Comment and Reply Why eye movements and perceptual factors have to be controlled in studies on “representational momentum”

In order to study memory of the final position of a smoothly moving target, Hubbard (e.g., Hubbard & Bharucha, 1988) presented smooth stimulus motion and used motor responses. In contrast, Freyd (e.g., Freyd & Finke, 1984) presented implied stimulus motion and used the method of constant stimuli. The same forward error was observed in both paradigms. However, the processes underlying the error may be very different. When smooth stimulus motion is followed by smooth pursuit eye movements, the forward error is associated with asynchronous processing of retinal and extraretinal information. In the absence of eye movements, no forward displacement is observed with smooth motion. In contrast, implied motion produces a forward error even without eye movements, suggesting that observers extrapolate the next target step when successive target presentations are far apart. Finally, motor responses produce errors that are not observed with perceptual judgments, indicating that the motor system may compensate for neuronal latencies.     

Attention maintains mental extrapolation of target position: irrelevant distractors eliminate forward displacement after implied motion

Observers' judgments of the final position of a moving target are typically shifted in the direction of implied motion ("representational momentum"). The role of attention is unclear: visual attention may be necessary to maintain or halt target displacement. When attention was captured by irrelevant distractors presented during the retention interval, forward displacement after implied target motion disappeared, suggesting that attention may be necessary to maintain mental extrapolation of target motion. In a further corroborative experiment, the deployment of attention was measured after a sequence of implied motion, and faster responses were observed to stimuli appearing in the direction of motion. Thus, attention may guide the mental extrapolation of target motion. Additionally, eye movements were measured during stimulus presentation and retention interval. The results showed that forward displacement with implied motion does not depend on eye movements. Differences between implied and smooth motion are discussed with respect to recent neurophysiological findings.     

Representational Momentum Beyond Internalized Physics

Abstract— Prediction of future motion is necessary in order to successfully deal with moving objects. Implicit measures have been used to evaluate the sources of information used in this task. For instance, observers may be asked to localize the final position of a moving target. Judgments have been found to be displaced in the direction of motion (forward displacement), suggesting that observers have internalized a mental analogue of physical momentum. However, more recent studies have shown that forward displacement may not be caused by cognitive mechanisms alone. Rather, predictive mechanisms at the perceptual and motor levels may contribute to the forward error. Supporting the notion that mechanisms of anticipation may be embodied, the forward error was found to depend on the execution of eye and pointing movements. Also, forward displacement depended on the motion type that was presented (smooth vs. jerky or implied), which suggests that attention moves to the next expected target position to facilitate responses to this position.     

Representational momentum for rotations in depth: effects of shadings and axis

Representational momentum is a positive memory distortion for an object's final position following the presentation of an implied event (J.J. Freyd, 1987). Positive memory distortions occur when observers accept test positions beyond the final presented position, or forward along the implied trajectory, as the same more readily than positions behind the final position. Four experiments explored implied events depicting rotations about various depth axes in shaded and silhouette conditions. Positive memory distortions were observed for all depth rotations under certain shading conditions, with some differences in the size of the distortion between axes. No directional effects (e.g., right vs. left) were observed. The overall positive memory distortions observed for depth rotations contrasted with the negative distortions previously observed for translation motion in depth (T.L. Hubbard, 1995 ).     

线索提示对表征动量的影响

研究结合线索提示和表征动量范式,实验1、2均采用2有无线索(有线索,无线索)×4诱导期间时距(1250ms,1750ms,2250ms,2750ms)混合实验设计,探讨线索呈现的加工阶段和时距对表征动量的影响。实验1恒定保持间隔时距,在不同时距的诱导期间呈现线索,发现线索主效应不显著,但表征动量呈减小趋势;时距主效应不显著。实验2变化诱导时距,在恒定的保持间隔呈现线索,发生向后偏移现象,线索主效应显著;时距主效应不显著。研究结果表明,随着注意的增加,表征动量效应减小;注意时距不显著影响表征动量,而注意阶段显著影响表征动量。研究结果为表征动量的双加工理论提供了实证支持。     

Inhibition of return is composed of attentional and oculomotor processes.

Response time can be delayed if a target stimulus appears at a location or object that was previously cued. This inhibition of return (IOR) phenomenon has been attributed to a delay in activating attentional or motor processes to a previously cued stimulus. Two experiments required subjects to localize or identify a target stimulus. In Experiment 1, the subjects' eyes were not monitored. In Experiment 2, the subjects' eyes were monitored, and the subjects were instructed to either execute or withhold an eye movement to a target stimulus. The results indicated that IOR was always present for location and identification responses, supporting an attentional account of IOR. However, IOR was larger when eye movements were executed, indicating that a motor component can contribute to IOR. Finally, when eye movements were withheld, IOR was larger when a target was presented alone than when it was presented with a distractor, suggesting that IOR is larger for exogenous than for endogenous covert orienting. Together, the data indicate that IOR is composed of both an oculomotor component and an attentional component.     

