• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content

Loading…

Flash Player 9 (or above) is needed to view presentations.
We have detected that you do not have it on your computer. To install it, go here.

Like this presentation? Why not share!

A Higher Order Motion Region

on

  • 178 views

 

Statistics

Views

Total Views
178
Views on SlideShare
178
Embed Views
0

Actions

Likes
0
Downloads
0
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment
  • -short range mechanism vs. long range mechanism spatiotemporal factor - first order system : extract motion from moving luminance modulation using a primitive motion energy algorithm second order system : extract motion from moving stimuli in which the expected luminance is the same everywhere but some feature (contrast, orientation, spatial frequency) deviate from the back ground. third order system : detects movement of feature salience, that is, change location of areas marked as “salient” computes motion from a dynamic salience map, the locations of the salient feature of time. (Lu,2000,vision res. 40. 173-186)
  • Visual motion is a powerful signal for drawing attention to important target, conversely, attention can also be a powerful signal for deriving( 유도하다 ) visual attention Example. 평지를 달리는 호랑이를 볼 때 , 호랑이의 줄무늬와 윤곽은 low level detectors ( 시간과 공간 상의 brightness 의 변화를 탐지 ) 에 의해 감지 그러나 이 시스템만으로 perception 이 부족한 경우가 생김 만약 호랑이가 나무가 있는 숲으로 간다면 나무 뒤로 움직임이 보이게 되고 나무의 그림자 등이 false luminance signal 을 만들어 낼 수 있음 . => 호랑이의 움직임을 인지하기 위한 정교한 시스템이 필요 . 많은 심리학자 들이 lower order luminance based system 과는 별도로 higher order motion system (luminance cue 가 충분하지 않을 때 motion processing 을 담당 ) 이 있을 것이라 생각
  • Simple moving grating, random dot patterns (pre-attentive)
  • -
  • isoluminant sinewave gratings, produced by antiphase superposition of reddish and greenish component gratings of low-, medium-, and high-green saturation relative to the red components High level salience motion mechanism : grating components differ significantly in saturation. Vs. grating saturation similar, relative salience differences are diminished, neither grating component preferentially engages attention, motion is not perceived. (B) “iso-saliency” condition
  • In the analysis of main experiment 1, we first tested for higher-level motion regions by contrasting the motion and stationary control conditions of the salience- defined stimuli, averaged over the high- and low-green saturation conditions Contrasting the motion and stationary control condition. Right IPL (inferior parietal lobule), ipsilaterly to the stimulation, and bilaterally in hMT/V5+ c) isosalient-isoluminant (I, blue), different salience-isoluminant (Sa, yellow), isosalient-different luminance (L, red) conditions
  • To ensure the generality of the results, data obtained in the first experiment were subjected to three separate group analyses, each comprising two sessions, ranked according to the subject's own estimated level of attention to the stimuli and clarity of the attention-based motion percept d) a) 의 coronal session. e) Percentages indicate size of saliency-based motion effect, other conventions as in (C) => Attention 이 salience based process 에 영향을 미침… !
  • Single-subject analyses confirmed the results of the group analysis A right IPL activation was observed in each of the six subjects in the salience-defined motion conditions but not in the luminance-defined motion condition (Figures 3A and 3B). Furthermore, the right IPL activation by salience-based motion was significant (z = 5.32, p < 0.05 corr.) in a conjunction analysis across the six subjects (Friston et al., 1999) of the two highest attention sessions, underscoring again the generality of the results.
  • The activation of R IPL by a right-sided motion stimulus is consistent with either an ipsilateral or a bilateral representation of higher-level motion. In fact, in the group analysis of Figure 2A, the left (L) IPL (-63,-36, 39) reached a lower threshold (z = 4.39, p < 0.001 uncorrected for multiple comparisons) for salience- based motion, suggesting that the representation might be bilateral. To confirm this alternative, we enrolled three subjects (S1­S3) in a control experiment (Table 1) in which the stimuli were positioned in the left visual field (Figure 4). This control experiment revealed an activation (p < 0.05 corr.) of the L IPL region by salience-based motion only (Figure 4B), with the contralateral (right) IPL activated at a less significant (p < 0.001 uncorr.) level. The activity profiles confirm that the IPL region in both hemispheres represents salience-specific motion in the two hemifields, though ipsilateral responsiveness was stronger
  • We next compared the motion regions activated in our first main experiment with the potential lower-level motion regions revealed in a second control experiment (same six participants, Table 1). The stimulus consisted of a moving or stationary random texture pattern , positioned in the central, left, and right visual field. We focus here on the results obtained for the right visual field in analogy with the main experiment By contrasting the moving and stationary condition (Figure 5A), a predominantly left-sided, contralateral, activation pattern was observed, including area hV3A, hMT/V5+, superior temporal sulcus (STS), posterior insular cortex (PIC), parieto-occipital intraparietal sulcus (POIPS), dorsal intraparietal sulcus medial (DIPSM), and dorsal intraparietal sulcus anterior (DIPSA). This pattern corresponds to the known motion regions (Sunaert et al., 1999). Activity in all these left-sided regions was larger for contralateral (right) than ipsilateral (left) visual field stimulation (Fig- ure 5B). We then tested which of these traditional motion regions, mapped out in the control experiment, were activated by the salience-defined and luminance-defined motion in the first main experiment. As expected, all known motion areas were activated by luminance based-motion (Figure 5C). Many extrastriate areas, such as hV3A and hMT/V5+, also showed activity for salience-based motion, but far extrastriate motion areas STS and DIPSA revealed activity exclusively for luminance-defined motion . Notice that these two regions and also DIPSM and PIC did not respond to motion in the isoluminant-isosalient condition, in which little motion is perceived.
