Eye movements disrupt spatial but not visual mental imagery

It has long been known that eye movements are functionally involved in the generation and maintenance of mental images. Indeed, a number of studies demonstrated that voluntary eye movements interfere with mental imagery tasks (e.g., Laeng and Teodorescu in Cogn Sci 26:207–231, 2002). However, mental imagery is conceived as a multifarious cognitive function with at least two components, a spatial component and a visual component. The present study investigated the question of whether eye movements disrupt mental imagery in general or only its spatial component. We present data on healthy young adults, who performed visual and spatial imagery tasks concurrently with a smooth pursuit. In line with previous literature, results revealed that eye movements had a strong disruptive effect on spatial imagery. Moreover, we crucially demonstrated that eye movements had no disruptive effect when participants visualized the depictive aspects of an object. Therefore, we suggest that eye movements serve to a greater extent the spatial than the visual component of mental imagery.     

Face detection differs from categorization: Evidence from visual search in natural scenes

In this study, we examined whether the detection of frontal, ¾, and profile face views differs from their categorization as faces. In Experiment 1, we compared three tasks that required observers to determine the presence or absence of a face, but varied in the extents to which participants had to search for the faces in simple displays and in small or large scenes to make this decision. Performance was equivalent for all of the face views in simple displays and small scenes, but it was notably slower for profile views when this required the search for faces in extended scene displays. This search effect was confirmed in Experiment 2, in which we compared observers’ eye movements with their response times to faces in visual scenes. These results demonstrate that the categorization of faces at fixation is dissociable from the detection of faces in space. Consequently, we suggest that face detection should be studied with extended visual displays, such as natural scenes.     

Incidental learning speeds visual search by lowering response thresholds, not by improving efficiency: evidence from eye movements

When observers search for a target object, they incidentally learn the identities and locations of "background" objects in the same display. This learning can facilitate search performance, eliciting faster reaction times for repeated displays. Despite these findings, visual search has been successfully modeled using architectures that maintain no history of attentional deployments; they are amnesic (e.g., Guided Search Theory). In the current study, we asked two questions: 1) under what conditions does such incidental learning occur? And 2) what does viewing behavior reveal about the efficiency of attentional deployments over time? In two experiments, we tracked eye movements during repeated visual search, and we tested incidental memory for repeated nontarget objects. Across conditions, the consistency of search sets and spatial layouts were manipulated to assess their respective contributions to learning. Using viewing behavior, we contrasted three potential accounts for faster searching with experience. The results indicate that learning does not result in faster object identification or greater search efficiency. Instead, familiar search arrays appear to allow faster resolution of search decisions, whether targets are present or absent.     

Persisting effect of prior experience of change blindness

Most cognitive scientists know that an airplane tends to lose its engine when the display is flickering. How does such prior experience influence visual search? We recorded eye movements made by vision researchers while they were actively performing a change-detection task. In selected trials, we presented Rensink's familiar 'airplane' display, but with changes occurring at locations other than the jet engine. The observers immediately noticed that there was no change in the location where the engine had changed in the previous change-blindness demonstration. Nevertheless, eye-movement analyses indicated that the observers were compelled to look at the location of the unchanged engine. These results demonstrate the powerful effect of prior experience on eye movements, even when the observers are aware of the futility of doing so.     

Rapid eye-fixation training without eyetracking

Maintenance of stable central eye fixation is crucial for a variety of behavioral, electrophysiological, and neuroimaging experiments. Naive observers in these experiments are not typically accustomed to fixating, either requiring the use of cumbersome and costly eyetracking or producing confounds in results. We devised a flicker display that produced an easily detectable visual phenomenon whenever the eyes moved. A few minutes of training using this display dramatically improved the accuracy of eye fixation while observers performed a demanding spatial attention cuing task. The same amount of training using control displays did not produce significant fixation improvements, and some observers consistently made eye movements to the peripheral attention cue, contaminating the cuing effect. Our results indicate that (1) eye fixation can be rapidly improved in naive observers by providing real-time feedback about eye movements, and (2) our simple flicker technique provides an easy and effective method for providing this feedback. S. Suzuki, satoru@northwestern.edu     

