Occluded motion alters event perception

We employed audiovisual stream/bounce displays, in which two moving objects with crossing trajectories are more likely to be perceived as bouncing off, rather than streaming through, each other when a brief sound is presented at the coincidence of the two objects. However, Kawachi and Gyoba (Perception 35:1289–1294, 2006b) reported that the presence of an additional moving object near the two objects altered the perception of a bouncing event to that of a streaming event. In this study, we extended this finding and examined whether alteration of the event perception could be induced by the visual context, such as by occluded object motion near the stream/bounce display. The results demonstrated that even when the sound was presented, the continuous occluded motion strongly biased observers’ percepts toward the streaming percept during a short occlusion interval (approximately 100 ms). In contrast, when the continuous occluded motion was disrupted by introducing a spatiotemporal gap in the motion trajectory or by removing occlusion cues such as deletion/accretion, the bias toward the streaming percept declined. Thus, we suggest that a representation of object motion generated under a limited occlusion interval interferes with audiovisual event perception.     

How visual spatial attention alters perception

Visual attention is essential for visual perception. Spatial attention allows us to grant priority in processing and selectively process information at a given location. In this paper, I explain how two kinds of spatial attention: covert (allocated to the target location, without accompanying eye movements) and presaccadic (allocated to the location of the upcoming saccade’s target) affect performance and alter appearance. First, I highlight some behavioral and neuroimaging research on covert attention, which alters performance and appearance in many basic visual tasks. Second, I review studies showing that presaccadic attention improves performance and alters appearance at the saccade target location. Further, these modulations change the processing of feature information automatically, even when it is detrimental to the task at hand. We propose that saccade preparation may support transsaccadic integration. Systematically investigating the common and differential characteristics of covert attention and presaccadic attention will continue to further our understanding of the pervasive selective processing of information, which enables us to make sense of our complex visual world.     

Voluntary action alters the perception of visual illusions

Attention, Perception, & Psychophysics - “Intentional binding” refers to the finding that people judge voluntary actions and their effects as having occurred closer together in time...     

A theory of visual interpolation in object perception

We describe a new theory explaining the perception of partly occluded objects and illusory figures, from both static and kinematic information, in a unified framework. Three ideas guide our approach. First, perception of partly occluded objects, perception of illusory figures, and some other object perception phenomena derive from a single boundary interpolation process. These phenomena differ only in respects that are not part of the unit formation process, such as the depth placement of units formed. Second, unit formation from static and kinematic information can be treated in the same general framework. Third, spatial and spatiotemporal discontinuities in the boundaries of optically projected areas are fundamental to the unit formation process. Consistent with these ideas, we develop a detailed theory of unit formation that accounts for most cases of boundary perception in the absence of local physical specification. According to this theory, discontinuities in the first derivative of projected edges are initiating conditions for unit formation. A formal notion of relatability is defined, specifying which physically given edges leading into discontinuities can be connected to others by interpolated edges. Intuitively, relatability requires that two edges be connectable by a smooth, monotonic curve. The roots of the discontinuity and relatability notions in ecological constraints on object perception are discussed. Finally, we elaborate our approach by discussing related issues, some new phenomena, connections to other approaches, and issues for future research.     

The visual and haptic perception of natural object shape

In this study, we evaluated observers' ability to compare naturally shaped three-dimensional (3-D) objects, using their senses of vision and touch. In one experiment, the observers haptically manipulated 1 object and then indicated which of 12 visible objects possessed the same shape. In the second experiment, pairs of objects were presented, and the observers indicated whether their 3-D shape was the same or different. The 2 objects were presented either unimodally (vision-vision or haptic-haptic) or cross-modally (vision-haptic or haptic-vision). In both experiments, the observers were able to compare 3-D shape across modalities with reasonably high levels of accuracy. In Experiment 1, for example, the observers' matching performance rose to 72% correct (chance performance was 8.3%) after five experimental sessions. In Experiment 2, small (but significant) differences in performance were obtained between the unimodal vision-vision condition and the two cross-modal conditions. Taken together, the results suggest that vision and touch have functionally overlapping, but not necessarily equivalent, representations of 3-D shape.     

