Suprathreshold asymmetries in human motion perception

A moving visual field can induce the feeling of self-motion or vection. Illusory motion from static repeated asymmetric patterns creates a compelling visual motion stimulus, but it is unclear if such illusory motion can induce a feeling of self-motion or alter self-motion perception. In these experiments, human subjects reported the perceived direction of self-motion for sway translation and yaw rotation at the end of a period of viewing set visual stimuli coordinated with varying inertial stimuli. This tested the hypothesis that illusory visual motion would influence self-motion perception in the horizontal plane. Trials were arranged into 5 blocks based on stimulus type: moving star field with yaw rotation, moving star field with sway translation, illusory motion with yaw, illusory motion with sway, and static arrows with sway. Static arrows were used to evaluate the effect of cognitive suggestion on self-motion perception. Each trial had a control condition; the illusory motion controls were altered versions of the experimental image, which removed the illusory motion effect. For the moving visual stimulus, controls were carried out in a dark room. With the arrow visual stimulus, controls were a gray screen. In blocks containing a visual stimulus there was an 8s viewing interval with the inertial stimulus occurring over the final 1s. This allowed measurement of the visual illusion perception using objective methods. When no visual stimulus was present, only the 1s motion stimulus was presented. Eight women and five men (mean age 37) participated. To assess for a shift in self-motion perception, the effect of each visual stimulus on the self-motion stimulus (cm/s) at which subjects were equally likely to report motion in either direction was measured. Significant effects were seen for moving star fields for both translation (p = 0.001) and rotation (p<0.001), and arrows (p = 0.02). For the visual motion stimuli, inertial motion perception was shifted in the direction consistent with the visual stimulus. Arrows had a small effect on self-motion perception driven by a minority of subjects. There was no significant effect of illusory motion on self-motion perception for either translation or rotation (p>0.1 for both). Thus, although a true moving visual field can induce self-motion, results of this study show that illusory motion does not.

Heading direction is determined from visual and vestibular cues. Both sensory modalities have been shown to have better direction discrimination for headings near straight ahead. Previous studies of visual heading estimation have not used the full range of stimuli, and vestibular heading estimation has not previously been reported. The current experiments measure human heading estimation in the horizontal plane to vestibular, visual, and spoken stimuli. The vestibular and visual tasks involved 16 cm of platform or visual motion. The spoken stimulus was a voice command speaking a heading angle. All conditions demonstrated direction dependent biases in perceived headings such that biases increased with headings further from the fore-aft axis. The bias was larger with the visual stimulus when compared with the vestibular stimulus in all 10 subjects. For the visual and vestibular tasks precision was best for headings near fore-aft. The spoken headings had the least bias, and the variation in precision was less dependent on direction. In a separate experiment when headings were limited to ±45°, the biases were much less, demonstrating the range of headings influences perception. There was a strong and highly significant correlation between the bias curves for visual and spoken stimuli in every subject. The correlation between visual-vestibular and vestibular-spoken biases were weaker but remained significant. The observed biases in both visual and vestibular heading perception qualitatively resembled predictions of a recent population vector decoder model (Gu et al., 2010) based on the known distribution of neuronal sensitivities.

Effect of the concreteness of robot motion visual stimulus on an event-related potential-based brain-computer interface

