A pilot study of how the past, present, and future are represented in three-dimensional space.

Numerous studies have shown that the representation of temporal concepts is associated with spatial features such as position and size. In a conventional task called the "Circle Test (CT)," participants are asked to express the relative importance of the past, present, and future and to demonstrate relationships among them by drawing three circles representing the past, present, and future. Studies on various participants, including refugees, patients living with serious illnesses, and adolescents, have used it to understand the temporal perspectives of different test takers. On the other hand, several studies have suggested that concepts of time are represented in three-dimensional (3D) space. It is expected that temporal concepts of the past, present, and future could be recorded using a 3D drawing task. Here we created a 3D version of CT (the "Sphere Test [ST]") to investigate the sagittal representation of time and to record the relative time importance and relatedness, allowing for the shielding relationships and the laws of perspective. We conducted experiments with university students to compare the results from the CT and the ST. Our results suggested that not all on-screen overlapping can be interpreted as representing a connection between two time zones in 3D space. We also found correlations between the chosen sizes of the three circles in the CT and ST, i.e., the on-screen sizes of the past and present circles were positively correlated. In contrast, we observed no correlation between the on-screen sizes of the future circles in the two tests. The alignment pattern along the sagittal axis showed different patterns from the horizontal and vertical axes. In conclusion, this study sheds new light on the third dimension of the spatial representation of time and may help us understand the relationship between temporal perspectives and other factors, including mental health.

Stopwatch training improves cognitive functions in patients with Parkinson's disease.

Parkinson's disease (PD) impairs various cognitive functions, including time perception. Dysfunctional time perception in PD is poorly understood, and no study has investigated the rehabilitation of time perception in patients with PD. We aimed to induce the recovery of time perception in PD patients and investigated the potential relationship between recovery and cognitive functions/domains other than time perception. Sixty patients with PD (27 females) and 20 healthy controls (10 females) were recruited. The participants underwent a feedback training protocol for 4 weeks to improve the accuracy of subjective spatial distance or time duration using a ruler or stopwatch, respectively. They participated in three tests at weekly intervals, each comprising 10 types of cognitive tasks and assessments. After duration feedback training for 1 month, performance on the Go/No-go task, Stroop task, and impulsivity assessment improved in patients with PD, while no effect was observed after distance feedback training. Additionally, the effect of training on duration production correlated with extended reaction time and improved accuracy in the Go/No-go and Stroop tasks. These findings suggest that time perception is functionally linked to inhibitory systems. If the feedback training protocol can modulate and maintain time perception, it may improve various cognitive/psychiatric functions in patients with PD. It may also be useful in the treatment of diseases other than PD that cause dysfunctions in temporal processing.

Pupil size is modulated by the size of equal-luminance gratings.

Pupil size changes with light. For this reason, researchers studying the effect of attention, contextual processing, and arousal on the pupillary response have matched the mean luminance of their stimuli across conditions to eliminate the contribution of differences in light levels. Here, we argue that the match of mean luminance is not enough. In Experiment 1, we presented a circular sinewave grating on a gray background for 2 seconds. The area of the grating could be 3°, 6°, or 9°. The mean luminance of each grating was equal to the luminance of the gray background, such that regardless of the size of the grating there was no change in mean luminance between conditions. Participants were asked to fixate the center of the grating and passively view it. We found that in all size conditions, there was a pupil constriction starting at about 300 ms after stimulus onset, and the pupil constriction increased with the size of the grating. In Experiment 2, when a small grating was presented immediately after the presentation of a large grating (or vice versa), the pupil constriction changed accordingly. In Experiment 3, we replicated Experiment 1 but had the subjects perform an attention-demanding fixation task in one session, and passively view the stimuli in the other. We found that the main effect of task was not significant. In sum, our results show that stimulus size can modulate pupil size robustly and steadily even when the luminance is matched across the different stimuli.

Investigating the perceived timing of sensory events triggering actions in patients with Parkinson's disease and the effects of dopaminergic therapy.

Few studies have investigated if Parkinson's disease (PD), advancing age, or exogenous dopamine therapy affect the perceived timing of past events. Here we show a phenomenon of 'temporal repulsion' of a sensory event relative to an action decision in patients with PD. In these patients, the timing of a sensory event triggering an action was perceived to have occurred earlier in time than it really did. In other words, the event appeared to be pushed away in time from the performance of the action. This finding stands in sharp contrast to the 'temporal binding' we have observed here and elsewhere (Yabe et al., 2017; Yabe & Goodale, 2015) in young healthy participants for whom the perceived onset of a sensory event triggering an action is typically delayed, as if it were pulled towards the action in time. In elderly patients, sensory events were neither repulsed nor pulled toward the action decision event. Exogenous dopamine alleviated the temporal repulsion in PD patients and normalized the temporal binding in healthy elderly controls. In contrast, dopaminergic therapy worsened temporal binding in healthy young participants. We discuss this pattern of findings, relating temporal binding processes to dopaminergic and striatal mechanisms.

Temporal distortion in the perception of actions and events.