Inhibition of return is composed of attentional and oculomotor processes

Response time can be delayed if a target stimulus appears at a location or object that was previously cued. This inhibition of return (IOR) phenomenon has been attributed to a delay in activating attentional or motor processes to a previously cued stimulus. Two experiments required subjects to localize or identify a target stimulus. In Experiment 1, the subjects’ eyes were not monitored. In Experiment 2, the subjects’ eyes were monitored, and the subjects were instructed to either execute or withhold an eye movement to a target stimulus. The results indicated that IOR was always present for location and identification responses, supporting an attentional account of IOR. However, IOR was larger when eye movements were executed, indicating that a motor component can contribute to IOR. Finally, when eye movements were withheld, IOR was larger when a target was presented alone than when it was presented with a distractor, suggesting that IOR is larger for exogenous than for endogenous covert orienting. Together, the data indicate that IOR is composed of both an oculomotor component and an attentional component.     

Oculomanual Coordination in Tracking of Pseudorandom Target Motion Stimuli

Oculomanual coordination was investigated in 9 healthy subjects during tracking of pseudorandom motion stimuli. Each subject was required to track visual stimuli under eye-hand (EH) and eye-alone (EA) conditions. Subjects were exposed to 3 types of mixed sinusoidal stimulus with varying frequency or amplitude of the highest frequency component, or various degrees of irregularity. Progressive degradation in tracking performance was nonlinearly induced by an increase in either (a) the highest frequency component or (b) its amplitude, but not by stimulus irregularity. No significant difference was found in eye velocity gain and phase under the EH and EA conditions. Eye and hand responses were found to be highly correlated in gain and phase when compared across frequencies and motion stimuli. The results suggest that frequency and amplitude are dominant factors controlling the breakdown of oculomanual performance in response to pseudorandom stimuli. Frequency responses of smooth pursuit eye movements are not affected by the hand motion in pursuit of unpredictable stimuli. Eye and hand motor systems appear to share common nonlinear drive mechanisms when pursuing pseudorandom target motion stimuli.     

The two‐thirds power law in motion perception

If a visual motion abruptly vanishes, the vanishing point is mislocalized in the anticipated direction of the motion (cf. Freyd & Finke, 1984; Hubbard & Bharucha, 1988; Verfaillie & d'Ydewalle, 1991). Here, we replicate this effect for curvilinear motions, showing that the compatibility with human movements, as expressed by the two‐thirds power law (cf. Lacquaniti, Terzuolo, & Viviani, 1983; Viviani, 2002), specifically contribute to this anticipation error. Thus, the compatibility effect does not manifest itself solely in an overshooting of the judged vanishing position in comparison to the objective vanishing position, but also in a more accurate anticipation of the curvilinearity of the forthcoming motion. The latter effect only occurred for spatially unpredictable target motions. Spatially more predictable target motions allowed for a different kind of anticipation, which overrode the compatibility effect. The results are discussed with regard to the notion of an action‐related influence on motion perception.     

Motion illusion reveals fixation stability of karate athletes

To investigate the effect of smooth pursuit effort against optokinetic nystagmus (OKN) on the magnitude of induced motion, we measured the magnitude of induced motion and eye movements of karate athletes and novices. In Experiment 1, participants were required to pursue a horizontally moving fixation stimulus against a vertically moving inducing stimulus and to point at the most distorted position of the perceived pathway of the fixation stimulus. In Experiments 2 and 3, participants were presented with the inducing stimulus with or without a static fixation stimulus. Experiments 1 and 2 showed a larger magnitude of induced motion and more stable fixation for the athletes than for the novices. Experiment 3 showed no difference in eye movements between the two groups. These results suggest that the magnitude of induced motion reflects fixation stability that may have been strengthened in karate athletes through their experience and training.     

