The proposal that the processing of visual time might rely on a network of distributed mechanisms that are vision-specific and timescale-specific stands in contrast to the classical view of time perception as the product of a single supramodal clock. Evidence showing that some of these mechanisms have a sensory component that can be locally adapted is at odds with another traditional assumption, namely that time is completely divorced from space. Recent evidence suggests that multiple timing mechanisms exist across and within sensory modalities and that they operate in various neural regions. The current review summarizes this evidence and frames it into the broader scope of models for time perception in the visual domain.

Multiple channels of visual time perception

As perception of time is fundamental for action planning and execution, we investigated how action distorts the perception of visual duration. Participants adapted to tapping in midair for a few seconds, either slowly or quickly, then judged the relative duration of 2 drifting gratings, 1 spatially coincident with the tapped region and the other in the opposite field. Fast tapping decreased apparent duration in the tapping region while slow tapping increased it. The effect was spatially specific in external (not body-centered) coordinates, occurring within a 10° region centered on the tapping hand. Within this space, motor adaptation similarly distorts visual numerosity, suggesting common mechanisms for number and time. However, motor adaptation did not affect the perception of speed, a lower level visual property, suggesting that the interactions were at a high level of processing. These results reinforce studies that suggest that visual time perception is coupled with action and suggest the existence of multiple local visuomotor clocks. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

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Distortions of visual time induced by motor adaptation.

Perceived time undergoes distortions when we prepare and perform movements, showing compression and/or expansion for visual, tactile and auditory stimuli. However, the actual motor system contribution to these time distortions is far from clear. In this study we investigated visual time perception during preparation of isometric contractions and real movements of the hand in two different directions (right/left). Comparable modulations of visual event-timing are found in the isometric and in the movement condition, excluding explanations based on movement-induced sensory masking or attenuation. Most importantly, and surprisingly, visual time depends on the movement direction, being expanded for hand movements pointing away from the body and compressed in the other direction. Furthermore, the effect of movement direction is not constant, but rather undergoes non-monotonic modulations in the brief moments preceding movement initiation. Our findings indicate that time distortions are strongly linked to the motor system, and they may be unavoidable consequences of the mechanisms subserving sensory-motor integration.

/pdf/perceived-visual-time-depends-on-motor-preparation-and-4vzkjctxtn.pdf

Perceived visual time depends on motor preparation and direction of hand movements

How Movements Shape the Perception of Time.

Temporal processing is fundamental for an accurate synchronization between motor behaviour and sensory processing. Here, we investigate how motor timing during rhythmic tapping influences perception of visual time. Participants listen to a sequence of four auditory tones played at 1 Hz and continue the sequence (without auditory stimulation) by tapping four times with their finger. During finger tapping, they are presented with an empty visual interval and are asked to judge its length compared to a previously internalized interval of 150 ms. The visual temporal estimates show non-monotonic changes locked to the finger tapping: perceived time is maximally expanded at halftime between the two consecutive finger taps, and maximally compressed near tap onsets. Importantly, the temporal dynamics of the perceptual time distortion scales linearly with the timing of the motor tapping, with maximal expansion always being anchored to the centre of the inter-tap interval. These results reveal an intrinsic coupling between distortion of perceptual time and production of self-timed motor rhythms, suggesting the existence of a timing mechanism that keeps perception and action accurately synchronized.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2018.1597

Rhythmic motor behaviour influences perception of visual time.

The influence of body movements on visual time perception is receiving increased attention. Past studies showed apparent expansion of visual time before and after the execution of hand movements and apparent compression of visual time during the execution of eye movements. Here we examined whether the estimation of sub-second time intervals between visual events is expanded, compressed, or unaffected during the execution of hand movements. The results show that hand movements, at least the fast ones, reduced the apparent time interval between visual events. A control experiment indicated that the apparent time compression was not produced by the participants’ involuntary eye movements during the hand movements. These results, together with earlier findings, suggest hand movement can change apparent visual time either in a compressive way or in an expansive way, depending on the relative timing between the hand movement and visual stimulus.

/pdf/apparent-time-interval-of-visual-stimuli-is-compressed-3aepvtezc2.pdf

Apparent time interval of visual stimuli is compressed during fast hand movement.

We actively move our hands and eyes when exploring the external world and gaining information about object’s attributes. Previous studies showing that how we touch might be related to how we felt led us to consider whether we could decode observers’ subjective tactile experiences only by analyzing their exploratory movements without explicitly asking how they perceived. However, in those studies, explicit judgment tasks were performed about specific tactile attributes that were prearranged by experimenters. Here, we systematically investigated whether exploratory movements can explain tactile ratings even when participants do not need to judge any tactile attributes. While measuring both hand and eye movements, we asked participants to touch materials freely without judging any specific tactile attributes (free-touch task) or to evaluate one of four tactile attributes (roughness, hardness, slipperiness, and temperature). We found that tactile ratings in the judgment tasks correlated with exploratory movements even in the free-touch task and that eye movements as well as hand movements correlated with tactile ratings. These results might open up the possibility of decoding tactile experiences by exploratory movements.

