Humans are capable of picking up the invariance of an object's physical speed regardless of the distance from which it is seen. This ability is known as speed constancy. Typically the studies of speed constancy focus on the spatiotemporal cues present in the stimulus. In this work we present a series of experiments that introduce the object's familiarity in combination with other cues to study the speed constancy. The results of the first experiment show that human observers use said familiarity in the estimation of the physical speed of the objects. When distance cues are added to the stimulus, the results show that familiarity helps the system to achieve speed constancy. In the second experiment we remove the contextual cues and show the effect of familiarity on speed constancy. Finally, we propose that familiarity needs to be included in the analysis of speed constancy perhaps by considering the prototypical size of the objects.
We present three experiments that explored the effect of binocular disparity on the perception of contours defined by motion in a Spatiotemporal Boundary Formation. Depending on the disparity, the stimulus is perceived as an object that moves behind a holed surface (occluded configuration) or as a luminous transparency that moves over a surface that contains dots (occluding configuration). In all of the experiments, we used a Vernier task to assess the strength of contour perception. In the first experiment, we measured acuity as a function of disparity for a range of speeds and dot densities. The results showed that, despite the difference in the percepts, acuity was similar in both situations, replicating the dependence on speed and dot density demonstrated in previous studies. In the second experiment, the results showed that the dynamics of contour integration were identical for both occluded and occluding configurations. In the third experiment, we tested whether the mechanism of contour integration works independently from the interpretation of the scene. In this experiment, we inverted the disparity during stimulus presentation so that the stimulus switched between occluded and occluding configurations. The results showed that the switch of the depth order increased the threshold to the value obtained with a shorter presentation time. This might be produced by a resetting of the integration process driven by the change of depth order. The results are discussed within a conceptual model that places the process of contour integration in the context of the perception of objects in a Spatiotemporal Boundary Formation.
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