Probing Representations of Gymnastics Movements: A Visual Priming Study

In this study, we designed a visual short‐term priming paradigm to investigate the mechanisms underlying the priming of movements and to probe movement representations in motor experts and matched controls. We employed static visual stimuli that implied or not human whole‐body movements, that is, gymnastics movements and static positions. Twelve elite female gymnasts and twelve matched controls performed a speeded two‐choice response time task. The participants were presented with congruent and incongruent prime‐target pairs and had to decide whether the target stimulus represented a gymnastics movement or a static position. First, a visual priming effect was observed in the two groups. Second, a stimulus–response rote association could not easily account for our results. Novel primes never presented as targets could also prime the targets. Third, by manipulating three levels of prime‐target relations in moving congruent pairs, we demonstrated that the more similar prime‐target pairs, the greater the facilitation in target. Lastly, gymnastics motor expertise impacted on priming effects.     

Representational momentum and related displacements in spatial memory: A review of the findings

Memory for the final location of a moving target is often displaced in the direction of target motion, and this has been referred to asrepresentational momentum. Characteristics of the target (e.g., velocity, size, direction, and identity), display (e.g., target format, retention interval, and response method), context (landmarks, expectations, and attribution of motion source), and observer (e.g., allocation of attention, eye movements, and psychopathology) that influence the direction and magnitude of displacement are reviewed. Specific conclusions regarding numerous variables that influence displacement (e.g., presence of landmarks or surrounding context), as well as broad-based conclusions regarding displacement in general (e.g., displacement does not reflect objective physical principles, may reflect aspects of naive physics, does not solely reflect eye movements, may involve some modular processing, and reflects high-level processes) are drawn. A possible computational theory of displacement is suggested in which displacement (1) helps bridge the gap between perception and action and (2) plays a critical part in localizing stimuli in the environment.     

Cues and control strategies in visually guided tracking

Detailed quantitative models are required to investigate the neurological basis of motor behavior. Previous studies of visually guided manual tracking have either identified a variety of control signals (cues) for planning tracking movements or analyzed how a single cue is used (i.e., one-tracking strategy). A systematic, quantitative analysis of the effects and interactions of cues in terms of human manual-tracking performance is presented here together with measurements of concomitant eye movements. These measurements help define the routes by which information reaches the CNS, and the analysis elucidates how the control signals are processed and combined. The results quantify not only the large improvement in performance observed when the target waveform being tracked is predictable but also the extent to which this improvement depends on the availability of current information about target movements and positional error. Target information is shown to provide short-term prediction independent of the error signals used in on-line negative feedback control.     

Centripetal force draws the eyes,not memory of the target,toward the center

Many observers believe that a target will continue on a curved trajectory after exiting a spiral tube. Similarly, when observers were asked to localize the final position of a target moving on a circular orbit, displacement of the judged position in the direction of forward motion ("representational momentum") and toward the center of the orbit was observed (cf. T. L. Hubbard, 1996). The present study shows that memory displacement of targets on a circular orbit is affected by eye movements. Forward displacement was larger with ocular pursuit of the target, whereas inward displacement was larger with motionless eyes. The results challenge an account attributing forward and inward displacement to mental analogues of momentum and centripetal force, respectively.     

Movement-based compatibility in simple response tasks

Previous studies reported that movement observation affected movement execution. Using one and the same set of responses (i.e., lifting or tapping the finger), correspondence effects were observed for simple responses when the go-signals were similar to the responses (i.e., movies of finger movements) but not when they were dissimilar (i.e., moving squares). The difference was attributed to a higher degree of ideomotor compatibility with visible limb movements. We tried to provide further evidence for ideomotor theory by manipulating the degree to which different responses matched one and the same set of stimuli (drifting sine-wave gratings). To this end, we measured simple reaction time of dynamic (hand movements) or static (key presses) movements in response to the onset of object motion. Object motion and dynamic responses showed ideomotor compatibility without looking alike; however, both stimulus and response involved continuous displacements. Correspondence effects were observed for dynamic responses, but not for static responses.     

Effects of saccades and response type on the Simon effect: If you look at the stimulus,the Simon effect may be gone

The Simon effect has most often been investigated with key-press responses and eye fixation. In the present study, we asked how the type of eye movement and the type of manual response affect response selection in a Simon task. We investigated three eye movement instructions (spontaneous, saccade, and fixation) while participants performed goal-directed (i.e., reaching) or symbolic (i.e., finger-lift) responses. Initially, no oculomotor constraints were imposed, and a Simon effect was present for both response types. Next, eye movements were constrained. Participants had to either make a saccade toward the stimulus or maintain gaze fixed in the screen centre. While a congruency effect was always observed in reaching responses, it disappeared in finger-lift responses. We suggest that the redirection of saccades from the stimulus to the correct response location in noncorresponding trials contributes to the Simon effect. Because of eye–hand coupling, this occurred in a mandatory manner with reaching responses but not with finger-lift responses. Thus, the Simon effect with key-presses disappears when participants do what they typically do—look at the stimulus.     