Linkage between Free Exploratory Movements and Subjective Tactile Ratings

When we acquire tactile information about an object's surface, we actively move our hands. Past studies have shown a correlation between participants’ (i.e., touchers’) hand motion in tactile exploration and the evaluated tactile attributes of the object, which suggests that tactile perception can be estimated from statistical analysis of touchers’ hand motion. Though it has been reported that the statistical analysis of hand motion can indeed estimate tactile perception, whether humans can estimate tactile perception by observing the hand motion of others remains unclear. To investigate this, we conducted experiments wherein observers watched point-light moving hands of touchers in tactile exploration and evaluated the material being touched. Our results show that, although observers’ estimation of touchers’ perception was not accurate, observers extracted information from touchers’ hand motion for estimation, and the correlations within observers’ estimation were high. These results suggest that human observers can estimate tactile perception through visual observation of the hand motion of others by adopting common strategies about the relationships between touchers’ hand motion and tactile perception.

Estimating Tactile Perception by Observing Explorative Hand Motion of Others

Imposing a delay between an action (e.g., a limb movement) and its related visual feedback (e.g., a cursor movement on the display) induces a peculiar sensation of heaviness or stiffness. Earlier studies have examined this delay-induced heaviness or stiffness sensation in relation to the non-arbitrary causal relationship between an action and its effect. Here, “non-arbitrary causal relationship” means that an action produces a specific and deterministic pattern of visual feedback; for example, a leftward limb movement consistently and deterministically causes a leftward visual motion. In modern graphical user interfaces, on the other hand, users often control visual information by pressing keys, wherein the relationship between the keystroke and the change in visual information is arbitrary. The present study examined whether the sensation of heaviness, stiffness and bumpiness could be caused when participants' keystroke produced a delayed arbitrary visual feedback. Participants were asked to press and hold down an assigned key to cause temporal luminance changes in a square centered on the display, an arbitrary visual feedback of their keystroke. Not only the onset delay of the temporal luminance change from the participant's keystroke but also the speed of the temporal luminance change were examined as a visual cue to heaviness, stiffness, or bumpiness. In Experiment 1, the participants' task was to give a rating for the strength of the heaviness, stiffness, or bumpiness perceived when they pressed the key. Our results showed that the heaviness and stiffness ratings increased as the delay increased and decreased as the speed increased. To check whether the manipulation of the delay and speed of the visual feedback caused changes in the subjective evaluation of sensorimotor incongruence, in Experiment 2, we asked the participants to give a rating for the sense of agency. The rating scores decreased as the delay increased and increased as the speed increased. The delay and speed influenced the rating scores for the sense of agency in the opposite direction to those for heaviness/stiffness. We discuss that the brain determines the heaviness and stiffness during a keystroke based on internalized statistics relating to the delay and speed of the action feedback.

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Delay and Speed of Visual Feedback of a Keystroke Cause Illusory Heaviness and Stiffness

When sandwiching two moving parallel metallic wires between both hands, one often experiences an unexpected tactile sensation known as the “velvet hand illusion” (VHI). Researchers have revealed the optimal conditions for inducing VHI, while the subjective nature of VHI remains obscure. In this article, we conducted a psychophysical experiment to investigate the quality and magnitude of the illusory sensation felt during VHI. Participants were asked to evaluate the tactile sensation of moving wires by giving tactile adjective and intensity ratings of the illusory sensation. In the same experiment, for the sake of comparison, participants also rated the sensation for various common materials one may encounter in daily life. We found that, as the intensity of the illusory sensation increased, the tactile sensation became softer, wetter, warmer, and more favorable. We also found that, when a strong illusion was reported, the sensation was similar to those for leather and fabrics rather than metallic wire, which suggests that the illusion indeed changes the perceived material category. These findings provide a better characterization of VHI as well as a better understanding of tactile texture perception.

/pdf/describing-the-sensation-of-the-velvet-hand-illusion-in-12amkuy2ga.pdf

Takumi Yokosaka

Papers

Apparent time interval of visual stimuli is compressed during fast hand movement.

Linkage between Free Exploratory Movements and Subjective Tactile Ratings

Estimating Tactile Perception by Observing Explorative Hand Motion of Others

Delay and Speed of Visual Feedback of a Keystroke Cause Illusory Heaviness and Stiffness

Describing the Sensation of the ‘Velvet Hand Illusion’ in Terms of Common Materials