In everyday life, actions and sensory events occur in complex sequences, with events triggering actions that in turn give rise to additional events and so on. Earlier work has shown that a sensory event that is triggered by a voluntary action is perceived to have occurred earlier in time than an identical event that is not triggered by an action. In other words, events that are believed to be caused by our actions are drawn forward in time towards our actions. Similarly, when a sensory event triggers an action, that event is again drawn in time towards the action and is thus perceived to have occurred later than it really did. This alteration in time perception serves to bind together events and actions that are causally linked. It is not clear, however, whether or not the perceived timing of a sensory event embedded within a longer series of actions and sensory events is also temporally bound to the actions in that sequence. In the current study, we measured the temporal binding in sequences consisting of two simple dyads of event-action and action-event in a series of manual action tasks: an event-action-event triad (Experiment 1) and an action-event-action triad (Experiment 2). Auditory tones either triggered an action or were presented 250ms after an action was performed. To reduce the influence of sensory events other than the tone, such as a noise associated with pressing a key on a keyboard, we used an optical sensor to detect hand movements where no contact was made with a surface. In Experiment 1, there appeared to be no change in the perceived onset of an auditory tone when the onset of that tone followed a hand movement and then the tone triggered a second hand movement. It was as if the temporal binding between the action and the tone and then the tone and the subsequent action summed algebraically and cancelled each other out. In Experiment 2, both the perceived onset of an initial tone which triggered an action and the perceived onset of a second tone which was presented 250ms after the action were temporally bound to the action. Taken together, the present study suggests that the temporal binding between our actions and sensory events occur separately in each dyad within a longer sequence of actions and events.

Time flies when we intend to act: temporal distortion in a go/no-go task.

Although many of our actions are triggered by sensory events, almost nothing is known about our perception of the timing of those sensory events. Here we show that, when people react to a sudden visual stimulus that triggers an action, that stimulus is perceived to occur later than an identical stimulus that does not trigger an action. In our experiments, participants fixated the center of a clock face with a rotating second hand. When the clock changed color, they were required to make a motor response and then to report the position of the second hand at the moment the clock changed color. In Experiment 1, in which participants made a target-directed saccade, the color change was perceived to occur 59 ms later than when they maintained fixation. In Experiment 2, in which we used a go/no-go paradigm, this temporal distortion was observed even when participants were required to cancel a prepared saccade. Finally, in Experiment 3, the same distortion in perceived time was observed for both go and no-go trials in a manual task in which no eye movements were required. These results suggest that, when a visual stimulus triggers an action, it is perceived to occur significantly later than an identical stimulus unrelated to action. Moreover, this temporal distortion appears to be related not to the execution of the action (or its effect) but rather to the programming of the action. In short, there seems to be a temporal binding between a triggering event and the triggered action.

Temporal order judgments are disrupted more by reflexive than by voluntary saccades.

We do not always perceive the sequence of events as they actually unfold. For example, when two events occur before a rapid eye movement (saccade), the interval between them is often perceived as shorter than it really is and the order of those events can be sometimes reversed (Morrone MC, Ross J, Burr DC. Nat Neurosci 8: 950-954, 2005). In the present article we show that these misperceptions of the temporal order of events critically depend on whether the saccade is reflexive or voluntary. In the first experiment, participants judged the temporal order of two visual stimuli that were presented one after the other just before a reflexive or voluntary saccadic eye movement. In the reflexive saccade condition, participants moved their eyes to a target that suddenly appeared. In the voluntary saccade condition, participants moved their eyes to a target that was present already. Similarly to the above-cited study, we found that the temporal order of events was often misjudged just before a reflexive saccade to a suddenly appearing target. However, when people made a voluntary saccade to a target that was already present, there was a significant reduction in the probability of misjudging the temporal order of the same events. In the second experiment, the reduction was seen in a memory-delay task. It is likely that the nature of the motor command and its origin determine how time is perceived during the moments preceding the motor act.

Treadmill experience alters treadmill effects on perceived visual motion.

Information on ongoing body movements can affect the perception of ambiguous visual motion. Previous studies on "treadmill capture" have shown that treadmill walking biases the perception of ambiguous apparent motion in backward direction in accordance with the optic flow during normal walking, and that long-term treadmill experience changes the effect of treadmill capture. To understand the underlying mechanisms for these phenomena, we conducted Experiment 1 with non-treadmill runners and Experiment 2 with treadmill runners. The participants judged the motion direction of the apparent motion stimuli of horizontal gratings in front of their feet under three conditions: walking on a treadmill, standing on a treadmill, and standing on the floor. The non-treadmill runners showed the presence of downward bias only under the walking condition, indicating that ongoing treadmill walking but not the awareness of being on a treadmill biased the visual directional discrimination. In contrast, the treadmill runners showed no downward bias under any of the conditions, indicating that neither ongoing activity nor the awareness of spatial context produced perception bias. This suggests that the long-term repetitive experience of treadmill walking without optic flow induced the formation of a treadmill-specific locomotor-visual linkage to perceive the complex relationship between self and the environment.

Treadmill locomotion captures visual perception of apparent motion.

A visual illusion of perceived motion direction induced by treadmill locomotion is reported. Directionally ambiguous motions of shifting frames of sinusoidal horizontal gratings are perceived moving downward more frequently when the stimuli are shown in front of the observers' feet while walking on a treadmill. To confirm this effect quantitatively, we asked naive observers to answer whether the direction of the motion of the grating pattern was perceived as upward or downward while they were walking or standing on a treadmill. The frequency of the "downward" response was significantly higher under the walking condition. This effect reveals that treadmill locomotion captures perceived direction of ambiguous motion in accordance with the direction of the optic flow during natural walking. This finding suggests that the effect reflects a perceptual mechanism to compensate for the absence of inputs in the action-perception cycle during locomotion.