist). In the present investigation, the eye movements of a patient with visual agnosia were recorded while she searched for objects within photographs of natural scenes and compared to those made by students and age-matched controls. Agnosia is assumed to disrupt the top-down knowledge available in this task, and so may increase the reliance on bottom-up cues. The patient's deficit in object recognition was seen in poor search performance and inefficient scanning. The low-level saliency of target objects had an effect on responses in visual agnosia, and the most salient region in the scene was more likely to be fixated by the patient than by controls. An analysis of model-predicted saliency at fixation locations indicated a closer match between fixations and low-level saliency in agnosia than in controls. These findings are discussed in relation to saliency-map models and the balance between high and low-level factors in eye guidance.

Does conspicuity enhance distraction? Saliency and eye landing position when searching for objects.

While visual saliency may sometimes capture attention, the guidance of eye movements in search is often dominated by knowledge of the target. How is the search for an object influenced by the saliency of an adjacent distractor? Participants searched for a target amongst an array of objects, with distractor saliency having an effect on response time and on the speed at which targets were found. Saliency did not predict the order in which objects in target-absent trials were fixated. The within-target landing position was distributed around a modal position close to the centre of the object. Saliency did not affect this position, the latency of the initial saccade, or the likelihood of the distractor being fixated, suggesting that saliency affects the allocation of covert attention and not just eye movements.

Domain knowledge moderates the influence of visual saliency in scene recognition.

Is the sequence of eye-movements made when viewing a picture related to encoding the image into memory? The suggestion of a relationship is supported by studies that have found that scanpaths are more similar over multiple viewings of a stimulus than would be expected by chance. It has also been found that low-level visual saliency contributes to the initial formation of these scanpaths, and has lead to formation of theories such as the saliency map hypothesis. However, bottom-up processes such as these can be overridden by top-down cognitive knowledge in the form of domain proficiency. Domain specialists were asked to look at a set of photographs of real-world scenes in preparation for a memory test. Then they were given a second set of stimuli and were asked to identify the picture as old (from the previous set) or new (never seen before). Eye tracking analyses (including scanpath comparison using a string editing algorithm) revealed that saliency did influence where participants looked and in what sequence. However, this was reliably reduced when participants viewed pictures from their specialist domain. This effect is shown to be robust in a repeated viewing of the stimuli.

Turning the world around: patterns in saccade direction vary with picture orientation.

The eye movements made by viewers of natural images often feature a predominance of horizontal saccades. Can this behaviour be explained by the distribution of saliency around the horizon, low-level oculomotor factors, top-down control or laboratory artefacts? Two experiments explored this bias by recording saccades whilst subjects viewed photographs rotated to varying extents, but within a constant square frame. The findings show that the dominant saccade direction follows the orientation of the scene, though this pattern varies in interiors and during recognition of previously seen pictures. This demonstrates that a horizon bias is robust and affected by both the distribution of features and more global representations of the scene layout.

Attentional and automatic processes in line tracing: is tracing obligatory?

When comparing two target elements placed on the same convoluted curve, response times are dependent on the distance between the targets along the curve, despite being separated by a constant Euclidean distance. The present study assessed whether such line tracing is obligatory across the whole of the line even when the task demands do not require it, or whether it is an optional strategy that can be disregarded when the circumstances favor a different method of attentional deployment. Three experiments were conducted to assess whether attention can select only a portion of a curve to trace when it is strategically sensible to do so. The results suggest that attention can indeed jump over portions of a line that are irrelevant to task performance before tracing has begun. However, the final experiment suggests that line tracing may continue beyond the task-relevant portion of the line. We conclude that line tracing is a strategy whose initial deployment can be influenced by top-down factors, rather than an obligatory response triggered by the stimuli-although, once engaged, line tracing may be hard to stop.

Does attention move or spread during mental curve tracing?

There are two theories that attempt to explain how attention is deployed when lines are traced. Initially, it was believed that a covert zoom lens moved along the line. Recent evidence has, however, suggested that attention spreads along the line, rather than moving along it, perhaps as part of an effortful object-parsing process. Three experiments tested the spreading and moving accounts of line tracing. Participants were presented with two intertwined lines and were required to trace one to find the correct target. On half the trials, a masked change occurred, most often near the top of the target line, that reversed the required response. If attention spreads along the line, the participants should have been able to notice the change whenever it occurred during the tracing process. However, the participants found it harder to spot the change if it occurred late in the tracing process. This suggests that resources were less frequently available to detect changes on portions of the line that had already been traced when the change occurred. The results argue against a spreading trace of attention that encompasses the whole line.

What can saliency models predict about eye movements? Spatial and sequential aspects of fixations during encoding and recognition.

Saliency map models account for a small but significant amount of the variance in where people fixate, but evaluating these models with natural stimuli has led to mixed results. In the present study, the eye movements of participants were recorded while they viewed color photographs of natural scenes in preparation for a memory test (encoding) and when recognizing them later. These eye movements were then compared to the predictions of a well defined saliency map model (L. Itti & C. Koch, 2000), in terms of both individual fixation locations and fixation sequences (scanpaths). The saliency model is a significantly better predictor of fixation location than random models that take into account bias toward central fixations, and this is the case at both encoding and recognition. However, similarity between scanpaths made at multiple viewings of the same stimulus suggests that repetitive scanpaths also contribute to where people look. Top-down recapitulation of scanpaths is a key prediction of scanpath theory (D. Noton & L. Stark, 1971), but it might also be explained by bottom-up guidance. The present data suggest that saliency cannot account for scanpaths and that incorporating these sequences could improve model predictions.