Auditory-induced bouncing is a perceptual (rather than a cognitive) phenomenon: Evidence from illusory crescents

The influence of tDCS on perceived bouncing/streaming

Processing ambiguous situations is a constant challenge in everyday life and sensory input from different modalities needs to be integrated to form a coherent mental representation on the environment. The bouncing/streaming illusion can be studied to provide insights into the ambiguous perception and processing of multi-modal environments. In short, the likelihood of reporting bouncing rather than streaming impressions increases when a sound coincides with the moment of overlap between two moving disks. Neuroimaging studies revealed that the right posterior parietal cortex is crucial in cross-modal integration and is active during the bouncing/streaming illusion. Consequently, in the present study, we used transcranial direct current stimulation to stimulate this brain area. In the active stimulation conditions, a 9 cm² electrode was positioned over the P4-EEG position and the 35 cm² reference positioned over the left upper arm. The stimulation lasted 15 min. Each participant did the bouncing/streaming task three times: before, during and after anodal or sham stimulation. In a sample of N = 60 healthy, young adults, we found no influence of anodal tDCS. Bayesian analysis showed strong evidence against tDCS effects. There are two possible explanations for the finding that anodal tDCS over perceptual areas did not modulate multimodal integration. First, upregulation of multimodal integration is not possible using tDCS over the PPC as the integration process already functions at maximum capacity. Second, prefrontal decision-making areas may have overruled any modulated input from the PPC as it may not have matched their decision-making criterion and compensated for the modulation.

Long-term memory representations for audio-visual scenes

In this study, we investigated the nature of long-term memory representations for naturalistic audio-visual scenes. Whereas previous research has shown that audio-visual scenes are recognized more accurately than their unimodal counterparts, it remains unclear whether this benefit stems from audio-visually integrated long-term memory representations or a summation of independent retrieval cues. We tested two predictions for audio-visually integrated memory representations. First, we used a modeling approach to test whether recognition performance for audio-visual scenes is more accurate than would be expected from independent retrieval cues. This analysis shows that audio-visual integration is not necessary to explain the benefit of audio-visual scenes relative to purely auditory or purely visual scenes. Second, we report a series of experiments investigating the occurrence of study-test congruency effects for unimodal and audio-visual scenes. Most importantly, visually encoded information was immune to additional auditory information presented during testing, whereas auditory encoded information was susceptible to additional visual information presented during testing. This renders a true integration of visual and auditory information in long-term memory representations unlikely. In sum, our results instead provide evidence for visual dominance in long-term memory. Whereas associative auditory information is capable of enhancing memory performance, the long-term memory representations appear to be primarily visual.

Context modulates the impact of auditory information on visual anticipation

Research on the impact of auditory information on visual anticipation in tennis suggests that the intensity of racket-ball-contact sounds systematically biases estimates of the ball’s speed, thereby influencing anticipatory judgments. Here we examined whether the effect of auditory information on visual anticipation is dependent on the sport-specific context in two separate experiments. In Exp. 1, participants watched short videos of tennis rallies that were occluded at racket-ball-contact. Racket-ball-contact sounds of the final shot were either present or absent. Participants faced different tasks in two counterbalanced blocks: In one block they estimated the ball’s speed; in the other block they indicated the ball’s landing location. Results showed that participants estimated longer ball flight trajectories and higher ball speeds in the sound present condition than in the sound absent condition. To probe whether this effect is dependent on the sport-specific context, Exp. 2 introduced an abstract (i.e., context-free) version of the previous stimuli. Based on the ball locations in the original videos used in Exp. 1, we rendered new videos that displayed only a moving circle against a blank background. Sine tones replaced the original racket-ball contact sounds. Results showed no impact of sound presence on location anticipation judgments. However, similar to Exp. 1, object speeds were judged to be faster when the final sound was present. Together, these findings suggest that the impact of auditory information on anticipation does not seem to be driven by sound alone, but to be moderated by contextual information.

