Insightful inference compensates for distorted perception

Introspective agents can recognize the extent to which their internal perceptual experiences deviate from the actual states of the external world. This ability, also known as insight, is critically required for reality testing and is impaired in psychosis, yet very little is known about its cognitive underpinnings. We developed a Bayesian modeling framework and a novel psychophysics paradigm to quantitatively characterize this type of insight while participants experienced a motion-aftereffect illusion. Participants could compensate for the illusion when judging the actual direction of a motion stimulus. Furthermore, confidence, reaction-time, and pupil-dilation data all showed signatures consistent with inferential adjustments in the Bayesian insight model. Our results suggest that people can question what they see and make insightful inferences that incorporate introspective knowledge about internal distortions.

The implied motion aftereffect changes decisions, but not confidence

Viewing static images depicting movement can result in a motion aftereffect: people tend to categorise direction signals as moving in the opposite direction relative to the implied motion in still photographs. This finding could indicate that inferred motion direction can penetrate sensory processing and change perception. Equally possible, however, is that inferred motion changes decision processes, but not perception. Here we test these two possibilities. Since both categorical decisions and subjective confidence are informed by sensory information, confidence can be informative about whether an aftereffect probably results from changes to perceptual or decision processes. We therefore used subjective confidence as an additional measure of the implied motion aftereffect. In Experiment 1 (implied motion), we find support for decision-level changes only, with no change in subjective confidence. In Experiment 2 (real motion), we find equal changes to decisions and confidence. Our results suggest the implied motion aftereffect produces a bias in decision-making, but leaves perceptual processing unchanged.

Cross-modal motion aftereffects transfer between vision and touch in early deaf adults

Previous research on early deafness has primarily focused on the behavioral and neural changes in the intact visual and tactile modalities. However, how early deafness changes the interplay of these two modalities is not well understood. In the current study, we investigated the effect of auditory deprivation on visuo-tactile interaction by measuring the cross-modal motion aftereffect. Consistent with previous findings, motion aftereffect transferred between vision and touch in a bidirectional manner in hearing participants. However, for deaf participants, the cross-modal transfer occurred only in the tactile-to-visual direction but not in the visual-to-tactile direction. This unidirectional cross-modal motion aftereffect found in the deaf participants could not be explained by unisensory motion aftereffect or discrimination threshold. The results suggest a reduced visual influence on tactile motion perception in early deaf individuals.

Contribution of the slow motion mechanism to global motion revealed by an MAE technique

Two different motion mechanisms have been identified with motion aftereffect (MAE). (1) A slow motion mechanism, accessed by a static MAE, is sensitive to high-spatial and low-temporal frequency; (2) a fast motion mechanism, accessed by a flicker MAE, is sensitive to low-spatial and high-temporal frequency. We examined their respective responses to global motion after adapting to a global motion pattern constructed of multiple compound Gabor patches arranged circularly. Each compound Gabor patch contained two gratings at different spatial frequencies (0.53 and 2.13 cpd) drifting in opposite directions. The participants reported the direction and duration of the MAE for a variety of global motion patterns. We discovered that static MAE durations depended on the global motion patterns, e.g., longer MAE duration to patches arranged to see rotation than to random motion (Exp 1), and increase with global motion strength (patch number in Exp 2). In contrast, flicker MAEs durations are similar across different patterns and adaptation strength. Further, the global integration occurred at the adaptation stage, rather than at the test stage (Exp 3). These results suggest that slow motion mechanism, assessed by static MAE, integrate motion signals over space while fast motion mechanisms do not, at least under the conditions used.

A motion aftereffect from viewing other people’s gaze

SummaryRecent work suggests that our brains may generate subtle, false motion signals streaming from other people to the objects of their attention, aiding social cognition. For instance, brief exposure to static images depicting other people gazing at objects made subjects slower at detecting subsequent motion in the direction of gaze, suggesting that looking at someone else’s gaze caused a directional motion adaptation. Here we confirm, using a more stringent method, that viewing static images of another person gazing in a particular direction, at an object, produced motion aftereffects in the opposite direction. The aftereffect was manifested as a change in perceptual decision threshold for detecting left versus right motion. The effect disappeared when the person was looking away from the object. These findings suggest that the attentive gaze of others is encoded as an implied agent-to-object motion that is sufficiently robust to cause genuine motion aftereffects, though subtle enough to remain subthreshold.

