Evaluation of critical flicker-fusion frequency measurement methods using a touchscreen-based visual temporal discrimination task in the behaving mouse.

The critical flicker-fusion frequency (CFF), defined as the frequency at which a flickering light is indistinguishable from a continuous light, is a useful measure of visual temporal resolution. The mouse CFF has been studied by electrophysiological approaches such as recordings of the electroretinogram (ERG) and the visually evoked potential (VEP), but it has not been measured behaviorally. Here we estimated the mouse CFF by using a touchscreen based operant system. The test with ascending series of frequencies and that with randomized frequencies resulted in about 17 and 14 Hz, respectively, as the frequency which could not be distinguished from steady lights. Since the ascending method of limits tend to overestimate the threshold than the descending method, we estimated the mouse CFF to be about 14 Hz. Our results highlight usefulness of the operant conditioning method in measurement of the mouse visual temporal resolution.

Relationship between vection and motion perception in depth.

This study examined the effects of cues to motion in depth - namely, stereoscopic (i.e., changing-disparity cues and interocular velocity differences) and changing-size cues on forward and backward vection. We conducted four experiments in which participants viewed expanding or contracting optical flows with the addition of either or both cues. In Experiment 1, participants reported vection by pressing a button whenever they felt it. After each trial, they also rated the magnitude of the vection (from 0 to 100). In Experiments 2 and 3, the participants rated the perceived velocity and motion-in-depth impression of the flows relative to standard stimuli, respectively. In Experiment 4, the participants rated the perceived depth and distance of the display. We observed enhancements in vection, motion-in-depth impression, and perceived depth and distance when either or both types of cues indicated motion-in-depth, as compared to those when the cues did not (Experiments 1, 3, and 4). The perceived velocity changed with cue conditions only for the high velocity condition (Experiment 2). Correlational analyses showed that the vection can be best explained by the motion-in-depth impression. This was partially supported by the multiple regression analyses. These results indicate that the enhancement of vection caused by cues is related to the impression of motion-in-depth rather than the perceived velocity and perceived three-dimensionality.

Up-down asymmetry in vertical vection.

To investigate whether up-down asymmetry similar to that reported in vertical optokinetic nystagmus (OKN), that is, larger OKN responses for upward motion than for downward motion, would appear in vertical vection, we conducted three experiments. In all three experiments, participants viewed a vertically moving random-dot pattern. In Experiments 1 and 2, participants reported vection using a joystick. After each trial, they were also asked to rate the vection magnitude experienced during the stimulus presentation. In Experiment 3, eye movements and vection magnitude (rated after each trial) in response to the stimulus were measured. The results of Experiment 1 showed larger vection magnitude for the upward motion of the stimulus than for the downward motion of it. However, vection onset latency did not change much with stimulus motion direction. Experiment 2 revealed that the up-down asymmetry in vection manifested progressively during the latter part of the stimulus presentation period. Experiment 3 showed clear up-down asymmetry in both OKN and vection magnitude. These results not only indicate that up-down asymmetry similar to that reported in vertical OKN appears in vertical vection, but they also support the notion that the mechanisms underlying vection and OKN are closely related to each other.

Single stimulus color can modulate vection.

In the present study, we investigated the effects of single color on forward and backward vection. The approaching or receding optical flow observed during forward or backward locomotion was simulated by using random dots with changing size, velocity, and disparity. The dots were presented on a black (Experiments 1 and 2) or white background (Experiment 3) in equiluminant colors; namely, white (or gray), red, yellow, green, or blue. The participant's task was to press and hold one of three buttons whenever they felt vection. The three buttons corresponded to the subjective strength of vection: strong, same, and weak relative to vection induced by the standard modulus. In Experiments 1 and 2, the participants were also asked to rate the strength and direction of vection after each trial. In Experiment 3, they rated the visibility and the perceived velocity of dot motion. Experiment 1 showed that the induced vection was stronger for the chromatic than for the achromatic dots. Particularly at low velocity conditions (±10 km/h), the vection induced for red dots was stronger than that for the other colored dots. Experiment 2 showed that the order effects of stimulus presentation could not explain the findings of Experiment 1. Experiment 3's pattern of results was similar to that of Experiment 1, and this suggested that a luminance artifact between color conditions could not account for Experiment 1's findings. These results suggest that a stimulus color can modulate vection even when a single color is added to the optical flow.

Tradeoff between manual response speed and pursuit accuracy revealed by a deadline procedure.

