Human cortical area responding to stimuli in apparent motion

Modulation of spatial orientation processing by mental imagery instructions: a MEG study of representational momentum

Under appropriate conditions, an observer's memory for the final position of an abruptly halted moving object is distorted in the direction of the represented motion. This phenomenon is called "representational momentum" (RM). We examined the effect of mental imagery instructions on the modulation of spatial orientation processing by testing for RM under conditions of picture versus body rotation perception and imagination. Behavioral data were gathered via classical reaction time and error measurements, whereas brain activity was recorded with the help of magnetoencephalography (MEG). Due to the so-called inverse problem and to signal complexity, results were described at the signal level rather than with the source location modeling. Brain magnetic field strength and spatial distribution, as well as latency of P200m evoked fields were used as neurocognitive markers. A task was devised where a subject examined a rotating sea horizon as seen from a virtual boat in order to extrapolate either the picture motion or the body motion relative to the picture while the latter disappeared temporarily until a test-view was displayed as a final orientation candidate. Results suggest that perceptual interpretation and extrapolation of visual motion in the roll plane capitalize on the fronto-parietal cortical networks involving working memory processes. Extrapolation of the rotational dynamics of sea horizon revealed a RM effect simulating the role of gravity in rotational equilibrium. Modulation of the P200m component reflected spatial orientation processing and a non-voluntary detection of an incongruity between displayed and expected final orientations given the implied motion. Neuromagnetic properties of anticipatory (Contingent Magnetic Variation) and evoked (P200m) brain magnetic fields suggest, respectively, differential allocation of attentional resources by mental imagery instructions (picture vs. body tilt), and a communality of neural structures (in the right centro-parietal region) for the control of both RM and mental rotation processes. Finally, the RM of the body motion is less prone to forward shifts than that of picture motion evidencing an internalization of the implied mass of the virtual body of the observer.

Asymmetry of the human visual field in magnetic response to apparent motion

Predominance of the lower visual field has been shown in various visual tasks, but whether the upper visual field is involved in a specific neural process is unknown. We used magnetoencephalography to study the effect of orientation and direction on the responses of five subjects to apparent motion from the human extrastriate cortex. The first magnetic response always was the largest, and the peak latency of about 200 ms did not change with the stimulus conditions. Amplitudes of the first responses were highest when motions were oriented at the horizontal meridian, decreasing with the degree of the angle between motion orientation and the horizontal meridian. There was no difference in amplitude between the two directions in the lower visual field, whereas the value of the response to downward motion in the upper visual field was significantly larger than that to upward motion. These amplitude changes are not due to differences in the anatomical distribution of neural activities because the estimated origins for the first responses always were in the same cortical area (around the occipito-parieto-temporal region) and the directions of the current vectors did not change with the stimulus conditions, and the estimated current strength changed with the stimulus conditions as did the response amplitude. These findings suggest that the human extrastriate cortex has a directional preference for downward versus upward motion in the upper visual field.

Perception of apparent motion is related to the neural activity in the human extrastriate cortex as measured by magnetoencephalography

To determine the neural correlate of apparent motion perception, we measured magnetic responses to visual stimuli in apparent motion and compared the results with subjective rating of the quality of perceived motion with varied stimulus timing. The latency of the magnetic response was about 150 ms, and its origin was estimated to be in the occipito-parieto-temporal junction. The strength of the first component in the response varied with the stimulus timing, the maximum value being at the interval 0. The change could not be explained by the simple summation of onset and offset responses and this value was related to the subjective rating of quality (smoothness) of motion measured of the stimulus. Results indicate there is a localized cortical region of neural activity which is closely related to the subjective assessment of quality of perceived motion.

The functional neuroanatomy of implicit-motion perception or representational momentum

BACKGROUND

When we view static scenes that imply motion - such as an object dropping off a shelf - recognition memory for the position of the object is extrapolated forward. It is as if the object in our mind's eye comes alive and continues on its course. This phenomenon is known as representational momentum and results in a distortion of recognition memory in the implied direction of motion. Representational momentum is modifiable; simply labelling a drawing of a pointed object as 'rocket' will facilitate the effect, whereas the label 'steeple' will impede it. We used functional magnetic resonance imaging (fMRI) to explore the neural substrate for representational momentum.

RESULTS

Subjects participated in two experiments. In the first, they were presented with video excerpts of objects in motion (versus the same objects in a resting position). This identified brain areas responsible for motion perception. In the second experiment, they were presented with still photographs of the same target items, only some of which implied motion (representational momentum stimuli). When viewing still photographs of scenes implying motion, activity was revealed in secondary visual cortical regions that overlap with areas responsible for the perception of actual motion. Additional bilateral activity was revealed within a posterior satellite of V5 for the representational momentum stimuli. Activation was also engendered in the anterior cingulate cortex.

CONCLUSIONS

Considering the implicit nature of representational momentum and its modifiability, the findings suggest that higher-order semantic information can act on secondary visual cortex to alter perception without explicit awareness.

Activation in human MT/MST by static images with implied motion

A still photograph of an object in motion may convey dynamic information about the position of the object immediately before and after the photograph was taken (implied motion). Medial temporal/medial superior temporal cortex (MT/MST) is one of the main brain regions engaged in the perceptual analysis of visual motion. In two experiments we examined whether MT/MST is also involved in representing implied motion from static images. We found stronger functional magnetic resonance imaging (fMRI) activation within MT/MST during viewing of static photographs with implied motion compared to viewing of photographs without implied motion. These results suggest that brain regions involved in the visual analysis of motion are also engaged in processing implied dynamic information from static images.