Don’t Go Chasing Waterfalls: Motion Aftereffects and the Dynamic Snapshot Theory of Temporal Experience

The philosophical investigation of perceptual illusions can generate fruitful insights in the study of subjective time consciousness. However, the way illusions are interpreted is often controversial. Recently, proponents of the so-called dynamic snapshot theory have appealed to the Waterfall Illusion, a kind of motion aftereffect, to support a particular view of temporal consciousness according to which experience is structured as a series of instantaneous snapshots with dynamic qualities. This dynamism is meant to account for familiar features of the phenomenology of time, such as succession, continuity, and change. Previous theories have typically appealed to a subjective present occupying an interval of time; that is, a “specious present.” I argue, through analysis of motion aftereffect illusions and the rare condition of akinetopsia, i.e. motion-blindness, that the Waterfall Illusion fails to support the dynamic snapshot theory as intended. Furthermore, I suggest that future theories of subjective time should see temporal phenomenology as the result of non-localised processes closely tied to the mechanism underlying consciousness generally.

Invisible Adaptation: The Effect of Awareness on the Strength of the Motion Aftereffect

The ability to process information despite the lack of perceptual awareness is one of the most fascinating aspects of the visual system. Such unconscious processing is often investigated using adaptation, where any presence of the former can be traced by its footprint on aftereffects following the latter. We have investigated the mechanisms of the motion aftereffect (MAE) using random dot displays of varying motion coherence as well as crowding to modulate both the physical as well as the perceptual strength of the adaptation stimulus. Perceptual strength was quantitatively measured as the performance in a forced-choice direction-discrimination task. A motion-nulling technique was used to quantitatively measure the strength of the MAE. We show that the strength of the dynamic MAE is independently influenced by both the physical stimulus strength as well as the subjective perceptual strength, with the effect of the former being more prominent than that of the latter. We further show that the MAE still persists under conditions of subthreshold perception. Our results suggest that perceptual awareness can influence the strength of visual processing, but the latter is not fully dependent on the former and can still take place at its partial or even total absence.

Rotating One’s Head Modulates the Perceived Velocity of Motion Aftereffect

As a prominent illusion, the motion aftereffect (MAE) has traditionally been considered a visual phenomenon. Recent neuroimaging work has revealed increased activities in MT+ and decreased activities in vestibular regions during the MAE, supporting the notion of visual–vestibular interaction on the MAE. Since the head had to remain stationary in fMRI experiments, vestibular self-motion signals were absent in those studies. Accordingly, more direct evidence is still lacking in terms of whether and how vestibular signals modulate the MAE. By developing a virtual reality approach, the present study for the first time demonstrates that horizontal head rotation affects the perceived velocity of the MAE. We found that the MAE was predominantly perceived as moving faster when its direction was opposite to the direction of head rotation than when its direction was the same as head rotation. The magnitude of this effect was positively correlated with the velocity of head rotation. Similar result patterns were not observed for the real motion stimuli. Our findings support a ‘cross-modal bias’ hypothesis that after living in a multisensory environment long-term the brain develops a strong association between signals from the visual and vestibular pathways. Consequently, weak biasing visual signals in the associated direction can spontaneously emerge with the input of vestibular signals in the multisensory brain areas, substantially modulating the illusory visual motion represented in those areas as well. The hypothesis can also be used to explain other multisensory integration phenomena.

Indolent Retinal Peripheries Attenuate Motion Aftereffect

We previously found that the retinal peripheries may not signal the human visual awareness when ‘spatial wrapping’ stimulus has very low contrast, or when the human subjects perform deep inhalation, see reference 19 and 20. In this study, we found that those techniques are able to significantly reduce the motion aftereffect (MAE) too. Namely, when we reduce the contrast of the MAE stimulator, the MAE is significantly reduced. Similarly, when we ask the subjects to perform deep inhalation in the end of viewing a ‘high contrast’ MAE stimulator, the MAE is drastically attenuated. The neurophysiological processes of the previous techniques are vastly different, as explained in our previous work. Namely, significant contrast reduction deactivates the retinal peripheries due to the following reasons; first, extremely low contrast stimulus constricts the pupil that disallows the retinal peripheries from receiving enough light rays to signal the brain actively, second, for extremely low contrast conditions, the center-surround antagonism process in the retinal peripheries might not signal the brain at all. Deep inhalation, however, may cause idle links between the retinal peripheries and their corresponding neurological pathways that eventually signal the visual awareness, a process that is also found to weaken the MAE.