To examine the tradeoff between manual reaction times (RTs) and smooth pursuit accuracy, we manipulated manual RTs to a visual target presented during pursuit by using a deadline procedure that required different response speeds to a target (300, 400, or 500 ms). Participants attempted to pursue a moving row of circles as accurately as possible, while responding to a target within a preset time. Stimulus velocity and target position were manipulated. As the preset time became shorter, participants responded with faster manual RTs and larger pursuit velocity errors, irrespective of the stimulus velocity, indicating a tradeoff between manual RTs and pursuit accuracy. Pursuit velocity errors were also larger after target onset. These results not only suggest that attentional resources as well as spatial shifts of attention play an important role in maintaining accurate pursuit, but also support the notion that a manual RT task is useful for revealing the operation of attention during pursuit.

Up-down asymmetry in vertical induced motion and optokinetic nystagmus.

We investigated the effects of pursuit effort against the optokinetic nystagmus (OKN) on induced motion (IM) by measuring vertical IM and eye movements. Participants viewed an inducing stimulus (a random dot pattern) moving either upward or downward at the velocity of 10 or 40 °/s. A horizontally moving target (a single dot) was then presented within the inducing stimulus. Participants were asked to pursue the target and report the perceived slant of the target motion path by using a joystick. The results showed that IM magnitude was larger with an upward stimulation than with a downward stimulation. IM magnitude was also larger at 40 °/s than at 10 °/s. The results of eye movements prior to the target presentation showed that OKN was elicited more effectively with an upward stimulation than with a downward stimulation and at 40 °/s than at 10 °/s. OKN was markedly reduced when the target was presented within the inducing stimulus. These results support the oculomotor theory that IM magnitude reflects pursuit effort against OKN in response to an inducing stimulus.

Effect of depth order on linear vection with optical flows.

In the present study, the effects of depth order on forward and backward vection were examined using optical flows simulating motion in depth (i.e., approaching or receding). In an experiment, space extending 10 or 20 m in depth was simulated, and the space was divided into foreground and background spaces. In each space, a random-dot pattern was presented and the binocular disparity, size, and velocity of each dot were continuously manipulated in a way consistent with the depth being simulated. Participants reported whether they perceived vection. Latency, total duration (i.e., the amount of time that participants reported perceiving vection during a 60-s presentation), and strong-vection duration (i.e., the amount of time that participants reported perceiving strong vection) were measured. The results indicated that, even though the dots making up the optical flow were much smaller and slower moving in the background space than in the foreground space, vection was strongly dependent on flow motion in the background space. This supports the idea that the perceptual system uses background stimulus motion as a reliable cue for self-motion perception.

Useful field of view in simulated driving: Reaction times and eye movements of drivers.

To examine the spatial distribution of a useful field of view (UFOV) in driving, reaction times (RTs) and eye movements were measured in simulated driving. In the experiment, a normal or mirror-reversed letter "E" was presented on driving images with different eccentricities and directions from the current gaze position. The results showed significantly slower RTs in the upper and upper left directions than in the other directions. The RTs were significantly slower in the left directions than in the right directions. These results suggest that the UFOV in driving may be asymmetrical among the meridians in the visual field.

Rule for scaling shoulder rotation angles while walking through apertures.

BACKGROUND: When an individual is trying to fit into a narrow aperture, the amplitude of shoulder rotations in the yaw dimension is well proportioned to the relative aperture width to body width (referred to as the critical ratio value). Based on this fact, it is generally considered that the central nervous system (CNS) determines the amplitudes of shoulder rotations in response to the ratio value. The present study was designed to determine whether the CNS follows another rule in which a minimal spatial margin is created at the aperture passage; this rule is beneficial particularly when spatial requirements for passage (i.e., the minimum passable width) become wider than the body with an external object. METHODOLOGY/PRINCIPAL FINDINGS: Eight young participants walked through narrow apertures of three widths (ratio value = 0.9, 1.0, and 1.1) while holding one of three horizontal bars (short, 1.5 and 2.5 times the body width). The results showed that the amplitude of rotation angles became smaller for the respective ratio value as the bar increased in length. This was clearly inconsistent with the general hypothesis that predicted the same rotation angles for the same ratio value. Instead, the results were better explained with a new hypothesis which predicted that a smaller rotation angle was sufficient to produce a constant spatial margin as the bar-length increased in length. CONCLUSION: The results show that, at least under safe circumstances, the CNS is likely to determine the amplitudes of shoulder rotations to ensure the minimal spatial margin being created at one side of the body at the time of crossing. This was new in that the aperture width subtracted from the width of the body (plus object) was taken into account for the visuomotor control of locomotion through apertures.

