Endogenous cueing attenuates object substitution masking.

Object substitution masking (OSM) is a form of visual masking in which a briefly presented target surrounded by four small dots is masked by the continuing presence of the four dots after target offset. A major parameter in the prediction of OSM is the time required for attention to be directed to the target following its onset. Object substitution theory (Di Lollo et al. in J Exp Psychol Gen 129:481-507, 2000) predicts that the sooner attention can be focused at the target's location, the less masking will ensue. However, recently Luiga and Bachmann (Psychol Res 71:634-640, 2007) presented evidence that precueing of attention to the target location prior to target-plus-mask onset by means of a central (endogenous) arrow cue does not reduce OSM. When attention was cued exogenously, OSM was attenuated. Based on these results, Luiga and Bachmann argued that object substitution theory should be adapted by differentiating the ways of directing attention to the target location. The goal of the present study was to further examine the dissociation between the effects of endogenous and exogenous precueing on OSM. Contrary to Luiga and Bachmann, our results show that prior shifts of attention to the target location initiated by both exogenous and endogenous cues reduce OSM as predicted by object substitution theory and its computational model CMOS.

Transsaccadic memory for position and orientation of saccade source and target.

Participants made a saccade from one biological-motion figure to another and had to detect saccadecontingent changes in either the walker to which the eyes were sent (the target) or the walker that served as launch site (the source). Intrasaccadic displacements in both source and target were relatively hard to detect, whereas changes in the walkers' depth orientation were readily noticed, indicating that previous findings on within-object saccades generalize to between-objects saccades. Contrary to predictions derived from theories that assign a privileged status to the saccade target, transsaccadic memory for the target's position and orientation was not more accurate than memory for the source. Displacements or rotations of one object toward the other object were more detectable than the same changes away from each other, suggesting that relational coding plays a prominent role in the integration of information across saccades.

Local and global contextual constraints on the identification of objects in scenes.

Objects likely to appear in a given real-world scene are frequently found to be easier to recognize. Two different sources of contextual information have been proposed as the basis for this effect: global scene background and individual companion objects. The present paper examines the relative importance of these two elements in explaining the context-sensitivity of object identification in full scenes. Specific sequences of object fixations were elicited during free scene exploration, while fixation times on designated target objects were recorded as a measure of ease of target identification. Episodic consistency between the target, the global scene background, and the object fixated just prior to the target (the prime), were manipulated orthogonally. Target fixation times were examined for effects of prime and background. Analyses show effects of both factors, which are modulated by the chronology and spatial extent of scene exploration. The results are discussed in terms of their implications for a model of visual object recognition in the context of real-world scenes.

Perceptual effects of scene context on object identification.

In a number of studies the context provided by a real-world scene has been claimed to have a mandatory, perceptual effect on the identification of individual objects in such a scene. This claim has provided a basis for challenging widely accepted data-driven models of visual perception in order to advocate alternative models with an outspoken top-down character. The present paper offers a review of the evidence to demonstrate that the observed scene-context effects may be the product of post-perceptual and task-dependent guessing strategies. A new research paradigm providing an on-line measure of genuine perceptual effects of context on object identification is proposed. First-fixation durations for objects incidentally fixated during the free exploration of real-world scenes are shown to increase when the objects are improbable in the scene or violate certain aspects of their typical spatial appearance in it. These effects of contextual violations are shown to emerge only at later stages of scene exploration, contrary to the notion of schema-driven scene perception effective from the very first scene fixation. In addition, evidence is reported in support of the existence of a facilitatory component in scene-context effects. This is taken to indicate that the context directly affects the ease of perceptual object processing and does not merely serve as a framework for checking the plausibility of the output of perceptual processes. Finally, our findings are situated against other contrasting results. Some future research questions are high-lighted.