Categorical perception of relative orientation in visual object recognition

The purpose of the present investigation was to determine whether the orientation between an object's parts is coded categorically for object recognition and physical discrimination. In three experiments, line drawings of novel objects in which the relative orientation of object parts varied by steps of 30 degrees were used. Participants performed either an object recognition task, in which they had to determine whether two objects were composed of the same set of parts, or a physical discrimination task, in which they had to determine whether two objects were physically identical. For object recognition, participants found it more difficult to compare the 0 degrees and 30 degrees versions and the 90 degrees and 60 degrees versions of an object than to compare the 30 degrees and 60 degrees versions, but only at an extended interstimulus interval (ISI). Categorical coding was also found in the physical discrimination task. These results suggest that relative orientation is coded categorically for both object recognition and physical discrimination, although metric information appears to be coded as well, especially at brief ISIs.     

Attention level oscillations during visual perception of moving stimuli

Optokinetic nystagmus (OKN) pursuit phase velocity oscillations were studied in seven undergraduates during repeated 4 min presentation of optokinetic stimuli. The following variable parameters of the stimuli motion were used with each subject: horizontal direction, angular velocity (AV), and frequency-to-velocity ratio. AV of the OKN pursuit phases was found to decrease markedly within the first 30 sec of stimuli presentation with its successive increase and variously marked oscillations. Gradual decrease of the AV of OKN pursuit phases was observed at the end of the whole examination as compared to its beginning already within 4 min presentation of the moving stimuli. The results are discussed from the point of view of the arousal, and the activation components of visual attention.     

The effect of object and event orientation on perception of biological motion

Detection and recognition of point-light walking is reduced when the display is inverted, or turned upside down. This indicates that past experience influences biological motion perception. The effect could be the result of either presenting the human form in a novel orientation or presenting the event of walking in a novel orientation, as the two are confounded in the case of walking on feet. This study teased apart the effects of object and event orientation by examining detection accuracy for upright and inverted displays of a point-light figure walking on his hands. Detection of this walker was greater in the upright display, which had a familiar event orientation and an unfamiliar object orientation, than in the inverted display, which had a familiar object orientation and an unfamiliar event orientation. This finding supports accounts of event perception and recognition that are based on spatiotemporal patterns of motion associated with the dynamics of an event.     

Erratum to: Voluntary action alters the perception of visual illusions

Attention, Perception, & Psychophysics -     

The stream/bounce effect occurs for luminance- and disparity-defined motion targets

We generalised the stream/bounce effect to dynamic random element displays containing luminance- or disparity-defined targets. Previous studies investigating audio-visual interactions in this context have exclusively employed motion sequences with luminance-defined disks or squares and have focused on properties of the accompanying brief stimuli rather than the visual properties of the motion targets. We found that the presence of a brief sound temporally close to coincidence, or a visual flash at coincidence significantly promote bounce perception for motion targets defined by either luminance contrast or disparity contrast. A brief tone significantly promoted bouncing of luminance-defined targets above a no-sound baseline when it was presented at least 250 ms before coincidence and 100 ms after coincidence. A similar pattern was observed for disparity-defined targets, though the tone promoted bouncing above the no-sound baseline when presented at least 350 ms before and 300 ms after coincidence. We further explored the temporal properties of audio-visual interactions for these two display types and found that bounce perception saturated at similar durations after coincidence. The stream/bounce illusion manifests itself in dynamic random-element displays and is similar for luminance- and disparity-defined motion targets.     

Body ownership affects visual perception of object size by rescaling the visual representation of external space

Size perception is most often explained by a combination of cues derived from the visual system. However, this traditional cue approach neglects the role of the observer’s body beyond mere visual comparison. In a previous study, we used a full-body illusion to show that objects appear larger and farther away when participants experience a small artificial body as their own and that objects appear smaller and closer when they assume ownership of a large artificial body (“Barbie-doll illusion”; van der Hoort, Guterstam, & Ehrsson, PLoS ONE, 6(5), e20195, 2011). The first aim of the present study was to test the hypothesis that this own-body-size effect is distinct from the role of the seen body as a direct familiar-size cue. To this end, we developed a novel setup that allowed for occlusion of the artificial body during the presentation of test objects. Our results demonstrate that the feeling of ownership of an artificial body can alter the perceived sizes of objects without the need for a visible body. Second, we demonstrate that fixation shifts do not contribute to the own-body-size effect. Third, we show that the effect exists in both peri-personal space and distant extra-personal space. Finally, through a meta-analysis, we demonstrate that the own-body-size effect is independent of and adds to the classical visual familiar-size cue effect. Our results suggest that, by changing body size, the entire spatial layout rescales and new objects are now perceived according to this rescaling, without the need to see the body.     