Segregation by color and stereoscopic depth in three-dimensional visual space

Two experiments were conducted to investigate how color and stereoscopic depth information are used to segregate objects for visual search in three-dimensional (3-D) visual space. Eight observers were asked to indicate the alphanumeric category (letter or digit) of the target which had its unique color and unique depth plane. In Experiment 1, distractors sharing a common depth plane or a common color appeared in spatial contiguity in thexy plane. The results suggest that visual search for the target involves examination of kernels formed by homogeneous items sharing the same color and depth. In Experiment 2, thexy contiguity of distractors sharing a common color or a common depth plane was varied. The results showed that when target-distractor distinction becomes more difficult on one dimension, the other dimension becomes more important in performing visual search, as indicated by a larger effect on search time. This suggests that observers can make optimal use of the information available. Finally, color had a larger effect on search time than did stereoscopic depth. Overall, the results support models of visual processing which maintain that perceptual segregation and selective attention are determined by similarity among objects in 3-D visual space on both spatial and nonspatial stimulus dimensions.     

Waldo reveals cultural differences in return fixations

ABSTRACT

Humans routinely perform visual search towards targets to adapt to the environment. These sequences of ballistic eye movements are shaped by a combination of top–down and bottom–up factors. Recent research documented that human observers display cultural-specific fixation patterns in a range of visual processing tasks. In particular, eye movement strategies extracting information from faces clearly differs between Western Caucasian (WC) and East Asian (EA) observers. However, whether such cultural differences are also present for visual scene processing remains debated. To this aim, we recorded the eye movements of WC and EA observers while they were solving visual search problems parametrically varying in difficulty: Where’s Waldo. Both groups had a comparable familiarity with the Waldo books reaching a comparable level of accuracy in target detection. Both cultural groups also showed a comparable temporal effect on inhibition of return, with longer fixation durations when saccades were performed to a return location compared to other locations. Westerners, however, located Waldo faster than Easterners. Interestingly, this modulation of speed was likely related to differences occurring on the low-level mechanisms of spatial inhibition of return, with EA observers returning more often to previously visited locations than the WC observers. This suboptimal eye movement strategy in the Easterners might be engendered by their cultural perceptual bias consisting in? a greater use of extra-foveal information. Overall, our data point towards the existence of a subtle, but significant difference in the processing of visual scenes across observers from different cultures during active visual search.     

比较视觉搜索任务的认知老化研究

本研究通过增加组成图片的图形数量和改变目标图形的特征,考察老年人和大学生在比较视觉搜索任务中的眼动特点和图形特征加工的优先性。结果表明与青年人相比,老年人在比较视觉搜索过程中总注视时间和注视次数增加,平均眼跳幅度减少,对目标刺激的注视时间增加。老年人和青年人在目标刺激的注视过程中都表现出图形维度数量的优先性,即表现为颜色和形状都不同的目标刺激注视时间最短,颜色不同和形状不同的目标刺激在注视时间上差异不显著。说明老年人在比较视觉搜索过程中存在认知老化,在图形特征加工的优先性上结果和青年人一致,以上结果与年龄和研究任务有关。     

Memory representations guide targeting eye movements in a natural task

The change blindness phenomenon suggests that visual representations retained across saccades are very limited. In this paper we sought to specify the kind of information that is in fact retained. We investigated targeting performance for saccadic eye movements, since one need for visual representations across eye and body positions may be to guide coordinated movements. We examined saccades in the context of an ongoing sensory motor task in order to make stronger generalizations about natural visual functioning and deployment of attention. Human subjects copied random patterns of coloured blocks on a computer display. Their eye movement pattern was consistent from block to block, including a precise saccade to a previously-placed, neighbouring block during each additional block placement. This natural, consistent eye movement allowed the previously-placed, neighbouring block to serve as an implicit target without instructions to the subject. On random trials, we removed the target object from the display during a preceding saccade, so that observers were required to make the targeting saccade without a currently visible target. Targeting performance was excellent, and appeared to be influenced by spatial information that was not visible during the preceding fixation. Subjects were generally unaware of the disappearance and reappearance of the target. We conclude that spatial information about visual targets is retained across eye movements and used to guide subsequent movements.     

