Feature-based attention across saccades: Pop-out in color search is spatiotopic

Our perception of the world remains stable despite the retinal shifts that occur with each saccade. The role of spatial attention in matching pre- to postsaccadic visual information has been well established, but the role of feature-based attention remains unclear. In this study, we examined the transsaccadic processing of a color pop-out target. Participants made a saccade towards a neutral target and performed a search task on a peripheral array presented once the saccade landed. A similar array was presented just before the saccade and we analyzed what aspect of this preview benefitted the postsaccadic search task. We assessed the preview effect in the spatiotopic and retinotopic reference frames, and the potential transfer of feature selectivity across the saccade. In the first experiment, the target and distractor colors remained identical for the preview and the postsaccadic array and performance improved. The largest benefit was observed at the spatiotopic location. In the second experiment, the target and distractor colors were swapped across the saccade. All responses were slowed but the cost was least at the spatiotopic location. Our results show that the preview attracted spatial attention to the target location, which was then remapped, and suggest that previewed features, specifically colors, were transferred across the saccade. Furthermore, the preview induced a spatiotopic advantage regardless of whether the target switched color or not, suggesting that spatiotopy was established independently of feature processing. Our results support independent priming effects of features versus location and underline the role of feature-based selection in visual stability.     

Attention doesn’t slide: spatiotopic updating after eye movements instantiates a new, discrete attentional locus

During natural vision, eye movements can drastically alter the retinotopic (eye-centered) coordinates of locations and objects, yet the spatiotopic (world-centered) percept remains stable. Maintaining visuospatial attention in spatiotopic coordinates requires updating of attentional representations following each eye movement. However, this updating is not instantaneous; attentional facilitation temporarily lingers at the previous retinotopic location after a saccade, a phenomenon known as the retinotopic attentional trace. At various times after a saccade, we probed attention at an intermediate location between the retinotopic and spatiotopic locations to determine whether a single locus of attentional facilitation slides progressively from the previous retinotopic location to the appropriate spatiotopic location, or whether retinotopic facilitation decays while a new, independent spatiotopic locus concurrently becomes active. Facilitation at the intermediate location was not significant at any time, suggesting that top-down attention can result in enhancement of discrete retinotopic and spatiotopic locations without passing through intermediate locations.     

Timing the shift in retinal local signs that accompanies a saccadic eye movement

Thephantom array was used to probe the time course of the shift in retinal local signs that accompanies a saccadic eye movement. The phantom array materializes when one saccades in the dark across a point light source blinking 120 times per second. One sees a stationary array of flashes—the first materializes discretely near the intended endpoint of the saccade, and subsequent flashes materialize progressively closer to the actual position of the blinking light. Four trained observers indicated the perceived location, relative to the phantom array, of a 1-msec marker flash (M) produced by two LEDs (light-emitting diodes) that vertically bracketed the blinking light. The marker was seen as spatially coincident with the first flash when it flashed 80 to 0 msec before the saccade, and was seen as spatially coincident with either the first flash or the actual position of the blinking light when it flashed mare than 80 msec before the saccade, indicating, respectively, that the shaft is presaccadic and rather abrupt.     

Orientation tuning of shapefrom shading

Four experiments were performed to assess the effect of different orientations and direction of lighting on the visual processing of shaded or bipartite disks. In the first two experiments, observers were presented with nine different shading orientations from 0° to 180°. Targets were detected in a rapid and parallel fashion for shaded disks when the orientation of the shading gradient was not horizontal (90°) or oriented at 67.5°. Search asymmetries favoring the detection of “pock” targets over “ball” targets were found for all orientations. The search rates for bipartite disks were similar to the shaded disks at 0°, 22.5°, and 90° but not for intermediate orientations, and no search asymmetries were found. These differences suggest that shaded displays and bipartite displays are processed by different underlying mechanisms. The third experiment showed that the direction of the light source (left or right) had no influence on search asymmetries around the 90° point. Shading gradient orientation affected magnitude estimates of depth in the fourth experiment. These experiments show that the visual system’s “as-sumption” of overhead lighting is broadly tuned.     

