Perceptual grouping of object contours survives saccades.

Human observers explore scenes by shifting their gaze from object to object. Before each eye movement, a peripheral glimpse of the next object to be fixated has however already been caught. Here we investigate whether the perceptual organization extracted from such a preview could guide the perceptual analysis of the same object during the next fixation. We observed that participants were indeed significantly faster at grouping together spatially separate elements into an object contour, when the same contour elements had also been grouped together in the peripheral preview display. Importantly, this facilitation occurred despite a change in the grouping cue defining the object contour (similarity versus collinearity). We conclude that an intermediate-level description of object shape persists in the visual system across gaze shifts, providing it with a robust basis for balancing efficiency and continuity during scene exploration.

The visual analog: evidence for a preattentive representation across saccades.

Earlier research supports the idea that transsaccadic memory involves a relatively sparse and abstract representation with little detail, much like visual short-term memory (VSTM) within a fixation. We examined whether transsaccadic memory is restricted to VSTM representations or whether it also includes a maskable, short-lived, and more detailed representation, referred to as the visual analog. First, a within-fixation change detection experiment is reported, aimed at clarifying the distinction between VSTM and the visual analog, and also the relationship between the two components. We then report 4 transsaccadic change detection experiments that make use of a modified version of the blanking paradigm originally introduced by H. Deubel, W. X. Schneider, and B. Bridgeman (1996). The results support the idea that transsaccadic memory includes a VSTM representation for attended objects (i.e., the saccade target) and a visual analog component for both attended and non-attended objects.

Object form discontinuity facilitates displacement discrimination across saccades.

Stimulus displacements coinciding with a saccadic eye movement are poorly detected by human observers. In recent years, converging evidence has shown that this phenomenon does not result from poor transsaccadic retention of presaccadic stimulus position information, but from the visual system's efforts to spatially align presaccadic and postsaccadic perception on the basis of visual landmarks. It is known that this process can be disrupted, and transsaccadic displacement detection performance can be improved, by briefly blanking the stimulus display during and immediately after the saccade. In the present study, we investigated whether this improvement could also follow from a discontinuity in the task-irrelevant form of the displaced stimulus. We observed this to be the case: Subjects more accurately identified the direction of intrasaccadic displacements when the displaced stimulus simultaneously changed form, compared to conditions without a form change. However, larger improvements were still observed under blanking conditions. In a second experiment, we show that facilitation induced by form changes and blanks can combine. We conclude that a strong assumption of visual stability underlies the suppression of transsaccadic change detection performance, the rejection of which generalizes from stimulus form to stimulus position.

Face inversion impairs holistic perception: evidence from gaze-contingent stimulation.

Human observers are experts at face recognition, yet a simple 180 degrees rotation of a face photograph decreases recognition performance substantially. A full understanding of this phenomenon-which is believed to be important for clarifying the nature of our expertise in face recognition-is still waiting. According to a long-standing and influential hypothesis, an inverted face cannot be perceived as holistically as an upright face and has to be analyzed local feature by local feature. Here, we tested this holistic perception hypothesis of the face inversion effect by means of a gaze-contingent stimulus presentation. When observers' perception was restricted to one fixated feature at a time by a gaze-contingent window, performance in an individual face matching task was almost unaffected by inversion. However, when a mask covered the fixated feature, preventing the use of local information at high resolution, the decrement of performance with inversion was even larger than in a normal-full view-condition. These observations provide evidence that the face inversion effect is caused by an inability to perceive the individual face as a whole rather than as a collection of specific features and thus support the view that observers' expertise at upright face recognition is due to the ability to perceive an individual face holistically.

Whole not hole: expert face recognition requires holistic perception.

Face recognition is an important ability of the human brain, yet its underlying mechanisms are still poorly understood. Two opposite views have been proposed to account for human face recognition expertise: the ability to extract the most diagnostic local information, feature-by feature (analytical view), or the ability to process all features at once over the whole face (holistic view). To help clarifying this debate, we used an original gaze-contingent stimulus presentation method to compare normal observers and a brain-damaged patient specifically impaired at face recognition (prosopagnosia). When a single central facial feature was revealed at a time through a gaze-contingent window, normal observers' performance at an individual face matching task decreased to the patient level. However, when only the central feature was masked, forcing normal observers to rely on the whole face but the fixated feature, their performance was almost not affected. In contrast, the prosopagnosic patient's performance decreased dramatically in this latter condition. These results were independent of the absolute size of the face and window/mask. This dissociation indicates that expertise in face recognition does not rest on the ability to analyze diagnostic local detailed features sequentially but rather on the ability to see the individual features of a face all at once, a function that is critically impaired in acquired prosopagnosia.

Parametric integration of visual form across saccades.