Fixation disengagement and eye-movement latency

We examined eye-movement latencies to a target that appeared during visual fixation of a stationary stimulus, a moving stimulus, or an extrafoveal stimulus. The stimulus at fixation was turned off either before target onset (gap condition) or after target onset (overlap condition). Consistent with previous research, saccadic latencies were shorter in gap conditions than they were in overlap conditions (the gap effect). In Experiment 1, a gap effect was observed for vergence eye movements. In Experiment 2, a gap effect was observed for saccades directed at a target that appeared during visual pursuit of a moving stimulus. In Experiment 3, a gap effect was observed for saccades directed at a target that appeared during extrafoveal fixation. The present results extend reports of the gap effect for saccadic shifts during visual fixation to (a) vergence shifts during visual fixation, (b) saccadic shifts during smooth visual pursuit, and (c) saccadic shifts during extrafoveal fixation. The present findings are discussed with respect to the incompatible goals of fixation-locking and fixation-shifting oculomotor responses.     

Inhibition of return in discrimination tasks

Although inhibition of return is known to affect a wide range of detection tasks, it has not been found consistently in discrimination tasks. To examine this issue, 5 experiments were conducted in which participants discriminated between a visual target and a distractor. The responses were not inhibited if, before the onset of stimuli, attention had been overtly oriented (i.e., an eye movement was made) to the future target location and the stimulus at that location was the same symbol as the upcoming target. However, if attention was covertly oriented (i.e., no eye movement was made) to the future location of the target, or if the stimulus at the earlier attended location was a symbol different from the target, responses to the target were inhibited. Overall, the findings provide insights into the relation between movements of attention and discrimination judgments and support the notion that inhibition of return is an attentional phenomenon.     

Neurophysiology and neuroanatomy of smooth pursuit in humans

Smooth pursuit eye movements enable us to focus our eyes on moving objects by utilizing well-established mechanisms of visual motion processing, sensorimotor transformation and cognition. Novel smooth pursuit tasks and quantitative measurement techniques can help unravel the different smooth pursuit components and complex neural systems involved in its control. The maintenance of smooth pursuit is driven by a combination of the prediction of target velocity and visual feedback about performance quality, thus a combination of retinal and extraretinal information that has to be integrated in various networks. Different models of smooth pursuit with specific in- and output parameters have been developed for a better understanding of the underlying neurophysiological mechanisms and to make quantitative predictions that can be tested in experiments. Functional brain imaging and neurophysiological studies have defined motion sensitive visual area V5, frontal (FEF) and supplementary (SEF) eye fields as core cortical smooth pursuit regions. In addition, a dense neural network is involved in the adjustment of an optimal smooth pursuit response by integrating also extraretinal information. These networks facilitate interaction of the smooth pursuit system with multiple other visual and non-visual sensorimotor systems on the cortical and subcortical level. Future studies with fMRI advanced techniques (e.g., event-related fMRI) promise to provide an insight into how smooth pursuit eye movements are linked to specific brain activation. Applying this approach to neurological and also mental illness can reveal distinct disturbances within neural networks being present in these disorders and also the impact of medication on this circuitry.     

Neurophysiology and neuroanatomy of smooth pursuit in humans

Smooth pursuit eye movements enable us to focus our eyes on moving objects by utilizing well-established mechanisms of visual motion processing, sensorimotor transformation and cognition. Novel smooth pursuit tasks and quantitative measurement techniques can help unravel the different smooth pursuit components and complex neural systems involved in its control. The maintenance of smooth pursuit is driven by a combination of the prediction of target velocity and visual feedback about performance quality, thus a combination of retinal and extraretinal information that has to be integrated in various networks. Different models of smooth pursuit with specific in- and output parameters have been developed for a better understanding of the underlying neurophysiological mechanisms and to make quantitative predictions that can be tested in experiments. Functional brain imaging and neurophysiological studies have defined motion sensitive visual area V5, frontal (FEF) and supplementary (SEF) eye fields as core cortical smooth pursuit regions. In addition, a dense neural network is involved in the adjustment of an optimal smooth pursuit response by integrating also extraretinal information. These networks facilitate interaction of the smooth pursuit system with multiple other visual and non-visual sensorimotor systems on the cortical and subcortical level. Future studies with fMRI advanced techniques (e.g., event-related fMRI) promise to provide an insight into how smooth pursuit eye movements are linked to specific brain activation. Applying this approach to neurological and also mental illness can reveal distinct disturbances within neural networks being present in these disorders and also the impact of medication on this circuitry.