The Visual Priming of Motion-Defined 3D Objects

Perceptual bias contextualized in visually ambiguous stimuli

The visual appearance of an object is a function of stimulus properties as well as perceptual biases imposed by the observer. The context-specific trade-off between both can be measured accurately in a perceptual judgment task, involving grouping by proximity in ambiguous dot lattices. Such grouping depends lawfully on a stimulus parameter of the dot lattices known as their aspect ratio (AR), whose effect is modulated by a perceptual bias representing the preference for a cardinal orientation. In two experiments, we investigated how preceding context can lead to bias modulation, either in a top-down fashion via visual working memory (VWM) or bottom-up via sensory priming. In Experiment 1, we embedded the perceptual judgment task in a change detection paradigm and studied how the factors of VWM load (complexity of the memory array) and content (congruency in orientation to the ensuing dot lattice) affect the prominence of perceptual bias. A robust vertical orientation bias was observed, which was increased by VWM load and modulated by congruent VWM content. In Experiment 2, dot lattices were preceded by oriented primes. Here, primes regardless of orientation elicited a vertical orientation bias in dot lattices compared to a neutral baseline. Taken together, the two experiments demonstrate that top-down context (VWM load and content) effectively controls orientation bias modulation, while bottom-up context (i.e., priming) merely acts as an undifferentiated trigger to perceptual bias. These findings characterize the temporal context sensitivity of Gestalt perception, shed light on the processes responsible for different perceptual outcomes of ambiguous stimuli, and identify some of the mechanisms controlling perceptual bias.

Priming and reversals of the perceived ambiguous orientation of a structure-from-motion shape and relation to personality traits

We demonstrate contributions of top-down and bottom-up influences in perception as explored by priming and counts of perceived reversals and mixed percepts, as probed by an ambiguously slanted structure-from-motion (SFM) test-cylinder. We included three different disambiguated primes: a SFM cylinder, a still image of a cylinder, and an imagined cylinder. In Experiment 1 where the prime and test sequentially occupied the same location, we also administered questionnaires with the Big-5 trait openness and vividness of visual imagery to probe possible relations to top-down driven priming. Since influences of gaze or position in the prime conditions in Experiment 1 could not be ruled out completely, Experiment 2 was conducted where the test cylinder appeared at a randomly chosen position after the prime. In Experiment 2 we also measured the number of perceptual reversals and mixed percepts during prolonged viewing of our ambiguous SFM-cylinder, and administered questionnaires to measure all Big-5 traits, autism, spatial and object imagery, and rational or experiential cognitive styles, associated with bottom-up and top-down processes. The results revealed contributions of position-invariant and cue-invariant priming. In addition, residual contributions of low-level priming was found when the prime and test were both defined by SFM, and were presented at the same location, and the correlation between the SFM priming and the other two priming conditions were weaker than between the pictorial and imagery priming. As previously found with ambiguous binocular rivalry stimuli, we found positive correlations between mixed percepts and the Big-5 dimension openness to experience, and between reversals, mixed percepts and neuroticism. Surprisingly, no correlations between the scores from the vividness of imagery questionnaires and influence from any of the primes were obtained. An intriguing finding was the significant differences between the positive correlation from the experiential cognitive style scores, and the negative correlation between rational style and the cue invariant priming. Among other results, negative correlations between agreeableness and all priming conditions were obtained. These results not only support the notion of multiple processes involved in the perception of ambiguous SFM, but also link these processes in perception to specific personality traits.

Information for perceiving blurry events: Optic flow and color are additive

Information used in visual event perception includes both static image structure projected from opaque object surfaces and dynamic optic flow generated by motion. Events presented in static blurry grayscale displays have been shown to be recognized only when and after presented with optic flow. In this study, we investigate the effects of optic flow and color on identifying blurry events by studying the identification accuracy and eye-movement patterns. Three types of color displays were tested: grayscale, original colors, or rearranged colors (where the RGB values of the original colors were adjusted). In each color condition, participants identified 12 blurry events in five experimental phases. In the first two phases, static blurry images were presented alone or sequentially with a motion mask between consecutive frames, and identification was poor. In Phase 3, where optic flow was added, identification was comparably good. In Phases 4 and 5, motion was removed, but identification remained good. Thus, optic flow improved event identification during and after its presentation. Color also improved performance, where participants were consistently better at identifying color displays than grayscale or rearranged color displays. Importantly, the effects of optic flow and color were additive. Finally, in both motion and postmotion phases, a significant portion of eye fixations fell in strong optic flow areas, suggesting that participants continued to look where flow was available even after it stopped. We infer that optic flow specified depth structure in the blurry image structure and yielded an improvement in identification from static blurry images.

Sentence plausibility influences the link between action words and the perception of biological human movements

The present study aimed to assess the role of sentence plausibility in the functional link between action words and visual judgments of point-light human actions. Following the oral presentation of action verbs included in a plausible or implausible sentence, participants were asked to detect the presence of congruent or incongruent biological movements. Sentence plausibility was manipulated by inverting the positions of the subject and the complement (e.g., the neighbor is running in the garden vs the garden is running in the neighbor). The results showed that for both plausible and implausible sentences, the detection of human movements is greater following presentation of congruent action verbs. These results suggest that the presentation of action verbs affects the subsequent perception of point-light human movements, regardless of the associated semantic context. However, the link between action verbs and judgment of biological movements is strengthened when plausible sentences are presented, as illustrated by the increase in visual detection capacity in plausible congruent conditions. Concerning the analysis of the detection speed, the performance is only affected in plausible sentences with slower response times associated with the presentation of an incongruent action verb. These findings are discussed in light of an embodied mechanism and the domain of biological movement perception.