Spatiotemporal activity of a cortical network for processing visual motion revealed by MEG and fMRI

A sudden change in the direction of motion is a particularly salient and relevant feature of visual information. Extensive research has identified cortical areas responsive to visual motion and characterized their sensitivity to different features of motion, such as directional specificity. However, relatively little is known about responses to sudden changes in direction. Electrophysiological data from animals and functional imaging data from humans suggest a number of brain areas responsive to motion, presumably working as a network. Temporal patterns of activity allow the same network to process information in different ways. The present study in humans sought to determine which motion-sensitive areas are involved in processing changes in the direction of motion and to characterize the temporal patterns of processing within this network of brain regions. To accomplish this, we used both magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). The fMRI data were used as supplementary information in the localization of MEG sources. The change in the direction of visual motion was found to activate a number of areas, each displaying a different temporal behavior. The fMRI revealed motion-related activity in areas MT+ (the human homologue of monkey middle temporal area and possibly also other motion sensitive areas next to MT), a region near the posterior end of the superior temporal sulcus (pSTS), V3A, and V1/V2. The MEG data suggested additional frontal sources. An equivalent dipole model for the generators of MEG signals indicated activity in MT+, starting at 130 ms and peaking at 170 ms after the reversal of the direction of motion, and then again at approximately 260 ms. Frontal activity began 0-20 ms later than in MT+, and peaked approximately 180 ms. Both pSTS and FEF+ showed long-duration activity continuing over the latency range of 200-400 ms. MEG responses in the region of V3A and V1/V2 were relatively small, and peaked at longer latencies than the initial peak in MT+. These data revealed characteristic patterns of activity in this cortical network for processing sudden changes in the direction of visual motion.

Effects of distraction on pain perception: magneto- and electro-encephalographic studies

After a painful CO2 laser stimulation to the skin, the magnetoencephalography (MEG) response (164 ms in average peak latency) was not affected by distraction, but the sequential electroencephalography (EEG) responses (240-340 ms), probably generated by a summation of activities in multiple areas, were markedly affected. We suspect that the MEG response, whose dipole is estimated in the bilateral second somatosensory cortex (SII) and insula, reflects the primary activities of pain in humans.

Effects of visual and auditory stimulation on somatosensory evoked magnetic fields

DESIGN AND METHODS

We investigated the effects of continuous visual (cartoon and random dot motion) and auditory (music) stimulation on somatosensory evoked magnetic fields (SEFs) following electrical stimulation of the median nerve on 12 normal subjects using paired t test and two way ANOVA for the statistics.

RESULTS

In the hemisphere contralateral to the stimulated nerve, the middle-latency components (35-60 ms in latency) were significantly enhanced by visual, but not by auditory stimulation. The dipoles of all components within 60-70 ms following stimulation were estimated to be very close each other, around the hand area of the primary sensory cortex (SI). In the ipsilateral hemisphere, the middle-latency components (70-100 ms in latency), the dipoles of which were estimated to be in the second sensory cortex (SII), were markedly decreased in amplitude by both the visual and auditory stimulation.

CONCLUSIONS

These changes in waveform by visual and auditory stimulation are thought to be due to the effects of the activation of polymodal neurons, which receive not only somatosensory but also visual and/or auditory inputs, in areas 5 and/or 7 as well as in the medial superior temporal region (MST) and superior temporal sulcus (STS), although a change of attention might also be a factor causing such findings.

Timing of motion representation in the human visual system

Visual stimulus in apparent motion evokes a magnetic field from the extrastriate cortex in humans. To investigate what this magnetic field represents, we measured the latencies of the responses in three subjects to the stimuli in apparent motion at various spatial separations. These different latencies were inversely related to the spatial separations of the stimuli (range of 74 to 182 ms) and correlated with each subject's reaction time. The direction of motion affected neither the latency of the magnetic response nor the reaction times. Estimations of the origins of the evoked magnetic fields showed they were always in the same area. In two subjects, the sites were around the meeting point of the ascending limb of the inferior temporal sulcus and the lateral occipital sulcus. In the third subject, the site was in the vicinity of the angular gyrus. The difference between the magnetic response and reaction time was fairly constant (about 64 ms) among the subjects. We consider the magnetic response to be related to the generation of a motion image: First, the response clearly corresponded to human reaction times to the same stimuli: Second, the fact that the magnetic response was related to the spatial separations but independent of the direction of motion is not explained if the response is evoked simply by both the onset and offset of the object in the stimulus. Furthermore, individual reaction times were mainly delayed by the speed of the process that generated the motion image.

Human brain potentials observed using the line-motion method: the neurophysiological correlates of visual illusory motion perception

This study shows the temporal dynamics of neurophysiological activities in illusory motion perception. Event-related brain potentials were recorded from 12 healthy subjects while they performed a two-alternative (motion/no motion), forced-choice task using the line motion method. Amplitudes of a late positive component at Fz, Cz, Pz, O1 and O2 increased as cue lead time (CLT) increased. At a CLT of 50 ms, the amplitudes of the late positive component (the peak latency at O1, O2: 310 ms; Fz, Cz, Pz: 360-390 ms) observed during illusory motion perception was larger than that observed during no motion perception, even though the physical stimuli were the same. These results suggest that the perception of illusory motion correlates to a relatively late stage of visual information processing.