Transcranial magnetic stimulation over MT/MST fails to impair judgments of implied motion

The medial temporal and medial superior temporal cortex (MT/MST) is involved in the processing of visual motion, and fMRI experiments indicate that there is greater activation when subjects view static images that imply motion than when they view images that do not imply motion at all. We applied transcranial magnetic stimulation (TMS) to MT/MST in order to assess the functional necessity of this region for the processing of implied motion represented in static images. Area MT/MST was localized by the use of a TMS-induced misperception of visual motion, and its location was verified through the monitored completion of a motion discrimination task. We controlled for possible impairments in general visual processing by having subjects perform an object categorization task with and without TMS. Although MT/MST stimulation impaired performance in a motion discrimination task (and vertex stimulation did not), there was no difference in performance between the two forms of stimulation in the implied motion discrimination task. MT/MST stimulation did, however, improve subjects’ performance in the object categorization task. These results indicate that, within 150 msec of stimulus presentation, MT/MST is not directly involved in the visual processing of static images in which motion is implied. The results do, however, confirm previous findings that disruption of MT/MST may improve efficiency in more ventral visual processing streams.     

Representational momentum when attention is divided

Observers tend to misremember a transforming object's final appearance as further along in the direction of continued transformation. This forward bias, termed representational momentum (RM), suggests that the dynamics associated with an object cannot be ignored in the effort to remember a particular instance of the object. Two experiments tested how attentional focus affects this memory bias. Observers attended to one object, divided attention across more than one object, or performed a secondary task simultaneously with the RM task. For objects translating in space, diminished attention increased the forward memory shift, suggesting that under distraction, motion can be represented but the stopping point is less effectively represented. We propose that object dynamics are well represented when attention is distracted, but that representing a change—including stopping—in the dynamics requires attention. We suggest some experiments to examine this proposal further.     

The pointedness effect on representational momentum

An observer's memory for the final position of a moving object is shifted forward in the direction of that object's motion. It is called representational momentum (RM). This study addressed stimulus-specific effects on RM. In Experiment 1, participants showed larger memory shift for an object moving in its typical direction of motion than when it moved in a nontypical direction of motion. In Experiment 2, participants indicated larger memory shift for a pointed pattern moving in the direction of its point than when it moved in the opposite direction. In Experiment 3, we again examined the influences of knowledge about objects' typical motions and the pointedness of objects, because we did not control the shape (pointedness) of objects in Experiment 1. The results showed that only pointedness affected the magnitude of memory shift and that the effect was smaller than the momentum effect.     

Recovery from object substitution masking induced by transient suppression of visual motion processing: a repetitive transcranial magnetic stimulation study

Object substitution masking is a form of visual backward masking in which a briefly presented target is rendered invisible by a lingering mask that is too sparse to produce lower image-level interference. Recent studies suggested the importance of an updating process in a higher object-level representation, which should rely on the processing of visual motion, in this masking. Repetitive transcranial magnetic stimulation (rTMS) was used to investigate whether functional suppression of motion processing would selectively reduce substitution masking. rTMS-induced transient functional disruption of cortical area V5/MT+, which is important for motion analysis, or V1, which is reciprocally connected with V5/MT+, produced recovery from masking, whereas sham stimulation did not. Furthermore, masking remained undiminished following rTMS over the region 2 cm posterior to V5/MT+, ruling out nonspecific effects of real stimulation and confirming regional specificity of the rTMS effect. The results suggest that object continuity via the normal function of the visual motion processing system might in part contribute to this masking. The relation of these findings to the reentrant processing view of object substitution masking and other visual phenomena is discussed.     

Parallels between remembering and predicting an object's location

Three experiments explore effects of rotational axis and velocity on observers' predictions regarding an object's future position, and begin to explore connections between this extrapolation task and representational momentum (RM). In general, observers accept as "correct" positions that are behind the correct extrapolated location, as shown in previous work (Cooper & Munger, 1993; Finke & Shyi, 1998). These prediction distortions are in the opposite direction of typical RM memory distortions, suggesting that these tasks are unrelated. However, new effects of axis for the extrapolation task are reported which parallel axis effects previously observed for RM and mental rotation tasks. Specifically, participants make larger negative distortion errors for axes of rotation that are not coincident with the viewer's coordinate system, as if these paths of rotation are harder to extrapolate. Effects of velocity and axis are examined for RM and extrapolation tasks, and the overall pattern of distortions supports a link. In particular, participants who misremember the location of an object as further along the implied path of motion also accept as "correct" positions relatively further along the extrapolated path of motion, suggesting that these apparently opposite types of errors are indeed related.     