Through saccadic eye movements, the retinal projection of an extrafoveally glimpsed object can be brought into foveal vision quickly. We investigated what influence visual detail collected before the saccade exerts on the postsaccadic percept. Participants were instructed to saccade towards a peripheral stimulus, and to indicate on a continuum of ellipses with varying aspect ratios which exact shape they had perceived to be present after saccade landing. Compared to both an identical ellipse preview and a qualitatively different square preview, a quantitatively different ellipse preview was observed to shift the mean postsaccadic percept towards the presaccadic aspect ratio parameter value. This integration of subtly different form information was accompanied by an integration of the identity of both stimuli presented: In the great majority of these trials, subjects indicated that they had not noticed the occurrence of a change to the stimulus. When a blank screen preceded the postsaccadic stimulus onset the influence of presaccadic stimulus information on postsaccadic perception was weaker. An immediate postsaccadic mask on the other hand abolished the effect entirely. We conclude that integration of parametric visual form information occurs across saccades, but that it relies on a quickly decaying and maskable visual memory.

Transsaccadic identification of highly similar artificial shapes.

Multiple times per second, the visual system succeeds in making a seamless transition between presaccadic and postsaccadic perception. The nature of the transsaccadic representation needed to support this was commonly thought to be sparse and abstract. However, recent studies have suggested that detailed visual information is transferred across saccades as well. Here, we seek to confirm that preview effects of visual detail on postsaccadic perception do indeed occur. We presented subjects with highly similar artificial shapes, preceded by a congruent, an incongruent, or no preview. Postsaccadic recognition performance was measured, while the contrast of presaccadic and postsaccadic stimuli was manipulated independently. The results show that congruent previews provided a benefit to the recognition performance of postsaccadic stimuli, compared to no-preview conditions. Incongruent previews induced a recognition accuracy cost, combined with a recognition speed benefit. A second experiment showed that these effects can disappear when stimulus presentation is interrupted with a postsaccadic visual mask. We conclude that visual detail contained in transsaccadic memory can affect the postsaccadic percept. Furthermore, we find that the transsaccadic representation supporting this process is contrast-independent, but that postsaccadic contrast, through its effect on the reliability of information, can affect the degree to which it is employed.

Configural and featural processing during face perception: a new stimulus set.

A new stimulus set of 60 male-face stimuli in seven in-depth orientations was developed. The set can be used in research on configural versus featural mechanisms of face processing. Configural, or holistic, changes are produced by changing the global form of the face, whereas featural, or part-based, changes are attained by altering the local form of internal facial features. For each face in the set, there is one other face that differs only by its global form and one other face that differs only by its internal features. In all faces, extrafacial cues have been eliminated or standardized. The stimulus set also contains a color-coded division of each face in areas of interest, which is useful for eye movement research on face scanning strategies. We report a matching experiment with upright and inverted face pairs that demonstrates that the face stimulus set is indeed useful for research on configural and featural face perception. The stimulus set may be downloaded from the Psychonomic Society's archive (brm.psychonomic-journals.org/content/supplemental) or from our Web site (http://ppw.kuleuven.be/labexppsy/newSite/resources).

Eccentric grouping by proximity in multistable dot lattices.

The Pure Distance Law predicts grouping by proximity in dot lattices that can be organised in four ways by grouping dots along parallel lines. It specifies a quantitative relationship between the relative probability of perceiving an organisation and the relative distance between the grouped dots. The current study was set up to investigate whether this principle holds both for centrally and for eccentrically displayed dot lattices. To this end, dot lattices were displayed either in central vision, or to the right of fixation with their closest border at 3 degrees or 15 degrees. We found that the Pure Distance Law adequately predicted grouping of centrally displayed dot lattices but did not capture the eccentric data well, even when the eccentric dot lattices were scaled. Specifically, a better fit was obtained when we included the possibility in the model that in some trials participants could not report an organisation and consequently responded randomly. A plausible interpretation for the occurrence of random responses in the eccentric conditions is that under these circumstances an attention shift is required from the locus of fixation towards the dot lattice, which occasionally fails to take place. When grouping could be reported, scale and eccentricity appeared to interact. The effect of the relative interdot distances on the perceptual organisation of the dot lattices was estimated to be stronger in peripheral vision than in central vision at the two largest scales, but this difference disappeared when the smallest scale was applied.

Coding of identity-diagnostic information in transsaccadic object perception.

In four experiments, we examined the hypothesis that a presaccadic extrafoveal preview of an object normally affects subsequent postsaccadic foveal processing of the object. On each trial, viewers inspected an array of three objects and were instructed to remember one object characteristic (in-depth orientation, image-plane orientation, color, or semantic category). During the saccade to one of the objects, an intrasaccadic change in the in-depth orientation or the color could occur and its effect on gaze duration on the object was analyzed. When participants were instructed to remember the objects' depth orientation, gaze durations increased after an intrasaccadic depth rotation but not after a color change, demonstrating task dependence. Color information was only integrated when it was task relevant (i.e., when it had to be remembered). When the task required access to stored object models (categorizing the object or deciding whether it was upright or inverted), an intrasaccadic depth rotation again prolonged gaze durations, even though there was no explicit instruction to remember the objects' depth orientation. This suggests that orientation-dependent object models are accessed during object perception across saccades and that transsaccadic integration serves to expedite object identification through the integration of presaccadic and postsaccadic object-diagnostic information.