Mental imagery of visual motion modifies the perception of roll-vection stimulation

When viewing a wide-angle visual display, which rotates in the frontoparallel plane around the line of sight, observers experience an illusory shift of the direction of gravity; this shift leads to an apparent tilt of the body and displaces allocentric space coordinates. In this study, subjects adjusted an indicator to the apparent horizontal while viewing a rotating display. To determine whether top down processes could affect the illusion, the subjects were asked to visualize a rotating configuration of dots onto a blank central portion of the moving visual field. Visualizing dots and actually viewing the dots deflected the spatial judgment in very similar ways. These results demonstrate that top down processing can affect allocentric space coordinates.     

Postsaccadic processing of the retinal image during picture scanning

Eye movements were monitored while observers inspected photographs of natural scenes. At the end of each saccade (i.e., at the beginning of each period of steady fixation), the stimulus was replaced for a certain period of time by a uniform field (Experiment 1) or a blurred version of the stimulus scene (Experiment 2). Total fixation duration was measured as a function of the duration of the initial uniform field or the blurred image that followed the saccade. It was found that fixation duration increased proportionally with the duration of the initial replacement field, even for durations as short as 25 msec. These results suggest that the visual system uses information on the retina right after each saccade is completed and that the blurred, low-resolution information used in Experiment 2 (cutoff frequency of 0.8 cpd) is not sufficient for the requirements of picture processing in this task.     

Remapping versus short-term memory in visual stability across saccades

Saccadic eye movements cause displacements of the image of the visual world projected on the retina. Despite the ubiquitous nature of saccades, subjective experience of the world is continuous and stable. In five experiments, we addressed the mechanisms that may support visual stability: matching of pre- and postsaccadic locations of the target by an internal copy of the saccade, or retention of the visual attributes of the target in short-term memory across the saccade. Healthy human adults were instructed to make a saccade to a peripheral Gabor patch. While the saccade was in midflight, the patch could change location, orientation, or both. The change occurred either immediately or following a 250-ms blank during which no visual stimuli were available. In separate experiments, subjects had to report either whether the patch stepped to the left or right or whether the orientation rotated clockwise or counterclockwise. Consistent with previous findings, we found that transsaccadic displacement discrimination was enhanced by the addition of the blank. However, contrary to previous findings reported in the literature, the feature change did not improve performance. Transsaccadic orientation change discrimination did not depend on either an irrelevant temporal blank or a simultaneous irrelevant target displacement. Taken together, these findings suggest that orientation is not a relevant visual feature for transsaccadic correspondence.     

Visual memory and the perception of a stable visual environment

The visual world appears stable and continuous despite eye movements. One hypothesis about how this perception is achieved is that the contents of successive fixations are fused in memory according to environmental coordinates. Two experiments failed to support this hypothesis; they showed that one's ability to detect a grating presented after a saccade is unaffected by the presentation of a grating with the same spatial frequency in the same spatial location before the saccade. A third experiment tested an alternative explanation of perceptual stability that claims that the contents of successive fixations are compared, rather than fused, across saccades, allowing one to determine whether the world has remained stable. This hypothesis was supported: Experienced subjects could accurately determine whether two patterns viewed in successive fixations were identical or different, even when the two patterns appeared in different spatial positions across the saccade. Taken together, these results suggest that perceptual stability and information integration across saccades rely on memory for the relative positions of objects in the environment, rather than on the spatiotopic fusion of visual information from successive fixations.     

返回抑制的空间、视网膜和客体参照系

返回抑制是指当刺激出现在先前注意过的位置(或客体)时,人们的加工效率降低的一种抑制性注意机制。该注意机制对个体有适应性价值,它能够降低注意返回先前注意过的位置(或客体)的概率(PosnerCohen,1984),从而提高视觉采样(或搜索)的效率(Klein,1988)。返回抑制的参照系是返回抑制领域的重要理论问题。先前研究发现返回抑制的参照系可以是视网膜、空间和客体。本文介绍了返回抑制参照系研究的实验范式以及相关的行为、脑损伤及神经影像发现。此外,本文还就未来研究的方向和应该注意的问题进行了探讨。     