Representational momentum in scenes: Learning spatial layout

In four experiments, we examined whether watching a scene from the perspective of a camera rotating across it allowed participants to recognize or identify the scene's spatial layout. Completing a representational momentum (RM) task, participants viewed a smoothly animated display and then indicated whether test probes were in the same position as they were in the final view of the animation. We found RM anticipations for the camera's movement across the scene, with larger distortions resulting from camera rotations that brought objects into the viewing frame compared with camera rotations that took objects out of the viewing frame. However, the RM task alone did not lead to successful recognition of the scene's map or identification of spatial relations between objects. Watching a scene from a rotating camera's perspective and making position judgments is not sufficient for learning spatial layout.     

The role of motion direction selective extrastriate regions in reading: a transcranial magnetic stimulation study

Why reading ability is correlated with motion processing ability is perplexing. Activity in motion direction processing regions (Area V5/MT+) was perturbed by means of repetitive transcranial magnetic stimulation (rTMS) to examine its effect on reading. A functional probe (significant shortening of the motion aftereffect) was used to identify Area V5/MT+. Right-handed participants (8 m, 8 f) received three 7.5 min blocks of rTMS, after which two phonological and one orthographic reading tasks were administered. Application of rTMS to Area V5/MT+ (as compared to a non-rTMS baseline) significantly decreased performance only during non-word naming. The pattern of naming errors and the absence of deficits on the second phonological task were not consistent with a role for Area V5/MT+ in phonological decoding. Instead, its role in reading may be limited to image stabilization and/or letter localization.     

Representational momentum in older adults

Humans have a tendency to perceive motion even in static images that simply “imply” movement. This tendency is so strong that our memory for actions depicted in static images is distorted in the direction of implied motion - a phenomenon known as representational momentum (RM). In the present study, we created an RM display depicting a pattern of implied (clockwise) rotation of a rectangle. Young adults viewers’ memory of the final position of the test rectangle was biased in the direction of continuing rotation, but older adults did not show a similar memory bias. We discuss several possible explanations for this group difference, but argue that the failure of older adults to shown an RM effect most likely reflects age-related changes in areas of the brain involved in processing real and implied motion.     

The relationship between mental rotation and representational momentum

Two experiments explored a possible relationship between mental rotation and representational momentum, a task in which participants were asked to remember an object's position following a sequence of images implying motion. Typically, participants misremember the position as distorted forward along the implied trajectory. If representational momentum relies on mental imagery, the magnitude of memory distortion in a representational momentum task should be positively correlated with the rate of mental rotation. As predicted, faster mental rotation rates and larger memory distortions for object position were observed for rotational axes aligned with the viewers' coordinate system. In addition, participants with slower mental rotation rates produced smaller memory distortions in the implied-event task.     

Representational momentum and the flash‐lag effect

Representational momentum (RM) is a distortion where the final orientation of a moving object is misremembered as further along its trajectory. Experiments reported here examine RM when an additional object was flashed just as the moving object disappeared. When the task was to judge the flashed object, participants reported that the flash appeared to lag behind (flash‐lag effect; FLE). When the task was to judge the moving object, larger forward distortions for the moving object were found when the flash was present, despite previous evidence that the FLE depends on the moving object's continued presence. The results suggest that some part of the FLE depends upon what precedes the flash. In addition, equivalent RM was observed for implied and smoothly animated events, a possible limit to the velocity effect for RM was found, and larger positive distortions were found for downward rotations.     

整体运动知觉老化伴随颞中回静息态功能改变

以个体整体运动一致性阈值为指标, 探讨老年人整体运动敏感性(GMS)下降和静息态下兴趣脑区功能活动的关系。发现与阈值负相关且老年人低于青年人的指标主要有：MT/V5区的ReHo和ALFF值, 各网络拓扑属性; 与阈值正相关且老年人显著高于青年人的有：MT/V5区与前运动皮层之间的、各兴趣脑区之间的功能连接。结果用“去分化”等观点进行了解释, 提示老年人GMS的下降可能不仅与安静状态下MT/V5区的功能改变有关, 还可能与全脑更广泛区域的功能改变有关。     