1. In the companion paper we reported that the predominant signal of the population of neurons in the lateral intraparietal area (area LIP) of the monkey's posterior parietal cortex (PPC) encode the next intended saccadic eye movement during the delay period of a memory-saccade task. This result predicts that, should be monkey change his intention of what the next saccade will be, LIP activity should change accordingly to reflect the new plan. We tested this prediction by training monkeys to change their saccadic plan on command and recording the activity of LIP neurons across plan changes. 2. We trained rhesus monkeys (Macaca mulatta) to maintain fixation on a light spot as long as this spot remained on. During this period we briefly presented one, two, or three peripheral visual stimuli in sequence, each followed by a delay (memory period, M). After the final delay the fixation spot was extinguished, and the monkey had to quickly make a saccade to the location of the last target to have appeared. The monkey could not predict which stimuli, nor how many, would appear on each trial. He thus had to plan a saccade to each stimulus as it appeared and change his saccade plan whenever a stimulus appeared at a different location. 3. We recorded the M period activity of 81 area LIP neurons (from 3 hemispheres of 2 monkeys) in this task. We predicted that, if a neuron's activity reflected the monkey's planned saccade, its activity should be high while the monkey planned a saccade in the neuron's motor field (MF), and low while the planned saccade was in the opposite direction. The activity of most of the neurons in our sample changed in accordance with our hypothesis as the monkey's planned saccade changed. 4. In one condition the monkey was instructed by visual stimuli to change his plan from a saccade in the neuron's preferred direction to a saccade planned in the opposite direction. In this condition activity decreased significantly (P < 0.05) in 65 (80%) of 81 neurons tested. These neurons' activity changed to reflect the new saccade plan even though the cue for this change was not presented in their RF. 5. As a control we randomly interleaved, among trials requiring a plan change, trials in which the monkey had to formulate two consecutive plans to make a saccade in the neuron's preferred direction. The activity remained unchanged (P < 0.05) in 22 of 31 neurons tested (79%), indicating that the neurons continued to encode the same saccade plan. 6. In a variant of the task, the cue to the location of the required saccade was either a light spot or a noise burst from a loudspeaker. Of 22 neurons tested in this task, 16 (73%) showed activity changes consistent with plan changes cued by visual or auditory stimuli. 7. Alterations in the monkey's intentions, even in the absence of overt behavior, are manifested in altered LIP activity. These activity changes could be induced whether visual or auditory cues were used to indicate the required plan changes. Most LIP neurons thus do not encode only the locations of visual stimuli, but also the intention to direct gaze to specific locations, independently of whether a gaze shift actually occurs.

Visual motion stimuli can sometimes distort our perception of time. This effect is dependent on the apparent speed of the moving stimulus, where faster stimuli are usually perceived lasting longer than slower stimuli. Although it has been shown that neural and cognitive processing of biological motion stimuli differ from non-biological motion stimuli, no study has yet investigated whether perceived durations of biological stimuli differ from non-biological stimuli across different speeds. Here, a prospective temporal reproduction task was used to assess that question. Biological motion stimuli consisted of a human silhouette running in place. Non-biological motion stimuli consisted of a rectangle moving in a pendular way. Amount and plausibility of movement for each stimulus and frame-rate (speed) were evaluated by an independent group of participants. Although the amount of movement perceived was positively correlated to frame rate both for biological and non-biological stimuli, movie clips involving biological motion stimuli were judged to last longer than non-biological motion stimuli only at frame rates for which movement was rated as plausible. These results suggest that plausible representations of biomechanical movement induce additional temporal distortions to those modulated by increases in stimulus speed. Moreover, most studies reporting neural and cognitive differences in the processing of biological and non-biological motion stimuli acquired neurophysiological data using fMRI. Here, we report differences in the processing of biological and non-biological motion stimuli across different speeds using functional near-infrared spectroscopy (fNIRS), a less costly and portable form of neurophysiological data acquisition.