  • Since experiment 1 demonstrated that human R IPL is a higher order motion region, we wondered whether the IPL region processes other types of stimuli for which a higher-level status had been proposed . A recent human lesion study (Battelli et al., 2001) suggested that a quartet variant of the two dots apparent motion display (Figure 6A) (Ternus, 1938), which has previously been considered a long-range motion stimulus (Braddick, 1974), might be processed by the IPL. Patients with a unilateral R IPL lesion were shown to suffer from a bilateral deficit for long-range apparent motion, without deficit on lower order motion tests. Patients failed to distinguish apparent motion from flicker at high frequencies (6­8 Hz), but not at frequencies below 5 Hz.
  • Since experiment 1 demonstrated that human R IPL is a higher order motion region, we wondered whether the IPL region processes other types of stimuli for which a higher-level status had been proposed . Therefore, in the second main experiment (Table 1), we presented the quartet display with apparent motion at 2 Hz (Goebel et al., 1998) and 7 Hz, and a control flicker at 7 Hz, and positioned these stimuli in right and left visual fields. A stringent random-effect analysis (Friston et al., 1999) was performed on the group data (n = 12). Averaging over left and right visual field presentations, apparent motion at 7 Hz compared to flicker activated a similar R IPL region as in our first study (Figure 6B). The activation of the left IPL was weaker, but the activity profiles of the two IPL regions are similar, with equally large activity for 7 Hz apparent motion in both visual hemifields (Figures 6C and 3D). Single-subject analysis, also averaged over left and right visual field presentations, confirmed the results of the group analysis: R IPL was activated (p < 0.001 uncorr.) in 10/12 subjects and L IPL in 8/12 subjects (Figure 6E). Responses in three of the subjects that participated in both main experiments are illustrated in Figures 3C and 3D to show that the location of the IPL activation in both main experiments was very similar . The only other significant (p < 0.0001 uncorr.) activation by 7 Hz apparent motion was bilateral hMT/V5+. No activation was observed in ventral visual regions, suggesting that the MR activation in temporal cortex by long-range apparent motion reported by Zhuo et al. (2003) reflects change in size rather than motion as such.
  • Testing the conditions of main experiment 2 on the lower-level motion regions revealed that these areas were generally responsive to the 2 Hz apparent motion , and in general responded predominantly to contralateral visual field stimulation (Figure 5D). Many of them were also responsive to apparent motion at 7 Hz. The two regions, however, which failed to respond to saliency- based motion in main experiment 1, DIPSA and STS, also failed to respond to the apparent motion at 7 Hz . Notice also that several regions especially the near extrastriate areas hV3A and hMT/V5+ responded to flicker . Flicker responses, however, were strongly reduced in those four regions that in main experiment 1 failed to respond in the isosaliency-isoluminance condition, STS, PIC, DIPSM, and DIPSA, confirming that these regions are active only in conditions in which motion is perceived.
  • The previous experiments indicate that IPL represents motion bilaterally in the visual field while the traditional motion regions represent predominantly motion in the contralateral field. To explore these differences more fully, we analyzed the response to the random texture motion presented in three positions (central and 5° peripheral in left and right visual field) in the second control experiment. Additionally, we measured in two subjects the response to apparent motion and flicker at 7 Hz in the same three positions (control experiment 3, Table 1). As shown in Figure 7, the traditional motion regions all had a clear bias in favor of the contralateral visual field and in most cases a higher magnification in the center of the visual field: their response to the central motion was stronger than to contralateral motion, even if the central stimulus was physically smaller. Weak responses to random texture motion, reaching only p < 0.001 uncorr. in the group analysis, were also observed in IPL, but here the response to ipsilateral motion was slightly stronger than to central or contralateral motion. With apparent motion, which was physically identical in all three stimulus positions, the ipsilateral response clearly exceeded the two other responses (Figure 7). Notice that the stronger response to ipsilateral stimulation than to contralateral stimulus is a constant feature of IPL since it was also observed in experiment 1 (Figure 4).
  • contrast-modulated checkerboard stimuli as Vaina and Cowey (1996) and Vaina et al. (1999) used to demonstrate a dissociation between first and second- order motion processing in patients In control experiment 5 (Table 1) we manipulated the coherence of these stimuli just as Vaina et al. (1999) had done in their patients. In control experiment 6, we investigated the effect of density of the stimuli in a more restricted group of subjects (Table 1). This latter experiment demonstrated that in most visual cortical areas the middle density used in control experiment 5 and in Vaina et al.'s patients was near optimal. Using this middle density, the results of control experiment 5 revealed that in most lower-level motion regions, MR activity increased with motion coherence, as Rees et al. (2000) reported for first-order stimuli. A notable exception was hV3A, which responded strongly to low-coherence stimuli (Figure 5E).
  • On the other hand, the higher-level motion IPL region responded little to these second-order motion stimuli, not even at 100% coherence (Figure 6G), as was the case for first-order stimuli (Figure 6F). Interestingly, the individual IPL responses to second-order and first-order motion, relative to static control, correlated significantly (r = 0.72, p < 0.005), while there was no significant correlation between individual IPL responses to apparent motion on one hand and first- (r 0.31, p 0.2) or second- order motion (r = 0.44, p > 0.1) on the other. Comparison of the second-order motion at the three coherence levels to their stationary counterpart revealed a significant IPL activation in the right but not the left hemisphere . This second-order motion site was located more ventrally than the higher-level motion region. The distance between these two activation sites in the right hemisphere was 18 mm in the group analysis and 14 mm averaged over individual subjects (in which a smaller smoothing kernel was used).
  • Both motion in the auditory and tactile modality activates a number of parietal regions

A Higher Order Motion Region A Higher Order Motion Region Presentation Transcript