Motor affordance and its role for visual working memory: evidence from fMRI studies

We examined the role of motor affordances of objects for working memory retention processes. Three experiments are reported in which participants passively viewed pictures of real world objects or had to retain the objects in working memory for a comparison with an S2 stimulus. Brain activation was recorded by means of functional magnetic resonance imaging (fMRI). Retaining information about objects for which hand actions could easily be retrieved (manipulable objects) in working memory activated the hand region of the ventral premotor cortex (PMC) contralateral to the dominant hand. Conversely, nonmanipulable objects activated the left inferior frontal gyrus. This suggests that working memory for objects with motor affordance is based on motor programs associated with their use. An additional study revealed that motor program activation can be modulated by task demands: Holding manipulable objects in working memory for an upcoming motor comparison task was associated with left ventral PMC activation. However, retaining the same objects for a subsequent size comparison task led to activation in posterior brain regions. This suggests that the activation of hand motor programs are under top down control. By this they can flexibly be adapted to various task demands. It is argued that hand motor programs may serve a similar working memory function as speech motor programs for verbalizable working memory contents, and that the premotor system mediates the temporal integration of motor representations with other task-relevant representations in support of goal oriented behavior.     

The effect of body and part-based motion on the recognition of unfamiliar objects

We investigated the role of global (body) and local (parts) motion on the recognition of unfamiliar objects. Participants were trained to categorise moving objects and were then tested on their recognition of static images of these targets using a priming paradigm. Each static target shape was primed by a moving object that comprised either the same body and parts motion; same body, different parts motion; different body, same part motion as the learned target or was non-moving. Only the same body but not the same part motion facilitated shape recognition (Experiment 1), even when either motion was diagnostic of object identity (Experiment 2). When parts motion was more related to the object's body motion then it facilitated the recognition of the static target (Experiment 3). Our results suggest that global and local motions are independently accessed during object recognition and have important implications for how objects are represented in memory.     

Enhancement of phonological memory following transcranial magnetic stimulation (TMS)

Phonologically similar items (mell, rell, gell) are more difficult to remember than dissimilar items (shen, floy, stap), likely because of mutual interference of the items in the phonological store. Low-frequency transcranial magnetic stimulation (TMS), guided by functional magnetic resonance imaging (fMRI) was used to disrupt this phonological confusion by stimulation of the left inferior parietal (LIP) lobule. Subjects received TMS or placebo stimulation while remembering sets of phonologically similar or dissimilar pseudo-words. Consistent with behavioral performance of patients with neurological damage, memory for phonologically similar, but not dissimilar, items was enhanced following TMS relative to placebo stimulation. Stimulation of a control region of the brain did not produce any changes in memory performance. These results provide new insights into how the brain processes verbal information by establishing the necessity of the inferior parietal region for optimal phonological storage. A mechanism is proposed for how TMS reduces phonological confusion and leads to facilitation of phonological memory.     

老年人整体运动敏感性降低的脑灰质体积变化基础

本研究使用多体素模式分析方法和随机点阵范式,首次探索了老年人整体运动敏感性（GMS）下降和其脑灰质体积下降间的关系。结果发现,老年人GMS显著低于年轻人,老年人V5/MT、V3和额顶等脑区灰质体积显著小于年轻人;V5/MT和V3区的灰质体积信号可以有效预测个体的GMS。结果提示,V5/MT区和V3区,特别是V3区的灰质体积下降可能是老年人GMS下降的主要原因;而基于“去分化假设”,全脑范围内其余脑区的灰质体积下降可能也在一定程度上与老年人GMS下降有关。     

Magnetic stimulation studies of visual cognition

The panoply of non-invasive techniques for brain imaging is responsible for much of the current excitement in cognitive neuroscience; sensory, perceptual and cognitive behaviour can now be correlated with cerebral blood flow as assessed by functional imaging, the electrical fields generated by populations of neurons or changes in magnetic fields created by electrical activity. Correlations between localized brain activity and behaviour, however, do not of themselves establish that any brain area is necessary for a particular task; necessity is the domain of the lesion technique. Transcranial magnetic stimulation (TMS) is a technique that can be used non-invasively to produce reversible functional disruption and has already been used to investigate visual detection, discrimination, attention and plasticity. The power of TMS as a `lesion' technique lies in the opportunity to combine reversible disruption with high degrees of spatial and temporal resolution. In this review we trace some of the major developments in the use of TMS as a technique for the investigation of visual cognition.     