The effect of perceptual history on the interpretation of causality

The ability to interpret spatiotemporal contingencies in terms of causal relationships plays a key role in human understanding of the external world. Indeed, the detection of such simple properties enables us to attribute causal attributes to interactions between objects. Here, we investigated the degree to which this perception of causality depends on recent experience, as has been found for other low-level properties of visual stimuli. Participants were shown launching sequences of colliding circles with varying collision lags and were asked to report their impression of causality. We found short-term attractive and long-term repulsive and attractive effects of perceptual history on the interpretation of causality. Stimuli directly following a causal impression were more likely to be judged as causal and vice versa. However, prior judgments on less recent (>5) trials biased current perception with both positive/attractive and negative/repulsive influences. We interpret these results in terms of two potential mechanisms: adaptive temporal binding windows and updating of internal representations of causality. Overall, these results demonstrate the important role of prior experience even for causality, a fundamental building block of how we understand our world.

The effect of movement speed on audiovisual temporal integration in streaming-bouncing illusion

Motion perception in real situations is often stimulated by multisensory information. Speed is an essential characteristic of moving objects; however, at present, it is not clear whether speed affects the process of audiovisual temporal integration in motion perception. Therefore, this study used a streaming-bouncing task (a bistable motion perception; SB task) combined with a simultaneous judgment task (SJ task) to explore the effect of speed on audiovisual temporal integration from implicit and explicit perspectives. The experiment had a within-subjects design, two speed conditions (fast/slow), eleven audiovisual conditions [stimulus onset asynchrony (SOA): 0 ms/ ± 60 ms/ ± 120 ms/ ± 180 ms/ ± 240 ms/ ± 300 ms], and a visual-only condition. A total of 30 subjects were recruited for the study. These participants completed the SB task and the SJ task successively. The results showed the following outcomes: (1) the optimal times needed to induce the "bouncing" illusion and maximum audiovisual bounce-inducing effect (ABE) magnitude were much earlier than that for the optimal time of audiovisual synchrony, (2) speed as a bottom-up factor could affect the proportion of "bouncing" perception in SB illusions but did not affect the ABE magnitude, (3) speed could also affect the ability of audiovisual temporal integration in motion perception, and the main manifestation was that the point of subjective simultaneity (PSS) in fast speed conditions was earlier than that of slow speed conditions in the SJ task and (4) the SB task and SJ task were not related. In conclusion, the time to complete the maximum audiovisual integration was different from the optimal time for synchrony perception; moreover, speed could affect audiovisual temporal integration in motion perception but only in explicit temporal tasks.

Tactile temporal offset cues reduce visual representational momentum

The perception of dynamic objects is sometimes biased. For example, localizing a moving object after it has disappeared results in a perceptual shift in the direction of motion, a bias known as representational momentum. We investigated whether the temporal characteristics of an irrelevant, spatially uninformative vibrotactile stimulus bias the perceived location of a visual target. In two visuotactile experiments, participants judged the final location of a dynamic, visual target. Simultaneously, a continuous (starting with the onset of the visual target, Experiments 1 and 2) or brief (33-ms stimulation, Experiment 2) vibrotactile stimulus (at the palm of participant's hands) was presented, and the offset disparity between the visual target and tactile stimulation was systematically varied. The results indicate a cross-modal influence of tactile stimulation on the perceived final location of the visual target. Closer inspection of the nature of this cross-modal influence, observed here for the first time, reveals that the vibrotactile stimulus was likely just taken as a temporal cue regarding the offset of the visual target, but no strong interaction and combined processing of the two stimuli occurred. The present results are related to similar cross-modal temporal illusions and current accounts of multisensory perception, integration, and cross-modal facilitation.