Object-location binding across a saccade: A retinotopic spatial congruency bias

Despite frequent eye movements that rapidly shift the locations of objects on our retinas, our visual system creates a stable perception of the world. To do this, it must convert eye-centered (retinotopic) input to world-centered (spatiotopic) percepts. Moreover, for successful behavior we must also incorporate information about object features/identities during this updating – a fundamental challenge that remains to be understood. Here we adapted a recent behavioral paradigm, the “spatial congruency bias,” to investigate object-location binding across an eye movement. In two initial baseline experiments, we showed that the spatial congruency bias was present for both gabor and face stimuli in addition to the object stimuli used in the original paradigm. Then, across three main experiments, we found the bias was preserved across an eye movement, but only in retinotopic coordinates: Subjects were more likely to perceive two stimuli as having the same features/identity when they were presented in the same retinotopic location. Strikingly, there was no evidence of location binding in the more ecologically relevant spatiotopic (world-centered) coordinates; the reference frame did not update to spatiotopic even at longer post-saccade delays, nor did it transition to spatiotopic with more complex stimuli (gabors, shapes, and faces all showed a retinotopic congruency bias). Our results suggest that object-location binding may be tied to retinotopic coordinates, and that it may need to be re-established following each eye movement rather than being automatically updated to spatiotopic coordinates.     

Investigating the parameters of transsaccadic memory: inhibition of return impedes information acquisition near a saccade target

A limited amount of visual information is retained between saccades, which is subsequently stored into a memory system, such as transsaccadic memory. Since the capacity of transsaccadic memory is limited, selection of information is crucial. Selection of relevant information is modulated by attentional processes such as the presaccadic shift of attention. This involuntary shift of attention occurs prior to execution of the saccade and leads to information acquisition at an intended saccade target. The aim of the present study was to investigate the influence that another attentional effect, inhibition of return (IOR), has on the information that gets stored into transsaccadic memory. IOR is the phenomenon where participants are slower to respond to a cue at a previously attended location. To this end, we used a transsaccadic memory paradigm in which stimuli, oriented on a horizontal axis relative to saccade direction, are only visible to the participant before executing a saccade. Previous research showed that items in close proximity to a saccade target are likely to be reported more accurately. In our current study, participants were cued to fixate one of the stimulus locations and subsequently refixated the centre fixation point before executing the transsaccadic memory task. Results indicate that information at a location near a saccade landing point is less likely to be acquired into transsaccadic memory when this location was previously associated with IOR. Furthermore, we found evidence which implicates a reduction of the overall amount of elements retained in transsaccadic memory when a location near a saccade target is associated with IOR. These results suggest that the presaccadic shift of attention may be modulated by IOR and thereby reduces information acquisition by transsaccadic memory.     

Memory for retinotopic locations is more accurate than memory for spatiotopic locations,even for visually guided reaching

To interact successfully with objects, we must maintain stable representations of their locations in the world. However, their images on the retina may be displaced several times per second by large, rapid eye movements. A number of studies have demonstrated that visual processing is heavily influenced by gaze-centered (retinotopic) information, including a recent finding that memory for an object’s location is more accurate and precise in gaze-centered (retinotopic) than world-centered (spatiotopic) coordinates (Golomb & Kanwisher, 2012b). This effect is somewhat surprising, given our intuition that behavior is successfully guided by spatiotopic representations. In the present experiment, we asked whether the visual system may rely on a more spatiotopic memory store depending on the mode of responding. Specifically, we tested whether reaching toward and tapping directly on an object’s location could improve memory for its spatiotopic location. Participants performed a spatial working memory task under four conditions: retinotopic vs. spatiotopic task, and computer mouse click vs. touchscreen reaching response. When participants responded by clicking with a mouse on the screen, we replicated Golomb & Kanwisher’s original results, finding that memory was more accurate in retinotopic than spatiotopic coordinates and that the accuracy of spatiotopic memory deteriorated substantially more than retinotopic memory with additional eye movements during the memory delay. Critically, we found the same pattern of results when participants responded by using their finger to reach and tap the remembered location on the monitor. These results further support the hypothesis that spatial memory is natively retinotopic; we found no evidence that engaging the motor system improves spatiotopic memory across saccades.     