Intrinsic and extrinsic contributions to heavy tails in visual foraging

Eyes move over visual scenes to gather visual information. Studies have found heavy-tailed distributions in measures of eye movements during visual search, which raises questions about whether these distributions are pervasive to eye movements, and whether they arise from intrinsic or extrinsic factors. Three different measures of eye movement trajectories were examined during visual foraging of complex images, and all three were found to exhibit heavy tails: Spatial clustering of eye movements followed a power law distribution, saccade length distributions were lognormally distributed, and the speeds of slow, small amplitude movements occurring during fixations followed a 1/f spectral power law relation. Images were varied to test whether the spatial clustering of visual scene information is responsible for heavy tails in eye movements. Spatial clustering of eye movements and saccade length distributions were found to vary with image type and task demands, but no such effects were found for eye movement speeds during fixations. Results showed that heavy-tailed distributions are general and intrinsic to visual foraging, but some of them become aligned with visual stimuli when required by task demands. The potentially adaptive value of heavy-tailed distributions in visual foraging is discussed.     

Eye movements during visual mental imagery

It has long been debated whether eye movements play a functional role in visual mental imagery. A recent paper by Laeng and Teodorescu presents new evidence that eye movements are stored as a spatial index that is used to arrange the component parts correctly when mental images are generated.     

Eye movements during mental time travel follow a diagonal line

Recent research showed that past events are associated with the back and left side, whereas future events are associated with the front and right side of space. These spatial–temporal associations have an impact on our sensorimotor system: thinking about one’s past and future leads to subtle body sways in the sagittal dimension of space (Miles, Nind, & Macrae, 2010). In this study we investigated whether mental time travel leads to sensorimotor correlates in the horizontal dimension of space. Participants were asked to mentally displace themselves into the past or future while measuring their spontaneous eye movements on a blank screen. Eye gaze was directed more rightward and upward when thinking about the future than when thinking about the past. Our results provide further insight into the spatial nature of temporal thoughts, and show that not only body, but also eye movements follow a (diagonal) “time line” during mental time travel.     

Exocentric pointing to opposite targets

We use an exocentric pointing task to study exocentric visual directions to targets that are opposite to a pointer relative to the observer. (The apparent distance between the target and the pointer always exceeded 90 degrees of visual angle.) All pointing takes place in the horizontal plane at eye height. Observers could not see both target and pointer at a single glance. They had to look back and forth between them, using combinations of eye movements, head turns, twists at the waist and turning on the feet. In the limit of diametrically opposite targets we find that the observers pick either one of two distinct orientations of the pointer as equally "visually correct". Which one results depends on the stance assumed by the observer. The difference between the two equally acceptable pointings is between 5 degrees and 10 degrees. Such a result is predicted from earlier measurements in the context of a model that describes the geometry of the horizon as a Riemannian space with varying intrinsic curvature. The present results thus fit--perhaps surprisingly--very well in such a picture.     

Eye movements during search and detection in comparative visual search

Motivated by the fact that previous visual memory paradigms have imposed encoding and retrieval constraints, the present article presents two experiments that address how observers allocate eye movements in memory and comparison processes in the absence of constraints. A comparative visual search design (Pomplun, Sichelschmidt, et al., 2001) was utilized in which observers searched for a difference between two images presented side by side. Robust time course effects were obtained, whereby search was characterized by brief fixations and a high proportion of comparative saccades. Then, upon target detection, fixations were extended, more comparative saccades were elicited, and the search focus was narrowed. The saliency and presence of differences did not guide attention, and detection was contingent upon direct fixation of the targets. The results indicate that, when full control is given, observers adopt a strategy that cuts down on memory usage in favor of restricted encoding and active scanning.     