The Relationship Between Illusory Crescents and the Stream/Bounce Effect

We conducted two experiments to evaluate Meyerhoff and Scholl's (2018, Cognition 170, 88-94) hypothesis that illusory crescents contribute to resolutions in audiovisual stream/bounce displays. In Experiment 1, we measured illusory crescent size in the launching effect as a function of speed, overlap, and sound. In Experiment 2, we tabulated stream and bounce responses to similar stimuli with the same speed, sound, and overlap conditions as Experiment 1. Our critical manipulation of target speed spanned the range of values from typical stream/bounce investigations of ∼5 degrees/s up to the target speeds employed by Meyerhoff and Scholl ∼38 degrees/s. We replicated Meyerhoff and Scholl's findings at higher speeds, but not at slower speeds. Critically, we found that speed influenced crescent size judgements and bouncing responses in opposite directions. As target speed increased, illusory crescent size increased (Experiment 1), but the overall percentage of bounce responses decreased (Experiment 2). Additionally, we found that sound failed to enhance illusory crescent size at slower speeds but promotes bouncing responses at all speeds. The disassociation of the effects of speed and sound on illusory crescents with those effects on reported streaming/bouncing in similar displays provides compelling evidence against Meyerhoff and Scholl's hypothesis. Therefore, we conclude that illusory crescents do not account for the pattern of responses attributed to the stream/bounce effect.

Congruent audio-visual stimulation during adaptation modulates the subsequently experienced visual motion aftereffect

Sensory information registered in one modality can influence perception associated with sensory information registered in another modality. The current work focuses on one particularly salient form of such multisensory interaction: audio-visual motion perception. Previous studies have shown that watching visual motion and listening to auditory motion influence each other, but results from those studies are mixed with regard to the nature of the interactions promoting that influence and where within the sequence of information processing those interactions transpire. To address these issues, we investigated whether (i) concurrent audio-visual motion stimulation during an adaptation phase impacts the strength of the visual motion aftereffect (MAE) during a subsequent test phase, and (ii) whether the magnitude of that impact was dependent on the congruence between auditory and visual motion experienced during adaptation. Results show that congruent direction of audio-visual motion during adaptation induced a stronger initial impression and a slower decay of the MAE than did the incongruent direction, which is not attributable to differential patterns of eye movements during adaptation. The audio-visual congruency effects measured here imply that visual motion perception emerges from integration of audio-visual motion information at a sensory neural stage of processing.

Multiple phases of cross-sensory interactions associated with the audiovisual bounce-inducing effect

Using event-related potential (ERP) recordings, the present study investigated the cross-modal neural activities underlying the audiovisual bounce-inducing effect (ABE) via a novel experimental design wherein the audiovisual bouncing trials were induced solely by the ABE. The within-subject (percept-based) analysis showed that early cross-modal interactions within 100-200 ms after sound onset over fronto-central and occipital regions were associated with the occurrence of the ABE, but the cross-modal interaction at a later latency (ND250, 220-280 ms) over fronto-central region did not differ between ABE trials and non-ABE trials. The between-subject analysis indicated that the cross-modal interaction revealed by ND250 was larger for subjects who perceived the ABE more frequently. These findings suggest that the ABE is generated as a consequence of the rapid interplay between the variations of early cross-modal interactions and the general multisensory binding predisposition at an individual level.