Gradual remapping results in early retinotopic and late spatiotopic inhibition of return

Here we report that immediately following the execution of an eye movement, oculomotor inhibition of return resides in retinotopic (eye-centered) coordinates. At longer postsaccadic intervals, inhibition resides in spatiotopic (world-centered) coordinates. These results are explained in terms of perisaccadic remapping. In the interval surrounding an eye movement, information is remapped within retinotopic maps to compensate for the retinal displacement. Because remapping is not an instantaneous process, a fast, but gradual, transfer of inhibition of return from retinotopic to spatiotopic coordinates can be observed in the postsaccadic interval. The observation that visual stability is preserved in inhibition of return is consistent with its function as a "foraging facilitator," which requires locations to be inhibited across multiple eye movements. The current results support the idea that the visual system is retinotopically organized and that the appearance of a spatiotopic organization is due to remapping of visual information to compensate for eye movements.     

The effect of orientation on tactual braille recognition: Optimal touching positions

Subjects in five experiments matched tangible braille against a visible matching code. In Experiment 1, braille recognition suffered when entire lines of braille characters were tilted in varying amounts from the upright. Experiment 2 showed that tilt lowered performance for tangible, large embossed letters, as well as for braille. However, recognition was better for print letters than it was for braille. In Experiment 3, subjects attempted to match the upright array against embossed braille that was left/right reversed, inverted up/down, or rotated +180°. Performance was close to that for normal braille in the left/right reversal condition, and very low for the +180° rotation group. These results on braille tilt in the “picture plane” may reflect difficulty in manipulating the tangible “image.” Braille recognition performance was not lowered whenthe visible matching array was tilted ?45° or ?90° from the upright but the tangible stimuli were upright. In Experiment 4, recognition of left/right reversed braille that was physically horizontal (on the bottom of a shelf) was compared with that of braille left/right reversed due to its location on the back of a panel, in the vertical plane. Braille recognition accuracy was higher with braille located vertically. An additional experiment showed the beneficial effect of locating braille in the vertical, frontoparallel plane, obtained with +90° degree rotated braille. It is proposed that optimal tactual performance with tangible arrays might depend on touching position, and on the physical position of stimuli in space. Just as there are good and poor viewing positions, there may be optimal touching positions. The effects of tilt on braille identification were diminished for blind subjects, suggesting the importance of tactile experience and skill.     

Visual field differences in recognizing letters

Differences due to visual field location were examined for single letters placed at one of 12 clockface positions 3° and 6° from fixation. Results compared closely with established findings using simple light stimuli, showing best recognition on the horizontal meridian, poorest on the vertical and intermediate on oblique meridians. Subjects’ confidence ratings followed the same pattern. There was evidence for a specific right superiority along the horizontal meridian, as found in previous studies, but no evidence for a general right hemifield superiority. The difficulty of arguing from these findings to available dominance or scanning explanations is pointed out. It is proposed that effects due to visual field variability may have a pervasive yet largely unrecognized influence in visual perception research.     

Saccadic eye movements and localization of visual stimuli

Visual localization phenomena were studied before, during, and after a saccade. Light flashes of 5 and 9 msec duration presented before and during the eye movement were mislocated in the saccade direction, the localization error being a time function. When the 9-msec duration stimulus and saccade did not overlap in time, a stripe was reported, when they did not, the stimulus was perceived as a point. If a long-duration stimulus moved perpendicularly to the saccade direction with the same “sigmoidal” velocity, a curvilinear trace was perceived, regardless of the linear trace of the image on the retina. A stimulus with stabilized retinal image was perceived as a stationary point during the saccade. A possible theory to deal with the data was suggested by modifying the algebra of outflow-inflow theories.     

Effects of mental imagery styles on shoulder and hip rotations during preparation of pirouettes

To analyze individual behavior in spatial navigation especially for pirouette preparations (complete whole-body rotations), the authors studied horizontal shoulder-hip interactions under 2 constraints: postural (right and left supporting legs [SL]) and spatial (clockwise [CW] and counterclockwise [CCW]). They performed kinematic analysis at the start and end of the shoulder-hip horizontal rotations (run-up) with regard to imagery of motor actions. On the basis of the Vividness of Movement Imagery Questionnaire, they classified 8 female expert ballet dancers and 7 untrained female participants according to their movement imagery style (kinesthetic and visual). At the run-up's end, the shoulders initiated the turn independently of SL but differently depending on training: CW for dancers and CCW for untrained participants (their commonly used direction). Kinesthetic and mixed imagery styles prevailed in dancers, whereas simply a mixed style appeared among untrained participants. Thus, dance training enhances the imagery of kinesthetic sensation and influences the choice of spatial direction, facilitating the body-space interaction.     