The effect of stimulus blanking on the detection of intrasaccadic displacements of translating objects.

In a display with a stationary and a translating object, subjects made a saccade towards one of the objects and had to detect intrasaccadic changes in the position of either the saccade target or the saccade flanker. Sensitivity for displacements of the stationary and moving objects was measured in conditions with (60 and 220 ms) and without blanking. In the conditions without blanking, displacement detection for translating objects was better than detection for stationary objects, which confirmed previous results (Vis. Res. 42 (2002) 379). This pattern was reversed in the blanking conditions: Sensitivity for intrasaccadic displacements of the translating object decreased drastically in comparison to conditions without a blank and was even lower than sensitivity for the stationary object. The results suggest differences in the transsaccadic spatial representation of translating and stationary objects. While a change in the spatial position of a stationary object can be detected after a blank period of 60 and 220 ms, this seems impossible for a translating object, indicating timing differences in postsaccadic spatial localization processes. Accounts in terms of a fast and accurate motion processing mechanism that possibly makes use of gain control are discussed.

Transsaccadic perception of saccade target and flanker objects.

To account for location-dependent and location-independent preview benefits in transsaccadic object perception, J. M. Henderson (1994) and J. M. Henderson and M. D. Anes (1994) proposed a dual-route model in which both episodic object representations and long-term memory representations store information across a saccade. Four experiments are reported in which the dual-route model was assessed. Preview benefits for saccade target objects were found to be location independent, whereas preview benefits for flanker objects were location dependent. These results support a single-route, 2-stage model of transsaccadic object perception. First, preattentive object files are set up to parse a set of attentional and/or saccade targets from peripheral vision, causing location-dependent preview benefits. Second, 1 object is attentionally selected for further processing, activating long-term memory representations and resulting in location-independent preview benefits.

Transsaccadic perception of translating objects: effects of landmark objects and visual field position.

Previously Gysen, De Graef, and Verfaillie [Vision Research 42 (2002) 379] showed that, with stimulus displays presenting one stationary and one translating object, sensitivity for intrasaccadic displacements was higher for translating than for stationary objects. In the present paper the importance of the relative encoding of the path of the translating object towards the stationary object is investigated. In three experiments we compared detection of intrasaccadic displacements of translating objects in relative motion (moving towards the landmark object) and translating objects moving in isolation. No 'facilitatory' effect of relative motion was found. However a visual field effect was present. Performance was always better for the translating object presented in the lower part in comparison to the upper part of the visual field. A fourth experiment investigated the sensitivity for intrasaccadic displacements of stationary and translating objects presented in the upper as well as in the lower visual field. A lower visual field advantage was observed. The superior performance for translating objects, as was found previously, was confirmed in the lower and upper visual field.

Detection of intrasaccadic displacements and depth rotations of moving objects.

In a display with a stationary and a moving object, subjects saccaded towards one of the objects and had to detect intrasaccadic changes in position or orientation of either the saccade target or the saccade flanker. Compared to performance for stationary objects, displacement detection for translating objects was better and unaffected by saccadic status of the changed object. This pattern proved to be specific to position changes in translating objects and did not generalize to other types of motion (i.e., rotation) or to other types of intrasaccadic changes (i.e., orientation shifts). Superior transsaccadic coding of the position of a translating object was also observed in control experiments with only a single object present on each trial. Possible accounts in terms of selective attention to moving objects and perceptual relevance of object position are pitted against the data, suggesting qualitative differences in the transsaccadic representation of translating and stationary objects.

Transsaccadic memory for visual object detail.

When we move our eyes around in real-world scenes, we typically have several peripheral previews of an object before we direct our eyes straight at the object. Numerous studies on transsaccadic memory have investigated whether there is any evidence for the integration of peripheral object information acquired presaccadically with foveal object information acquired postsaccadically. We review this evidence to illustrate the currently dominant view that transsaccadic object memory is sparse and contains little visual object detail. However, based on some recent studies of the role of postsaccadic stimulus blanking in transsaccadic change detection, we hypothesize that transsaccadic object memory involves the automatic emergence of a visual analog: a high-capacity, non-selective, internal representation of visual object detail. This hypothesis is tested by examining cued detection of intrasaccadic changes in the in-depth orientation of objects in scenes. The data provide preliminary support for the presence of the visual analog, but also show that its functionality is strictly limited by attentional and temporal constraints on the process of reading out information from the visual analog.