Auditory capture of visual apparent motion, both laterally and looming

Traditional tests of multisensory stimuli typically support that vision dominates spatial judgments and audition dominates temporal ones. Here, we examine if unambiguous auditory spatial cues can capture ambiguous visual ones in judgments of direction of apparent motion. The visual motion judgments include both lateral movement and movement in depth, each when coupled with auditory stimuli moving at one of four rates. Experiment 1 tested lateral visual movement judgments (leftward vs rightward) coupled with auditory stimuli that moved laterally. Experiment 2 tested depth visual movement judgments (approaching vs receding) coupled with auditory stimuli that got louder or quieter. Results of Experiment 1 revealed and replicated an overall leftward motion bias, but with additional acoustic capture to experience visual movement away from the side on which sound initially occurred, and no effect of auditory motion speed. Results of Experiment 2 revealed and replicated an approaching motion bias, but with no effect of initial sound intensity, and an additional systematic capture effect of auditory motion speed. Faster changes in acoustic intensity produced larger visual motion capture consistent with the direction of acoustic intensity change. Findings of both experiments generalized over conditions of listening device (head phones vs speakers) and test-setting (Laboratory vs Web-based data-collection). The leftward and approaching motion bias results replicate previous research. Our principal new findings, the auditory motion capture effects, confirm the multisensory nature of dynamic spatial perception and support that extent of inter-sensory capture is a function of the relative reliability of spatial information acquired by each sensory modality.

The Effect of Transient Location on the Resolution of Bistable Visual and Audiovisual Motion Sequences

We examined the attention and inference accounts of audiovisual perception using the stream/bounce display, a visual stimulus wherein two identical objects move toward each other, completely superimpose, then move apart. This display has two candidate percepts: stream past each other or bounce off each other. Presented without additional visual or auditory transients, the motion sequence tends to yield the streaming percept, but when coupled with a tone or flash at the point of coincidence, the response bias flips toward bouncing. We explored two competing accounts of this effect: the attentional hypothesis and the inference hypothesis. Participants watched a series of motion sequences where a transient, when present, occurred at the moment of coincidence either colocalised with the motion sequence (congruent presentation) or on the opposite side of the display (incongruent presentation). Assuming the spotlight or zoom lens metaphor, an attentional account predicts that incongruent presentations should be associated with a higher percentage of bouncing responses than congruent presentations, while the inferential account predicts the opposite effect. No effect was found for tone-only trials. However, in trials containing a visual transient, results showed higher proportions of bounce responses within congruent over incongruent presentations, favouring the inference hypothesis over a spotlight or zoom lens attentional account.

Audiovisual Temporal Perception in Aging: The Role of Multisensory Integration and Age-Related Sensory Loss

Within each sensory modality, age-related deficits in temporal perception contribute to the difficulties older adults experience when performing everyday tasks. Since perceptual experience is inherently multisensory, older adults also face the added challenge of appropriately integrating or segregating the auditory and visual cues present in our dynamic environment into coherent representations of distinct objects. As such, many studies have investigated how older adults perform when integrating temporal information across audition and vision. This review covers both direct judgments about temporal information (the sound-induced flash illusion, temporal order, perceived synchrony, and temporal rate discrimination) and judgments regarding stimuli containing temporal information (the audiovisual bounce effect and speech perception). Although an age-related increase in integration has been demonstrated on a variety of tasks, research specifically investigating the ability of older adults to integrate temporal auditory and visual cues has produced disparate results. In this short review, we explore what factors could underlie these divergent findings. We conclude that both task-specific differences and age-related sensory loss play a role in the reported disparity in age-related effects on the integration of auditory and visual temporal information.

Tactile stimulation disambiguates the perception of visual motion paths

Although visual perception traditionally has been considered to be impenetrable by non-visual information, there are a rising number of reports discussing cross-modal influences on visual perception. In two experiments, we investigated how coinciding vibrotactile stimulation affects the perception of two discs that move toward each other, superimpose in the center of the screen, and then move apart. Whereas two discs streaming past each other was the dominant impression when the visual event was presented in isolation, a brief coinciding vibrotactile stimulation at the moment of overlap biased the visual impression toward two discs bouncing off each other (Experiment 1). Further, the vibrotactile stimulation actually changed perceptual processing by reducing the amount of perceived overlap between the discs (Experiment 2), which has been demonstrated to be associated with a higher proportion of bouncing impressions. We propose that tactile-induced quantitative changes in the visual percept might alter the quality of the visual percept (from streaming to bouncing), thereby adding to the understanding of how cross-modal information interacts with early visual perception and how this interaction influences subsequent visual impressions.