Anisotropic perception of visual angle: Implications for the horizontal-vertical illusion,overconstancy of size,and the moon illusion

Three experiments investigated anisotropic perception of visual angle outdoors. In Experiment 1, scales for vertical and horizontal visual angles ranging from 20° to 80° were constructed with the method of angle production (in which the subject reproduced a visual angle with a protractor) and the method of distance production (in which the subject produced a visual angle by adjusting viewing distance). In Experiment 2, scales for vertical and horizontal visual angles of 5°–30° were constructed with the method of angle production and were compared with scales for orientation in the frontal plane. In Experiment 3, vertical and horizontal visual angles of 3°-80° were judged with the method of verbal estimation. The main results of the experiments were as follows: (1) The obtained angles for visual angle are described by a quadratic equation, θ′=a+bθ+cθ² (where θ is the visual angle; θ′, the obtained angle;a, b, andc, constants). (2) The linear coefficientb is larger than unity and is steeper for vertical direction than for horizontal direction. (3) The quadratic coefficientc is generally smaller than zero and is negatively larger for vertical direction than for horizontal direction. And (4) the obtained angle for visual angle is larger than that for orientation. From these results, it was possible to predict the horizontal-vertical illusion, over-constancy of size, and the moon illusion.     

Visual perception of direction when voluntary saccades occur. I. Relation of visual direction of a fixation target extinguished before a saccade to a flash presented during the saccade

In experiments designed to clarify the mechanisms underlying the normal stability of visual direction for stationary objects when voluntary saccades occur, Ss reported on the horizontal visual direction of a brief test [lash presented when the eye was at a specific point in the saccade (the trigger point) relative to a fixation target viewed and extinguished prior to the saccade. From these reports, PSEs (points of subjective equality) were calculated for the fixation target as measured by the test [lashes. The distance of the trigger point from the previous fixation position was systematically varied in each experiment. Different experiments required saccades of different lengths and directions. With the exception of the presentation of the test [lash the saccades were carried out in complete darkness so that the possible utilization of an extraretinal signal regarding the eye movement (change in eye position, the intention to turn the eye, or a change of attention related to the eye movement) in the determination of visual direction could be observed uncomplicated by a continuing visual context. According to classical theories, an extraretinal signal proportional to the change in eye position acts to maintain direction constancy by compensating for the Shift of the retinal image resulting from the movement of the eye. In general, direction constancy was not preserved in the present experiments, and thus the data would not be predicted by classical theories. However, the PSE varied with distance of the trigger point from the fixation target. Since this displacement of PSE from the trigger point was in the correct direction for compensation, the presence of an extraretinal signal was confirmed. However, the growth of this signal appears to be time-locked to the saccade rather than locked to eye position; it is suggested that this growth takes place over a time period which is longer than the duration of the saccade itself.     

Target localization after saccades and at fixation: Nontargets both facilitate and bias responses

ABSTRACT

The image on our retina changes every time we make an eye movement. To maintain visual stability after saccades, specifically to locate visual targets, we may use nontarget objects as “landmarks”. In the current study, we compared how the presence of nontargets affects target localization after saccades and during sustained fixation. Participants fixated a target object, which either maintained its location on the screen (sustained-fixation trials), or displaced to trigger a saccade (saccade trials). After the target disappeared, participants reported the most recent target location with a mouse click. We found that the presence of nontargets decreased response error magnitude and variability. However, this nontarget facilitation effect was not larger for saccade trials than sustained-fixation trials, indicating that nontarget facilitation might be a general effect for target localization, rather than of particular importance to post-saccadic stability. Additionally, participants’ responses were biased towards the nontarget locations, particularly when the nontarget-target relationships were preserved in relative coordinates across the saccade. This nontarget bias interacted with biases from other spatial references, e.g., eye movement paths, possibly in a way that emphasized non-redundant information. In summary, the presence of nontargets is one of several sources of reference that combine to influence (both facilitate and bias) target localization.