Visual behavior and perception of trajectories of moving objects with visual occlusion

Experienced athletes in sports with moving objects have shown greater skill when using visual information to anticipate the direction of a moving object than nonexperienced athletes of those sports. Studies have shown that expert athletes are more effective than novices in occlusion situations in the first stages of the sports sequence. In this study, 12 athletes with different competitive experience in sports with moving objects viewed a sequence of tennis ball launches with and without visual occlusion, launched by a ball-shooting machine toward different areas with respect to the participant's position. The relation among visual behavior, occlusion time, and the precision of the task is reviewed. The spot where the balls bounced was analysed by a digital camera and visual behavior by an Eye Tracking System. Analysis showed that the nonexperienced athletes made significantly more errors and were more variable in visual occlusion conditions. Participants had a stable visual search strategy.     

The way the ball bounces: visual and auditory perception of elasticity and control of the bounce pass

Human observers may perceive not only spatial and temporal dimensions of the environment, but also dynamic physical properties that are useful for the control of behavior. A study is presented in which visual and auditory perception of elasticity in bouncing objects, which was specified by kinematic (spatiotemporal) patterns of object motion, were examined. In experiment 1, observers could perceive the elasticity of a bouncing ball and were able to regulate the impulse applied to the ball in a bounce pass. In experiments 2 and 3, it was demonstrated that visual perception of elasticity was based on relative height information, when it was available, and on the duration of a single period under other conditions. Observers did not make effective use of velocity information. In experiment 4, visual and auditory period information were compared and equivalent performance in both modalities was found. The results are interpreted as support for the view that dynamic properties of environmental events are perceived by means of kinematic information.     

Learning by selection: visual search and object perception in young infants

The authors examined how visual selection mechanisms may relate to developing cognitive functions in infancy. Twenty-two 3-month-old infants were tested in 2 tasks on the same day: perceptual completion and visual search. In the perceptual completion task, infants were habituated to a partly occluded moving rod and subsequently presented with unoccluded broken and complete rod test stimuli. In the visual search task, infants viewed displays in which single targets of varying levels of salience were cast among homogeneous static vertical distractors. Infants whose posthabituation preference indicated unity perception in the completion task provided evidence of a functional visual selective attention mechanism in the search task. The authors discuss the implications of the efficiency of attentional mechanisms for information processing and learning.     

The relationship between visual persistence and event perception in bistable motion display

Observers viewed two alternating frames, each consisting of three rectangular bars displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three bars moving as a whole (group motion), and at short IFIs the overlapping elements in the two frames appeared stationary, while the third element appeared to move from one end of the display to the other (element motion). The upper temporal limit for perceiving element motion was reduced when bars with blurred edges were used and when either frame duration or bar size was increased. However, when inner and outer elements had different sizes, the element motion percept was dominant up to 230 ms IFI. These findings may be interpreted in terms of spatial tuning of motion mechanisms involved in the perception of bistable apparent motion.     

Infant perception of a manual pick-up event

Manual pick-up of an object is a simple causal event frequently observed by infants. A habituation-recovery of looking technique with filmed stimuli is used in experiments which seek to investigate aspects of the perception and encoding of such events in infants. In the first study with 28-week-olds, it is found that ‘lateral mirror-image’ pick-ups are hardly discriminable, while a change in the contact relation of hand and object is readily discriminable. In the second, again with 28-week-olds, the discriminability of the contact relation appears to be specific to a dynamic context involving a hand (rather than another inanimate object). The results of a further experiment make it appear unlikely that the previous results were simply due to the partial occlusion of the picked-up object produced by the grasping. The implications of these results for infant perception of causality are briefly considered.     

Binocular masking induced by a moving object

Movement in a part of either of two binocular fields can, under some conditions, produce temporary obliteration of the corresponding part of the other field. This paper is a mainly qualitative study of this rather surprising phenomenon. The effect is found to increase from the fovea to the periphery, to be greatest at a velocity of about 20° visual angle per sec. and to vary with the orientation of the fixation point in the visual field. Some further lines of research designed to elucidate the relation of the effect described here to certain other visual phenomena are suggested.