1. Neurons in the pretectal nuclear complex that project to the ipsilateral dorsal lateral geniculate nucleus (LGNd) were identified by antidromic activation after electrical LGNd stimulation in awake cats, and their response properties were characterized to retinal image shifts elicited either by external visual stimulus movements or during spontaneous saccadic eye movements on a stationary visual stimulus, and to saccades in darkness. Eye position was monitored with the use of a scleral search coil and care was taken to assure stability of the eyes during presentation of moving visual stimuli. 2. Of a total sample of 134 cells recorded, 27 neurons were antidromically activated by electrical LGNd stimulation. In addition, responses from neurons that were not activated from the LGNd were also analyzed, including 19 "retinal slip" cells, which selectively respond to slow horizontal stimulus movements, and 21 "jerk" cells, which are specifically activated by rapid stimulus shifts. All recorded neurons were located in the nucleus of the optic tract and in the posterior pretectal nucleus. 3. In the light, neurons identified as projecting to the LGNd responded maximally to saccadic eye movements and to externally generated sudden shifts of large visual stimuli. Slow stimulus drifts did not activate these neurons. Response latencies were shorter and peak activities were increased during saccades compared with pure visual stimulation. No systematic correlation between response latency, response duration, or the number of spikes in the response and saccade direction, saccade amplitude, or saccade duration was found. Saccades and rapid stimulus shifts in the light also activated jerk cells but not retinal slip cells. 4. All 27 antidromically activated neurons also responded to spontaneous saccadic eye movements in complete darkness. Responses to saccades in the dark, however, had longer response latencies and lower peak activities than responses to saccades in light. As in the light, response parameters in darkness seemed not to code specific saccade parameters. Cells that were not activated from LGNd were found to be unresponsive to saccades in the dark. 5. According to their specific activation by saccades in darkness, LGNd-projecting pretectal neurons are termed "saccade neurons" to distinguish them from other pretectal cell populations, in particular from jerk neurons, which show similar response properties in light. 6. The saccade-related activation of pretectal saccade neurons may be used to modulate visual responses of LGNd relay cells following saccadic eye movements. Because the pretectogeniculate projection in cat most likely is GABAergic and terminates on inhibitory LGNd interneurons, its activation may lead to a saccade-locked disinhibition of relay cells. This input could counter the strong inhibition induced in the LGNd after shifts of gaze direction and lead to a resetting of LGNd cell activity.

Selective Engagement of Plasticity Mechanisms for Motor Memory Storage

Hemodynamic responses to visual stimuli in cortex of adults and 3- to 4-year-old children

Decision Making in Recurrent Neuronal Circuits

The simultaneous presentation of a visual and an auditory stimulus can lead to a decrease in people's ability to perceive or respond to the auditory stimulus. In this study, we investigate the effect that threat has upon this phenomenon, known as the Colavita visual dominance effect. Participants performed two blocks of trials containing 40% visual, 40% auditory, and 20% bimodal trials. The first block of trials was identical for all participants, while in the second block, either the visual stimulus (visual threat condition), auditory stimulus (auditory threat condition), or neither stimulus (control condition) was fear-conditioned using aversive electrocutaneous stimuli. We predicted that, when compared with the control condition, this visual dominance effect would increase in the visual threat condition and decrease in the auditory threat condition. This hypothesis was partially supported by the data. In particular, the results showed that the fear-conditioning of the visual stimulus significantly increased the visual dominance effect relative to the control condition. However, the fear-conditioning of the auditory stimulus did not reduce the visual dominance effect but instead increased it slightly. These findings are discussed in terms of the role that attention and arousal play in the dominance of vision over audition.

During a smooth pursuit eye movement of a target stimulus, a briefly flashed stationary background appears to move in the opposite direction as the eye's motion-an effect known as the Filehne illusion. Similar illusions occur in audition, in the vestibular system, and in touch. Recently, we found that the movement of a surface perceived from tactile slip was biased if this surface was sensed with the moving hand. The analogy between these two illusions suggests similar mechanisms of motion processing between the vision and touch. In the present study, we further assessed the interplay between these two sensory channels by investigating a novel paradigm that associated an eye pursuit of a visual target with a tactile motion over the skin of the fingertip. We showed that smooth pursuit eye movements can bias the perceived direction of motion in touch. Similarly to the classical report from the Filehne illusion in vision, a static tactile surface was perceived as moving rightward with a leftward eye pursuit movement, and vice versa. However, this time the direction of surface motion was perceived from touch. The biasing effects of eye pursuit on tactile motion were modulated by the reliability of the tactile and visual stimuli, consistently with a Bayesian model of motion perception. Overall, these results support a modality- and effector-independent process with common representations for motion perception.NEW & NOTEWORTHY The study showed that smooth pursuit eye movement produces a bias in tactile motion perception. This phenomenon is modulated by the reliability of the tactile estimate and by the presence of a visual background, in line with the predictions of the Bayesian framework of motion perception. Overall, these results support the hypothesis of shared representations for motion perception.

