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.

Specificity of regions processing biological motion.

Using functional magnetic resonance imaging and point light displays portraying six different human actions, we were able to show that several visual cortical regions, including human MT/V5 complex, posterior inferior temporal gyrus and superior temporal sulcus, are differentially active in the subtraction comparing biological motion to scrambled motion. Comparison of biological motion to three-dimensional rotation (of a human figure), articulated motion and translation suggests that human superior temporal sulcus activity reflects the action portrayed in the biological motion stimuli, whereas posterior inferior temporal gyrus responds to the figure and hMT/V5+ to the complex motion pattern present in biological motion stimuli. These results were confirmed with implied action stimuli.

Perceiving human locomotion: priming effects in direction discrimination.

During the perception of biological motion, the available stimulus information is confined to a small number of lights attached to the major joints of a moving actor. Despite this drastic impoverishment of the stimulus, the human visual apparatus organizes the swarm of moving dots in a vivid percept of a human figure. In addition, observers effortlessly identify the action the figure is involved in. After a historical introduction and a short walk through the literature, data from a priming experiment are presented. In a serial two-choice reaction-time task, participants were presented with a point-light walker, facing either to the right or to the left and walking either forward or backward on a treadmill. Subjects had to identify the direction of articulatory movements. Reliable priming effects were established in consecutive trials, but these effects were tempered by the relation between priming and primed walker. The reaction time to a walker was shorter when the walker in the preceding trial moved in the same direction and was facing in the same direction. The findings are discussed in relation to recent data from neuropsychological case studies, neuroimaging, and single-cell recording.

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.

Recognition times of different views of 56 depth-rotated objects: a note concerning Verfaillie and Boutsen (1995).

The present study examines the effect of the goodness of view on the minimal exposure time required to recognize depth-rotated objects. In a previous study, Verfaillie and Boutsen (1995) derived scales of goodness of view, using a new corpus of images of depth-rotated objects. In the present experiment, a subset of this corpus (five views of 56 objects) is used to determine the recognition exposure time for each view, by increasing exposure time across successive presentations until the object is recognized. The results indicate that, for two thirds of the objects, good views are recognized more frequently and have lower recognition exposure times than bad views.

A corpus of 714 full-color images of depth-rotated objects.

A set of full-color images of objects is described for use in experiments investigating the effects of in-depth rotation on the identification of three-dimensional objects. The corpus contains up to 11 perspective views of 70 nameable objects. We also provide ratings of the "goodness" of each view, based on Thurstonian scaling of subjects' preferences in a paired-comparison experiment. An exploratory cluster analysis on the scaling solutions indicates that the amount of information available in a given view generally is the major determinant of the goodness of the view. For instance, objects with an elongated front-back axis tend to cluster together, and the front and back views of these objects, which do not reveal the object's major surfaces and features, are evaluated as the worst views.

Transsaccadic integration of biological motion.

In a transsaccadic integration paradigm, Ss had to detect saccade-contingent changes in a moving point-light walker. First, the nature of the object representation surviving a saccade was examined. The low detection of changes in the image-plane position of the figure and the high detection of changes in the upright walker's in-depth orientation indicated that transsaccadic object representations are position invariant but orientation dependent. Implications for object recognition are highlighted. The second issue concerned transsaccadic anticipation of the future event course. Ss anticipated the postsaccadic relative positions of the walker's body parts. In contrast, there was no anticipation of the postsaccadic absolute position of a translating figure; instead, Ss relied on memory of the figure's presaccadic position. The anticipated in-depth orientation of a rotating walker seemed to be distorted in the direction of canonical views.

Orientation-dependent priming effects in the perception of biological motion.

In a serial 2-choice reaction time task, subjects discriminated between a biological motion walker and a similar distractor. The point-light walker appeared in 1 of 2 possible in-depth orientations: The figure was walking either to the right or to the left in the sagittal plane. Reliable priming effects were established in consecutive trials but only when priming and primed walkers had the same in-depth orientation. This orientation-dependent priming effect was not tempered when priming and primed figures had different directions of articulatory motion (Experiments 1 to 6), different starting positions in the step cycle (Experiment 2), and different point-light localizations (Experiment 3) or when the figures were translating (Experiments 4 to 6). The data converge with neurophysiological findings that suggest that object recognition is accomplished by accessing high-level, orientation-dependent representations.

Variant points of view on viewpoint invariance.

In order to recognize an object, the visual system must make abstraction of proximal stimulus variations concomitant with the incidental vantage point. Theoretical models can be distinguished according to the degree to which they require the achievement of viewpoint independence prior to matching a stored object model. Recognition-by-components is one theory which incorporates the realization of general viewpoint invariance as one of its hallmarks. Some aspects of this theory, especially the orientation independence of the represented relations between object parts, are scrutinized. Next, an alternative approach is sketched in which object recognition is accomplished on the basis of a stimulus description which is dependent on the object's orientation, but which makes abstraction of other stimulus variations. Relevant neurophysiological findings are discussed, as well as behavioural evidence from experiments investigating orientation-dependent priming effects in the perception of biological motion.