Short theta burst stimulation to left frontal cortex prior to encoding enhances subsequent recognition memory

Deep semantic encoding of verbal stimuli can aid in later successful retrieval of those stimuli from long-term episodic memory. Evidence from numerous neuropsychological and neuroimaging experiments demonstrate regions in left prefrontal cortex, including left dorsolateral prefrontal cortex (DLPFC), are important for processes related to encoding. Here, we investigated the relationship between left DLPFC activity during encoding and successful subsequent memory with transcranial magnetic stimulation (TMS). In a pair of experiments using a 2-session within-subjects design, we stimulated either left DLPFC or a control region (Vertex) with a single 2-s train of short theta burst stimulation (sTBS) during a semantic encoding task and then gave participants a recognition memory test. We found that subsequent memory was enhanced on the day left DLPFC was stimulated, relative to the day Vertex was stimulated, and that DLPFC stimulation also increased participants’ confidence in their decisions during the recognition task. We also explored the time course of how long the effects of sTBS persisted. Our data suggest 2 s of sTBS to left DLPFC is capable of enhancing subsequent memory for items encoded up to 15 s following stimulation. Collectively, these data demonstrate sTBS is capable of enhancing long-term memory and provide evidence that TBS protocols are a potentially powerful tool for modulating cognitive function.     

Measuring causal perception: connections to representational momentum?

In a collision between two objects, we can perceive not only low-level properties, such as color and motion, but also the seemingly high-level property of causality. It has proven difficult, however, to measure causal perception in a quantitatively rigorous way which goes beyond perceptual reports. Here we focus on the possibility of measuring perceived causality using the phenomenon of representational momentum (RM). Recent studies suggest a relationship between causal perception and RM, based on the fact that RM appears to be attenuated for causally 'launched' objects. This is explained by appeal to the visual expectation that a 'launched' object is inert and thus should eventually cease its movement after a collision, without a source of self-propulsion. We first replicated these demonstrations, and then evaluated this alleged connection by exploring RM for different types of displays, including the contrast between causal launching and non-causal 'passing'. These experiments suggest that the RM-attenuation effect is not a pure measure of causal perception, but rather may reflect lower-level spatiotemporal correlates of only some causal displays. We conclude by discussing the strengths and pitfalls of various methods of measuring causal perception.     

Neural substrates of successful working memory and long-term memory formation in a relational spatial memory task

Working memory (WM) tasks may involve brain activation actually implicated in long-term memory (LTM). In order to disentangle these two memory systems, we employed a combined WM/LTM task, using a spatial relational (object-location) memory paradigm and analyzed which brain areas were associated with successful performance for either task using fMRI. Critically, we corrected for the performance on the respective memory task when analyzing subsequent memory effects. The WM task consisted of a delayed-match-to-sample task assessed in an MRI scanner. Each trial consisted of an indoor or outdoor scene in which the exact configuration of four objects had to be remembered. After a short delay (7–13 s), the scene was presented from a different angle and spatial recognition for two objects was tested. After scanning, participants received an unexpected subsequent recognition memory (LTM) task, where the two previously unprobed objects were tested. Brain activity during encoding, delay phase and probe phase was analyzed based on WM and LTM performance. Results showed that successful WM performance, when corrected for LTM performance, was associated with greater activation in the inferior frontal gyrus and left fusiform gyrus during the early stage of the maintenance phase. A correct decision during the WM probe was accompanied by greater activation in a wide network, including bilateral hippocampus, right superior parietal gyrus and bilateral insula. No voxels exhibited supra-threshold activity during the encoding phase, and we did not find any differential activity for correct versus incorrect trials in the WM task when comparing LTM correct versus LTM incorrect trials.     

Representational momentum,spatial layout,and viewpoint dependency

Completing a representational momentum (RM) task, participants viewed one of three camera motions through a scene and indicated whether test probes were in the same position as they were in the final view of the animation. All camera motions led to RM anticipations in the direction of motion, with larger distortions resulting from rotations than a compound motion of a rotation and a translation. A surprise test of spatial layout, using an aerial map, revealed that the correct map was identified only following aerial views during the RM task. When the RM task displayed field views, including repeated views of multiple object groups, participants were unable to identify the overall spatial layout of the scene. These results suggest that the object–location binding thought to support certain change detection and visual search tasks might be viewpoint dependent.