Two effects on memory have been described in the literature: the emotional enhancement of memory (EEM) (i.e., an emotional stimulus is better remembered than a neutral stimulus) and the dynamic superiority effect (DSE) (i.e., a moving visual stimulus is better remembered than a static stimulus). However, the DSE has previously only been studied using complex visual stimuli (e.g., video clips). Thus, the first objective of the present study was to examine whether the DSE will be observed with simple visual stimuli (i.e., isolated moving stimuli). The second objective was to examine whether people’s emotional memory will be affected by stimulus motion. We conducted three experiments, two using a free recall task, Experiment 1A (online) and 1B (in-person), and one using a recognition task (in-person). Participants viewed negative, positive, and neutral stimuli in two motion conditions, dynamic and static, and then had to recall or recognize them. In all three experiments, we observed an EEM but no DSE. Thus, our data verify that emotions affect memory performance but provide no evidence of motion effects on memory of simple stimuli.

Observer's active control of visual stimulus movement by the use of computer mouse reduces the flash-lag effect (Ichikawa & Masakura, 2006, Vision Research). This reduction of the flash-lag effect in visual motion depends upon directional relationship between hand movement and visual stimulus movement (Ichikawa & Masakura, 2010 AP&P). These studies indicate that the reduction of the flash-lag effect depends upon the sensory-motor learning of the directional consistency between the hand movement and stimulus movement in everyday-computer use. In this study, we examined how directional relationship between hand movement and stimulus change, which is not involved in every-computer use, affects the reduction of the flash-lag effect if there is no inevitable directional relationship between hand movement and stimulus change. While the luminance of the visual stimulus was controlled by the use of computer-mouse, a flash was presented. Observer judged which of the flash and luminance change stimulus is lighter. We found significant reduction of the flash-lag effect only when the directional relationship between hand movement and stimulus change was fixed. The results suggest that the proprioceptive signal to control the visual stimulus would facilitate the visual processing if the directional relationship between hand movement and stimulus change is consistent.

Modulation of rat cortical area 17 neuronal responses to moving visual stimuli during norepinephrine and serotonin microiontophoresis

The adaptive plasticity of the spatial organization of the vestibuloocular reflex (VOR) has been investigated in intact and canal-plugged primates using 2-h exposure to conflicting visual (optokinetic, OKN) and vestibular rotational stimuli about mutually orthogonal axes (generating torsional VOR + vertical OKN, torsional VOR + horizontal OKN, vertical VOR + horizontal OKN, and horizontal VOR + vertical OKN). Adaptation protocols with 0.5-Hz (+/-18 degrees ) head movements about either an earth-vertical or an earth-horizontal axis induced orthogonal response components as high as 40-70% of those required for ideal adaptation. Orthogonal response gains were highest at the adapting frequency with phase leads present at lower and phase lags present at higher frequencies. Furthermore, the time course of adaptation, as well as orthogonal response dynamics were similar and relatively independent of the particular visual/vestibular stimulus combination. Low-frequency (0. 05 Hz, vestibular stimulus: +/-60 degrees ; optokinetic stimulus: +/-180 degrees ) adaptation protocols with head movements about an earth-vertical axis induced smaller orthogonal response components that did not exceed 20-40% of the head velocity stimulus (i.e., approximately 10% of that required for ideal adaptation). At the same frequency, adaptation with head movements about an earth-horizontal axis generated large orthogonal responses that reached values as high as 100-120% of head velocity after 2 h of adaptation (i.e., approximately 40% of ideal adaptation gains). The particular spatial and temporal response characteristics after low-frequency, earth-horizontal axis adaptation in both intact and canal-plugged animals strongly suggests that the orienting (and perhaps translational) but not inertial (velocity storage) components of the primate otolith-ocular system exhibit spatial adaptability. Due to the particular nested arrangement of the visual and vestibular stimuli, the optic flow pattern exhibited a significant component about the third spatial axis (i.e., orthogonal to the axes of rotation of the head and visual surround) at twice the oscillation frequency. Accordingly, the adapted VOR was characterized consistently by a third response component (orthogonal to both the axes of head and optokinetic drum rotation) at twice the oscillation frequency after earth-horizontal but not after earth-vertical axis 0.05-Hz adaptation. This suggests that the otolith-ocular (but not the semicircular canal-ocular) system can adaptively change its spatial organization at frequencies different from those of the head movement.