Response times and eye movements in feature and conjunction search as a function of target eccentricity

In four experiments, saccadic eye movements, reaction times (RTs), and accuracy were measured as observers searched for feature or conjunction targets presented at several eccentricities. A conjunction search deficit, evidenced by a large eccentricity effect on RTs, accuracy, and number of saccades, was seen in Experiments 1A and 1B. Experiment 2 indicated that, when saccades were precluded, there was an even larger eccentricity effect for conjunction search targets. In Experiment 3, practice in a conjunction search task allowed both RT and number of saccades to become independent of eccentricity. Additionally, there was evidence of feature-based selectivity in that observers were more likely to fixate distractors that had the same contrast as the target. Results are consistent with the view that the oculomotor and attentional systems are functionally linked and provide constraints for models of visual attention and search.     

A model of saccade generation based on parallel processing and competitive inhibition

During active vision, the eyes continually scan the visual environment using saccadic scanning movements. This target article presents an information processing model for the control of these movements, with some close parallels to established physiological processes in the oculomotor system. Two separate pathways are concerned with the spatial and the temporal programming of the movement. In the temporal pathway there is spatially distributed coding and the saccade target is selected from a "salience map." Both pathways descend through a hierarchy of levels, the lower ones operating automatically. Visual onsets have automatic access to the eye control system via the lower levels. Various centres in each pathway are interconnected via reciprocal inhibition. The model accounts for a number of well-established phenomena in target-elicited saccades: the gap effect, express saccades, the remote distractor effect, and the global effect. High-level control of the pathways in tasks such as visual search and reading is discussed; it operates through spatial selection and search selection, which generally combine in an automated way. The model is examined in relation to data from patients with unilateral neglect.     

视觉搜索中空间不对称性的眼动研究

采用视觉搜索任务对33名大学生在不同视野中目标搜索过程的眼睛运动进行记录,以探讨不同视野位置的视觉搜索的差异性。研究结果表明,视觉搜索存在明显的空间不对称性,它主要体现在左右视野之间的差异上,具体表现在搜索反应时、平均注视时间以及眼睛跳动等方面。视觉搜索中存在很强的策略,其中主要为水平搜索或垂直搜索,因此,长期的练习和习惯也将影响视觉搜索过程。     

Eye movements and attention in reading,scene perception,and visual search

Eye movements are now widely used to investigate cognitive processes during reading, scene perception, and visual search. In this article, research on the following topics is reviewed with respect to reading: (a) the perceptual span (or span of effective vision), (b) preview benefit, (c) eye movement control, and (d) models of eye movements. Related issues with respect to eye movements during scene perception and visual search are also reviewed. It is argued that research on eye movements during reading has been somewhat advanced over research on eye movements in scene perception and visual search and that some of the paradigms developed to study reading should be more widely adopted in the study of scene perception and visual search. Research dealing with “real-world” tasks and research utilizing the visual-world paradigm are also briefly discussed.     

图形视觉与心理表象眼动模式的比较研究

本研究通过比较图形视觉和心理表象以及不同认知框架下表象加工的眼动参数,揭示图形视觉加工和心理表象加工的特点.结果表明,从视知觉到视觉心理表象,眼动被币新编码,眼动模式更加简洁,视觉心理表象具有一定的概括性;认知框架影响视觉心理表象加工的眼动模式.     

Intentionally-evoked modulations of smooth pursuit eye movements

When observers pursue a moving target with their eyes, they use predictions of future target positions in order to keep the target within the fovea. It was suggested that these predictions of smooth pursuit (SP) eye movements are computed only from the visual feedback of the target characteristics. As a consequence, if the target vanishes unexpectedly, the eye movements do not stop immediately, but they overshoot the vanishing point. We compared the spatial and temporal features of such predictive eye movements in a task with or without intentional control over the target vanishing point. If the observers stopped the target with a button press, the overshoot of the eyes was reduced compared to a condition where the offset was computer generated. Accordingly, the eyes started to decelerate well before the target offset and lagged further behind the target when it disappeared. The involvement of intentionally-generated expectancies in eye movement control was also obvious in the spatial trajectories of the eyes, which showed a clear flexion in anticipation of the circular motion path we used. These findings are discussed together with neurophysiological mechanisms underlying the SP eye movements.