The minimal time required to process visual information in visual search tasks measured by using gaze-contingent visual masking.

To estimate the minimal time required to process visual information (i.e., "effective acquisition time") during a visual search task, we used a gaze-contingent visual masking method. In the experiment, an opaque mask that restricted the central vision was presented at a current gaze position. We manipulated a temporal delay from a gaze shift to mask movement. Participants were asked to search for a target letter (T) among distractor letters (L)s as quickly as possible under various delays. The results showed that the reaction times and search rate decreased when the delay was increased. When the delay was longer than 50 ms, the reaction times and search rate reached a plateau. These results indicate that the effective acquisition time during the visual search task used in the study is equal to or less than 50 ms. The present study indicates that the gaze-contingent visual masking method used is useful for revealing the effective acquisition time.

Attentional capture without awareness in complex visual tasks.

Abrupt onsets of visual cues capture an observer's attention, even when the cues do not reach the observer's visual awareness. In the present study, we investigated the effects of subthreshold cues on the performance of a useful field of view task. Participants localized a target stimulus presented in the peripheral visual field while identifying a character presented at the fovea. Before the presentation of central and peripheral targets, a suprathreshold or subthreshold cue indicating a likely location of the peripheral target was presented. We found that the suprathreshold cue led to both a benefit in the valid trials and cost in the invalid trials, while the subthreshold cue produced only a benefit in the valid trials without a cost in the invalid trials. Similar patterns of results were also observed when the cue preceded the targets by 10-200 ms, although a small cost was observed for the 12 deg eccentricity at the stimulus onset asynchronies of 50 ms and 100 ms in the subthreshold condition. These results indicate that attentional capture occurs without awareness of the cue and suggest that the effect of the cue on the spatial shift of attention would be different between the suprathreshold and subthreshold conditions.

Spatial attention and reaction times during smooth pursuit eye movement.

To examine the spatial shift of attention during smooth pursuit, we measured reaction times (RTs) to a visual target that appeared during pursuit. Participants pursued a moving row of circular frames and responded to a target presented within one of the frames. The results showed large RT differences between stimulus velocities up to 5º/s and 10º/s or above. RTs were faster for a target appearing in the pursuit direction than for one in the opposite direction. When an auditory precue was presented, the RTs during pursuit at 10º/s were faster with increases in the stimulus onset asynchrony (SOA) between the cue and the target. Furthermore, RTs were faster in the cued than in the uncued direction. These results not only support the idea that RTs during pursuit reflect the operation of attention, but also suggest that attention during pursuit can be shifted by the abrupt onset of a target stimulus and/or by prior information regarding the onset of a target stimulus.

Athletic experience influences shoulder rotations when running through apertures.

In order to pass through apertures safely and efficiently, individuals must perceive the width of the aperture relative to (1) the width of the person-plus-object system and to (2) their (anticipated) movement speed. The present study investigated whether athletes who have extensive experience playing sports that require running through narrow spaces while wearing shoulder pads control their shoulder rotations differently while performing this behavior than athletes who lack such experience. Groups of athletes with experience competing in different sports (American football, rugby, and control athletes) performed a behavioral task in which they ran or walked between two tucking dummies with or without wearing shoulder pads. They also performed a psychophysical task in which they reported perceived width of the body and shoulder pads. When running through the apertures, the athletes who played American football exhibited smaller magnitudes and later onset of shoulder rotations than control athletes. No such difference was found when walking through the apertures. There was no difference in perception of the width of the shoulder pads among three groups. These findings suggest that performance of this behavior is action-scaled and task-specific.

Tradeoff between response speed and pursuit accuracy.

We examined simple and choice reaction times (RTs) to a visual target that appears during smooth pursuit. Participants pursued a moving fixation stimulus accurately before a target stimulus was presented either above or below the fixation stimulus. In the simple RT task, the participants responded to the onset of the target as soon as possible. In the choice RT task, they indicated the target position, i.e., above or below the fixation stimulus, as soon and as accurately as possible. The results showed that, in both tasks, the RTs during smooth pursuit at 10 degrees /s were longer than those during stationary fixation, and the RTs decreased as the fixation stimulus velocity further increased to 40 degrees /s. Since pursuit gains (the ratio of eye velocity to fixation stimulus velocity) decreased as the fixation stimulus velocity increased, these results suggest that there is a tradeoff between pursuit accuracy and RT.